Need advice on my engine build (top and bottom end). Details inside...

302 LX Eric · 07-23-2002, 08:23 AM

Good to hear that you're going with a forged SCAT crank and H-beams - very nice.

As far as the compression goes, getting ~8.7:1 with the TFS heads at 61 cc's will be nearly impossible w/out a dished piston of some kind. Just some quick reference numbers for you to consider:

61 cc head with a flat top piston = ~ 11.2:1
61 cc head with 29 cc dish piston = ~ 9.1:1

This information was taken from DSS's compression ratio chart for a 357 (overbored 351) and TFS TW heads. Not the exact combo you've got, but darn close. Tom Naegle at DSS can give you a real good idea of where you'll end up depending upon the amount of cc's you dish the pistons.

Obviously, more cc's in the combustion chamber will reduce compression (about a .1 of compression reduction for each additional cc)

Will you be boring the engine? A 357 is nice because you can have the machine shop bore the cylinders and have a nice cross-hatch to have 'brand-new' cylinders that will seal very well. I also recommend upgrading the ring package to the plasma-moly (ductile iron) rings. Excellent sealing for blower motors.

FWIW, my 331 came in at 9.2:1 compression and I'm putting a D-1SC blower on as well (injected car though).

Good luck,
E

07-23-2002, 08:23 AM	#1
302 LX Eric or '331 LX Eric' Join Date: Jan 1999 Location: Columbus, Ohio Posts: 2,142	Good to hear that you're going with a forged SCAT crank and H-beams - very nice. As far as the compression goes, getting ~8.7:1 with the TFS heads at 61 cc's will be nearly impossible w/out a dished piston of some kind. Just some quick reference numbers for you to consider: 61 cc head with a flat top piston = ~ 11.2:1 61 cc head with 29 cc dish piston = ~ 9.1:1 This information was taken from DSS's compression ratio chart for a 357 (overbored 351) and TFS TW heads. Not the exact combo you've got, but darn close. Tom Naegle at DSS can give you a real good idea of where you'll end up depending upon the amount of cc's you dish the pistons. Obviously, more cc's in the combustion chamber will reduce compression (about a .1 of compression reduction for each additional cc) Will you be boring the engine? A 357 is nice because you can have the machine shop bore the cylinders and have a nice cross-hatch to have 'brand-new' cylinders that will seal very well. I also recommend upgrading the ring package to the plasma-moly (ductile iron) rings. Excellent sealing for blower motors. FWIW, my 331 came in at 9.2:1 compression and I'm putting a D-1SC blower on as well (injected car though). Good luck, E __________________ 1991 5.0 LX Coupe - 40,750 miles 331 cu. in. / Tremec 3550 / BFG Drag Radials 12.22 @ 114.31 mph - w/1.89 60'