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A friend and I had a conversation/discussion/argument about engine detonation the other day. I have known detonation to sound like knocking against a thick metal surface, but my friend says it can even sound like an aluminum can crinkling or flopping around on the ground. What have you guys heard when detonation occurred in your engines? Can detonation occur AFTER a shift, but not during acceleration up to that shift point? Can a loose baffle in a muffler make the same noise? Thanks for your input!
 

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Sometimes detonation occurs and you can't even hear it. Sometimes detonation occurs and the next thing you see is your crankshaft passing you on the highway.

Detonation occurs more when the engine is under extreme load and a demand is put on it. We can talk about detonation for days. I think the sound of an engine detonating is pretty distinct. Yes, immediately after a shift would be a great time for detonation because the engine is put on a more severe load as the transmission shifts into a higher gear that the engine has a harder time pulling.

Detonation is bad, that's what timing and higher octane fuels are for...
 

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Using vacuum advance?:texas:
 

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I had a bad detonation problem when i first got my El Camino, only 102057 miles on it and it was pinging like crazy and dieseled when i shut it off. I changed the sparkplugs and found the passenger side valve cover gaskets were broken from overtightning, changed them and found the oil passages were clogged. Fixed all that and started using 92 octane fuel with octane booster at each fill up. Stopped the pinging and dieseling. The reason the person who owned this sweet 83 SS before me, they thought the engine was blown from the smoking at startup, it was the valve spring seals oil saturated from the oil passages being clogged. I'm not keeping this " boat anchor " 120 horsepower 305 smog motor for long. Planning on a 1994 350 roller cam engine with Vortec heads.:beer:
 
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One of my buddys stopped by today with detonation in his 305. He has a 80s shortbed and had been driving it around for almost a week since he didn't know what the sound was. I told him,adjusted his qjet and found out his distributor hold down clamp was not tight. Luckily I had a spare one in my parts box. I re-timed it by ear and and it stopped. He now knows the distinct sound of detonation. It sounds like two big spoons hitting eachother.
 

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There is pinging and then there is DETONATION. Pinging is the light rattle sound like the cans bouncing on the street. Pinging occurs when two flame fronts meet in the combustion chamber. The spark sets the fuel burning across the chamber which creates pressure on the other side. This pressure when high enough causes the fuel on that side to start to burn (aka how a diesel engine runs) and when the two flame fronts meet you get the two spoons hitting each other sound.
Detonation is like a bomb going off in the cylinder. Pressures are so high the fuel explodes instead of burning. This sounds like two big rocks hitting each other or a car wreck down at the corner when you are sitting in the house and hear it.
Pinging is not a good thing - detonation is a horrible thing for the engine.
If it pings under light to moderate acceleration it will probably cause detonation under heavy acceleration.
 

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Discussion Starter #8
So I guess changing out the mechanical advance springs will only help pinging at certain rpm. I think he told me his pinging (which is what he is hearing--the flicking of an aluminum soda can sound) occurs at half-throttle downshifts, which probably goes into gear around 1700-2000 rpm. A stiffer spring might keep the advance from coming on that soon. He doesn't want to slow down his initial timing, because it runs nice at idle and right off idle. He doesn't own an El Camino, or I'd refer him to the forum.
 
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