what causes detonation?

[67chevemall]

I have played with the timing for weeks now.

I got it to idle nice but it still ping pop pings when you put a load on it.

Should I just keep playing with the timing or could it be something else?

Stumped.

[Greg2]

Here is a link to a good basic article on detonation and pre-ignition. It's a good starting point.

http://www.streetrodstuff.com/Articl...tion/index.php

Page 4 covers possible causes.

[67chevemall]

Originally Posted by Greg2

Here is a link to a good basic article on detonation and pre-ignition. It's a good starting point.

http://www.streetrodstuff.com/Articl...tion/index.php

Page 4 covers possible causes.

Man that is a sweet ass article.
Thanks

I hope I can get the timing to wear it is safe to be said that it is in the right spot.

Engine damage scares my wallet to pieces....

[SactoJim]

Detonation is basically the uncontrolled ignition of unburnt fuels typically after top dead center. It is not good, but many engines can withstand some detonation. Mfrs. even take this into account when designing components for engines.

Pre-ignition is the worse and basically uncontrolled ignition of fuel too far before top dead center. So the rotation assembly has momentum turning in one direction and pre-ignition is trying to make it turn the opposite way......very bad and most engines will not live long with this.

Bottom line is that both aren't good and should be avoided with proper tuning and the correct octane rated fuels.

[67chevemall]

Maybe I still don't have the timing on.
It is the same with 94 oct and 87 oct

ahhh it is so nice out ahhhhh

[seabee]

what kinda compression are you running . have the heads been decked . cause it could be from to much compression . i have seen this happen to a engine were the heads and block were decked to much . to fix it we ended up replacing the heads.

[vfrdude]

Originally Posted by 67chevemall

Maybe I still don't have the timing on.
It is the same with 94 oct and 87 oct

ahhh it is so nice out ahhhhh

OK - lets start at the beginning -

Set your timing at somthing like 4 degrees BTDC. Disconnect the the vacuum line to distributor and plug it (a golf tee works good).

Take the truck out, and do some full throttle acceleration runs. Listen for the pinging, if you don't hear the ping/knock, then advance the timing by another 2 degrees, and repeat. Do this until the motor starts to ping/knock, then back off the timing 2 degrees.

Now connect up the vacuum advance, take the truck out on a road where upi can cruise at about 50 MPH - accelerate from 50 to about 70 - not full throttle just use light throttle. You will probably hear the ping/knocking under light/part throttle at cruise.

You may have too much total advance for the enigine combo, or the vacuum advance is coming in too quickly. There are vacuum advance kits that will address both of these problems. I've used the Accel kit:
http://store.summitracing.com/partde...5&autoview=sku\

Hope this helps...

[Bob 68327]

Originally Posted by vfrdude

OK - lets start at the beginning -

Set your timing at somthing like 4 degrees BTDC. Disconnect the the vacuum line to distributor and plug it (a golf tee works good).

Take the truck out, and do some full throttle acceleration runs. Listen for the pinging, if you don't hear the ping/knock, then advance the timing by another 2 degrees, and repeat. Do this until the motor starts to ping/knock, then back off the timing 2 degrees.

Now connect up the vacuum advance, take the truck out on a road where upi can cruise at about 50 MPH - accelerate from 50 to about 70 - not full throttle just use light throttle. You will probably hear the ping/knocking under light/part throttle at cruise.

You may have too much total advance for the enigine combo, or the vacuum advance is coming in too quickly. There are vacuum advance kits that will address both of these problems. I've used the Accel kit:
http://store.summitracing.com/partde...5&autoview=sku\

Hope this helps...

I Agree!!!

[beautimus]

okay,
i'll take a stab at this one. if the engine has a bunch of miles on it, (if not, ignore this post) it could simply be carbon build up. to check for this, i usually take a soda bottle, fill it with water, and very sloowly dribble it ito the carburator while the engine is idiling. don't drop it in fast enough to kill the engine. just a few drops, then a few more, and so on until the contents of the soda bottle are all gone, then don't let the engine die on you and take it for a spin around the block.
the water in very small amounts will soften the carbon deposits on top of the pistons and allow them to break free and exit through the exhaust port. with the carbon removed your compression will be back where it should be, and the detonation should stop.
and you should be able to set the ignition timing properly.
If this is indeed the problem, it is because the carbon raises the compression ratio high enough that the engine can't run on the octane of your fuel. plus the carbon will glow hot enough to cause pre-ignition.
An old timer passed this trick on to me, when i was having problems with a camaro i owned, he was pretty smart, and in my case right on the money.
If this doesn't help you, i appologize. but maybe it will help someone else in the future so i threw the info out here.

[larry may]

http://zhome.com/ZCMnL/PICS/detonation/detonation.html

[mnunn454]

Vacuum leak, vac advance canister or centrifugal advance under the rotor not working, would be my guess.

Did you do anything recently that may have caused this, or has it been there all along, or has it been getting worse over time?