what does compression ratio mean?

[SaabJohan]

Originally Posted by MustangRoadRacer

you can also prevent detonation without upping the octane by adjusting the timing, or cooling the intake/fuel. or both.

When using ignition timing to prevent knock this comes with the price of a powerloss and increase in fuel consumtion.

[JohnnyWash1]

SJ, when you retard timing to prevent preignition, you are increasing fuel consumption? How so?

Jon

[SaabJohan]

Originally Posted by JohnnyWash1

SJ, when you retard timing to prevent preignition, you are increasing fuel consumption? How so?

Jon

The efficiency of the engine drops. When timing is advanced we get a higher combustion pressure and higher efficiency. It's the lower combustion pressure that prevents knocking. So the more we can advance the timing the better, up to the point when pressure build-up will be too great before TDC. However, modern combustion chambers can run with less ignition advance with no loss since they have a faster combustion.

[JohnnyWash1]

I get it...it would never be noticeable, it is more theoretical.


Jon

[ivymike1031]

Originally Posted by JohnnyWash1

I get it...it would never be noticeable, it is more theoretical.
Jon

It's at least as noticeable as any power gain due to ignition advance.

[JohnnyWash1]

Which, surprisingly, was noticeable for me on my last car. Thanks for the tech...

[87montekid]

Does anyone know what comp ratio is safe to run a 283cid chevy on 87 to 93 octane regular pump gas?