Engine/Transmission (1994 - 1998) Compression Question

[coonrod70]

A friend has a '98 12 valve. We were wondering if anyone out there can answer this question... . If the engine is carrying about 18:1 compression (cranking pressure), What would the compression be when the turbo is spooled up to 34-36 psi? And yes, this engine has had the headbolts upgraded. Thanks in advance for your input!

 

[JGheen]

Compression would be the same regardless of boost pressure. Compression is calculated from many things such as swept volume, combustion chamber size, cylinder bore size, etc. Cylinder pressure and compression ratio are two different things.

 

[coonrod70]

O. K, Maybe I asked the question wrong or even the wrong question... . What is the average cylinder pressure on a CTD at cranking and then again at 34-36 psi boost?

 

[BushWakr - RIP]

See TDR issue 44, page 164 starting at the top left...



"... ... . If a cylinder of uncompressed air were mixed with a hydrocarbon fuel and ignited, it's pressure would rise by about seven times (7). As atomospheric pressure is about 15psi; this would result in a peak pressure of about 7 X 15 = 105 psi... . rule of thumb is that peak combustion pressure is roughly equal to 100 times the compression ratio. ... . In a 17:1 compression ratio and that it has just burned it's injected fuel to a peak pressure of 1700 psi. ... and so on... ".



Anyone care to extrapolate the numbers when factoring in humoungous amounts of timing advance... . say 30*...



Pastor Bob... .