Mark,
I've tried almost every possible configuration of compression, so I am talking from experience and am not blinkered at all. I totally understand what each change means as an on cost in other changes required. EVERYTHING brings with it compromises, but in my experience high compression brings the worse type of compromise (on pump fuel) and that is retarded ignition (for equal boost pressure on a lower compression engine).
Let's use Phil's engine as an example, a relatively low 7.9:1, but to stop it from detting at 32psi, he is forced to have MASSIVELY retarded ignition (Phil's engine is running single figures at high rpm
). This puts HUGE amounts of heat in an engine, and on a road car is totally unacceptable (I shouldn't think it is too sharp on a race engine either
). His engine shouldn't go bang, but his exhaust manifold and turbo might fall off wth the high EGTs / heat
. Now he has quoted another tuner's car running even HIGHER compression, yet can't seem to grasp what that must mean to the ignition curve or boost curve - either or both of them
must be severly retarded at the top end to give acceptable PCPs to stop the engine from going bang.
Ideally, you want something like Saab developed, which was a variable compression engine - now THAT was
.