[High transfer - high exhaust] VS [high transfer - low exhaust]

[GiulioEX125E]

Hi everyone, first of all excuse me for writing in english, but I don't speak german 

I have a question about cylinder timings, I would like to discuss it in a "unspecific" way, without mentioning any specific cylinder brand, carb type, exhaust, etc.

 

Let's say I have an engine that has 130-190°. This is the power/torque graph:

 

 

31.5 hp @ 8500 rpm

26.1 nm @ 8200 rpm

 

From general knowledge, if I simply lowered both the transfer and the exhaust (let's say 125-185°), the torque band would move to the left, giving me more torque at lower rpm but also less peak power and less over-rev.

 

Now: how would this curve change, if instead I only lowered the exhaust? Let's say, from 130-190°, to 130-180°? How does lowering the exhaust only, affect the curve?

If I lower the exhaust only, it probably won't be exactly like I just described for lowering both transfer and exhaust, right?

If someone here already experimented this combination (high transfer-low exhaust), feel free to draw on my graph to show how you think the curve would change.

Bearbeitet 4. Dezember 2021 von GiulioEX125E

[AIC-PX]

.... 

 

 

 

[AIC-PX]

 

 

Here is another test with a change the Blowdowne.

 

the same i test on Polini 177 and Malssi MHR with the same effect.

 

26°-28° in my experience, that's enough for the road.

depending of Setup.... so you have more power from below.

 

for pure top performance you can go more than 30 °.

but then you often lose more power in the lower area than what you put on top. 

 

 

[GiulioEX125E]

@AIC PX

I couldn't find anything related  to my question, in those 2 topics :(

You surely tested a lot in terms of cylinder timings, but I didn't find a test where you only lowered the exhaust, keeping the transfers at the same level. You tested blowdown changes but in all the tests, you also changed transfers...