ESE's works engine tuner

[Frits Overmars]

We use 20:1 oil ratio. This rod has not failed but I noticed our cranks getting really hot on the dyno. They were hot when we were pulling 12,000rpm now we are pulling near 15,000 rpm they get really really hot.
How do the 20+ RWHP Dutch guys get their cranks to survive at 15-18,000 rpm?
I suspect that crankshaft flywheel heating is the major source of power fade we observe after a generous number of dyno pulls.My casually asking about the fuel-oil ratio was a tongue-in-cheek way of saying that there was no oil at all in that fuel. I advise 1:20, same as you.
The 20+ RWHP Dutch guys rev between 15.000 and 16.000 rpm. The front runners have about 24 RWHP. I do not know of anyone revving to 18.000 rpm, let alone survive at those revs.
You're right about the crankshaft heating. That is one of the reasons for me not to use direct fuel injection yet. Dry air is not very effective at cooling the con rod.

[wobbly]

Frits, what is the actual problem with the 50cc racers crank reliability.
We run the 125 KZ engines to 14800 all day, and the basically same configured OKN 125 direct drive engines are rev limited at 15,000 with no reliability issues at all.
That level is of rpm with a 54.5 stroke is 27M/s, with a 40 stroke in a 50cc its only 20M/s.
I know some were a bit upset when I opined after watching a few video's, that the Freetech guys were hardly pushing the envelope, not much more than a chainsaw when you look at the piston speed - why is that ?

[ken seeber]

I remember when I was at Orbital and we were initially dealing with Mercury, this being prior to the Optimax engine. The engineers were talking about the Rouen 24 hour boat races. To prevent both seizures and failed bearings, they filled the carb float bowls with straight petrol so the engine would start without loading up. Then, after starting, the fuel was fed from the tanks…..this was on an 8:1 ratio. Oil is good (and now expensive).

[F5 Dave]

I was brought up using dreadful Suzuki commuter parts. If you revved the crank regularly to 13,000 the life was short, a yearly rebuild was not soon enough. I think they upgraded the rods slot a bit but not much change. They were 15mm be pins. Perhaps they whipped enough to cause issues. 17mm yamaha parts made for years of reliability at 13 - almost 14 peak.

Too slow i realised the old rules of engagement were constraining me to a fictional peak revs.

But Perhaps even with much less mass the smaller bearings be and main and thin be pin constrain rev reliability where a 125 size setup despite the much bigger mass is a sweet spot?

Just conjecture with no evidence.

[TZ350]

TeeZee, what oil are you using.

357982

Shell Advance Ultra2 Full Synthetic.

We bought several boxes of 1liter bottles. A job lot cheap, end of line runout. We have used lots of it over the years and still have a dozen or so bottles left. It has been a good oil, no oil related engine failures so far.

With these you could hand the apprentice a one liter bottle of oil and a 20 liter fuel container. And tell them to go Ardmore airfield or Pukekohe and fill it up with Avgas and tip that pack of oil into into it. Bring it all back. If you got a full 20L container and an empty 1L oil bottle there was a pretty good chance you had fuel at 20:1. Helpers who tried to mix fuel 20:1 5L at a time often got it wrong.

[Vannik]

Frits, what is the actual problem with the 50cc racers crank reliability.
We run the 125 KZ engines to 14800 all day, and the basically same configured OKN 125 direct drive engines are rev limited at 15,000 with no reliability issues at all.
That level is of rpm with a 54.5 stroke is 27M/s, with a 40 stroke in a 50cc its only 20M/s.

I have the same question.

I do know that things do not scale linearly with engine size, maybe the issue is the big-end bearing inertia? And in a 50cc it is a much bigger percentage than on a bigger engine. The mode of failure is that the rollers start skidding as they are accelerated and decelerated per revolution. Maybe the big end pin on a 50cc has too big a diameter. That leads to a bigger cage and more inertia. I have never done cage acceleration value calculations but maybe that, more than mean piston speed is the real differentiator?

[koenich]

Gents, you are comparing high quality TM race parts developed as a package since ages for a specific race engine to Derbi aftermarket stuff. While you certainly can buy nice 85/90 mm conrods or good pistons none of this was ever developed as a package to achieve 24+ HP...

[Flettner]

You are all in trouble now, retired as of this week, parts are being sourced as we speak (read) for the 'ultimate' 100cc twostroke. Haha, I'm full of shit, but I have retired and 'we' are building a 100cc twostroke. Based loosely around a TF 125, very loosely. (And legally)

[F5 Dave]

Congratulations Neil :woohoo:

[Wos]

I remember when I was at Orbital and we were initially dealing with Mercury, this being prior to the Optimax engine. The engineers were talking about the Rouen 24 hour boat races. To prevent both seizures and failed bearings, they filled the carb float bowls with straight petrol so the engine would start without loading up. Then, after starting, the fuel was fed from the tanks…..this was on an 8:1 ratio. Oil is good (and now expensive).

Some of the aftermarket expensive 50cc " racing" cranks are very pure in quality...pure shit :(

[lohring]

We ran our 26 cc, 28 mm stroke Zenoahs up to 25,000 rpm during testing. That's around 23 m/sec. It was only for a short time on the water, though. Big end bearing life is limited at racing with 20,000 rpm maximum for a few seasons, even with over 16:1 oil mixes. Ask me how I know.

Lohring Miller

357983357984

[Frits Overmars]

I do know that things do not scale linearly with engine size, maybe the issue is the big-end bearing inertia? And in a 50cc it is a much bigger percentage than on a bigger engine. The mode of failure is that the rollers start skidding as they are accelerated and decelerated per revolution. Maybe the big end pin on a 50cc has too big a diameter. That leads to a bigger cage and more inertia. I have never done cage acceleration value calculations but maybe that, more than mean piston speed is the real differentiator?50cc big end pins are Ø15 or Ø16 mm; that is roughly equivalent to 22 mm for a 125cc engine. The RSA had a 24 mm big-end pin, which posed no problems; an RSA crankshaft survived a full season on the test bench. Wob, what is the big end pin diameter in the KZ engines?

What does fail on the 50cc engines, are poor-quality big end and small end cages and poor-quality axial thrust washers.
My mate emot.nl is concentrating on developing more reliable stuff for the Freetech racers. But I don't think they are going to rev to 20.000 rpm any time soon. Some things, like boundary layers, are not scalable which means the smaller the engine, the harder it becomes to create sufficient angle.area.

[Wos]

50cc big end pins are Ø15 or Ø16 mm; that is roughly equivalent to 22 mm for a 125cc engine. The RSA had a 24 mm big-end pin, which posed no problems; an RSA crankshaft survived a full season on the test bench. Wob, what is the big end pin diameter in the KZ engines?



