I have head alot on this site about detonation and that it will happen if your compression is to high for your fules octane. What is detonation? What can be doen to prevent/fix it? and what is the highest compression that can be properly used with 89 octane gas (premium is hard to find/expensive up here)?

Thanx JJ

 

detonation means blowing up your motor,prolly 10.5 to 1 for 89 octane fuel at the most. good luck

 

denotion is pinging or preignition. It is caused by extreme heat, low octane, to far advanced timing. So the keys are to keep timing close to factory spec, keep your engine cool, and use appropriate gas when needed. I think you can run pump gas with 9.5 compression but anything more will generally require a higher octane.

 

I understand a bad EGR valve can also cause or otherwise contribute to this problem.

Doug

 

It also depends on the material of the head's.With aluminum you can get away with more compression,it disapates heat better than cast iron.

 

JJ292,

detonation is good for your motor especially when it happens just before TDC.....the closer to TDC the better.

Pinging is the result of hotspots in the combustion chamber or piston crown
causing the air and fuel mixture to preignite creating a forced on the upbound piston before it is supposed to happen.....the result is the sound of marbles knocking around inside your engine especially on acceleration, uphill climbs, etc....

Reasons can include carbon deposit buildup in comb chambers, valves and piston crowns......improper cyl head to deck quench clearace, low octane fuel
timing too advanced (causing hotspots), running to hot of spark plugs....

the damage that can result includes pitting in your pistons, cracking of rings,
cracking of ring lands on the piston.....not very good.

Predetonation is the result of forced induction compressing the air too much...when this happens the "window" at which the fuel will combust is approached...(By compressing air you heat it up)

the result is air and fuel combustion in the intake ports...also bad...

So....first thing is first.....set the timing as close to stock as possible.....
advance it until you hear the pinging.....then back it off a degree at a time until it is gone....

Run cooler range spark plugs (running too hot of plug can be the hot spot you want to avoid)

Check air to fuel ratio....running too lean can also make the engine run on the hot side....bringing in the hot spots....running the engine with a vacuum leak can also do this....

10:1 is about the upper limit in compression on premium octane fuel,
good piston and combustion chamber combos can run up to 10.5:1 on premium fuel with no problems..

If quench clearance is incorrect, run thicker head gaskets...this will modify the tight spot between the combustion chamber and piston and lower comp ratio a bit.

A bad EGR will ram hot air into the intake allowing the intake charge to heat up excessively creating the right conditions for predetonation.

let us know what you find.
R