Author Topic: Bonneville Early Detonation  (Read 124 times)

Offline livesoundga

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Bonneville Early Detonation
« on: Mar 17, 2018, 07:55:22 »
Last year I noticed Iím getting a ping when the motor heats up and is under moderate pressure. I used 110 octane gas and noticed the pinging went away. Am I correct in assuming the timing is advanced to far, and that this is early detonation? I hope to get it right before it gets too much nicer out.

1970 TR6C with T120 Head

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Online jpmobius

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Re: Bonneville Early Detonation
« Reply #1 on: Mar 17, 2018, 12:07:33 »
Typically, too much compression, and/or too much spark advance, and/or too lean, and/or too rapid fuel burn (i.e. too low an octane rating), and/or running too hot.  Try the timing first. 
« Last Edit: Mar 17, 2018, 12:09:55 by jpmobius »

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Offline DesmoDog

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Re: Bonneville Early Detonation
« Reply #2 on: Mar 17, 2018, 13:14:11 »
Typically,<snip> too rapid fuel burn (i.e. too low an octane rating) 

This is a common misconception - Octane rating has nothing to do with flame front speed, higher octane gas does not reduce detonation by burning slower. It reduces detonation by resisiting auto-ignition at high temps/pressures longer than lower octane gas. Dual plugs, swirl in the intake charge, MSD ignitions, they all burn the mix faster. "More complete combustion" is touted for numerous mods. The only way to have "more complete" in the same amount of time is to do it faster. How does slowing down the flame front figure in with that? Slower burning makes detonation worse, not better.

Detonation is an explosion/shock wave, not a fast moving flame. Fast moving flames are your friend.

As for the original post, "early detonation" isn't something I've heard of, but it sounds similar to pre-detonation, which I have heard of but doesn't exist either. Pre-ignition does exist, but it is not the same as detonation. Pre-ignition simply means the mixture lights before the plug fires. This can lead to detonation (just like advanced timing) but you can have either one without the other.

Detonation is caused by a combination of high temp, high pressure, and time taken to burn. Anything that increases any of these will increase the tendancy to detonate. Higher octane gas can resist high temp/pressure for a longer amount of time than lower octane gas. If you have knock you can lower the temp, lower the pressure, burn the mix faster, or use a gas that can resist exploding under these conditions longer.

I'm not familiar with the engine/mods you have so can only guess that timing may be an issue, or switching the head has raised compression higher than it should be. Maybe the timing is off, maybe you could use a thicker head or cylinder base gasket.