I was speaking with someone today who used to own a 140 back in the late 70's and said that when the octane ratings were lowered, his volvo dealer suggested he replace the head gasket with a thicker one to change the compression so that the engine would run better on lower octane gas. He said he did this and it stopped the pinging and dieseling he had been experiencing. Since I'm getting the pinging & dieseling with high octane gas, should I consider changing to a thicker head gasket? Can these cars run well without this modification on 93 octane?

Also, if I switch carbs from the Dual Strombergs to Dual SU's will I notice any improvement in performance? Do I need a different manifold or do they just bolt right up? Is it the same manifold found on other B20 engines (like the p1800?).