ESE's works engine tuner

[seattle smitty]

I have read of tuners looking for evidence (burned paint, etc.) of the hottest point on the header pipe, as a guide to estimating wave speed. I wonder if you could do this sort of thing using the temperature-graded indicators that welders use. One company that has made these products for years is Tempil, and they have wax crayons with which you mark a line on your metal, and when it reaches the selected temperature, the wax liquefies. They are accurate to plus or minus 25F degrees (and are also marked for Celcius); I believe the same company also has a paint-on indicator substance, but I've never used that. The crayons are inexpensive, and maybe you could have a set of them with different target temperatures for various tuning purposes. (The only race-engine-related use I've ever used one of these temp-sticks for was pre-heating an old cast iron Konig outboard cylinder for welding, long ago).

[Frits Overmars]

...because it is an oversquare engine at 14000rpm the piston velocity is less than 25m/s so I think it's possible with this speed, but maybe unpossible from the port angle/areas...

That's right. Piston velocity is not a limiting factor in a two-stroke; angle.areas are. And oversquare, or short-stroke engines are at a disadvantage.
Imagine an engine with a bore and stroke of 40 x 40 mm. Make the bore twice as big, and all port widths can be doubled. But doubling the bore means that the stroke has to be made 4 times smaller in order to keep the cylinder capacity unchanged. And dividing the stroke by 4 means that for a given timing all ports will become 4 times lower. So all port areas and angle.areas will be halved! That low piston velocity won't do you any good...

[Frits Overmars]

I have read of tuners looking for evidence (burned paint, etc.) of the hottest point on the header pipe, as a guide to estimating wave speed. I wonder if you could do this sort of thing using the temperature-graded indicators that welders use.

No way Smitty. Those indicators will tell us the outside temperature of the pipe, not the temperature of the gas inside, which can be hugely different.
One lifetime ago I worked on pipe lines so I'm not unfamiliar with pre-heating high-grade steel pipes prior to welding.
I'll admit I did 'borrow' those indicators for use on crankcases, brake drums, etc, but never on exhaust pipes.

[seattle smitty]

Can you use any of the commercially available air-fuel O2 meters with crankcase-lubricated 2-stroke race motors, or does the lube confuse (and foul) the sensor too quickly? I just got one of these (from Innovate) to dial-in automotive engines.

[Haufen]

That's right. Piston velocity is not a limiting factor in a two-stroke; angle.areas are. And oversquare, or short-stroke engines are at a disadvantage.
Imagine an engine with a bore and stroke of 40 x 40 mm. Make the bore twice as big, and all port widths can be doubled. But doubling the bore means that the stroke has to be made 4 times smaller in order to keep the cylinder capacity unchanged. And dividing the stroke by 4 means that for a given timing all ports will become 4 times lower. So all port areas and angle.areas will be halved! That low piston velocity won't do you any good...

I am wondering why all these racing engines are "only" square and not long-stroke. What do you think?

[Muciek]

I think this answers Your question

Dont need to spend hours trying to get the numbers to work in the sim
The short stroker is capable of mechanically going to 15,500 @ 26M/Sec but the port STA is simply unable of supporting any power up there.
Yamaha tried forever to make it happen, but finally gave in with a square engine and won the 250 title with Olivier Jaques around 2000.
Going the other way the 52 by 58.5 is able to generate the STA needed but with the longer stroke is only capable of 13500 rpm absolute peak rpm
whereas the square engine runs out at 14500 when stressed to 26M/sec mean piston speed, as has been proven to be reliable with an Aprilia.
The extra 1000 rpm would easily blow away an equally tuned setup simply due to the gearing torque available for an equal terminal speed.

[Frits Overmars]

Can you use any of the commercially available air-fuel O2 meters with crankcase-lubricated 2-stroke race motors, or does the lube confuse (and foul) the sensor too quickly?

Provided that you don't mount it too close to the cylinder, where it would be hit by washed-through unburnt mixture (between the cylinder and the sensor there should be room in the header for at least once the cylinder capacity), that you use only unleaded fuel, and that you switch on the sensor's internal heating element and bring it up to working (=self-cleaning) temperature before starting the engine.

