Mr. B

iTrader: (1)

I know exactly what it sounds like.. both pinging and knock, and I'm familiar with piston slap as well.

What exactly causes the "marbles-in-the-coffee-can" sound???

nikon1999

iTrader: (22)

detonation i believe is what your talking, to much timing not enough octane, thats what i think your talking about at least, we experienced it in my friends mustang. He thought his timing was at Base 0 but it was at Base 10 and he cranked it up

1RawTA

iTrader: (1)

ya bob im thinking detonation as well... pull some timing and see what happends

NLinnear

iTrader: (8)

Bob, this must be your first Mustang. They all sound like that. That's why they're soooo cool. Just give it more timing and fill up with 87 octane. Then race around for awhile...

Slowhawk

iTrader: (12)

The sound is caused by combustion.It's kind of like multiple combustions in the cylinder raming into each other which builds hot spot's and chip's the piston.Ussual cause is pre ignition(high timing)/oil/low octain gas.

NoGo

iTrader: (2)

You want to know what makes the 'noise' right? Not why it makes the noise?

Detonation creates rattling noise because of the sheer force that detonation exerts on the piston top. A controlled ignition of the cylinder gasses travels in a predicable manner across the cylinder at roughly 5000 ft/sec and acting on the piston top at a predictable 10-12 degrees after TDC.
Detonation, the ignition of combustible gasses due to auto-ignition, creates a pressure/flame front that travels through the cylinder at roughly 20,000 to 25,000 ft/sec. The accelerated flame front quickly ignites the remaining air/fuel mixture within the cylinder at a rate that is too fast for the piston to relieve it. The result is a massive pressure spike exerting itself on the piston and the head. The rate and force at which the gasses strike the piston and the head give it a hammer "crack" or "ping". Not much unlike striking an anvil with a ball-peen hammer.
Detonation can also cause a knock sound. This occurrs when the piston is near TDC. The piston, being at TDC cannot travel down the bore when the pressure front strikes. The only give, is the oil wedge in the bearing. This lubricating wedge collapses and the bearing surfaces collide giving it a distinctive low frequency "knock" noise.

Mr. B

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Yeah.. I did that and it's 99.9% gone..

Mr. B

iTrader: (1)

That's what I was wondering about.. the noise itself.. thanks!!!!

I've pretty much eliminated it.. pulled some timing in the effected rpm/load and I have to be stuck in bumper-bumper traffic for an hour+ with the A/C on to hear it. Also.. the NY gas sucks.. if I get my gas in NJ it doesn't have that ethenol crap (at least I don't see the sticker that says "contains 10% ethanol") and all is well.

Mr. B

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