I am finally putting my motor togather this coming weekend and was wondering what kind of power you think I will get out of it. It is a 75 455 with ported and polished 71 heads. Heads are milled 20 thou. 2 1/2 inch dual ex. TA 310 cam with new bearings pushrods and stage one valve springs. My rearend is posi with 355 gears and running a 3000 stall converter. Also new lifters and all gasket matched
Without knowing if the porting work helped or hurt your heads a ball part hp number can't be made! If the porting work went in your favor , and seing your not running headers I will take a stab at 25 to 30 more hp then stock.
The 1975 pistons only have about a 27cc dish, but their Compression Height causes them to be as much as .090 in the hole at TDC. Even if your combustion chambers are 69cc, you would be lucky to have 8.5:1 static compression. The TA310 cam wants at least 9.5:1. With your current static compression, your Dynamic Compression Ratio will be down around 6.6 or so. The best way to get your compression up is to lose those sorry 75 pistons.
We'll have to wait and see if the OP ever comes back. He may have a 75 block with .030 pistons vs a stock 75 short block. There is no sense in speculating until we hear back from him.
My motor is a stock 75. I talked to Mike at TA and he is the one who told me to go with the 310 so that is what I ordered. If I don't have the compression of 9.5 will it hurt. Or can I shave more off the heads to get the compression up higher. Thanks alot for the help
Leave the heads as they are. Replace the pistons now before its too late ( as in the engine assembled and in car) The stock '75/'76 pistons are poopy, crappy, junk.
Or is it that the pistons are ok but the rods are too short?! Those are actually better pistons with a shallower dish than the older pistons, but they didn't lengthen the rods so they don't work very well with the shorter compression distance they have. With a set of these; https://www.ebay.com/itm/H-Beam-6-7...ash=item466024e4f9:g:cEwAAOSwOA1aBEi5&vxp=mtr Altered to fit a BBB, open wristpin hole to your Buick piston's size and have the big ends narrowed to fit a BBB crank. Then destroke the crank to dial in the compression ratio you want because the BBC rods have a .050" smaller big end hole than the BBB rods do.(2.200" vs 2.250") And TA DA, your '75 pistons aren't looking so bad anymore! OR, leave the stroke factory when the rod journals are cut down .050" and just get the gasket thickness you need to get the compression ratio you want for that cam. There are plenty of different thicknesses for 455 head gaskets to be able to dial in your compression. You can also have the deck milled .070" and run the .020" steel shim head gaskets and have the pistons .040" down that would be a good quench distance if those pistons had a quench pad. But yeah, different pistons would be the easiest and less expensive and best way to go. You have the opportunity to get rid of those crappy like ALL of the factory BBB full dish pistons are and get pistons with a quench pad! Might as well use the '75 open chamber heads because that is what a full diameter dish piston does, makes the engine think it has open chamber heads anyway!
Sorry guys been gone for awhile. Thanks for the input. I don't have the cash for new pistons so I had my block cut 50 thou. My pistons are now on average 38 in the hole. Will this bring my compression high enough to use the TA 310 cam. THANK YOU VERY MUCH
With .050 cut off the deck you MAY have to have the intake side of your heads milled so the intake fits properly again.
If you have not done any needed head work yet then installing bigger valves will gain you back 2 CC's of chamber volume also.
