ESE's works engine tuner

[wobbly]

The hybrid design was done for the TZ and YZR designs when Yamaha got themselves a CNC anemometric flow visualising machine.
Nakanos and Jaques TZ250s were so superior using the newly developed cylinders and pistons they were easily 1st and 2nd in the GP champs
after the TZ being severely blown away for years by Honda and Aprilia.
They obviously used that shape for a reason, imho that approach is probably the best for flow attachment to the piston and least heat soak area.
But yes I have done back to back dyno testing with A Kit Honda parts and in the end a flat top with a proper toroid made better power than the dome
and a bathtub as developed at Aprilia by Jan.
When pushed right to the edge with deto, a flat top wins in that when the dome collapses it does not trap the ring immediately as happens with the curved shape.
The latest developments in KZ2 karts has the dome changing from a 7* conic to a 4*, and just now we learn that VHM have been testing a flat top CNC billet piston
and have published a graph showing around 0.9 Hp advantage on the dyno.
Remains to be seen if the lack of transfer flow attachment, cooling the piston, actually is an issue in a 25 lap final.
Years ago we raced Pavesi 125 engines with flat top designs and at the time they were renowned for making great top end power with no more problems with deto
than the others with curved pistons.
But where the extra power came from I will never know as they refused all my attempts at getting them to increase the reverse transfer stagger, and double the size of the Aux Ex ports.
If they had they would have been just as fast as the Maxter and TM engines are now - 10 years later,47Hp instead of 42.

[F5 Dave]

Bumpity? .

Back to the 256 shrouding issue, I've ended up reversing my skirt (ooer) for more support (I went from having virtually no skirt with centre cut out and mooned piston to full piston & centre protrusion). But I've got the stub in the middle, I guess if I'm charitable like an RS Honda. Case reed mod to MB100.

this lightly encroaches into the reedblock stream but so be it. The Boost entry is now filled in on both sides from this picture, but it is shrouded from the centre to the duct, but not from the reed as much (but with 90*turn). The Rotax being rotary valve I guess this would be an issue more than a case reed valve? Or should I be looking at a hole?

[wobbly]

The 256 had an issue with smashing off the rear cylinder spigot as soon as piston clearance became even slightly loose - due to the skirt and boost cutaway
not giving much support to the bdc piston rock.
Most cylinder reeds have problems with the reed stops shrouding the boost entry, so as long as this isnt an issue ( maybe fit a reed spacer )
then I would say its fine - can you pic inside the reed box for a better view.

[senso]

When I do simple engines just to spice them up a bit, and given that they have a cylinder reed intake I just grind or cut the reed stops a bit(usually about 4-6mm) so the boost port is a bit less shrouded, its cheaper than making a spacer.

[jonny quest]

Good info Wobbly on pistons, thanks.

Wonder why RSA ran the domed piston? Frits? Ignition, triple port instead of bridge?

[richban]

I question for those in the know.

I need to really be cranking out of the corners on track. ( I'm getting smoked by the thumpers ) so I am planing to push the gearing on the bike so its in 6th and in over rev at the end of the big long straight. Sacrifice a little top end, for max corner exit speed. What I want to know is what is happing in the combustion chamber when the bike is reving at 12k but out of its happy place. My bike does have very good over rev. It does not drop off that bad. Peak power is just under 11 and it is happy to rev to 12 with no major loss. What I want to know is. When in over rev is it lean or rich?

[husaberg]

That is true if you look at transfer flow. But from a cooling perspective, scavenging through the piston does help.

It might work, and it might help cool the piston. But at the same time it would raise the average temperature of the fresh charge, so it would be useful only if piston temperature is a limiting factor in that engine.

Theoretically, yes. But where should I put those holes? They must not run over the exhaust windows, which leaves only the areas fore and aft (the exhaust ports are on the right and left sides). But mid-fore and mid-aft there are no transfer ports because I reserved those areas for the piston to lean against, and for the ring gap.
The picture of the cut cylinder below shows the available areas for piston cooling windows in red. But I'm not sure whether I want to make four holes in a piston that will be very highly stressed once the rpm potential of the FOS porting system is fully exploited.

I have been working on that C port piston hole and proper transfer duct combo for direct cooling of the underside of the piston crown and would be interested in other peoples experiences with the idea too.

I don't disagree with you....How do you see the classic MZ style 3rd transfer at the rear fed by a window in the piston ? Is this the exception ?
Is it worth looking at Joe Ehrlich's boost ports again - if room can be found for them ?

I have never noticed this cylinder Nor do I know what variant it is, Anyone?

