1981 stock piston specs?

[macx]

Trying to plan effective mods to the stock shortblock with upgraded cam.

Can't find the stock piston specs, like flat top or dished and cc's of either, and deck height (top of piston from top of deck)

Thanks for any info or leads!

[Jack]

Originally posted by macx
Trying to plan effective mods to the stock shortblock with upgraded cam.

Can't find the stock piston specs, like flat top or dished and cc's of either, and deck height (top of piston from top of deck)

Thanks for any info or leads!

Well ... I'm in Misery too (temporarily in Farmington MO on auto mfg consulting gig) ... am away from most of my books & specs. But I recall an 81 has dished pistons with 4 valve reliefs (they can be installed in either right or left cylinder banks) with a total volume of about 12.5 cc/piston and compression distance/height (from centerline of wrist pin to top of piston) is about 1.560" which places piston "down in the hole" about 0.025" in a stock, uncut, undecked sbc block with std deck height of 9.025". Your 81 heads probably have about 76 cc chambers. Stock head gasket is about 0.037" - 0.041" thick when compressed. Many older blocks have already been into & may have been decked ... may no longer be at 9.025" std deck height ... far better to measure such things before ordering parts. Zero-decking a block with 0.035" - 0.040" gaskets usually works quite well with flattops. Any competent counterman at parts store (a real parts store like NAPA ... not a place like AZ) can look up the 81 piston specifics in a Clevite / TRW etc book.
JACK

[macx]

Thanks for the info - was surprised at having a hard time finding that anywhere on the net!

Thinking upgraded 64cc Vortecs with thinner head gasket (such as .015 compressed). That should give the recommended minimum .040 piston to quench distance and about a 9.5cr. And I understand stock blocks are usually a bit higher than specs, so should be safe with that. Would prefer not to have to take block out, disassemble and machine at this point in time. Not going radical (probably Comp Cams XE262) and only an occasional romp, not going much over 5k, so it should not overstress the bottom end.

Vehicle has only 65k so don't believe block has been out or touched.

Again, thanks for the info!