Originally Posted by
miataspeed
ive seen as much a 30psi of increased compression through retard cam timing a few times. it only take a few 100ms for the whole combustion process to occur as it is anyways. when you have you timing not in sync with the stroke of the piston you can get a increased pressure due to a compress extra air but releaseing it late.
Really, you've compression tested a motor, with throttle wide open, CAS disconnected, taken the cam sprockets off, retarded cam timing, reassembled the motor, retested compression with throttle wide open, and pressure increased by 30psi across the board?
The entire combustion process has to occur a whole lot faster than a few hundred milliseconds.
A 12:1 CR gasoline engine at 1500 rshared_pm would have a flame speed of about 16.5 m/s.
At that speed, with a cylinder radius of 43mm, the entire combustion chamber has completely burned in 2milliseconds.
The type of intake timing you're talking about happens at much higher mass flow rates, associated with higher engine RPMs. The effect is called "inertial supercharging". You can read up on it a bit here:
Dune-Buggy.com - Fuel Injection Intake
This effect is tuned by intake manifold design, and is why aftermarket manifolds produce better top end power - they have a higher natural frequency at which the pressure waves resonate.
I assure you no manifold has a designed natural frequency down around cranking RPMs.
Here's some more reading on the issue:
Volumetric efficiency - Wikipedia, the free encyclopedia