If you had a 600hp yb low comp engine (let’s say 7.2:1) and an identical spec engine but a higher comp (let’s say 8.1:1) if boost pressure and everything else was identical would the higher comp engine make the same power as the lower comp one?
Or would it be more or less?

I know the higher comp engine would be more responsive lower down and quicker at spooling but is that where it ends

Cheers Paul

 

If all things equal bar comp, then higher comp would produce more power (if we are ignoring the topic of knock of course).

 

 

 

High comp by nature creates a cleaner and more efficient burn therefore more power for the same air/fuel mix.

Power difference - no idea what kind of % gain would be per point gained in compression. I doubt anyones done the maths/testing on a YB to give an absolute formula. Someone like Mark Shead or Stu will have the best insights for that

 

With all things equal surely the piston squeezing the mix in a tighter hole with the higher comp will make more power, logically it's got to and push the piston down harder

 

Before turbocharged cars became so popular ,people who had normally aspirated cars and wanted more power mainly went down the route of higher compression engines, stage 3 cylinder heads, hotter cams,free flow exhaust manifolds and twin side choke webers or dell-orto carbs. It was a tried and tested method of getting more power and when I first started modifying my 2wd Saff 25 years ago I was suprised when the tuner said he would be lowering the compression ratio to get more power!! It seemed at the time strange to me but was the accepted route to take with a YB engine. Times have changed and turned full circle with some people now building high compression YB engines. No doubt Mark Shead will be able to explain why?

 

 

 

 

 

 

 

Just out of interest, what is a yb's standard compression ratio? does it vary between 205 and 200 blocks?

 

 

 

Karl at NMS has been using the infinity for a while. Im using it on my E46 M3 turbo

 

 

 

Mine was 8.3.1 and run 2.6 BAR on a 70.64

 

 

 

made all the boost by 3100rpm and held it right up to 6000and dropped of to 2 bar iirc a massive chunk of torque very responsive every where . Low comp is for old type unleaded and poorly specced engine tbf

 

 

Yea same here ..2.7bar from 3100k up to 6k tailing off to 2bar

 

 

 

easy to get those figures on a dyno but low gears on the road is what counts

 

 

 

 

 

 

A small enough turbo will do it but not a big power one, my rs6 is making 400 ps at 3000 rpm and looks to be on full song by that point, but that's a 4 litre running 350 hp per 2 litres of capacity, but so I've read that's with a 9.3-1 comp ratio !

 

 

The power curve will show when it's on full boost mate that's all I ment, what power do these 7064s make on a yb ?

 

 

Even the plot above isn't making full boost til about 4000 rpm looking at the curve, I can't imagine any turbo capable of over 500 hp on a 2 litre being able to hit full boost at 3000 rpm in gear on the road except maybe 5th lol

 

Paul,I have to say that would be one hell of a YB to be making 2.6bar by 3000 revs!!! You would never need to worry about going up to 6500-7500 rpm!!

 

all stuff went with the car Paul and never bothered copying it mate

Wtf lol why wouldn't you pmsl what a statement pmsl ! It might make full boost but it's not making full power is it lol . Or my my focus makes full boost by 3500 rpm do I change gear at 3600 then?