Still trying to plan my 489 BB project and have come up to a critical issue concerning selection of flat top pistons. :confused:

With a 4.25 crank and 6.385 rods, should the top of the piston be exactly at deck height (which I want), or below? The block has not been decked before. I was hoping to end up somewhere around a 9.1 CR using GM closed oval '063 heads. I suspect compression height probably comes into play at some point here. Most of the piston manufacturers don't list compression height info for their products.

I'm sorry if I sound stupid about this, but I just don't know where to proceed from here or how to go about selecting the right brand piston.

I'd really appreciate some expertise, guys.

Thanks, Charles

Charles,
"Most of the piston manufacturers don't list compression height info for their products." :confused:
Don't know whose catalogs you are looking in, but every piston catalog I have shows compression heights for pistons, including the "el cheapo" stock replacement stuff. Maybe you need to find a better supplier that has some catalogs to look through ??

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Here is what SRP says:

SMALL DOME PROFILES
9.1-10.6 Compression Ratio
• Designed to fit Edelbrock® 112cc and GM® STD Series Heads.
• Forged from 4032 low expansion high silicon aluminum alloy heat treated to SRP specifications
• CNC machined domes with radiused valve reliefs provide optimum flame travel
• Pin fitting and double spiro locks included
• 990-2930-150 wall wrist pin (150 grams) included
• CNC Machined ring grooves accept 1/16 1/16 3/16 rings (Rings Sold Separately)
Closed Chamber Dome - Now machined for 1/16 1/16 3/16 Ring Grooves

Cubic Bore Over Stroke Rod Comp Compr Dome Gram Foot Part Required
Inch Size Size Length Height 112cc 118cc 124cc Volume Weight Notes Number Ring Set

489 4.280 .030 4.250 6.385 1.270 10.4 9.6 9.1 5cc 534 B 143593 J100F8-4280-0
496 4.310 .060 4.250 6.385 1.270 9.6 9.1 5cc 551 B 145376 J100F8-4310-0

B Includes Oil Rail Support.
www.SRP.com (http://www.SRP.com) Sales (714)373-5530 Fax (714)893-8297

I think you will find, most pistons have a Cr Ht that installs the piston about .015 - .020 down in a non-decked block. This allows you to deck the block dead square during a rebuild and adjust the final Cr Ht by cutting the block accordingly. Or you could use a non-decked block and a standard GM .022 head gasket to keep the quench where it needs to be.