72cutlassdog

Soon I will be rebuilding my 72 cs 350 with 7a heads. I want it to have the same 320 horsepower as the 70 350 engine. My questions I have is summit racing a good place to buy the performer rpm intake, pistons, and flat top lifters? The car already have a Qjet 4bbl and a mild cam with dual exhaust.

olds 307 and 403

Summit is good to deal with but I don't see the LF2321 6cc dished forged pistons that will put you at low to mid 9 to 1 compression. I have the mild Performer cam, with 9.5 to 1 compression with a lot changes it finally doesn't ping on 91 octane fuel. It will still be an improvement but step up to a larger cam at the same time, I guess it depends on what you call a mild cam? A change in converter and gear will make a big difference as well. I gained more swapping from 2.56 gears to 3.42 gears in the 1/8 mile than going from 7.9 to 1 to 9.5 to 1 compression with 1.72 true roller rockers in the 1/8 mile.

Fun71

Keep in mind that about the only difference between the 1970 350-4bbl engine and your 1972 350-4bbl engine was a couple points of compression and, most importantly, a completely different power rating method. The method used prior to 1971 gave inflated ratings that didn't reflect the actual engines that were installed in the vehicles.

Back in the 80s I raced my 70 Supreme against a friend's 72 Supreme and they were almost dead even up until the top of 1st gear, where I pulled ahead. How could a 72 with 200 hp (260 hp with the old rating method) keep up with my 70 with 310 hp, one might ask (both cars had 2.56 rear gears). The answer is the 70 rating was bogus. Both engines used the same cam, intake, carb, exhaust, etc, with the only real difference being the aforementioned couple points of compression ratio, which does not make for 50 hp difference.

Anyway, as stated above, swapping rear gears will give you more bang for the buck than anything else. I, too, swapped 2.56 gears for 3.08s then later for 3.55s and each time it felt as if the engine had a whole lot more power.

If you are rebuilding the engine, be sure that the compression ratio is actually what you expect. Measure the combustion chamber volumes and the piston-to-deck clearance to know for certain what those values are as they have a huge impact on compression. Also, cast pistons will be shorter than factory spec, so either compensate for that or bypass it altogether by purchasing pistons with the correct compression height (most forged pistons will be correct).