[peewee]

Most cylinder reeds have problems with the reed stops shrouding the boost entry,
.

ive seen a few cylinders like this. some hondas. and even the banshee with a stock reed block which plugs off nearly the entire boost entry. funny thing is the vf4 block leaves the boost entry almost fully open. another problem ive found with some reed cylinders, the reed block is so long and the inlet so short, the outer corners of the block sit over top of the boyesen ports . mostly clogging them from normal function

on my honda i cut back the stoppers which uncovered the boost quit a bit. still the boyesens were partually clogged but without a spacer there wasnt much i could do about that

[husaberg]

I question for those in the know.

I need to really be cranking out of the corners on track. ( I'm getting smoked by the thumpers ) so I am planing to push the gearing on the bike so its in 6th and in over rev at the end of the big long straight. Sacrifice a little top end, for max corner exit speed. What I want to know is what is happing in the combustion chamber when the bike is reving at 12k but out of its happy place. My bike does have very good over rev. It does not drop off that bad. Peak power is just under 11 and it is happy to rev to 12 with no major loss. What I want to know is. When in over rev is it lean or rich?

When using a simple powerjet nozzle the tip position matters in that no flow will occur until the slide is well past the exit hole, and there is sufficient airflow
to drag fuel up the feed tube above the bowl level.
With the aftermarket add ons and the ones as used by Lectron you can shorten the dump tube so that the flow will only occur at high slide openings,as well as high air flow.
These also have a built in "lag "control in that it takes time for the fuel to rise up the tube and dump out the exit into the air stream.
With a solenoid controlled setup all this is pretty much irrelevant as the flow can only occur when the solenoid is not powered up, and this
is TPS as well as rpm dependant inside the ECU program..
The carbs as used on the MX bikes has the dump tube very low in the bore as they added and subtracted fuel at low slide positions in those bikes.
For a race engine I bend the tube up to around 1/2 bore, as this is where the exit is on the Kehin SPJ carb for RS125/RS250 Honda.
And the general setting is the solenoid is powered up ie no flow below 4000 and 60% TPS and is powered up again at around 12400 to lean off the mixture and increase revon.
This causes a problem with Ignitechs that are used with only a capacitor, as at startup the solenoid is powered up, dragging all the voltage out of the ECU, so I convert the ECU output
to a 3 step truth table, and have the setting such that below 1500rpm the solenoid isnt powered.

Aha, I see. I think I got it now, Frits.
If the powerjet is positioned in the middle of the venturi or at a lower point, that will affect how much it will flow, correct?

I remember both Lectron and Mikuni aftermarket PJ kits' instructions, saying that the end tip of the pj should be around the middle of the carb.
Yet the Keihin PJ of the carbs for the mx250 models is down low! Position would also affect which fraction of the flow becomes more rich or not, or that doesn't matter??

Attachment 255006

Attachment 254941

Made an adjustable PJ out of a model aero engine carb needle jet for controlling the PJ. Now to get one of those solenoids the Husaburg posted to shut off the PJ for a bit of extra over rev.

Made some progress with the shorter inlet tract and expect to get the lower mid range back again with a bit of fiddling with the carburation.

Just a little bit more and the single exhaust port engine with the RS pipe will be very close to EngMod2T's predicted power output.

Attachment 254940 125cc rotary valve with a 24mm carb and air cooled.

Measured 31 rwhp (estimated 34 crank hp) on the dyno tonight, red line is last night before the inlet tract was shortened and the jetting/ignition adjusted.

I have ordered one of Wobblys special kitset "A" Kit Pipes for a Suzuki GP125 ..... so hopefully 1 or 2 more hp and a wider spread of power. Then there is the ATAC idea for better low end.

Nope. It is drawn by the dynamic pressure at the fuel exit points in the carburetter. And that pressure depends on the mean air flow velocity along those exits.
Air flow velocity is at its highest in the center of the narrowest part of the inlet tract, so the location of the fuel exit will make a difference. And by mean air flow I mean (air flow into the engine + backflow)/2.
You see, more than enough variables; more than enough differences between the exit points of the fuel flow through the main jet and the flow through the power jet.

Re the tiny bleed hole in the TZ powerjet tube - I always thought that this was a good idea to emulsify the fuel as it exited the dropper.
But years ago i did some wet tests on the flowbench with a VCR video camera ( pretty trick shit stuff back then ).
The Mikuni was a horror scene when played back slo mo,with huge "gobbs" of fuel exiting the main and powerjet.
We then stuck on a Lectron - wow, lovely fine mist of fuel from the back of the flat needle face - and it flowed 12% more air - size for size with a venturi 2mm smaller behind the slide.