What does fail on the 50cc engines, are poor-quality big end and small end cages and poor-quality axial thrust washers.
My mate emot.nl is concentrating on developing more reliable stuff for the Freetech racers. But I don't think they are going to rev to 20.000 rpm any time soon. Some things, like boundary layers, are not scalable which means the smaller the engine, the harder it becomes to create sufficient angle.area.


Wobbly and Frits,

Not Diameter of Bore ore Bolt Big end, some use 17mm..."quality " of components ;)...foregive me if i dont want to talk about to much ... dont use these "racing" cranks out of the box ...


Liedolsheim shows if you did everything for reliability

Grüße ;)

Wolfgang

[wobbly]

I believe three things were in play with the KZ engines. Firstly was the big end pin diameter, this was like many engines of the 125 size was 20mm ( Rotax was the same ) before 1980.
Quality control of the M cage rollers ( junk ) was atrocious, be the needles from INA or SKF, I used to buy twenty big end bearings and sort the rollers into 4 micron size groups, using a 4 decimal digital micrometer.
Lastly was the oil, this was the period when unleaded fuel became popular and or mandatory, and coincided with many companies producing fully synthetic race oils for two strokes.
Reliability , even early on was marginal, only pulling just over 13,000 on a regular basis.
The fix came in three steps as well.

Big end pins went from 20mm solid to 22mm hollow, this considerably increased the cantilevered beam strength.
The cages gradually changed from the M style to flat dividers between the rollers, this increased the cage strength, and prevented bad wear of the rod bore inner from the narrow " hoop " contact
area on each side - and the rollers specifically to be used in big ends were factory sorted into size groupings.

Lastly was a change in oil base stock. The full synthetics were OK when used in unleaded race engines at the time, as this fuel, very unlike leaded high octane race gas, made more power when run rich, with more timing
and less compression.

What was discovered in the two stroke world ( unlike the current on line shit storm it creates ) was that the results gained from the Timken/Falex oil test rig held true in the 2T race engines.
On that rig a pure synthetic can have a load to fail film strength over ten times that of a castor based oil, but the instant the film is broken the synthetic " burns " as it breaks down into its chemical constituents
that have no inherent lubricant properties.
This then resulted in the spinning test drum surface, being badly torn up at the point load, ball contact area.
A Castor oil " fails " at a much lower load on the ball, but when the oil film is broken, the wear generated is vey smooth and shiny, as the base chemical structure is still a good lubricant.

Thus many semi synthetic, ie those with a castor added to a synthetic base stock began to be produced. The Castor being very cleanly refined to prevent the old issue of burnt combustion carbon.
ELF 909 ( as used in GP by Aprilia ) Maxima 927, Vrooam, Castrol A747 etc were found to give superior performance ( both power wise, and wear reduction ) when used at very high ( 0ver 600*C ) EGT numbers.

I tested a huge range of oil ratio's and oil types for a customer using the KT100 air cooled engine up at 650*C.
The short of the result was that 20:1 gave more power ( more wasn't better ), the semi synthetic Elf 909 and a couple of others, gave more power and much less piston/bore wear in identical run times.
The popular Motul 800 fully synthetic made the least power, and gave the most wear - by a big margin.

Thus all these factors combined at about the same time, and the results enabled full reliability well past 14,000 in the karting world, from 100cc air cooled to 125 50 HP KZ's.
Specifically that for a period even the flat cage , larger diameter pins would still wear away the silver, and turn blue - alot later, but as soon as we switched away from fully synthetic oils such as Motul 976
the whole issue disappeared.

[pete376403]

Honda (4 strokes, sorry) were running tiny bore and stroke roller crank engines 125cc fives, 250cc sixes) at 18 - 20,000 rpms back in the 60s. I believe they ran castor based oils exclusively.

[Wos]

I believe three things were in play with the KZ engines. Firstly was the big end pin diameter, this was like many engines of the 125 size was 20mm ( Rotax was the same ) before 1980.
Quality control of the M cage rollers ( junk ) was atrocious, be the needles from INA or SKF, I used to buy twenty big end bearings and sort the rollers into 4 micron size groups, using a 4 decimal digital micrometer.
Lastly was the oil, this was the period when unleaded fuel became popular and or mandatory, and coincided with many companies producing fully synthetic race oils for two strokes.
Reliability , even early on was marginal, only pulling just over 13,000 on a regular basis.
The fix came in three steps as well.

Big end pins went from 20mm solid to 22mm hollow, this considerably increased the cantilevered beam strength.
The cages gradually changed from the M style to flat dividers between the rollers, this increased the cage strength, and prevented bad wear of the rod bore inner from the narrow " hoop " contact
area on each side - and the rollers specifically to be used in big ends were factory sorted into size groupings.

Lastly was a change in oil base stock. The full synthetics were OK when used in unleaded race engines at the time, as this fuel, very unlike leaded high octane race gas, made more power when run rich, with more timing
and less compression.

What was discovered in the two stroke world ( unlike the current on line shit storm it creates ) was that the results gained from the Timken/Falex oil test rig held true in the 2T race engines.
On that rig a pure synthetic can have a load to fail film strength over ten times that of a castor based oil, but the instant the film is broken the synthetic " burns " as it breaks down into its chemical constituents
that have no inherent lubricant properties.
This then resulted in the spinning test drum surface, being badly torn up at the point load, ball contact area.
A Castor oil " fails " at a much lower load on the ball, but when the oil film is broken, the wear generated is vey smooth and shiny, as the base chemical structure is still a good lubricant.

Thus many semi synthetic, ie those with a castor added to a synthetic base stock began to be produced. The Castor being very cleanly refined to prevent the old issue of burnt combustion carbon.
ELF 909 ( as used in GP by Aprilia ) Maxima 927, Vrooam, Castrol A747 etc were found to give superior performance ( both power wise, and wear reduction ) when used at very high ( 0ver 600*C ) EGT numbers.

I tested a huge range of oil ratio's and oil types for a customer using the KT100 air cooled engine up at 650*C.
The short of the result was that 20:1 gave more power ( more wasn't better ), the semi synthetic Elf 909 and a couple of others, gave more power and much less piston/bore wear in identical run times.
The popular Motul 800 fully synthetic made the least power, and gave the most wear - by a big margin.

Thus all these factors combined at about the same time, and the results enabled full reliability well past 14,000 in the karting world, from 100cc air cooled to 125 50 HP KZ's.
Specifically that for a period even the flat cage , larger diameter pins would still wear away the silver, and turn blue - alot later, but as soon as we switched away from fully synthetic oils such as Motul 976
the whole issue disappeared.