[breezy]

I am wondering why all these racing engines are "only" square and not long-stroke. What do you think?

didnt it used to be something about pisiton speeds? although with todays better quality materials perhaps thats no longer a problem. better torque but poor rpm levels?? although a friend of mine noted a recent moto cross engine ( may have been ktm 125) had a longer stroke but produced good power.

[Haufen]

I think this answers Your question

Well, as Frits just recently mentioned that piston velocity is NOT a limiting factor (any more?), there should be nothing in the way of going from square to long stroke for hunting max hp figures, or is it?

[breezy]

Yes it's all gone a bit quiet. But lets recap, for charge to flow from the crank case to the cylinder at speeds that would normally stall the transfer charge (not enough blow down time) there must be a method of "super" charging the crank case (I don't suggest mechanical) crank case pressure must be increased before transfer takes place. How is this done? That is the key, suggestions anyone.

May be exhaust returning wave, which stuffs fuel back via the exhaust port, also effects a transfer boost port via a reed valve to increase the cylinder filling?

[breezy]

Well, as Frits just recently mentioned that piston velocity is NOT a limiting factor (any more?), there should be nothing in the way of going from square to long stroke for hunting max hp figures, or is it?

"Shrinking the bore and increasing the stroke provide more opportunities for favorable compromise, but doing so requires exotic materials if the 18,000-rpm revving ability is to be maintained"

this passage was taken from a web site talking about 4 stroke ferrari f1 engine... so it looks like longer strokes are know less piston speed hinderd..

[peewee]

frits maybe im wrong on this but isnt the port timing of a modern 2t engine mostly useless numbers as its only the point where the window opens and closes relative to crankshaft degrees with no regard to time area or angle area ? you could have a tall window and still a small angle area

was there ever a usa 2t racing team worth mentioning ? it seems as if the usa tuners are 100 miles behind the rest of the worlds tuners. advancements in recent 2t development dont seem to be associated in any way with usa. im trying to think of one thing they could take credit for. even with some fairly modern designs like ktm to look at, they seem oblivious to the fact they could apply some of those ideas to older engines. maybe they like being stuck in 1980 with short rods, over sqaure pistons and small crankcases

[F5 Dave]

was there ever? Well the evil empire & of course Erv could hold their heads up at the time.

[wobbly]

As Frits has alluded to you can use a Lambda in a 2T.
I have been using one for ages on the dyno that screws into a fitting on the front of a muffler cap.
It must be pre heated before use and will be killed quickly by lead, or being covered in oil as when warming up or running in slowly.
But at the end of the day an egt will tell you all you need to know about whats going on, including things the A/F ignores like deto onset.

You simply cant use any info from 4T sources and try to translate this to a 2T scenario.
A 4T can easily be rpm limited by materials technology, but this has been helped alot in recent times by the short strokes NEEDED to allow a big bore to fit in
the huge valve area requirement for the power predicted.
A 2T is much more limited by the bore size and the area that can be fitted into that specific circumference,and THEN becomes limited by the mechanical issues of exceeding the 26M/Sec
that has become the currently accepted allowable max mean speed.
This is why a 50.6 stroke in a 125 is just as flawed from the outset as a 58.5 for the reasons I outlined in the quote shown above.

Yes, quoting port timing is a completely useless exercise without the analysis needed to compute the STA available - as this takes into consideration all the
important variables of swept vol/time/area

There are plenty of examples of well engineered USA engines we hear little about, in the SKI sports for example.
But most companies are dealing with aftermarket add ons to existing very flawed designs, the Banshee being the best example where say CPI produce exquisitely done
castings that do have square bore/stroke setups available, but usually cater for the Yank obsession with " if in doubt - bore it out " huge customer base.
And if you want to look deeper, of course you can't go past the efforts that the Roberts Team went to when trying to drag Yamaha GP kicking and screaming into new technology for
Wayne R to win races and titles.
They were one of the first to use the Czech flow visualizing technology that Yamaha finally got on board with when it was all too late in early 2000s.

[husaberg]

was there ever? Well the evil empire & of course Erv could hold their heads up at the time.

That Bud Aksland did all right, surprised you forgot about him Dave.


Center of the Pic, propping up Kenny Roberts.