Compression and turbos??

[M1LL10N]

As nooby as this may be...I'm going to ask. How can some cars run a compression of 11 with twin turbo and some cars need lower compression to run a turbo setup. I'm not understanding it. Can some explain this to me please? Thank you for your replies.

[Spannerhead]

It's all about the combustion chamber design that is the most effective in suppressing detonation. Ideally you want to keep the air as turbulent as possible once it is sucked/pushed into the chamber. This has the effect of slowing combustion and keeping detonation at bay. Combustion speed is cardinal--after all, that's all higher-octane gas does for you, effectively: it burns more slowly and thus resists detonation.

Chamber design is why an engine with an 8.5:1 compression ratio can sometimes be more prone to ping than one with 10:1.

Hemispherical chambers (as opposed to wedge, like our 10V engines) are generally better at creating turbulence and promoting uniform combustion. It's one of the big advantages of OHC engines--they allow greater flexibility in combustion chamber design. Obviously it's not a hard-and-fast rule, as Chevy makes their wedge-chambered SBC work very well indeed.

Hope that answers your question.

[mhb_1323]

chamber design + twin turbos dont always mean more boost, most inlines just use 1 to spool the 2nd quicker resulting in less turbo lag, although a V uses 1 for each bank. you can also run water injection which GREATLY reduces pre-detonation, my friends 87 subaru loyal (total sleeper) has a 2.2 turbo motor, 9 (i think) to 1 compression with water injection and can run 16 Lbs of boost easy. and even more if he got a bigger turbo. its possible to turbo an NF or NG, which ever has 10:1, but you either need VERY high octane, water injection, or both to redunce pre-detonation.

Everybody has to learn stuff from somewhere.

[M1LL10N]