:) wobb

Quality of Parts! tolerances ... roundnes ...axis...diameter...parallelity

Todays motul 800 for street/racing is often used in bikes of winners...sems not to be main problem

[wobbly]

The only help with tolerances etc I can give I learnt from Curt at Hot Rods, the big end clearance should be 1 micron per pin mm ie 20mm pin = 0.02 clearance.
When I spent hours measuring everything I would stack up the pin, rod bore and roller diameter to achieve this.

And any roller bearing surface must be Rc 58 min to a depth of 0.5mm.

Re winning with Motul 800 - if thats the case then they are not pushing the mechanical/thermodynamic limits, but in every case they are leaving power on the table.

[ApolloMotoMoto]

While we are on the subject of cranks and "reliability" ....

These are "motorized bicycle" cranks for a 90cc single speed direct drive kart track race bike engines.

42 stroke x 52 bore

Air Cooled running VP MRX02 (converting to E85 for next race event....)

Cylinder Reed induction with Minarelli AM6 reed's.

Portmap designed in JanBros with balanced blowdown/transfer STA for peak torque at 9,500 to match the pipes being used (any 80-85cc MX pipe you can find cheap on eBay...)

BMEP prediction in JanBros is 12.9; BHP prediction 24.6...

Based on how they run I would expect to see 16-20 RWHP on a dyno.

Spinning up to 13,800-14,200 RPM, but even one example engine with an overly long tuned length pipe which taps out at 12,250-12,500 (regardless of jet tune or ignition map adjustments) is also snapping these cranks, so it doesnt appear to be terminal RPM piston speed in my case that is the problem.

These cranks use a 16mm OD crankpin and ....15mm OD..... output/drive shaft.

They are mold-forged from "forty pound steel" (40cr?) a rather common chinese grade of steel; they come out of the forge mold red hot and are near immediately dropped into a water quench :D

Final hard machining occurs after this.

There is ALSO a custom crankshaft manufacturer who produces essentially this exact crank starting with 4140 prehard material, machining them in the hard state.

I am aware of exactly 1x of these cranks which has suffered the EXACT carbon copy crank output shaft failure. I call it a snap, but the clearly visible "beach lines/tide lines" on the face of the break zone clearly show that its a crack which progresses through the material over time;

And the brown/orange oxidation/corrosion on the outer perimiter of the break zone clearly shows it has been cracked open long enough for moisture to creep in and start corroding/oxidizing the steel.

And again, the 4140 prehard crank have 1x known failure that looks EXACTLY like the close-ups attached to this post...

The break profile has a novel "dimple-and-dome" or "crater-and-dome" shape where the crankwheel face is dimpled/cratered and the broken shaft end is domed.

At first I thought this confirmed that the ...horrible... heat treat procedure used on the stock chinese crankwheels was the "problem"; but the failure occuring in the 4140 prehard cranks, which looks exactly the same, suggest maybe thats not the root of the cause.

I dont know if this particular vendor of aftermark cranks made from 4140 prehard is doing any post-process hardening which might explain the carbon copy break profile, but its interesting nonetheless.

So, "what gives"?

Have I just exceeded the yield strength of 15mm shafting with the given specific power output?

[ApolloMotoMoto]

Pics of the dead 4140 prehard crank.

[Wos]

The only help with tolerances etc I can give I learnt from Curt at Hot Rods, the big end clearance should be 1 micron per pin mm ie 20mm pin = 0.02 clearance.
When I spent hours measuring everything I would stack up the pin, rod bore and roller diameter to achieve this.



And any roller bearing surface must be Rc 58 min to a depth of 0.5mm.

Re winning with Motul 800 - if thats the case then they are not pushing the mechanical/thermodynamic limits, but in every case they are leaving power on the table.

Good question where the limits are in diffrent Races:msn-wink:

Liedolsheim 8H wide open Throttle...think the limits are diffrent to freetech50

Maybe the Motul 800 changed, since you have testet it?

[husaberg]

2 strokes on overrev with closed throttle as well as the engine being driven by a wheel and rider or a drum on a Dyno do not get any significant lubricating oil. 4t's survive this better a most have positive lubrication systems not reliant on a petrol mist.
Honda for the 2ts at least (but pretty sure XR and the like also) used to colour code roller cages the big end even own the commuter bikes like H100's offer many different specs std for selective fit ,after market not so much.....
357991
Wobs way is obviously the preferred method
but different Honda ones used to be on one of the first few pages in the parts fiche.



Bell devotes a lot of space into how to build decent big ends and cranks in his book

[Wos]

2 strokes on overrev with closed throttle as well as the engine being driven by a wheel and rider or a drum on a Dyno do not get any significant lubricating oil. 4t's survive this better a most have positive lubrication systems not reliant on a petrol mist.
Honda for the 2ts at least (but pretty sure XR and the like also) used to colour code roller cages the big end even own the commuter bikes like H100's offer many different specs std for selective fit ,after market not so much.....
357991
Wobs way is obviously the preferred method
but different Honda ones used to be on one of the first few pages in the parts fiche.



Bell devotes a lot of space into how to build decent big ends and cranks in his book

Cloed Throttle...

The more important is to have a well tuned idle jet/ airscrew to be not too lean there...

[koenich]

Re winning with Motul 800 - if thats the case then they are not pushing the mechanical/thermodynamic limits, but in every case they are leaving power on the table.
We are talking 8h endurance racing - depending on the year we had differences of ~15 °C ambient temperature from start of the race 11:00 am to noon. Even if the weather is supposed to be stable, I wouldn't jet on the edge as a part of risk mitigation to make it the full race disctance.

[Peter1962]

50cc big end pins are Ø15 or Ø16 mm; that is roughly equivalent to 22 mm for a 125cc engine. The RSA had a 24 mm big-end pin, which posed no problems; an RSA crankshaft survived a full season on the test bench. Wob, what is the big end pin diameter in the KZ engines?

What does fail on the 50cc engines, are poor-quality big end and small end cages and poor-quality axial thrust washers.

Frits, could forced lubrication of the big end, like Neil Hintz is doing on his 360 engine make a difference on the freetech 50cc engines concerning reliabilty ?



My mate emot.nl is concentrating on developing more reliable stuff for the Freetech racers. But I don't think they are going to rev to 20.000 rpm any time soon. Some things, like boundary layers, are not scalable which means the smaller the engine, the harder it becomes to create sufficient angle.area.

Most certainly not with the actual trend of using more reed valve engines, compared to some years ago, when a lot of the freetech engines were rotary valved. Strange evolution...

[Larry Wiechman]

While we are on the subject of cranks and "reliability" ....





They are mold-forged from "forty pound steel" (40cr?) a rather common chinese grade of steel; they come out of the forge mold red hot and are near immediately dropped into a water quench :D

Final hard machining occurs after this.

There is ALSO a custom crankshaft manufacturer who produces essentially this exact crank starting with 4140 prehard material, machining them in the hard state.



