ESE's works engine tuner

[Yow Ling]

Maybe we will be on mobility scooters before Kickaha gets it bucket going again

[husaberg]

Nowhere did I say they were "truly out matched" just no one seems to be able to put together a fast two stroke with a good rider/frame combo and dominate the racing as some people seem to think will happen

Artistic license. But seriously the tracks for the most part are not generally HP tracks. (there are a couple of notable exclusions of course.)
I think the main reason is because the Fxr150's are now so ubiquitous that as 75 percent of the field is mounted on them and thus the number would then suggest that generally most of the fastest rider will probably be on them as well.
Also the FXR are a modern design as well they are a generation ahead of the 2 stroke engines freely available.

Its just that no manufacturer makes a serious 2 stroke liquid cooled bike case reed or disk valve power valve anymore or ever really, also no half way serious 125cc ac 2 strokes since the early 80's.
The people that have the skill to create or pay to have a genuine contender 2 stroke are pushing 40 or older with kids and responsibilities.
and are a little (lot) heavier.
I for one are going to try and stop the rot even if it means having to have someone else take up the ridding duties.

[TZ350]

Page 390 Technical Posts from the last 10 pages. There are other collections on each decade page back to page 80.

Husaberg has posted many interesting articles, the best way to find these is to use the Thread-Tools then View-Thread-Images and then sort them from the beginning and 70 a page, there are about 3,000 images on this thread.

... the BRA rules .. Bucket Racing in Australia ...

Poor 1970's commuter-bike crank... 13500 sounds like a big ask.

Phenolic main brgs with RGV250 rod assembly has proved reliable so far, the RGV rod doesn’t use side washers so gets better oiling and away from the b/e seizure problem TF/TS’s often suffer from ....

I'm pretty sure if you order a TS/TF rod you will be told they have been superceded. The only genuine rod you can get that fits is what used to be the RM rod. You have to wonder why they even bothered making two rods with different material specs.

Shh ... You may find something "legal" here http://www.pro-x.com/downloads/Technical.pdf …

Thanks, Mental; everything seems to be fine now. So here they are again:

http://www.kiwibiker.co.nz/manual/Aprilia-1.zip (6.8 MB)
http://www.kiwibiker.co.nz/manual/Aprilia-2.zip (8.3 MB)
http://www.kiwibiker.co.nz/manual/Aprilia-3.zip (9.2 MB)
http://www.kiwibiker.co.nz/manual/Aprilia-4.zip (7.2 MB)
http://www.kiwibiker.co.nz/manual/Aprilia-5.zip (5.6 MB)

… I made plastic plugs several years ago using glass reinforced Peek,and tested them with no positive results at all. But now we have tripple ports reaching around to 1/2 bore, and yes they do work a treat.

Some engine development tips

Re TuBMax, this is the temp of the unburnt end gases in the squish.
It is affected only by a few factors.The main ones being ignition advance and effective compression.
Effective com is composed of the static com as set by the cc in the head. Then you add dynamic com to this.

The dynamic com increases with charging efficiency ie more air/fuel in the cylinder per stroke - better trapping efficiency ie more air fuel kept in the cylinder per stroke, and lastly scavenging efficiency - less exhaust residuals left behind per stroke.

As you increase the last three mentioned, then the effective compression within the cylinder, as the piston approaches TDC, becomes greater, and more fuel is burnt - creating more pressure and heat, thus power.

Then you will reach a stage where the end gasses detonate, due to radicals forming, from excess heat and or uncontrolled pressure rise.

The only way to reduce this, is to drop the static com or reduce the ignition lead.
As you approach the theoretical limits of charging, trapping and scavenging efficiency, then you have to balance this with a static com and or ignition advance that will keep the piston alive.

This is exactly what happens on the dyno during development - its a juggling act to balance the com and advance to get the highest cylinder pressure you can, to release as much heat into the gas as is possible ,at the right time to suit the engine characteristics needed.

Com and advance put more of the finite fuel "energy" into the piston and cylinder and then eventually into the water - thus this energy is lost, and cannot be used in the external sense ie to heat up the pipe and generate more overev .

But pushing the limits of all the factors, in some form of synergy, is the black art we are only just beginning to be able to reliably juggle with in a good sim - without locking up a piston and a rod coming at you thru the screen.

Hope I never see that error on my screen - looks bad.

… we need to address two important factors in a 2T engine design.
Torque and rpm it all comes down to Hp = Tq*RPM/5252.

