Can Detonation Do This????

66sbcduece · 07-02-2007, 09:19 AM

can detonation do this????

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A friend has a bracket car with a 650 H.P. 502 11:1 motor that he runs on VP race fuel. Car would normally run 10.40 and has approx 15 runs on it. Last couple times out he said car was running hotter[maybe 230 by time he was back to pits which was about 30 degrees more than his norm and losing some oil pressure}.Car also slowed down to high 10.70's last couple runs. He ended up pulling a head and found approx a teaspoon full of what looked like glassbead media in each cylinder and exhaust port but was apparently aluminum dust from piston tops or combustion chambers????He then found a bolt loose on his belt drive which showed his cam 10 degrees retarded! Can a retarded cam be the culprit here creating detonation actually leaving aluminum dust in cylinders? I thought just the last 5 seconds idle time would have blown this dust out the exhaust. Spark plugs showed no signs of detonation and cylinders looked good. Just never seen or heard of this before and any responces are appreciated as always. thanks much, AL

Chris Hill · 07-02-2007, 11:02 AM

If the cam is retarded 10 degrees, what happened to the ignition timing? If it's a distributor system, the ignition timing would have moved too, but I'm not sure if it would advance or reatard the ignition timing.

The "aluminum dust" sounds correct for detonation. It almost looks like sand. I'd also do a compression check and the "dust" running around can screw up valve sealing as well.

Another way to check detonation is to look at the bottoms of the pistons. I can't remember what they should look like, but it will different as more of the oil should have vaporized due to the increased temps. I read something by Smokey Yunick that spoke about that. Also, the rod and main bearings could be pretty hammerd out due to the detonation. That could be the loss of oil pressure.

Chevelle6966 · 07-02-2007, 02:26 PM

I have seen the same thing due to detonation. I would defineately check the rod bearings, as has been said if it was detonation there should be some evidence at the bearings. I thought I heard that there was a problem with some VP fuels not being to spec (dont remember where I heard it). I was wondering if it showed any evidence of being lean that might account for higher engine temps also and could cause some burning of the piston material. Just a thought.

Bruce Fulper · 07-03-2007, 01:23 AM

If the dist was not moved after the cam slipped the ignition timing retarded right with it. If the ignition timing was reset after the cam slipped he could have been putting too much heat in the combustion chamber due to the advanced ignition timing. Also the late intake opening would not allow a complete burn of the A/F mixture at the rpm's he was trying to spin. Too much of that will make carbon deposits in a hurry. Lots of leftover unburned fuel.

If there was THAT much stuff laying in the cylinders the tops of the pistons would look like the surface of the moon. kinda. Heavy sandblasted look anyway.

John Duzac · 07-03-2007, 01:49 AM

Everytime I had detonation it hammered the rings out causing some 30 to 40 % cyl leakage. This was after 10 to 15 runs and evey run would get a little worst. Additionally, we would take the engine out of the car and remove the oil pan only to find what looked like sludge in the pan. The engine looked like we never changed the oil in 50,000 miles! What a mess and a costly on at that! L little colder spark plug and C-14 racing gas cured the problem.

Paul Precht · 07-06-2007, 12:13 AM

When the cam is retarded beyond normal the exaust valves may hit the pistons. The compression will go down at the same time so your chances of a detonation issue where there was none before are almost not possible. Paul.