A generous, ground & polished radius may help.

[Frits Overmars]

Frits, could forced lubrication of the big end, like Neil Hintz is doing on his 360 engine make a difference on the freetech 50cc engines concerning reliabilty ?Absolutely. It will easily double the lifespan of the big end.

[wobbly]

If you do any research on 4130/4140, the answer regarding its suitability as a crank or shaft material is obvious - At 45Rc you are asking 4130 for everything it's got. It has the lowest carbon content of any directly hardenable
alloy steel which is why it's used for welded structures.
Thus getting the required case hardness of Rc 58/62 to a minimum depth of 0.5mm is in reality, impossible.
This material is routinely carburized, but that is only microns deep.
To get the ground surface in a condition suitable for reliable direct needle roller use, with a suitably malleable core strength, something like EN35 or equivalent is a minimum requirement.

In the situation of a press in big end pin, these are easily case hardened to Rc 60 - 64 from 0.5mm to 1mm deep, using the right material.
Anything less creates rapid Brinelling where the needle point load eventually pulls the case hard surface off the substrate - as you see in many one piece forged crankshafts.

And yes, having the " correct " pilot/air screw setting is vitally important to the overun on closed throttle.
We use a very rich pilot in KZ, with alot of air screw to get some semblance of transition onto the needle/tube, and this setup is reliable and the fastest - but still creates the first deto signs above the boost port
indicating a leaner condition in transition off the bottom.

[Wos]

If you do any research on 4130/4140, the answer regarding its suitability as a crank or shaft material is obvious - At 45Rc you are asking 4130 for everything it's got. It has the lowest carbon content of any directly hardenable
alloy steel which is why it's used for welded structures.
Thus getting the required case hardness of Rc 58/62 to a minimum depth of 0.5mm is in reality, impossible.
This material is routinely carburized, but that is only microns deep.
To get the ground surface in a condition suitable for reliable direct needle roller use, with a suitably malleable core strength, something like EN35 or equivalent is a minimum requirement.

In the situation of a press in big end pin, these are easily case hardened to Rc 60 - 64 from 0.5mm to 1mm deep, using the right material.
Anything less creates rapid Brinelling where the needle point load eventually pulls the case hard surface off the substrate - as you see in many one piece forged crankshafts.

And yes, having the " correct " pilot/air screw setting is vitally important to the overun on closed throttle.
We use a very rich pilot in KZ, with alot of air screw to get some semblance of transition onto the needle/tube, and this setup is reliable and the fastest - but still creates the first deto signs above the boost port
indicating a leaner condition in transition off the bottom.

Thanks wobb! ;)

What is your experience to avoid Detos in transition area to Needle?

Lifting throttle slide by screw/ increasing idle RPM ?

50cc..which RPM fits.

Difficult to find prefered RPM for 3 diffrent Riders, there wishes, there individual downshifting point before corners..prefered braking forces of engine :( ;)

Forbid them to brake anyway!? :2thumbsup:cool:

Grüße Wolfgang

[Frits Overmars]

Difficult to find prefered RPM for 3 diffrent Riders, there wishes, there individual downshifting point before corners..prefered braking forces of engine.Don't give them what they want; give them what they need.
A trip down memory lane: I witnessed how Luca Cadalora wanted to change everything after his first practice session on the Garelli 125cc twin.
Old hands Nieto and Lazzarini, who knew the bike inside out, said: ‘Right, we’ll do all that as soon as you’re within a second of the lap record.’
The bike remained unchanged and Cadalora went on to become world champion on it.

[Wos]

Don't give them what they want; give them what they need.
A trip down memory lane: I witnessed how Luca Cadalora wanted to change everything after his first practice session on the Garelli 125cc twin.
Old hands Nieto and Lazzarini, who knew the bike inside out, said: ‘Right, we’ll do all that as soon as you’re within a second of the lap record.’
The bike remained unchanged and Cadalora went on to become world champion on it.

Wonderful Frits! THANKS!:niceone::niceone:

Grandma said something wise:

jedem Menschen Recht getan, ist eine Kunst die niemand kann

"Doing right by everyone is an art no one can master."... ;)

Grüße Wolfgang

[wobbly]

Wolfgang, the question regarding deto first forming due to a lean transition jetting has been driving all the best tuners in the World up the wall, forever.
No matter what " normal " fixes have been tried, the throttle response always suffers, and both the driver and the stopwatch complain bitterly.
We have to run the mad rich pilot inner and outer jets to cool the piston , and the pipe, when in the overrun down into a second gear hairpin, and although reducing more airscrew or
going fatter on the emulsion tube, or higher fuel level is better against the brake on the stand, its worse on track.
The result is low speed WOT deto, but as you will see on every title winning KZ piston picture, its just the reality of doing what is fast, not technically " better ".

[husaberg]

bell clickk three times.
357995357996357997357998357999358000

[husaberg]

One that never fixed
358001358002358003

[Wos]

Wolfgang, the question regarding deto first forming due to a lean transition jetting has been driving all the best tuners in the World up the wall, forever.
No matter what " normal " fixes have been tried, the throttle response always suffers, and both the driver and the stopwatch complain bitterly.
We have to run the mad rich pilot inner and outer jets to cool the piston , and the pipe, when in the overrun down into a second gear hairpin, and although reducing more airscrew or
going fatter on the emulsion tube, or higher fuel level is better against the brake on the stand, its worse on track.
The result is low speed WOT deto, but as you will see on every title winning KZ piston picture, its just the reality of doing what is fast, not technically " better ".

Thanks for telling your experiences !

LOW throttle

A carb is relatively slow reacting, extra slow on low air flow, smal RPMs i think

Injektion seems to be a s solution away from "normal"

Myself i had not to deal with, but the seen result i saw on Motocross Bikes is fantastic :)

Throttle Response and Power everywhere.

Liedolsheim 8 H Injektion is vorbidden... dont know if its free in freetech50 ?

Grüße Wolfgang

[Frits Overmars]

Liedolsheim 8 H Injektion is vorbidden... dont know if its free in freetech50 ?I wrote the original Freetech50 rulebook so yes, injection and a lot of other things are free in Freetech50 (what's in a name :msn-wink:)

About part throttle deto: it was a major problem at Aprilia. The RSA and RSW bikes were just about bulletproof regarding WOT deto, but they would detonate terribly at part throttle + high revs conditions. For that reason celebratory burnouts were strictly forbidden.
I figured out that the cause was actually quite simple: part throttle means low crankcase pressure and although there was ample blowdown time.area at WOT, the cylinder pressure drop before transfer opening was not deep enough for this part-throttle crankcase pressure, so exhaust gases entered the transfer ducts, heating up the fresh mixture.