Next is the current state of TeeZees GP125, here is the latest dyno curve digitised with 16% added to simulate crank power.
Then there is the sim with an actual RS early model pipe.
Then there is the new pipe of my design.
Of most interest is that in this case the sim is giving slightly too much crank power - but the shape and peak point are all but perfect.
I would be confident now that any change in the sim, would be reflected in reality on the dyno.
In my experience the later Dynojets like a twin roller 168 with Eddy current load control to slow the acceleration rate down ,seem to read around 5 to 10% lower
so this would put the sim and the dyno reading very close, as the shape is spot on now.

You have to be very carefull with the switch point and the run time on the dyno.
The switch point is dead critical to 100rpm,so i always set it too high initially and make sure that the dyno is loading the acceleration rate to be as close to that on track as you can.
This gives the pipe time to heat up and affect the power over the top, as it would in reality.
On a RS250 dropping the switch point from 12800 ( std) to 12400 gives easily another 800 rpm of virtually no power drop past peak.
On the track,if the rider can feel the switch point ( it feels like hooking another gear)the jet is too big,when its right it should be seamless and just keep reving out.
Leaded fuel is the opposite to unleaded, in that as leaded likes to run lean - you can only use a small powerjet and thus only switch off a small amount.
A leaded engine works best with around 35 to 38 PJ, the unleaded fuel can switch a 60, in Keihin numbering, as the crap fuel makes best power at peak when quite rich..

And something that I scraped from the net.........

""The solenoid control on TZ type powerjets really just shuts off fuel flow to the powerjets right at the top of the rev range to lean the mixture off to increase the over-rev once you are past peak power.

I don't have the solenoids plugged in currently though as I find they work well enough for my current needs with the powerjets simply responding to venturi vacuum pressure in pretty much the same way as the oem 3MA powerjets work.""

Attachment 233787Attachment 233788

And here is a picture of the carbs and what I can make out, a dyno graph without, and with the power jet solenoids shutting off (red line) and extending the over rev.

So it looks like you can use an electric power jet like a standard one and when the carburation is sorted, try switching it of by activating the solenoid at or just after peak power and see what happens with the over rev.

The FPE superkart engine that won the NZ road title at Manfield a few weeks ago makes 92 RWHp on the Dynojet 168 I use.
Still not quite as good as the RS250 setup we did that won at Laguna Superkart Worlds a couple of years ago.

The powerjet carb is controlled by the Ignitech with a combination of throttle position and rpm in a "truth table".
In general the solenoid is activated with 12V ( no fuel flowing) below 4000 rpm and 75% throttle on the TPS.
Above 75% and around 12400 rpm it is activated again to lean off the fuel curve over the top of the pipe.
Looks like you will be able to reverse the fuel exit, blocking off the hole on the throttle bore side, and take off fuel from the outside bung, thru a needle jet and into the top of the venturi next to the slide.

Recently I got myself (Ebay) a 38mm carb with Throttle PS and Electric PJ from a motor crosser.

Wobbly told me that on those the PJ nozzel is to low and starts to flow to soon for a road racer and the MX ones are hard to tune.

Attachment 230481

I couldn't afford to buy a good second hand TZ or RS unit. So I figure that moving the discharge nozzel.

Attachment 230483

And adding an adjustable jet from a large model aero engine could be worth a try.

Attachment 230482

On the dyno I have seen how a leaner mixture rev's on further and how richining it up for best power the over rev drops off.

I think that as the rpm goes up the mixture strength on an ordanery carb at max rpm goes over rich.

And at the moment I think the idea is that the PV is shutoff after peak power to get back to the correct mixture and by retarding the ignition at the same time extend the over rev, but I am sure there is more to it.

I would love to know more about how this type of carb should be used and/or setup.

The modern take on powerjets is to turn them off after peak power to extend the rev range. This assumes that you are happy for your engine to rev that much further past peak power & on many buckets perhaps this is not so good unless you have uprated the crank assembly. The jet will start to flow, depending on its position. Some don't seem to work well without an airbox if they aren't very prominant, or perhaps if the suction isn't so much (putting big carb on a smaller cylinder). In some cases they are best blocked off presumably if the air jet doesn't match very well & is tending to increasing richening with airflow as it is.

