Hi guys. Recently did a full rebuild on a 1973 Eldorado 500 convertable. Broke it in real easy, then noticed severe pinging when I put my foot in it. Pulled timing advance back some, no change. Then pulled base advance back to 0 degrees. No change. Swapped distributors, timing at 0, plugged vacuum advance. No change. Added octane booster to fresh premium fuel, no change. EGR valve is brand new from NAPA and hooked up. The rebuilt long block from is from S&S Engine in Spokane WA. Don't think that matters except to mention that my original block and heads which never did this, (15 years ago), went away as core return. Rebuilt air pump- all smog stuff new/ rebuilt and hooked up as far as I can tell. New/ rebuilt carb, new fuel pump, new or rebuilt everything. Pinging is so severe that the car is undrivable.
I bought a rebuilt long block from S&S Engine < http://www.rebuiltautoengines.com/ > who make big claims about the quality of their builds. This car ran perfectly with all smog, including EGR, diconnected 15 years ago.
The '74 had odd-ball pistons from what I remember, but the '73 shouldn't be that way. Some mechanics have a boroscope, to look into the cylinder through the spark plug hole, which may be a way to dee and identify the top of the pistons. The '73 is supposed to have a "soap dish" shaped dish, while the odd '74 has flat top pistons. If yours has flat top pistons with the '73 heads, it might be the problem, since without the dish, the comp ratio will be higher than stock '73 etc.
It looks like to get to the bottom of this you are going to have to take off a head to see what you have..Large or small chamber heads? What dish pistons... how much was milled off the heads? and the type of head gasket ? How thick is the compressed gasket? All these things can cause this type of problem...
The so-called rule of the thumb is : "don't mix early heads with late pistons" 12:1 ratio will be the likely result..
The head number may be visible with a valve cover removed. The small chamber heads numbers end in 250, 902, and 950. The late large chamber heads end in 552, and 493. The position of the Caddy spark plug holes are sort of visible enough to maybe get a look at the top of a piston....not sure, but worth a try...
Automobile(s): Cadillac 78 Seville, 78 Coupe de Ville, 92 Sedan de Ville
Re: 500 massive pinging!!!
A simple compression check might shed some light on the compression; especially since we aren't dealing with a wild camshaft. Most smog engines have 130-150 compression and older high performance engines can crank in the 180 range. If you really had mismatched heads and pistons I would think the compression gauge would read considerably over 180.
It sure is puzzling since you dialed back the timing so far with no change.