[JdG]

Just a brain fart…

Has anyone ever tried ceramic needles or ceramic bearings? My knowledge on the subject is limited. I’ve been told by people that claim to be more knowledgeable, that ceramic bearings in general can survive almost anything, as long as they don’t overheat. Lubrication isn’t overly important because of the hardness of the bearing materials.

Overheating is the issue here and I don’t know what temperatures are lethal for the ceramic bearings.

I also don’t know if the load cases are even suitable for ceramic materials.

Just wondering.


Verzonden vanaf mijn iPhone met Tapatalk

[pete376403]

Are the bearing races also ceramic? If the balls are super hard does that make the races wear faster?

[Frits Overmars]

Has anyone ever tried ceramic needles or ceramic bearings? My knowledge on the subject is limited. I’ve been told by people that claim to be more knowledgeable, that ceramic bearings in general can survive almost anything, as long as they don’t overheat. Lubrication isn’t overly important because of the hardness of the bearing materials. Overheating is the issue here and I don’t know what temperatures are lethal for the ceramic bearings.
I also don’t know if the load cases are even suitable for ceramic materials.
We've been using homemade hybrid crankshaft bearings (ceramic balls between steel inner and outer races) in 35.000 rpm model engines for about 30 years now; they have proven to be bulletproof.
I'd love to use ceramic rollers in big end bearings too, where their much lower specific mass would be very welcome for the constantly accelerating/decelerating masses within each crankshaft revolution, but the ceramics experts are still reluctant to let me apply them.

The main problem with ceramic bearings is not overheating (ceramic parts couldn't care less) but the fact that their elastic deformation under load is about zero. In English: they're as hard as a rock :p.
The outer race of a bearing exhibits a curvature in the same direction as the balls or rollers in contact with it, but the curvature of the inner race bends away from that of the roller bodies, causing the contact area to become so small and the contact pressure so high that the inner race fails. The ceramic roller bodies themselves almost never fail.

[Niels Abildgaard]

We've been using homemade hybrid crankshaft bearings (ceramic balls between steel inner and outer races) in 35.000 rpm model engines for about 30 years now; they have proven to be bulletproof.
I'd love to use ceramic rollers in big end bearings too, where their much lower specific mass would be very welcome for the constantly accelerating/decelerating masses within each crankshaft revolution, but the ceramics experts are still reluctant to let me apply them.

The main problem with ceramic bearings is not overheating (ceramic parts couldn't care less) but the fact that their elastic deformation under load is about zero. In English: they're as hard as a rock :p.
The outer race of a bearing exhibits a curvature in the same direction as the balls or rollers in contact with it, but the curvature of the inner race bends away from that of the roller bodies, causing the contact area to become so small and the contact pressure so high that the inner race fails. The ceramic roller bodies themselves almost never fail.

I seem to remember that You showed us a crossection view of one of these phenomenal 2.5ccm engines.

Have it been tried to make a crankshaft where the inner races have been made from ceramic,stellite or carbide material and brazed with cupper or nickel?

Are there a newer version?
https://itat.bmfa.uk/08-03-2022

[Wos]

I wrote the original Freetech50 rulebook so yes, injection and a lot of other things are free in Freetech50 (what's in a name :msn-wink:)

About part throttle deto: it was a major problem at Aprilia. The RSA and RSW bikes were just about bulletproof regarding WOT deto, but they would detonate terribly at part throttle + high revs conditions. For that reason celebratory burnouts were strictly forbidden.
I figured out that the cause was actually quite simple: part throttle means low crankcase pressure and although there was ample blowdown time.area at WOT, the cylinder pressure drop before transfer opening was not deep enough for this part-throttle crankcase pressure, so exhaust gases entered the transfer ducts, heating up the fresh mixture.

Frits!

Ktm had massiv problems with there first Injektion in motocross bikes :msn-wink:

Now they changed to throttle BODY Injektion to solve lubrication problems of Injektion into transfers...hard way of learning for ktm

Do you know if Injektion is used or was testet in freetech50 ?


Thanks!

Wolfgang

[Frits Overmars]

I seem to remember that You showed us a crossection view of one of these phenomenal 2.5ccm engines.
Have it been tried to make a crankshaft where the inner races have been made from ceramic,stellite or carbide material and brazed with cupper or nickel?
Are there a newer version?
https://itat.bmfa.uk/08-03-2022Hej Niels, it’s much simpler than that.
As you know, the MB40 model engines (6,5cc, not 2,5cc) have a rotary intake system in which the inhaled mixture flows through the hollow crankshaft.
For good power, that channel – and therefore the crankshaft journal – needs to have a decent diameter. But that diameter also determines the size of the crankshaft bearing, and that bearing in turn determines the maximum safe rpm.

The solution: take a standard steel ball bearing, keep the outer ring and the synthetic cage, and discard the steel balls and the inner ring.
The steel balls are replaced with ceramic balls and the inner raceway for the balls is ground directly onto the crankshaft itself, so that we achieve a combination of a substantial diameter for the intake channel and a relatively small diameter for the inner race.
So this inner race is simply the steel of the crankshaft. Nothing special, no ceramic, stellite or carbide material and no copper or nickel brazing.

The engines have remained virtually unchanged for roughly 25 years, but they have racked up a handful of world titles since then and they are reliable, so why change anything? With a fuel consisting of 80% methanol, 20% oil and 0(!) % nitro, a well-tuned MB40 delivers 5 hp at the crankshaft and the competition still hasn’t caught up :D.
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[Frits Overmars]

Frits! Ktm had massiv problems with there first Injektion in motocross bikes
Now they changed to throttle BODY Injektion to solve lubrication problems of Injektion into transfers...hard way of learning for ktm?The reason for KTM to change back from TPI (Transfer Port Injection) to TBI (Throttle Body Injection) was not so much a lubrication problem but more a power problem.
KTM had patented a system of injecting fuel into the B-transfer ducts only, claiming that the content of the A-transfer ducts was more prone to short-circuit into the exhaust ports. But at full throttle the rich mixture from the B-ports and the air-only content from the A-ports had not enough time to properly mix and form a homogeneous combustible mixture, whereas injecting fuel into the throttle body meant the mixture was thoroughly stirred and homogenized in the crankcase before it entered the cylinder.

As I said, KTM had patented the TPI system. But New Zealand genius Neil Hintz could prove that he had a fully functioning TPI system before KTM applied for their TPI patent, so KTM had to withdraw it, with a painful loss of face.
Neil Hintz too had experienced the full-throttle problem but instead of switching back to TBI he fitted injectors on the A-transfers as well as on the B-transfers. The A-injectors are only activated when full power is demanded, engine power is perfectly controllable and fuel economy is a lot better than with TBI.
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[F5 Dave]

His next move will probably leapfrog direct injection and inject at the expansion chamber :lol:

[Wos]

OK Frits:niceone:

In many forums was discussed that Tpi was reason for failures caused by bad lubrication.

