Hey guys, looking for some expert advice on my engine.

I put a built olds 455, bored 30 over, blue voodoo lunati cam, keith black higher compression pistons. My brother did a PSI test of several cylinders, over 200 psi.

Have had troubles timing it. I run 91 octane gas, and we have to time it to 30 degree max, without vac advance hooked up to stop the pinging.

Couple guys at work say that is too retarded for a BB, I am running the risk of burning the valves... Should be at least 36 degrees total. Then use either an octane booster or spike 91 gas with a few gallons of 110 race fuel - either way in a mixture that settles the pinging.

I would rather not pull the engine and swap pistons...

thoughts pro builders?

 

A bigger cam would help. 200 psi is a big number for a street car on 91 octane.

 

I agree, a different cam to bleed off some cylinder pressure or maybe different heads (or rework the ones on it) with larger combustion chambers.

 

I have considered pulling engine and replacing the pistons. Don't want to touch top end as after the machine work, was a bear to get the intake on and seal.

We have it timed now at 29.5 max and isn't pinging. But have heard that will make the engine run hotter and/or burn valves from co workers

 

Do you not have 93 octane in your area? Is your timing coming in too fast?

 

There are lots of places that don't have 93.
Op- which Voodoo cam is it?

 

I will post info from the timing card after work. One place close has 93 octane, 25 miles away. Otherwise 91 octane has been easier to find.

We set max timing to 29.5 to 30 without vac advance on. Have the heavy springs on in the distributor. I put a adjustable vac advance canister on when I replaced the lower half of the distributor. But opened it up fully as instructions indicated, then set the advance. Have not done any adjustments to the vac canister. Hooked it up and engine hasn't started pinging with it fully open...
I am out of my element on timing.
Several have told me to ignore the vac advance, set max and forget it.

 

For now, while it may not help, disconnect and plug your vacuum advance line and see if it stops pinging during moderate cruise, it won't help with pinging at wot.. I agree your compression is high and I would drive the distance for the 93.

 

I was at our local OCA meeting this summer (or was it last summer?) and the chapter president told me that acetone is a great octane boost (as long as it's pure). I don't remember exactly, was it five ounces per tank of gas? Is this legit? To be honest, I tried it a couple of times on my tired engine and didn't feel any difference.

 

We left the vac advance off to set the max timing. Then plugged the advance back in, but have the advance wide open. Haven't started adjusting it in, as it isn't pinging with it hooked up and wide open.

I think the instructions indicated to start turning it in, haven't looked into it further with it running well, and not wanting to lose drive time

 

Acetone is a strong solvent and I don't recommend it. It is also pretty expensive and tends to absorb water. If race gas is available, use some of it. a 1:4 mix with pump gas will give a good octane boost.

If you don't get pinging with no vacuum advance, then you should try ported advance, using a port on the carb that was provided for that purpose, if you have been using full manifold vacuum. Also try an adjustable vacuum advance pot which you can use to reduce the amount of advance that it provides.

 

Another way to fix it is with a degree wheel and see what it is actually installed at now. Retarding the cam 2 to 4 degrees from where it is now should drop the cranking compression some. A little richer fuel mix can help pinging as well, and lowering the running temps on your water. Running the vac advance off manifold vac makes engines run cooler around town..

 

So the acetone could wash the oil off the cylinder walls? Yeah, that doesn't sound like a good thing at all.

Fanatic, this a pic of the advance limiter I made out of a small piece of sheet steel. It was pretty easy to do.

 

Timing alone won't solve the problem. I agree retard the cam with an adjustable timing chain set. Another option is a cam change. We would like to see the specs on the cam you have now. I would recommend something like 230/240 on a 114 even 116 LSA. The new LS motors run 11:1 and some cams are even LSA of 122 degrees. Avoid 'tight' cams like 108 degrees LSA. They boost cylinder pressure in the lower rpm range where the pinging starts. How far in the hole are the pistons? Is the exhaust crossover blocked? Cold plugs? OAI?

 

Why do you think that is?