compression

[nismoboy]

will a high compression engine a make more power than a low comp engine at the same boost level?

 

[GTiR_Mic]

I thought the idea behind having a turbo'd enginge was to run a lower compression. When you see the turbo'd vtec's they are only running low psi to save the engine :lol: :lol:

Mic

 

[campbellju]

Yes, the higher compression is effectivley a secondary "boost". Problem is that this can cause detonation and is why you don't put a big turbo on a high compression NA car.

WRC car's use higher compression engines so they can develop broader torque ranges whilst still making 300hp on a little turbo

 

[nismoboy]

kk, so what would be a faster car?

1. 1.2 mm hg and 1.7 bar boost

2. 2.0mm hg and 2.0 bar boost

 

[campbellju]

Just looked through some of my old arhives for a bit more detail.

A standard 1.2mm hg gives a cr of 8.3
A larger 2mm hg gives a cr of around 7.3

If you're running a big turbo on a low cr then you will get laaaaaaaag but it will be safe and when the turbo kicks in it will be faster if you're running more boost.

The best analogy I can think of, that only you can answer, is which is faster, an EVO FQ400 or an EVO FQ340. In a drag strip its the FQ 400 but this has been shown being beaten by a a fiat skoda box from 30mph in 5th gear and taking nearly a mile to overtake (Feature was on top gear)

Maybe the question you should ask is which is safer rather than which is faster if you're running 2Bar. Other people with more experience of running turbo can answer that but IIRC, its normally gearboxes and diffs that fail with that boost than the engine (Assuming forged bits etc)

Jim

 

[nismoboy]

intersting. but what set up will be quicker? or what whould be the difference of

1.2mm hd and 1.7 bar

and 2.0mm hg and 2 bar

over the qtr?
bhp and lbft?

 

[ashills]

both be similar as a hole but the higher comp 1.2 will be a lot nicer drive and more responsive

 

[DOT2DOT]

But everyone loves booost :twisted:

 

[campbellju]

intersting. but what set up will be quicker? or what whould be the difference of

over the qtr?
bhp and lbft?

The best analogy I can think of, that only you can answer, is which is faster, an EVO FQ400 or an EVO FQ340. In a drag strip its the FQ 400 but this has been shown being beaten by a a fiat skoda box from 30mph in 5th gear and taking nearly a mile to overtake (Feature was on top gear)

Maybe I wasn't clear, on the drag stip, bhp, lb/ft, 2.0 Bar of boost will beat the 1.7Bar no arguments.

However, "off boost" power and boost response would be worse too with the lower cr. More liklehood of being caught in the wrong gear and getting embaressed by a saxo.

So back atcha, which is faster, a laggy fq400 or a responsive fq 340. Much has been written on the evo forums about this.

This will answer your own question.