Hello, Im brand new to this forum and had a few questions about my pontiac 400 motor. I'm fixing up an old trans am that has a 1968 400 "Big body car" motor in it. It has the #15 heads with 1.92/1.66 valves with the 066 cam in it. I know the compression ratio is supposed to be around 10.5:1, and i know thats too high for pump gas. I was wondering what I should eventually do to be able to run this motor on 93 octane without using any octane booster? Is there something that could be done to the heads to bring the compression down a bit? Or should i just look around for a different set of heads? Kind of on a tight budget, so I do not have the money for, nor do I want to put, edelbrock heads on it. Any suggestions would be greatly appreciated.
welcome! pontiac fibbed a little on compression. your 72cc heads on a stock bore 400 will be more like 9.8 to 1. witch will run just fine on 93 octane fuel providing you limit total timing to around 32 to 35*are you going to rebuild the 400?
76 455/4spd TRANS AM69 GRAND PRIX 455/5SPD
Really? Almost everyone I have talked to said that they have too high of a compression to run the way they are. I picked this car up as a repo from a bank (!) haha so I had absolutely no info on what it had or what had been done to the car, been trying to peice everything together. I would like to rebuild it eventually, I have been doing bodywork on the car for a little while and hope to have it done and painted soon. The motor would be the next project. So I have another question then, would it be worth porting and polishing these heads to get a little more flow out of them?
Everyone else is wrong and Rowsley is correct. That cam is big so it also reduces your compression a ***Yes with your compression and cam, porting those heads will get you some more hp. Installing bigger intake valves will help also. Just make sure it has screw in rocker arm studs.