I have a 69 chevelle with a 402 I'm going to put in. The motor has oval port closed chamber heads with standard valves and the 100 cc which might be about 98 because they were probly milled a little. The motor has the regular flat tops and was told by a machine shop that I have around 9:1 to 9:7 compression. I got a edelbrock performer rpm intake, holley 750 vs, msd igntion, 1 7/8 headers with 2 1/2 pipe, 4 speed with 4:10 gears. I would like input on which cam I should run, the 276/286 or 280/288. Got to be able to run power brakes. I'm interested in the 280 but think it might be a tad to big with my compression. I did a search on both but am still unsure. Strictly street car but I want the most power I can get. Any input would be appreciated. Thanks, KJ

276/286 f10 or f12 for power brakes.
280 is too big imop for CR in the 9's w/o more CID. If it really is 9.1 or so, then a 272/xxx might be better.

Are you sure about the flat tops? Even the later low compression 402's had .110 domes. You might want to double check what you have before makeing any cam decisions.

KJ,

What heads do you have? I run a '70 402 + .030 motor in my '69. TRW L2354 pistons (.180 dome), '290 semi open chamber heads actually CC'd to 104 - 105. With the block decked and heads cut, my CR is just 9.5. Are you looking at the hydraulic Lunati's or the solids? I run a Crane 286/296 - 112LSA hydraulic, no problem with power brakes. I would cinsider this the limit though of practicality for engine vaccuum, any longer duration and the engine vaccuum would drop too low. Have about 12 at 900 RPM idle now.

The heads are 3909802. I ended up pulling the head last night and the piston has a little bit of a dome in the middle. I got this motor last year from a girl I was talking to, it was her grandmothers son who had it rebuilt but he passed away a while ago. She told me about this motor that was sitting in the garage, so I went to checked it out and it was a bigblock all sealed up sitting under a tarp. They told me the machine shop that did the work but they didn't have paper work that far back. Anyways I picked up the motor for $400 and also got a set of front disks for a chevelle. Thats why the compression is a mystery but I might have a little more then I thought. Thanks for all the replys so far. KJ

Those are the '67 396 heads with the real small bathtub shape closed chambers. Your CR is closer to 10.0/1. Depending on how big of a cam you want to run, you could run something with 280 - 290 advertised duration. I would stay away from the short duration quick ramp cams in this motor as it will be detonation prone with too short of a cam.

Well.... :D Since you have the head off, how about we nail down the compression ratio. ;) Can you measure the piston to deck height? How about getting a picture of the piston tops and posting it for us? That way we can see what dome you have. With this info we could better help you with a cam selection. smile.gif

Rod

Thanks for the replys everybody. Got a part number off the bottom of the piston and it's 980P and from what I understand it's a sealed power piston. Dont have a camera but the best way I can describe is that the piston has another circle that is a little bit from the edge of the piston. That circle slopes up a little to a flat point in the middle. Thanks, Kevin

I called the machine shop that supposedly did the work on the motor. Gave him the piston part# and he said I have about 9:5 maybe a tad more. I searched the net a little bit and couldn't find anything on the pistons. Thanks, KJ.

What kind of pistons are they? Forged (shiny, bright silver), cast (grayish), hypereutectic? I ask because the 980p may just be a casting number and not necessarily a part #. TRW and Speed Pro forged are usually stamped on the combustion surface.

They got a dull silver look to them. So theyre probly cast but might be hyper. How could you tell if it was a hyper? Thanks, KJ.

I ended up calling Lunati and couldn't get ahold of Harold so tried the other extension for Steve who has worked for Harold for over 15 years. Told him I have about 9.5 comp and the rest of the combo and he said I should go with the 280/288 grind. He said I shouldn't have any problem with power brakes and the 280 would give me more peak torque and horsepower. Talked to him for over 20 minutes, real good guy. Should have it dropped in about 2 weeks and see how she runs. Thanks for everybody's input. KJ

Cool. Let us know how it goes.