On the other hand...every carb can be tuned to lean...and it was told that Ktm with Tpi reached for harder emmission standards...

Think Ktm not only has to hide Patent Problems these days...what a pitty :(

[Frits Overmars]

In many forums was discussed that Tpi was reason for failures caused by bad lubrication.
On the other hand...every carb can be tuned to lean...and it was told that Ktm with Tpi reached for harder emmission standards.As far as I know, the KTM oil pump that delivers oil to the intake manifold is identical in both the TPI and TBI versions. That pump can, of course, malfunction, but this is not specific to either the TPI or TBI systems.

Due to the increasingly stringent emission standards, internal combustion engines are being run leaner and leaner. If on top of that the fuel-air mixture is not homogeneous because the fuel is only injected in the B-transfers and not in the A-transfers, the engine may run too lean at full throttle and suffer from detonation.
Returning to Throttle Body Injection was the simple solution that KTM chose. They'd better have taken another look at Neil Hintz' TPI mk2 system.

[Wos]

Emission

Years ago thought about a pressure oil solution for 2strokes to lubricate every part that needs oil.

Minimum oil in combustion ...minimum oil wash wastet to ex - cleaner Emission ?

For sure very expensive to built ...
Dont know if this is the only way to really "clean" 2 stroke ;)

Wolfgang

[Peter1962]

As far as I know, the KTM oil pump that delivers oil to the intake manifold is identical in both the TPI and TBI versions. That pump can, of course, malfunction, but this is not specific to either the TPI or TBI systems.

One of the members on the ktmtalk forum said that it is in fact an industrial pump, and has been tested for several thousand hours without failure. Good that ktm did not try to re-invent the wheel and uses what is available and reliable on the market.


Due to the increasingly stringent emission standards, internal combustion engines are being run leaner and leaner. If on top of that the fuel-air mixture is not homogeneous because the fuel is only injected in the B-transfers and not in the A-transfers, the engine may run too lean at full throttle and suffer from detonation.


There is also the problem that KTM is using a crappy connection of the CCP sensor, the standard one is prone to leak, giving an unreliable signal to the ECU and that of course gives problems for the mixture. Some do simply use some white silicone to try to avoid leaks, but the better solution is to use an aftermarket quality connection. https://www.pinitracing.com/videos


Returning to Throttle Body Injection was the simple solution that KTM chose. They'd better have taken another look at Neil Hintz' TPI mk2 system.

Its a shame they did not do that...

[lohring]

Thoughts on this opposed piston design (https://www.youtube.com/watch?v=W_xmkTTCu9o) starting at 14 minutes into the video? The interesting features are the large 30 degree exhaust crankshaft lead, the 45 degree up angle on the intake transfers with no swirl, and the annular, four plug combustion chamber with a central squish. I worry about scavenging the central core of the cylinder and the effect of the returning tuned pipe pressure wave with the transfers open. You would need a higher supercharge pressure for this to work. Would an annular combustion chamber with a central squish detonate?

Lohring Miller

[Vannik]

I worry about scavenging the central core of the cylinder. Lohring Miller

I agree, it will form an unscavenged core.


And the effect of the returning tuned pipe pressure wave with the transfers open. Lohring Miller

Towards the end he moved to megaphone only.


Would an annular combustion chamber with a central squish detonate? Lohring Miller

This is an interesting take on the comustion chamber issues of an opposed piston engine - and it will probably need the 4 plugs.

[Niels Abildgaard]

I agree, it will form an unscavenged core.



Towards the end he moved to megaphone only.



This is an interesting take on the comustion chamber issues of an opposed piston engine - and it will probably need the 4 plugs.

Or a central spark plug in piston

[ken seeber]

I know, like everything else it has been done before, but has anyone recently pumped water through the transfer passages for a visual study of the flow stream?

Such a simulation would be done to represent the peak gaseous flow rate of the transfer stream. Obviously one would need to correct for the dynamic similarity between the 2 fluids to establish the appropriate water flow rate.

Such a test could be done by one passage at a time up to all passages at once. Whichever way, it’ll be a messy experience. While it could/would be done with a piston in place, the head could not be in place to allow the water to escape and also to allow visual access. One could use a current “state of the art” cylinder, eg KZ TM R25. :msn-wink:

[Frits Overmars]

Ken, I can’t think of a single reason why flowing with water would provide any more information than flowing with air on a standard flow bench.
As you say, flowing with water will be a messy business. After the first second, all you can see is water everywhere, so you can no longer see the direction of the flow. Moreover, the flow direction is deflected by gravity, so even if you could still see anything, it would be a distorted image.
A flow bench with the right software can provide information on mass flow and flow velocity.
And if you’re interested in flow directions, I’d recommend using a gas flame, as that produces clear images.

[Vannik]

I agree completely with Frits, a critical part of the flow, that coming off the hook in the B-port and curling back under the flow from the C-port is just not duplicated by the water.

[Flettner]

I agree, it will form an unscavenged core.



Towards the end he moved to megaphone only.



This is an interesting take on the comustion chamber issues of an opposed piston engine - and it will probably need the 4 plugs.


Probably not a lot of people have real life experience with petrol OP uniflow
I have had a bit of real world experience, my first uniflow, a 100cc twin cylinder, had a combustion chamber similar, two dome pistons facing each other. Initially it ran badly with just a single plug per cylinder. A lot of advance needed. There was swirl set in the transfers and you could see carbon on the pistons on the 'down wind' side of the plug.
A second combustion plate with twin plugs halved the advanced needed, still 20 degrees though, too much.
The next uniflow I changed transfers, two ports pointed straight across the cylinder, opposite each other and four more pointing slightly up and generating a swirl. Combustion chamber was different this time, still twin plug, but the transfer end piston was 56mm dia, dome, exhaust piston at 50mm giving some squish. Also meaning the combustion chamber was smaller in dia and longer (exhaust piston flat top) bringing a quicker burn again.
This was the 440 engine we used extensively in a small jet boat.

https://youtu.be/BPr694nlUKE?si=V85p_urEwK7y86m8

https://youtu.be/uiXsPkP9jvw?si=ySatuIKtWvata11F 9200 rpm at 5,20 minutes coming back across the lake. This was the second time ever run under load. First time the day before, in the Waikato river, the first part of the video. I was taking it easy in the river, not sure what was going to happen.

[lohring]

If you don't mind, what was the crankshaft phase angle you used? Also, did you only use one crankcase for the intake? I don't see a tuned pipe so were there issues with back flow into the transfers?

Lohring Miller

[Flettner]

If you don't mind, what was the crankshaft phase angle you used? Also, did you only use one crankcase for the intake? I don't see a tuned pipe so were there issues with back flow into the transfers?

