The pistons listed below were installed in my L-98 shortblock. They were dead ringers for the pistons removed during teardown. However, I appears that I'm left with only 8.9:1 w/ 64cc heads or about 9.3:1 with the 60cc aluminum heads I'm using. With a .028" head gasket, 9.5:1 should be in reach. The machinist claims this piston is the stock replacement and would deliver 9.3:1 w/ 64cc heads.

350 Chevy 8.5:1 Pistons <products_view.php?id=4>
Dish hypereutectic pistons for 350 Chevy. 4-valve reliefs. 9.45:1@58cc. 8.9:1@64cc. Set of 8 Part #H423NP.

The piston below looks more like the one I'm looking for. About 9.9:1 w/ 60cc heads.

350 Chevy 10:1 Pistons coated <products_view.php?id=55>
Flat-top hypereutectic teflon coated pistons for 350 Chevy. 4-valve reliefs. 10:1@58cc. 9.5:1@64cc. Set of 8 Part #H345NP.

Here are the questions...
1) What is the CR of a iron-head L-98?
2) Which of these pistons more closely resembles stock L-98 units?
3) Is 4 or 5 points of compression going to make a noticable difference?
4) Do I need a new machinist?

Click below to find the list of pistons.
http://www.fastengineparts.com/products.php?cid=69

For background, I'm using ... Edelbrock Centerbolt Performer heads, Edelbrock Hi-Flow baseplate, partially siamesed SLP runners, 52mm TB, ZZ4 cam and Hooker 2050 headers.

Thanks in advance, and tips on the combination are welcome.

www.picturetrail.com/clutch_grabwell

 

9.8:1 is listed in the GM service manual for 90 Z-28. A half a point of compression won't make a lot of difference, certainly not enough to tear down an engine for. Your dynamic compression is what's important. That is determined by your valve timing + static CR. You can always install a .015" shim steel head gasket.

 

Just to be a little clearer, the shortblock is still on the motor stand. This is the time to make up my mind and change if it's worthwhile.

Thanks
CG

 

He propably used rebuilder pistons, which have a slightly smaller compression height from stock. This leaves the pistons lower in the bore, killing compression and ruining any quench you would want.