ESE's works engine tuner

[Grumph]

You may have to work out your own. Based on experience.

May i suggest WTFF for a name - Wob's temperature fudge factor.

[Frits Overmars]

are there any newer , better correction factor systems that have been published. The one I have been using forever is SAE J1349 and with an ambient temp difference of say 5*C ( eg 12 * to 17 * ) the correction is nowhere near close enough. Anyone got some help here , as even trying the DIN , JIS and ISO corrections in the software im still way off.

I too have found that neither the SAE, DIN, JIS nor ISO correction factor systems are any good for high-performance two-strokes, so I developed my own system ages ago.

[porttiming124]

I too have found that neither the SAE, DIN, JIS nor ISO correction factor systems are any good for high-performance two-strokes, so I developed my own system ages ago. Here you go Wob.

Hello Frits.
Do you want to share this corection system?

[Frits Overmars]

Hello Frits.Do you want to share this corection system?

Yes, I was going to. I just needed some time to try and make it readable.

[Muhr]

We have thought and tested quite a lot regarding this. Do not really know what you mean by "double digits" but an HP curve within a tenth or two you want between the days, which I think you can do. On the other hand, we experience that there is a little difference between the seasons, which I suspect has to do with oxygenation in the air, which we do not measure and correct for in any correction factor that I know of. Then it is as it is with results between different dynos

Exactly as you mentioned earlier, good control of water temp and exhaust temp is a key regardless of correction

Excited to test Frits correction factor, hope you solved this.

[porttiming124]

Yes, I was going to. I just needed some time to try and make it readable.

I will try it, A big thank you Frits.

[wobbly]

Thanks Frits , I will have a go with this asap.
Double digits means our ambient air temp is often below 10*C at the moment.
But the power variation is way too big to get meaningful results when I go from say 10*C to 15 *C even if the humidity and mBar are the same.

[Muhr]

Ok understand!
Suppose you tried a web-based calculator (https://robrobinette.com/Dyno_Correction_Calculator.htm) to see that you have no problem with the software.

[Peter1962]

Peter , the RSA had a case ratio down at 1.24 , due in part to the very long rod.
An RV loves a big case - reeds do not like anything below 1.3 as to run below that Helmholtz volume , the petals have to be too thin to work with it , and loose more power from lack of tip control than any gain seen
from the bigger case ratio.
Been there done that , as its real easy to simply add a reedblock spacer to gain case volume.
Adding a 5mm spacer took the engine under 1.3 and I spent a fortune in time and money trying to tune the reed frequency to suit.
Power rose as I went thinner ( or smaller backups ) , but it never came close in power to the original case and reed setup.
Just another free lunch in the bin.

Thank you for a very clear answer. I keep making the wrong assumption that the advantage for a long rod is in the mechanical benefit of having less tilting of the piston in the cilinder when in fact the case ratio is the more important factor.

[wobbly]

You are correct though , the long rod absolutely has inherently less bore thrust friction.
But the effect on a two stroke is muddied somewhat by the dwell time differences at TDC/BDC as well.
This I suspect is another one of those Catch 22 situations like crank inertia's effect on acceleration Vs in cycle rotational speed variations effect on transfer STA.

Muhr , that calculator uses the J1349 correction , that I was complaining about as not having anything like the compensation needed. And all the other corrections in the SportsDevices code have quite similar final results.

[husaberg]

Forgive my ignorance but wouldn't the best correction factor just be a separate reference engine.
Much like the octane mule engine of old. I know it would be to be run often but it should give a pretty repeatable base reference?

Even with central heating and thermostats our house inside temp is variable here by 4 deg and about 12% humidity.
i would hate to think what the shed varies by.

[Muhr]

OK I understand.
The idea from my side with the page was to compare results to rule out that there is a local problem.
We use DIN. I think it is relatively good correction between days.
Here is an old picture I had in the phone on ref between 2 days with about 5 degrees difference.

[wobbly]

Trouble is we are talking a temp difference of 10*C to 30 *C , a baro of 990 to 1020 mBar and humidity from 45 to 85% in any combination.
I have various jetting programs that also give engine power correction and they are all close to the corrections given in the dyno software , but I see a difference of near 2 Hp in 50 with an identical
engine setup simply going from 25* C then a couple of days later its 15*C with the baro and humidity pretty much the same.
Thus I can only really do same day comparative tests using a baseline im trying to better - and that wastes a huge amount of time repeating the same setup every day , then having to make the change to the pipe or cylinder.
And more of annoyance is tests I did a month ago , bear no resemblance to the current one , unless the RAD , that drives the dyno compensation tables is essentially the same - even with identical egt targets.

[philou]

https://scooterlab.uk/quattrini-adds...e-kits-tuning/

[F5 Dave]

. . . And that's the desperate sort of stuff you might try to get around the fundamental constraints of through hole studs in a scooter engine I guess.

Outer ports are much longer, but ring still sees a square port with a plated edge just begging to be nibbled away.