compression ratio

[vkhawkey]

iv got a 5L vk. the gregorys says it has 9.2:1 comp. ratio. do the red or blue motors have a different ratio? what is the ideal comp ratio 4 a 308?
cheers

[Cane_It]

cant help you with the first question as I dont have a manual for the red 308. ideal compression ratio depends on what cam and fuel you are running and whether the motor is naturally apsirated or supercharged.... the higher the better obviously but you are limited by fuel octane rating, engine application and cam specs... 10-10.5:1 on the street running PULP is good but you wont be able to run normal unleaded at this ratio unless its with an octane booster.

[DANNY8]

Sry for asking this in here, but it's related to compression and it saves creating a new thread.

How do u work out a compression for a motor? I have a 173 (bored out to a 186), has got flat tops, and a 173 high compression head....any idea wat sort of compression I'd be looking at? Also gonna shave the head maybe 10-20 thou b4 it goes back on.

[immortality]

you need to measure the cc capacity ofthe head, then workout the capacity of the engine i.e. bore x stroke etc. then you need to measure the cc capacity with the piston at TDC and include the thickness ofthe headgasket.

then add the cc capacity of the head + cc capacity of the piston @ TDC incuding head gasket thickness and divide the capacity of the stroke by this number (very basic description) or


(stoke x bore ) + head volume (cc) (including headgasket thickness)
----------------------------------------------------------
head volume (cc) + piston @ TDC cc (including headgasket thickness)

or

you could just get yourself a morroso power speed calculator (slide rule) and all you need to do is line up the figures for bore and stroke, engine cubic rating and then read the figure for volume and compression ratio etc