Detonation stumping me

[stangbuilder]

x2 on the balancer is spun...go back and check TDC..

[Belgian1979]

I rebuilt a 351W with AllPro heads. Ran fine before. He ran it hot and warped the heads. Bored, cut .015 off heads to straighten, put rest together as came apart with .045 deck clearance. Didn't detonate before at 34 degrees total, 16 initial and vacuum advance. Now at part throttle above 2000 it pings horribly with 30 degrees total and no vacuum advance (unhooked it testing). Car sat for 1 year so I thought maybe it was gas. Added octane boost, ran that tank out and many others driving easy. Plugs look slightly lean but not extreme and it ran jetted like this before. Thinking may have vacuum leak somewhere but haven't found it. Couple thoughts:
1. PCV valve is teed into brake booster line- is this correct? Don't remember if this was the way it was before. Could this cause problem?
2. Could a vacuum leak from intake into lifter valley cause this issue? How do I check for that? The intake was not cut, should it have been with .015 off the heads?
Need to get this thing out of my life, any help would be appreciated.

oil will help create detonation.

Check with the smoke machines for intake to lifter valley leaks. Worked briljantly for me.

[Newold1]

Oil contamination into the cylinders can sometimes add to detonation prone situation in an engine on the "edge". Usually this much oil contamination will show up on plugs and usually shows up as blue smoke especially when the throttle is blipped up and down. Would probably be a good idea to use a borescope and look in at the tops of the pistons.

[af2]

x2 on the balancer is spun...go back and check TDC..

They go backwards and the timing would be retarded. When it shows 34* it could be way less.

[jeff swisher]

Fresh surfaced heads no pinging before ..Could the sharp finished edge of the chambers from surfacing create your issues.
I know it can and I always smooth that finished edge by hand sanding.

Those little things can ruin your day.
It only takes 1 cylinder to sound horrible.

[travis]

I had a pinging issue with one of my nearly stock 351w’s that turned out to be not enough timing...the vacuum advance diaphragm failed. The engine wasn’t running too hot according to the water temperature gauge, but apparently the combustion chambers was hotter than it liked. Took me a while to figure that one out.

[gtca9014]

How many degrees of vacuum only advance is set up in the distributor? You mention 16 degrees initial but you mention that when run at 30 degrees with vacuum advance not connected. I am assuming this means there is 14 degrees of mechanical advance in the distributor. So if there is more than 4 degrees of vacuum advance you are seeing over 34 degrees of advance if I am understanding what you have and are describing.
Most vacuum advances I have seen have more than 4 degrees total advance in the unit.
Something here is not working for me?
Am I understanding your description correctly.

Have you checked and verified the TDC timing mark on the damper to see how it corresponds to the piston TDC?

I have unplugged the vacuum advance to eliminate any additional timing since it is pinging so bad. It has 14 initial and 30 total, so 16 mechanical advance. Sorry for the confusion. I thought the timing mark could be off so timed it by ear and then kept backing off to try and eliminate pinging. It is still pinging at part throttle with 30 total and is down on power.

[gtca9014]

351W with AllPro heads. Didn't Know Bob made Ford heads??

Sorry, Pro Topline heads

[gtca9014]

Will it ping if you add plenty of vacuum advance, something like 45 degree total timing?

Not sure I understand this, if it is pinging as it transitions from 14 initial to 30 total mechanical, how will adding more timing prevent pinging?

[gtca9014]

Can't you just retard the timing until it stops pinging? Sounds like you set the initial timing at 34 degrees. Just set it back to 14.

It has 14 initial+16 mechanical to get to 30 total.

[gtca9014]

I rebuilt a 351W with AllPro heads. Ran fine before. He ran it hot and warped the heads. Bored, cut .015 off heads to straighten, put rest together as came apart with .045 deck clearance. Didn't detonate before at 34 degrees total, 16 initial and vacuum advance. Now at part throttle above 2000 it pings horribly with 30 degrees total and no vacuum advance (unhooked it testing). Car sat for 1 year so I thought maybe it was gas. Added octane boost, ran that tank out and many others driving easy. Plugs look slightly lean but not extreme and it ran jetted like this before. Thinking may have vacuum leak somewhere but haven't found it. Couple thoughts:
1. PCV valve is teed into brake booster line- is this correct? Don't remember if this was the way it was before. Could this cause problem?
2. Could a vacuum leak from intake into lifter valley cause this issue? How do I check for that? The intake was not cut, should it have been with .015 off the heads?
Need to get this thing out of my life, any help would be appreciated.

oil will help create detonation.

Check with the smoke machines for intake to lifter valley leaks. Worked briljantly for me.

I will try this, my friend has a smoke machine. I just don't see oil on the plugs and have never had one ping like this, you can hardly get on it.

[gtca9014]

I had a pinging issue with one of my nearly stock 351w’s that turned out to be not enough timing...the vacuum advance diaphragm failed. The engine wasn’t running too hot according to the water temperature gauge, but apparently the combustion chambers was hotter than it liked. Took me a while to figure that one out.

He was not using the vacuum advance before so I left it off. I can try adding it.

[gtca9014]

Fresh surfaced heads no pinging before ..Could the sharp finished edge of the chambers from surfacing create your issues.
I know it can and I always smooth that finished edge by hand sanding.

Those little things can ruin your day.
It only takes 1 cylinder to sound horrible.

God I hope you are wrong, I didn't notice a edge after getting back from machine shop but never looked for it either.

[jeff swisher]

After surfacing there is always a sharp finished edge.
Did you change to a different spark plug..sometimes a colder plug really helps out.
You could have a different brand in there and although it states same heat range I find this to not be true many times.

I always remove sharp edges on chambers and on piston tops including valve reliefs.
Just something I do. Really does not take much time.

I hope that is not your issue either.

[naukkis79]

Will it ping if you add plenty of vacuum advance, something like 45 degree total timing?

Not sure I understand this, if it is pinging as it transitions from 14 initial to 30 total mechanical, how will adding more timing prevent pinging?

At part throttle you burn it before it pings. With light throttle there's plenty of exhaust gas in cylinder fill which makes combustion extra slow, so with too little timing exhaust gas residual are also much hotter than with more timing so it can ping with low load.