i have a 71 olds 350 with a prefomer rpm cam plus intake with a pair of heads off a 69 400. the guy i got it from said it was 9.0:1 compression. i read some where that it is worthless to put 400 heads on a 350 unless you have the right compression. is this a good combo or should i change it up. the car has decent sack but seams like it should have more any info would help.

 

Who knows what he did when he built it. The only way to really know is to brake it down and check it all out. I took this from 442.com

Eng Head Head Stock *Cyl vol* New CRatio, w/ head of chamber size: [cc]
CID ID cc CR ci cc 57 60 64 67 75 79 83
330 3 60 9.0 5.16 84.5 9.29 9.00 8.64 8.39 7.79 7.53 7.29
330 4 60 9.0 5.16 84.5 9.29 9.00 8.64 8.39 7.79 7.53 7.29
350 5 64 9.0 5.47 89.6 9.68 9.37 9.00 8.74 8.13 7.85 7.60
350 6 64 9.0 5.47 89.6 9.68 9.37 9.00 8.74 8.13 7.85 7.60
350 7 64 8.2 6.08 99.6 8.74 8.50 8.20 7.99 7.48 7.26 7.05
350 7a 64 8.2 6.08 99.6 8.74 8.50 8.20 7.99 7.48 7.26 7.05
350 8 79 8.0 6.25 102.4 9.91 9.59 9.20 8.93 8.28 8.00 7.74
260 10 57 8.0 4.64 76.1 8.00 7.73 7.41 7.19 6.66 6.43 6.22
260 2A ?? 8.0 4.64 76.1 --can't do it w/o head cc info--
350 3A 75 8.0 6.25 102.4 9.49 9.20 8.84 8.59 8.00 7.74 7.49
403 4A 83 8.2 7.00 114.7 10.3 10.0 9.63 9.37 8.74 8.46 8.20
307 5A 67 8.2 5.33 87.3 9.13 8.83 8.46 8.20 7.60 7.33 7.09
307 7A 64 8.2 5.33 87.3 8.83 8.55 8.20 7.96 7.39 7.14 6.91
Interchange Head ID: 10 3-4 4-7 5A 3A 8 4A

With this chart. If your engine was stock with BB heads. Your looking at 7 to 1 compression. If you say it still has a sack. I bet it has higher compression pistions. Try taking a plug out and looking at the piston with a light. If it has a nice size dish in the piston, its stock. If its flat or domed. your in better shape. Who knows he could have milled the crap out of the heads too. Got any pics????

 

i did some research and found out the car came stock with a 350 olds with a 2 barrel carb so i know the heads didn't come with it. i got a hold of the old owner and he said the motor was honed not board and that he doesn't remember upgrading to high compression pistons. but he did port the heads. im going to try to see the pistion to see if they are domed. i just got to get an idea of the compression from what stock was then compare it to what i got know.