07-02-2007, 09:19 AM	#1
66sbcduece Junior Member Join Date: Sep 2005 Location: torrinton , ct. 06790 Posts: 3 Likes: 0 Liked 0 Times in 0 Posts	Can Detonation Do This???? can detonation do this???? -------------------------------------------------------------------------------- A friend has a bracket car with a 650 H.P. 502 11:1 motor that he runs on VP race fuel. Car would normally run 10.40 and has approx 15 runs on it. Last couple times out he said car was running hotter[maybe 230 by time he was back to pits which was about 30 degrees more than his norm and losing some oil pressure}.Car also slowed down to high 10.70's last couple runs. He ended up pulling a head and found approx a teaspoon full of what looked like glassbead media in each cylinder and exhaust port but was apparently aluminum dust from piston tops or combustion chambers????He then found a bolt loose on his belt drive which showed his cam 10 degrees retarded! Can a retarded cam be the culprit here creating detonation actually leaving aluminum dust in cylinders? I thought just the last 5 seconds idle time would have blown this dust out the exhaust. Spark plugs showed no signs of detonation and cylinders looked good. Just never seen or heard of this before and any responces are appreciated as always. thanks much, AL __________________ sbc residential yahoo

07-02-2007, 11:02 AM	#2
Chris Hill Senior Member Join Date: Jan 2002 Posts: 653 Likes: 8 Liked 238 Times in 25 Posts	Re: Can Detonation Do This???? If the cam is retarded 10 degrees, what happened to the ignition timing? If it's a distributor system, the ignition timing would have moved too, but I'm not sure if it would advance or reatard the ignition timing. The "aluminum dust" sounds correct for detonation. It almost looks like sand. I'd also do a compression check and the "dust" running around can screw up valve sealing as well. Another way to check detonation is to look at the bottoms of the pistons. I can't remember what they should look like, but it will different as more of the oil should have vaporized due to the increased temps. I read something by Smokey Yunick that spoke about that. Also, the rod and main bearings could be pretty hammerd out due to the detonation. That could be the loss of oil pressure.

07-02-2007, 02:26 PM	#3
Chevelle6966 Junior Member Join Date: Jul 2007 Posts: 6 Likes: 0 Liked 0 Times in 0 Posts	Re: Can Detonation Do This???? I have seen the same thing due to detonation. I would defineately check the rod bearings, as has been said if it was detonation there should be some evidence at the bearings. I thought I heard that there was a problem with some VP fuels not being to spec (dont remember where I heard it). I was wondering if it showed any evidence of being lean that might account for higher engine temps also and could cause some burning of the piston material. Just a thought.

07-03-2007, 01:23 AM	#4
Bruce Fulper Senior Member Join Date: Aug 2004 Location: So. Cal. Posts: 651 Likes: 4 Liked 54 Times in 33 Posts	Re: Can Detonation Do This???? If the dist was not moved after the cam slipped the ignition timing retarded right with it. If the ignition timing was reset after the cam slipped he could have been putting too much heat in the combustion chamber due to the advanced ignition timing. Also the late intake opening would not allow a complete burn of the A/F mixture at the rpm's he was trying to spin. Too much of that will make carbon deposits in a hurry. Lots of leftover unburned fuel. If there was THAT much stuff laying in the cylinders the tops of the pistons would look like the surface of the moon. kinda. Heavy sandblasted look anyway.

07-03-2007, 01:49 AM	#5
John Duzac Member Join Date: May 2005 Location: Covington, La Posts: 311 Likes: 63 Liked 85 Times in 20 Posts	Re: Can Detonation Do This???? Everytime I had detonation it hammered the rings out causing some 30 to 40 % cyl leakage. This was after 10 to 15 runs and evey run would get a little worst. Additionally, we would take the engine out of the car and remove the oil pan only to find what looked like sludge in the pan. The engine looked like we never changed the oil in 50,000 miles! What a mess and a costly on at that! L little colder spark plug and C-14 racing gas cured the problem. __________________ John Duzac D/S 4448 STK

07-06-2007, 12:13 AM	#6
Paul Precht Senior Member Join Date: Dec 2001 Location: Elysburg, Pa Posts: 698 Likes: 290 Liked 242 Times in 94 Posts	Re: Can Detonation Do This???? When the cam is retarded beyond normal the exaust valves may hit the pistons. The compression will go down at the same time so your chances of a detonation issue where there was none before are almost not possible. Paul.