Keep the torque constant and increase rpm by 10% and you get 10% more power.
Hard part is holding up the torque at the higher rpm level.

A short stroke will allow greater safe rpm, but the bore area needed to create the angle area needed, is limited more and more as you increase the piston size at the expense of stroke length.
The piston gets heavier as well, so ultimately the engine may not physically be able to rev to anything like what the stroke may allow.

The bottom line to all this is that the square engine has the best compromises of rpm capability Vs useful bore area.

Go short stroke and though you may be able to rev it, the scavenging is compromised by the bore availability. With long stroke - the reverse happens.

This all assumes we are talking max power capability - 250cc MX is all longer stroke now as this favours torque production from low rpms, and the extra rpm capability of a square engine isn’t needed to create peak power numbers.

The stinger config in pipe 21 is exactly what is needed for a 125 making anything like 50 Hp.



I have been using CNC nozzles I had made over 10 years ago that are 23.2 at the smallest section specifically for the pipes I have built for karts that make around 50.

For a 125 down at 40 Hp then 22 is about right, as is used by the CR125 engines in SKUSA stock class,down at 30 Hp I would say 20 or 21 ( never built one, sorry)

It all comes down to the amount of air that is dumped into the pipe, and this is totally reflected in the Hp numbers - empirically these sizes work every time to generate the correct back pressure, without causing deto or finicky tuning issues.

Like below? Red is the exchangeable restrictor. Blue is its container, welded to the yellow endcone at the left. The yellow pipe at the right is the tailpipe (held in place by a spring) with a bigger diameter than the restrictor.

NGK race plugs were originally designed to be about 1mm proud of the chamber,one reason there are no threads on the shell end.

This leads on to one reason that a toroidal chamber design works best.
I believe that plug position and indexing effects are reduced considerably by the quality of the CDI and the energy in the gap.

Using Ignitech and 0.2 Ohm primary Aprilia RS250 ( RGV) coils, I tested plug indexing and found no difference - but the fine wire R7376-10 plug made near on 2 Hp in 50 against a
Denso RS125 plug and a B10EGV.

That engine was running Avgas at 15.8:1 with a bronze toroidal insert that could be rotated to index the plug.
It was modified later to over 50 Hp at 13000 and won 3 straight 125 kart titles.

I was looking through some links posted by Husaberg and came across this one of a performance Kart engine and was very impressed by the finning on the crankcase, it sort of suggests that case cooling should be taken seriously.

A very informative post on specific heat ….. its worth a read.

Specific Heat - the quantity of heat required to raise the temperature of one gram of a substance by one degree Celsius.
Specific Heat of Fusion - the quantity of heat required to convert a substance from the solid to the liquid state with no temperature change.
Melting point - the temperature at which the substance changes from a solid to a liquid.

* Its specific heat as a solid
* Its melting point
* Its specific heat of fusion
* Its specific heat as a liquid

[TZ350]

Simulation for Husaburg to see if the simulator will show him any performance advantage with using a positive offset.





+5mm offset, not much in it. will try 12 forward next.



+12mm offset

Its negative offset or backwards compaired to crank rotation to reduce noise and positive for performance. The simulator doesn't see much in it. But it did affect the combustion chamber volume for correct compression ratio.

My experiance with wrist pin/cylinder offset as an engine re-building industry insider back in the day was that offset was in the negative direction, and about 2mm or so and was the manufacturers attempt to quietin piston slap as the crank passes through TDC. Get off set pistons the wrong way around in a reco engine and the engine became very noisy.

A bit of time on the net and you can find out all sorts of things.




More than anyone ever wanted to know about offset
http://homepages.cae.wisc.edu/~hessel/faqs/kiva4faqs/zpistnCalculationWAndWOWristpinOffset.html


Taken from
http://www.network54.com/Forum/74182/thread/1286357572/1286438278/Offset+vs.symmetrical+piston+pin+-+any+real+difference-

Right, there was a noticeable difference. Some NASCAR racers were disqualified when.....

