I have a built 390, with 10-1 compression and forged pistons. I am using 91 octane and my timing is currently at 26*. When i really get on the gas, i hear what sounds like something clinking under my truck. My exhaust is very loud so i cant pin point it. Is it pinging? What degree should my timing be? Thanks for any help in advance.

 

Base timing should be 6° BTDC.

 

So should i retard it all the way to 6*?

 

Pinging, i.e. detonation, pre-ignition, spark knock, sounds very much like glass marbles being shaken around inside a metal coffee can.

 

I retarded it back to 16*, It runs crappy before that. Anything 15 and under i mean. I will text drive it later and see how it performs. Can i go to a colder spark plug and still advance to the 20's?

 

The tinging noise, yes, tinging, is only under heavy throttle, in the 3500-redline range. It wont do it when i just rev the engine, or when i dont use alot of the skinny pedal.

 

Maybe my vacuum advance is hooked up wrong? I have a holley 600 Double Pumper 4 bbl and the vac adv is hooked in on the left side just under the air cleaner

 

Ok, i dropped it back to 16 and took her for a test drive. no more noise. so i will advance it to 18 and test drive, 20 and test drive and then drop back a few degrees if it starts to ping again

 

I'm an Eddy guy but IIRC Holley is the same, ported vacuum (what you want for vacuum advance) is sourced from the right side of the carb (passenger side).

 

Ok, mine is right then. left side looking at it from the front. still pass side. Thanks!

 

Your ping comes under heavy load. No load if your not moving. The pinging noise comes from little pieces of aluminum being blasted off the top of the piston. In time your burn a hole all the way through. 1. by running low octane gas/nolead. 2. to high of dizzy advance timing. So with your truck being over 5,400 lbs is way heavier then the 2wd trucks at are around 3,800 lbs. So what I'm getting at is you can't run the same high timing advance if your going to be putting you big foot all the gas peddle to the metal. Check spark plugs for little glass looking beads on the inner part of the porcelain part of the plug. If you find any this bits of aluminium from the piston top. This is when guys will start backing down the timing as it's slowly doing internal damage to the pistons. Use a octane booster additive will help. Plus don't do any towing with high timing as the ping will return back big time.my 2cents
orich

 

Well first off, thank you for the info. Second, i dont do any towing, i have nothing to tow. I have since backed down the timing and will keep it at 16* until i feel like it needs to gulp 93 octane. I also have a large cam that allows me to advance the timing to the 20's, i just really never experienced pinging before now. So, i did not know what i was hearing. Now i know and know what to look(listen) for. I think that if you are finding bits of piston on your spark plugs you have already done the damage. Too little too late.. IMO.. I drove it just up the street and back under heavy load and thats when i heard the pinging. So, very very little damage was done during that time period. Thank you for the input tho, if i want to go past 20* from now on i will make sure im running 100+ octane just to be safe

 

The hot Summer time heat adds to the condition the maybe why you just now are noticing the Pinging, Detonation, pre-ignition, Spark knock all ends up causing the same thing. Little red-hot carbon cinder on the piston,act as a lean condition. If engine was in a lighter vehicle you may not be having any problems. Plus it all depends where you live like elevation.. Many guys here try running high advance timing because others can, but since we don't all live and have the same vehicles we can't do it...
orich