Lohring Miller

Exhaust was 6 degrees advanced. Exhaust duration was 180 degrees, transfer 130 degrees, normal twostroke stuff apart from the 6 degree Exhaust advanced.
We ran the engine with tuned pipes one time, I have a picture somewhere, that certainly 'supercharged' performance with much higher BMEP, but only for a very short time. First time the gearbox failed with my half arsed welded gears, second time after I made new gears at great expense, the exhaust pistons failed. As you would expect. Pistons were cast from LM13 as that's all I knew how to cast. (Car piston alloy, higher expansion rate than hypereutectic alloy) and the bores were shrunk in cast iron sleeves, because of cost.
The worst heat transfer scenario.
It did teach me something about exhaust piston cooling and how to combat it that thermal loading.
Found it, the picture. Mid section outlets.

[Peter1962]

In a regional british championship, this guy got second place with his BRC 500 against an armada of 450 four stroke MX bikes. https://www.youtube.com/watch?v=ePiw7xli-6s

[F5 Dave]

Are we really celebrating a guy on a bigger cc bike losing to a smaller bike that has an inferior cycle stroke system?

[lohring]

Thanks, that seems like a more reasonable exhaust lead. Was the flow from one crankcase enough or did you use both crankcases?

Lohring Miller

[lohring]

I have a friend who worked for the now defunct Eco Motors. His main work was on their electric turbocharger (https://www.garrettmotion.com/news/newsroom/article/what-is-an-electric-turbocharger/) and he still works on it. Below is some of the information he sent me years ago on their small opposed piston engine with a cylinder bore in the 30 mm area. It was not successful. One of the most interesting articles was the effect of lead angle on power due to mechanical losses. It concluded that cylinder offset could give the same effects without the mechanical friction losses. The conclusion:

The effective design of an opposed piston two-stroke engine requires a compromise of crank phasing between the optimal phasing to achieve the desired scavenging performance and the resulting loss in work transmission efficiency - the amount of work actually transmitted to the crankshafts compared to the work done by the gases on the pistons. Non-zero phasing is required for effective scavenging and thereby achieving high power density, however this also results in the trailing piston trying to back-drive the crank during part of the stroke. Historically, phasing of the intake crank behind the exhaust crank of between 10 and 20 degrees has been typically selected. The high observed efficiency and power density of these engines has disguised the fact that one crank is fighting the other during part of the expansion stroke, which subtracts substantial work while contributing significant stresses to the trialing side components. The lost work can be eliminated by phasing the two pistons together, but this requires use of a valve mechanism on either the intake, exhaust, or both in order to restore effective scavenging. An alternative is to offset the two cranks in the same direction off of the bore centerline. This allows an effective phasing of the port openings similar to what is achieved with phased pistons for good scavenging and which realigns the torque contribution to eliminate the back-driving torque on one crank. There remains a small difference in torque contribution from each crankshaft with the in-phase crankshafts with the bore centerline offset.

Lohring Miller

[Peter1962]

Are we really celebrating a guy on a bigger cc bike losing to a smaller bike that has an inferior cycle stroke system?

3 rounds, and he finished second overall. Do you call that losing ?

The 50 cc difference is a detail when it comes to 450cc of 500cc. The point is that 'the industry' had the rules book changed in such a way that two strokes were handicaped at first in the world championship MX , (250cc two stroke versus 450 four stroke), and then just ruled out to kill every opposition. The younger generation that did not see the days when 250cc two strokes ruled MX do not know better than that two stroke technology is obsolete.

A practical -and public- experiment like this one proves to everyone that 2 stroke tech is totally competitive even in 2026 in direct comparison with four stroke in a competition setting.

[Frits Overmars]

...below is some of the information he sent me years ago on their small opposed piston engine...That is quite an interesting paper, Thanks Lohring. However it also contains some points that bother me, such as comparing the parts count of the OPOC engine to that of a four-stroke engine. I would have preferred a comparison to the parts count of a conventional two-stroke engine or even to that of a conventional opposed-piston two-stroke engine. There is no doubt who would have been the winner.
One comment bothered me in particular, because it undermines the credibility of an otherwise interesting paper:
"One of the unique features of the OPOC engine is its ability to utilize uniflow scavenging with asymmetric port timing."
There is nothing unique about that; any opposed-piston engine can do that. Just ask Neil Hintz.
Below are the Jumo 205 aircraft diesel engine of 1932, and a DKW blown opposed piston race engine showing the crankshaft phase difference.

[Flettner]

Thanks, that seems like a more reasonable exhaust lead. Was the flow from one crankcase enough or did you use both crankcases?

Lohring Miller

All crankcases pumped, note the four carburetors in the video.

[Niels Abildgaard]

Two gentlrmen from University of Michigan, Drallmeier and Siegel ,have analysed and measured on a single Achates OP diesel cylinder.
For most load cases exhaust crank lead was detrimental;
not much but measurable.
There was a case of four degree lead where thermal efficiency (47%)was 1.oo4 times better than none.

[MINGRET01]

Hello, I'm Bruno from France.

I'm not sure where to introduce myself in this forum, which I've been following for a while. I own several classic motorcycles, including a 125cc Garelli twin-cylinder from 1985 that I've just finished restoring.

358033


I now want to disassemble the fork, but I don't know how. Perhaps Frtis, who is on this forum, knows this type of fork and could help me.

358034

Bests regards

Bruno

[Niels Abildgaard]

The Garelli looks nice and it is a shame that twins were not allowed to compete against the 125 singles.
Two 50ccm cylinders could have ca 10% more blowdown time area than a single125 ccm but of course also 10% more combustion chamber area so ultimate power would have been more or less the same.(Aprilia 54 horsepower and two Kreidler27 horsepower?)
Engine and transmission of the twin lower mass than a single with balance shaft and much nicer two stroke sound.

[Frits Overmars]

I'm not sure where to introduce myself in this forum, which I've been following for a while. I own several classic motorcycles, including a 125cc Garelli twin-cylinder from 1985 that I've just finished restoring. I now want to disassemble the fork, but I don't know how. Perhaps Frits, who is on this forum, knows this type of fork and could help me.Bonjour Bruno, I actually worked on that front fork myself. Back then we called it ‘White Power’, the original Dutch company name, but because certain groups started using the same name for racist activities, the name became tainted, so nowadays it’s called WP.
At the time, I focused on the hydraulic stop, which was designed to prevent metal-on-metal contact when the fork was fully compressed.
The problem was that the hydraulic stop worked in both directions: when fully compressed, it also impeded rebound. I remember milling a couple of slots, which solved the problem. But unfortunately now, forty years later, I no longer have any documentation regarding this fork or my modification.

