4 replies to this topic

[akaz_mayfair]

hi,
can you check the compression ratio of an a series by using a compression tester and then comparing it to sea level air pressure of around 14psi creating a ratio or is this complete crap?

[mini_turbo_pete]

no you need to measure the cc's in the combustion chamber, head gasket and cylinder to work it out correctly

Edited by mini_turbo_pete, 10 March 2009 - 01:29 PM.

[Ethel]

Mmm - I could have a cunning plan


What if you carefully measured how much thick oil it took to fill the chamber through the plug hole? You could push one of the valves just off its seat to let the air out. Sounds as much hassle as pulling the head off tho'

[akaz_mayfair]

i remeber reading that somehwere now thanks (reply to above message)
i got onto the subject whilst thinking about forced induction,
if an engine has a compression ratio of 10:1 i understand this to mean that one part of atmospheric air is compresssed into a volume 10 times smaller than its orginal volume, but if a superchrger or turbo is fitted to an a series then the air on standard boost is compressed 50% more before it even gets compressed by the piston therefore on under the same circumstances as above the overall pressure of the air is much greater even though the compression ratio of the engine has remained a constant. how then is this compression tested?? is this the job of a simple £30 compression tester???
thanks

[Ethel]

Compression ratio is just a theoretical value really. Air is elastic so when it's been pulled through a twisty induction system at high revs that which makes it in to the cylinder before the valves close will be at a fair bit less than atmospheric pressure. A Series engines aren't the best breathers, which is why they like high compression ratios 'n respond so well to forced induction.