With all the talk about wanting to utilize only a couple of gear changes per lap, I would have thought that the solenoid powerjet was a gift from heaven.
A late model well tuned RS125 will rev to around 12400 if the PJ is disabled,turn the PJ function back on and it will go to 13800+.
Its so simple and you retain exactly the same lower rev power,but with easily another 1000rpm to work with you have the choice of adding teeth on the back, getting better acceleration from torque multiplication, or keeping the same gears - but increasing the terminal speed.
And from the dyno curves I have seen, most of the 100 buckets with short stroke lengths, arent even beginning to stress the bottom ends - with less peak rpm than the 54.5mm stroke 125 bikes or karts that will easily run to 13000 all day.

Some more RSA125 development info from Jan Thiel

"No pressure transducers were ever used in our engine development.
And time/aerea was never calculated.
The port timings remained practically the same during 15 years!
What we did was trying different angles and radiuses, mainly on
the transfer ducts. I think we tried 40 different types of transfer ducts
that did not chanche the time/aerea. It was all about in which direction
the charge entered the cilinder and how the tranfer streams influenced upon
each other! Also about 200 different exhaust pipes were tried. After 2004
nothing much was changed but we improved with different power jet and
ignition mapping. It seemed nearly impossible to improve the transfer ducts
any more. The exhaust ducts were CNC machined, using different programs,
mainly to reduce exhaust duct volume. Also about 100 head designs were tried"

Didnt calculate time area? Im guessing that means the time area requirement hasnt changed any in the last 15+ years.
So there you go its all about the transfer ducts, now where have I heard that before?
Check out the attached photos, I guess the idea of thinning the transfer duct bridge has gone out the window, and the exhaust duct hows that for a crazy shape


Attachment 231454
Attachment 231455
Attachment 231456

Recently I got myself (Ebay) a 38mm carb with Throttle PS and Electric PJ from a motor crosser.

Wobbly told me that on those the PJ nozzel is to low and starts to flow to soon for a road racer and the MX ones are hard to tune.

Attachment 230481

I couldn't afford to buy a good second hand TZ or RS unit. So I figure that moving the discharge nozzel.

Attachment 230483

And adding an adjustable jet from a large model aero engine could be worth a try.

Attachment 230482

On the dyno I have seen how a leaner mixture rev's on further and how richining it up for best power the over rev drops off.

I think that as the rpm goes up the mixture strength on an ordanery carb at max rpm goes over rich.

And at the moment I think the idea is that the PV is shutoff after peak power to get back to the correct mixture and by retarding the ignition at the same time extend the over rev, but I am sure there is more to it.

I would love to know more about how this type of carb should be used and/or setup.

Ok now we have a stepper motor controled power jet........

The 'high compression brickwall' is no longer as hard as it used to be. With leaded fuel the compression ratio was 19,5; nowadays it is about 15. The 'brickwall' arose from the high expansion ratio (which is identical to the compression ratio). The higher this ratio, the more the burnt gases in the cylinder cool down before they enter the exhaust, thus lowering the resonance frequency of the exhaust system.
Riders complained that the engine would not rev, especially not in the lower gears, where the revs rose so quickly that the rising wall temperature of the exhaust pipes could not keep up with them. So you had cold exhaust gas and cold pipes.

The problem was to a large extent solved when the solenoid-controlled on/off-power jets were replaced with stepper motor-controlled jets that could continuously adjust mixture strenght, allowing the engine to rev more freely.

Attachment 229455

This is it. The stepper motor itself originates from a Fiat Uno where it regulates the idling rpm

Regarding the Aprilia RSW/RSA125 single, Jan Thiel told me that in seven years of testing the racing department had not been able to establish which was best: low or high inertia. I would choose low.....

Frits Overmars

The tech term for what Frits is describing is Superposition of the Ex pulse.
This is easily described in a sim, where a residual pressure ratio is seen sitting at the Ex port when it is opening.
The "new " pulse is added to this residual, and a very large pressure ratio exits down the duct to the header.
The larger the initial ratio, the larger the amplitude of the wave in the diffuser - this creates a deeper depression around BDC, and it is this that initiates the biggest mass flow
from the transfers.
The lower Ex timings of 190 and below create larger residual pressure ratios,over a wider band, and thus these work with a good pipe design to use "resonance" to increase band width and also peak power.
Big problem though is this whole concept is at odds with maximising blowdown to allow good peak power and more importantly, overev power.

The sim shows RGV100 making serious power with the superposition pulse going down the duct - off the scale.

Re the trombone pipe results you did sims for TeeZee.
Look carefully when you say it seems to affect the top end "more ".
At 9000 the lowest reading is 13 Hp, the highest reading is 17 Hp, thats an increase of 4 Hp, thats 31% more power in the bottom end, that then allows the thing to rev to 17,000.
Seems a not bad result.