[MINGRET01]

Bonjour Bruno, I actually worked on that front fork myself. Back then we called it ‘White Power’, the original Dutch company name, but because certain groups started using the same name for racist activities, the name became tainted, so nowadays it’s called WP.
At the time, I focused on the hydraulic stop, which was designed to prevent metal-on-metal contact when the fork was fully compressed.
The problem was that the hydraulic stop worked in both directions: when fully compressed, it also impeded rebound. I remember milling a couple of slots, which solved the problem. But unfortunately now, forty years later, I no longer have any documentation regarding this fork or my modification.


Thank you for your reply.
Do you remember how to disassemble it?
I can't figure out how to remove the tube from the sheath.

[Frits Overmars]

Do you remember how to disassemble it? I can't figure out how to remove the tube from the sheath.It might be a hex socket screw from underneath, but I’m not sure anymore. As I said, it's forty years ago and I have done a lot of other things since then.

[Wos]

Dear Specialists ;)

What are the reasons for doing a ignition curve like the orange one?
There is advance added at higher reves? Look at the red circle !

Picture borrowed

Thanks! Grüße!

Wolfgang

[JanBros]

my guess : a soft rev limiter

[Frits Overmars]

my guess : a soft rev limiterA soft rev limiter can be an option, but there is also another possibility.
Delaying the ignition timing at high revs is intended to increase the exhaust gas temperature in order to bring the resonance frequency of the exhaust pipe into line with those high revs.
However, a late ignition timing, sometimes even after Top Dead Centre, means that combustion pressure development above the piston becomes less effective, sometimes so much less that it no longer compensates for that adjusted exhaust resonance. In that case, it is better not to ignite even later at those high revs, but rather slightly earlier again.

Below are the power curve and the ignition curve of a 100cc direct-drive kart engine that delivered its maximum power at 18.200 rpm but would only reach its maximum speed of 21.000 rpm by setting the ignition slightly earlier again at that speed.
It should be noted that the exhaust system of this engine – which had no centrifugal clutch and no gearbox – was deliberately designed not to be very efficient in order to avoid the notorious torque dip at two-thirds of the maximum torque rpm.
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[wobbly]

Adding advance back in over the pipe has been used for years in JetSki racing, where the max rpm is limited by cavitation in the pump.
It is used to achieve the same effect as adding advance up the front side at low rpm.
The pipes reduced efficiency at clearing out exhaust residuals means the combustion flame speed is also low, and the extra timing pulls the peak cylinder pressure back closer to the mechanical optimum of near 15* ATDC.
At rpm past the pipes most efficient range ( around peak torque ) the same thing occurs, so adding advance past peak power means a longer pipe can be used and the extra timing allows overev to the hard limit of the pump.

[jonny quest]

Hello, I'm Bruno from France.

I'm not sure where to introduce myself in this forum, which I've been following for a while. I own several classic motorcycles, including a 125cc Garelli twin-cylinder from 1985 that I've just finished restoring.

358033


I now want to disassemble the fork, but I don't know how. Perhaps Frtis, who is on this forum, knows this type of fork and could help me.

358034

Bests regards

Bruno

Pull off dust seal, look for a snap ring. Remove top cap, unscrew from damper rod. With snap ring removed you use the two tubes as a slide hammer and pull apart. Use a heat gun to warm the area by seals. There's bushings in there.

[jonny quest]

A soft rev limiter can be an option, but there is also another possibility.
Delaying the ignition timing at high revs is intended to increase the exhaust gas temperature in order to bring the resonance frequency of the exhaust pipe into line with those high revs.
However, a late ignition timing, sometimes even after Top Dead Centre, means that combustion pressure development above the piston becomes less effective, sometimes so much less that it no longer compensates for that adjusted exhaust resonance. In that case, it is better not to ignite even later at those high revs, but rather slightly earlier again.

Below are the power curve and the ignition curve of a 100cc direct-drive kart engine that delivered its maximum power at 18.200 rpm but would only reach its maximum speed of 21.000 rpm by setting the ignition slightly earlier again at that speed.
It should be noted that the exhaust system of this engine – which had no centrifugal clutch and no gearbox – was deliberately designed not to be very efficient in order to avoid the notorious torque dip at two-thirds of the maximum torque rpm.
358045


What are some of the causes of this dip?

Obviously many possibilities, let's say on a engine that has had some time spent on jetting and a good ignition curve.

[wobbly]

The torque hole is not jetting or ignition curve related.
There are an infinite number of port timing/tuned length combinations that will work in a specific rpm range.
The more efficient the pipe design, combined with port resonance, giving good superposition over the desired rpm range - the more " out of sync " that combination will
be at around 2/3 torque peak rpm.
That effect can be very much ameliorated by a PV, as that changes the effective port timing, but without this band aid, the better your design combination is - the worse the effect becomes.
You see the effect in EngMod, where no matter what you do there is a drop in TubMax that is impossible to " tune out ".

[Wos]

Specialists:niceone:
Thanks to you!

If we bring back some more combustion pressure to camber and cylinder by adding advance in overrev. Think ;)

Isnt there a danger of overheating and Detonation?
Specially if we put in to much added advance to early?...at a pipe that is not yet completely out of its effective rpm Range?

Dankeschön! ;)

Grüße Wolfgang

[Storbeck]

Saw this on one of the bookface pages:

I'm not so interested in the port, but the comment about pressure.

Tim seems to be a very knowledgeable guy, and I've seen this idea of measuring pipe pressure mentioned by other sources that also seem to be at least well above the average bookface commentator.

But....seems like actual pressure at any given point in the pipe is going to vary widely as positive and negative pressure waves bounce back and forth, so to talk about some single number you would have to be talking about an average.

I suppose that is useful as an indication of pipe exit restriction?

Any merit to it?

358046

[wobbly]

Yep, we used this as a metric to control the outlet restriction on a World Champ Jetski.
The two cylinders dumped into a single oversized stinger tube to bump up the front side power. - as this reduces the pipe efficiency at lower than the tuned rpm's.
Then the ECU controlled a RPM/PWM water nozzle from the ski's pump to gradually flood the stinger, during testing we changed the nozzle such that at 100% open the pipe pressure was 2.8 psi ( yes average of course ).
That was the max power number off the dyno with two normal stinger inserts.

Edit - re the adding advance past peak power - it is only at peak torque that the scavenging and trapping efficiency is at its highest.
Even at peak power the engines overall efficiency has already started to drop, and it is only helped by the linear relationship Hp = Torque x RPM - the constant is irrelevant.
If the RPM has increased faster than the Torque has dropped, then Power keeps rising.
You see a similar effect with electronic power jet operation, switching off fuel just past peak Hp, offsets the carbs natural modus operandi of continuing to supply more fuel and air, even though power is reducing.