Reply to "Question about expansion tank cap"

Yes it could be but a slight ping under no load, you just leave it alone. It just means that the ignition advance is maxed out.
That's determined by the characteristics of the fuel and how much of a combination of ignition advance and static compression the fuel will take. It's the fuel that determines that more than anything else.

Your camshaft timing probably has more duration on the exhaust than the intake. There is a calculator that the cam makers use where they determine the timed compression ratio or the "effective compression ratio". Theoretically they blow some static compression out of the exhausts.

The problem is that the ACTUAL octane rating on pump gas varies just enough to make that cam timing trick on the street not even worthwhile.

People say you can run the compression ratio higher with aluminum heads and fool the fuel octane.

In my experience, neither of those work at all. The ONLY consideration on this is the static compression ratio of the engine, the compressability of the fuel (the actual octane not the posted,i.e., resistance to detonation) and the ignition advance.

Ignition advance raises cylinder pressure like you are raising compression ratio.

The ONLY way you could fix that IF you deemed it needing to be fixed would be to change the CPU to one that controls the ignition completely and change the distributor to one that is compatible with that theory or process. Then completely re-write the advance program in the CPU.

You probably would need to install a knock sensor for the NEW CPU?



IF you have the vacuum can hooked up to the engine now, assuming that you have a vacuum advance on the distributor, it is that vacuum advance that is creating that slight ping probably.

At light load the vacuum advance is maxed out usually.

It is also tune able. There is an Allen set screw inside of the vacuum nipple that can be set to slightly reduce the total vacuum advance that is providing.

Usually for "high performance" useage vacuum advance mechanisms are removed and that part of the advance mechanism internally in the distributor is locked out.

Reason for that being is somewhere over 6,000 rpm that mechanism becomes unstable and bounces making the advance timing unstable and therefore that part of the rpm curve un-tuneable.



I would leave the entire thing alone at this point UNLESS when you WOT you feel the car loose power like it wants to stall. If it does that, you have detonation and maybe very serious untimed spark?

If it does that, get out your timing light and take a couple of degrees out of the static idle timing and try that again until it stops doing it.



Lots of engines like yours are being limited to somewhere between 32 and 34 degrees total advance. I wouldn't expect any Cleveland with a closed chamber head to be able to run 36 on pump gas. Even if it was able to, it may loose power there so what would be the point?