Buick 350 heads

[Dennis Borrett]

I have a 1975 350 in my LeSabre with 1968 heads ! They were on it when I bought it. What does it do for performance ( maybe nothing ) But what would I have set my timing at . ( Haven"t go a clue )
Any ideas will be gratefulluy recieved,
Regards,
Dennis in Australia or Ozz !

[raycow]

A major difference between the 1975 and 1968 engines is compression ratio. The 75 CR is 8.1 and the 68 is 9.0 for the 2 barrel and 10.25 for the 4 barrel. Unfortunately, I don't know how much of that difference was caused by head volume and how much was piston dome. If it is all in the head you would definitely notice a performance difference.

I would start with the stock 75 timing setting, which is 12° BTC at idle (in drive) with the vacuum line disconnected and plugged. Then try driving the car and listen for any detonation once the engine is up to normal operating temperature. Depending on your fuel octane and actual CR, you may need to retard the timing slightly if you do get detonation.

Ray

[bob k. mando]

Unfortunately, I don't know how much of that difference was caused by head volume and how much was piston dome.



CR variance for the Buick 350 is due to piston dish. combustion chamber wise, the heads are supposed to be pretty much interchangeable throughout the 1968-1981 production run, excepting certain more modern emissions controls like AIR passages on newer castings.

otoh, i *think* the early Bu350s oiled the rockers the same way the early BBBs did, by feeding oil through block passages into the heads and weeping out of the rocker shafts.

this doesn't really mean anything for old heads on a newer block ( i'm sure it's using the newer "oil through the pushrod" system ). if you tried to use new heads on an old block you'd need to plug the oil passages in the deck or you'd probably get oil into the water system.

[Dennis Borrett]

A major difference between the 1975 and 1968 engines is compression ratio. The 75 CR is 8.1 and the 68 is 9.0 for the 2 barrel and 10.25 for the 4 barrel. Unfortunately, I don't know how much of that difference was caused by head volume and how much was piston dome. If it is all in the head you would definitely notice a performance difference.

I would start with the stock 75 timing setting, which is 12° BTC at idle (in drive) with the vacuum line disconnected and plugged. Then try driving the car and listen for any detonation once the engine is up to normal operating temperature. Depending on your fuel octane and actual CR, you may need to retard the timing slightly if you do get detonation.

Ray

Thanks very much Ray I really appreciate it mate
regards
Dennis in Ozz

[Dennis Borrett]

Unfortunately, I don't know how much of that difference was caused by head volume and how much was piston dome.



CR variance for the Buick 350 is due to piston dish. combustion chamber wise, the heads are supposed to be pretty much interchangeable throughout the 1968-1981 production run, excepting certain more modern emissions controls like AIR passages on newer castings.

otoh, i *think* the early Bu350s oiled the rockers the same way the early BBBs did, by feeding oil through block passages into the heads and weeping out of the rocker shafts.

this doesn't really mean anything for old heads on a newer block ( i'm sure it's using the newer "oil through the pushrod" system ). if you tried to use new heads on an old block you'd need to plug the oil passages in the deck or you'd probably get oil into the water system.

Thanks very much Bob
regards
Dennis in Ozz.