I have a Buick Riviera 1975 with a Riviera 1971 engine. The original engine blew because of overheating. When replaced with a 1971 Riviera engine, the repair person installed the intake manifold toghether with the carburator of the 75 engine on to the 71 engine. Now the engine is running smoothly, except it has a pinging problem when hardly accelerating. The EGR valve has been checked and it's ok. All the vacuum hoses have been verified and they are ok and correctly routed. I have tried to disconnect and plug the EGR hose, that gave a little bit more power and more pinging. I replugged the EGR hose. I have tried 94 octane gas, it reduced somewhat the ping but it is always there. The 71 engine should give 330 horse power. If I retard the vacuum advance to eliminate the ping, I am loosing a lot of power and don't feel that I have a 330 horse power engine. The 71 engine, which by the way is a 455, is supposed to be very healthy as it came out of a 1971 riviera which had around 80000 miles. No oil consumption or noises whatsoever during normal operation. The cooling system has been completely checked. New water pump, thermostat and thermostatic fan.
I will appreciate any ideas to solve the problem.
The ping is only on acceleration.
The distributor is the original riviera 75.