October 6 2010, 10:12 AM

it was found upon teardown that they had reversed the pistons. Here's what the racers discovered. The factory installed offset was against the direction of rotation which quieted the piston slap noise. But performance suffered because the angle on the rod is increased even more than on a piston with an on center pin. More of the combustion pressure is wasted trying to get over center and pushing the rod "sideways" instead of down. So turning the piston 180 degrees puts the rod and pin at the same angle of offset, but in the direction of rotation. This gives the rod a more downward or straight orientation so that the combustion pressure is not wasted trying to get over center, but is used to push downward. This is the the same as the "long rod" principle. The geometry is reconfigured in a different manner than modifying the offset, but the end result is the same; the rod is straighter in the bore at any given degree of rotation. There are a couple more ways of doing the same thing. One is offset overboring in the direction of rotation. The other is casting the crank centerline in the block so that it does NOT intersect the cylinder bore centerlines. Example: the FH V8 cranks were .265" offcenter in the direction of rotation. An FH upside down on a stand really looks strange because the offset is very noticeable. And when it is rightside up and you turn the the crank you notice that as you turn the crank the piston comes up slowly on the upstroke but drops off quickly on the downstroke. This is the same thing that happens when you reverse and offset piston to the direction. The illustration I always use is the bicycle crank. You remember how hard it was to get you bike going when you tried to push the pedal the closer it was to top dead center. So you would keep pressure on the pedal with one foot while you pushed the bike forward a little with the other foot to get a better or more downward angle on the pedal. Same thing with pin offset in the direction of rotation. So in other words, the standard placement of the offset piston pin against the direction of rotation hurts performance. Hollis Franks Black 63 1/2 XL R Code Gray 65 289 Falcon Ranchero

[F5 Dave]

I seriously think a fit Nigel on a long track would just make the whole argument mute. Actually I wonder when Bren will do the same duwn sowth.

[jasonu]

I seriously think a fit Nigel on a long track would just make the whole argument mute. Actually I wonder when Bren will do the same duwn sowth.

He will have to address the reliability issues first.

[TZ350]

... I've got Vizard's formulas here somewhere for 4 stroke inlets - it's not simple arriving at a working inlet resonator, then you adjust on the dyno ...

I would be very interested in any numbers you can come up with.

[Fast Eddie]

Nowhere did I say they were "truly out matched" just no one seems to be able to put together a fast two stroke with a good rider/frame combo and dominate the racing as some people seem to think will happen


I reckon we'll be on electric bikes before it happens

hoping to race my 2 stroke thing in the garage I'm building up (when I get some replacement parts). I didn't think there was any real class I could race in though? f3 or whatever with the 400cc 4t's?

merry xmas too.

[Grumph]

When Vizard was here some years back he did a seminar for the Engine reconditioning assn in ChCh - fortunately it was an open seminar.

He was frank about inlet resonators - he didn't have the answers yet. the formulas he gave were guides at best and worked on large 4 strokes. Remember, as he said - 70% of all race engines in the world are Chevy based V8's....that's where he earns his $$$.

A maximum of 4 cylinders per plenum - volume for 4 cyl 50 -60% of the volume of all 4. 3 cylinders 65 - 80% of the volume of all 3.
Two cylinders - about equal to the volume of both.

RPM range - lower rpm = bigger plenum volume. Higher rpm = smaller volume.

[TZ350]

Thanks Grumph ...

Two cylinders - about equal to the volume of both.

RPM range - lower rpm = bigger plenum volume. Higher rpm = smaller volume.

If two 4-stroke cly - about equal to the volume of both

Then would a single 2-stroke cly - the volume of itself? sounds like my 125's plenum at 1.2l may be way to big.

[TZ350]

Hi Husaberg



here is a simulation with plus 12 and minus 12mm offset at the pin, you may get the same results by moving the cylinder.

[Grumph]

Sorry TZ that was only part of my original attempt post...

Volume within limits is not critical as he says the length of the inlet tract into the resonator can be varied on the dyno to change the system frequency hence torque peak rpm.
He says don't exceed 180 ft/min on the intake velocity into the plenum - doubt you'd exceed that with a 24mm carb on a 125.

Given the shape of your existing plenum TZ, flow lines could be a problem with making it smaller.

There's got to be more up to date info somewhere on the web - even if it's 4 stroke based the principles are the same

[TZ350]

There's got to be more up to date info somewhere on the web - even if it's 4 stroke based the principles are the same

Thanks, and yes, even if its 4-stroke it gives me the idea and I can halve or double the numbers to find a 2-stroke solution.

[TZ350]

More for Husaberg



Differences in combustion chamber volume for the same corrected compression ratio.



Plus 12mm Minus 12mm STA's

EngMod2T is very usefull and only $400 USD to buy, everyone should have a copy ....

[NordieBoy]

Anyone got anything that'll convert old Auto Sketch SKD files into something useful?