why does it seem people are so worried about detonation??

If your static compression is above 10:1, you should be looking very hard at the quality of your fuel and your cam profile.


What motors are you used to working on?
Were you pulling timing in order to run higher CR?

jason

Detonation is basically the fuel air mixture igniting before it should. It is a bad thing. So people with high compression engines need a higher octane fuel that resists pre igniting. This can also be accomplished by taking timing out of the engine.

you could also run water injection!

can you run a higher compression ratio with an aluminum head?

NOmoreHONDA said:

Well I am coming from building honda's.

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That's your problem right there; comparing apples to oranges. Hondas have pentroof combustion chambers, aluminum heads, smaller cylinders, and typically operate at much higher rpm than what we deal with around here. All those things work in favor of preventing ping. The Honda bike engines can run 12:1 on 87 octane.

The typical pushrod V8 still has iron heads with bathtub combustion chambers and operates at 6000rpm or less. My ~9.25:1 302 has aluminum heads with and a cam skewed toward lots of dynamic compression and it rattles sometimes in 100 degree weather on 87 gas and 12* initial timing.

That's why we worry about ping.

hungrymonkey said:

can you run a higher compression ratio with an aluminum head?

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Typically yes.

351w here with iron heads and roughly 12.7:1 static compression running on 93 PUMP GAS! Also has a 150 shot on it with 93 PUMP GAS.

Never heard detonation one time in 8 years with the car with a 10-12* base timing. About 8* with the nitrous. Even tried 100 octane unleaded and 16* base timing and ran SLOWER.

jmo... 11:1 compression is EASILY doable with pump gas!

Yeah, but how much dynamic compression is that cam making? Try 12.7:1 on a mild cam and see how long it lasts.

Pinging or spark knock is not the same as detonation.

Pinging is preignition of the fuel air charge by some source of ignition other than the spark plug. The source of the ignition can be a hot spot in the combustion chamber such as carbon, a spark plug insulator, side electrode, or a sharp edge on a valve. It occurs before the spark plug can fire and while the piston is still on its upward movement towards TDC. That is the cause of the characteristic ping or ringing sound, much like shaking a coffee can full of BB’s.

Detonation is the uncontrolled explosion of the fuel air charge after the spark plug fires and starts to burn. In a properly running engine, the spark plug ignites the fuel air charge and it burns slowly and evenly across the combustion chamber, much like a fire as it burns its way across a grassy field. When detonation occurs, the ignited fuel air charge causes an increase in the combustion chamber pressure and temperature. The remaining fuel air charge that has not been burned self–ignites explosively causing tremendous heat and pressure. The source of secondary ignition can be the same as preignition, or can be simply due to the heat and pressure. Detonation is what damages engine parts because of the excessive heat and pressure.

Pinging can lead to detonation, and the results are the same: engine damage because of the excessive heat and pressure