Compression ratios:

27th December 2007, 11:21

what are these all about?

I've had a bit of frustration searching the forums so i thought i'd start a thread.

All ANSWERS welcome

27th December 2007, 11:28

its a measure of the difference between the volume of the cylinder at BDC (bottom dead centre - the piston is at its 'lowest' point) and the volume in the cylinder at TDC (top dead centre - the piston is at his 'highest' point).

this is useful because it gives an indication of how much work is exerted on the air, it is compressed more, has a higher density and so has a higher potential energy.

as a result you get higher efficiency from the engine.

A downside is that with a higher compression ratio there is a higher liklihood is pre-ignition of the fuel (which lowers mechanical efficiency as is 'bangs' before its suppose to).

So with a high compression ratio you want a higher grade of fuel (higher RON number)

I could nag on forever about this lol

hope that gives you an idea

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27th December 2007, 11:30

So whats a higher RON number and are there any mechanical jobs that can be done to sort out pre ignition aswell?

27th December 2007, 11:34

the RON refers to the 'resistance' of a fuel to ignition. the higher the number the more 'resistance' it has. therefore you could run higher compression ratio's get a higher mechanical efficiency (or more power).

there should be a knock sensor which detects preignition and retards the spark timings as a result. mechanically im not sure man

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27th December 2007, 11:36

well thankyou very much you have expanded my knowledge at a very speedy rate.

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