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Originally Posted by Kev_205
by running a lower compression ratio you can prevent pre detonation, but this will come at an expence of power.
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not always it all depends on the trade off between increased thermal efficency of higher compression compaired to the smaller amount of mixture in the cylinders and the fact that turbos do not like the pumping losses that high c/r can create
imadgine this
1000CC engine
1000cc combustion chamber
this engine would have 2:1 compression, and have 2000cc of mixture in the cylinders on the compression stroke.
lets raise the compression
with a 500cc chamber
the engine now has 3:1 compression, but the engine now only has room for 1500cc of mixture
if we now use 2 bar boost
the low compression engine could hold say 4000cc mixture
but the high compression engine would have a mere 3000cc of mixture in it.
in this instance the low compression engine would have so much more mixture in it it would make more power than the high c/r engine despite the increased thermal efficency of the high c/r engine.
add a restricter and it all changes, if you cant get much mixture in then you have got to sqwash it hard,
WRC cars may all have high compressions, but they have restrictors, and ultimatly still have lower power outputs despite the high c/rs than many a clubman turbo car