Re the powerjet temp result you mentioned.
The effect of the solenoid powerjet is as you described - this I only discovered recently with a datalogger that I could set the sample rate of the EGT high enough to read the temps quick enough - along
with some exposed junction probes.
I was testing a RS125 on the dyno and it was making NO power past 12500, looking at the data you could see the egt drop from 640 C to 580 in around 400 rpm.
After fixing the fact some idiot had left out the rpm plug in the loom, the solenoid now switched on at 12200, and the temp stabilised at 650 past 12500 and the thing than reved out to 13500 +.
So the powerjet switching isnt making the mixture "lean"as such, it is simply maintaining the correct mixture, and thus the temp in the pipe.

Imagine the valve passes 60 cc of fuel per minute, but the engine only needs 30 cc. How would you go about that? You could open the valve for 30 seconds and then shut it, but by that time the engine may have drowned.
Open it for one second, close it during one second, open it for one second, sounds more sensible, doesn't it? That is why I quoted the valve's frequency: 13 Hz.
That means it can open and close up to 13 times per second. This again means it could open for 1/13 of a second and close the rest of the second, or open for 12/13 of a second and close during 1/13 s, or everything in between. And of course it can stay completely open or closed; enough possibilities to govern the mixture.

The ignition timing does not have to be changed when you use an electronic power jet. But both the ignition timing and the powerjet timing are means of influencing the exhaust gas temperature. A late ignition and/or a lean mixture both cause a higher EGT, so you can match the exhaust resonance frequency to a rising engine rpm.
And if you have that power jet available, the ignition does not have to do it all by itself anymore, so you can search for a timing that gives a better overall result.

I was trying to find wobs simple answer but gave up

Oh there it is

With todays technology the bar can now be raised to around 40 crank Hp without too much drama involved, and thus achieving around 35 RWHp.
Its just a matter of careful parts selection and very careful assembly.

The alloy inserts for the TZ350 was the customers choice - once its all proven, and we get a handle on what the engine likes, then I will do some bronze ones.

AvGas in NZ is all LL100, this is low lead 100 octain.But the rating is defined differently in avaition.Its approx equiv to 100 "pump" gas, but has a lean rating of 100 and a rich rating of 130.
MNZ Appendix E defines avgas as max 112 MON amd max 108 RON.

Avgas, or any leaded "race" fuel reacts completely differently to unleaded pump gas.
In general terms the unleaded hates compression, but loves timing.Avgas is the opposite in that it makes more power up to the knock limit with more com.
Unleaded makes better power when run rich,avgas makes more the leaner you go.
Tuning in the old days with RS and TZ engines meant using lean mains and small powerjets ( 35 ) as turning off a big jet over the top would mean being too lean in the overev.
Nowdays the unleaded fuel runs rich at peak power, then uses a big powerjet ( 55) to create some heat in the pipe over the top.

[richban]

I was trying to find wobs simple answer but gave up

Oh there it is

Nice one ta. Not time to sort the power jets but will get them sorted for the street race.

[husaberg]

Nice one ta. Not time to sort the power jets but will get them sorted for the street race.

Someone could come along later and suggest that if you really want it to leap out of corners, You might want to consider putting a 50kg midget on it

You could also make use of vitue that it has a cassette gearbox, with freely available alternate internal ratios, then gear it for specific corners..........
Pretty sure the similar year RS250 ratios work.
I posted the available ratios a while back. they seemed to be NF5 numbers in the f3 parts list.

[Peter1962]

I have never noticed this cylinder Nor do I know what variant it is, Anyone?

I think this is a DEA cylinder

[richban]

Someone could come along later and suggest that if you really want it to leap out of corners, You might want to consider putting a 50kg midget on it

You could also make use of vitue that it has a cassette gearbox, with freely available alternate internal ratios, then gear it for specific corners..........
Pretty sure the similar year RS250 ratios work.
I posted the available ratios a while back. they seemed to be NF5 numbers in the f3 parts list.

Yep or just splash the cash on an F3 box. Or man up and clutch it up. But when she goes from 40hp to 75 in half a second things get rather exciting.

[F5 Dave]

I've taken some pics I'll load them up tomorrow. Its all a compromise, just working out the best one I guess.

[Frits Overmars]

I have never noticed this cylinder Nor do I know what variant it is, Anyone?

I think this is a DEA cylinder

Right. In fact it's two DEA cylinders; the left and center pictures show a 2013 cylinder; the right pic shows a 2014 cylinder from the DEA superkart tandemtwin with RSA-based cylinders. The notches in the bore surface are supposed to retain some oil for the benefit of the exhaust bridges.