Question about 99 6.0L pistons
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On The Tree
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Ok, next question then.
If my pistons are the factory dished ones and I bolt on a set of L92 heads that have been milled .030 what would the compression ratio be?
I am wanting to use this shortblock as a platform to build my race motor.
If my pistons are the factory dished ones and I bolt on a set of L92 heads that have been milled .030 what would the compression ratio be?
I am wanting to use this shortblock as a platform to build my race motor.
The 99 LQ4 pistons use a pressed-in pin, while the newer (04+, i believe) Vortecs use a floating pin. Further, the LQ4 pistons have a 8cc dish, while the LY6's have a 6cc dish plus about 2cc's worth of valve reliefs (for 8cc total). Thus, CR on an LQ4 with L92s should be about equal to the LY6, which is 9.67:1.
I *think* I had my L92s milled .020", although I could be wrong. Mine came in at 66cc's (from 69cc's as-measured). The accepted math is .006" milled per 1cc. This would put you at 63-67cc's and bump your SCR to anywhere from 9.73:1 - 10.15:1, depending on the stock chamber size (which is 70 ± 2cc).
I *think* I had my L92s milled .020", although I could be wrong. Mine came in at 66cc's (from 69cc's as-measured). The accepted math is .006" milled per 1cc. This would put you at 63-67cc's and bump your SCR to anywhere from 9.73:1 - 10.15:1, depending on the stock chamber size (which is 70 ± 2cc).
Last edited by hookemdevils22; Sep 4, 2010 at 09:49 PM. Reason: Correct SCR calcs
Ya, the early design had weaker rods and the pressed-pin design. They changed the design in 04, I believe.
I did my initial calcs wrong (used my 4.030" bore, not the stock 4.000") - your SCR would be 10:1 with 64 cc's, 10.15:1 with 63 cc's. It could be as low as 9.7:1 if the OEM size is 72 cc's and you only mill .030" (roughly 5 cc's) though.
Have the machine shop check the cc's before and after milling. Just give 'em a figure (say, 64 cc) and they'll take care of it. Make sure to determine the proper pushrod length using a length checker.
I did my initial calcs wrong (used my 4.030" bore, not the stock 4.000") - your SCR would be 10:1 with 64 cc's, 10.15:1 with 63 cc's. It could be as low as 9.7:1 if the OEM size is 72 cc's and you only mill .030" (roughly 5 cc's) though.
Have the machine shop check the cc's before and after milling. Just give 'em a figure (say, 64 cc) and they'll take care of it. Make sure to determine the proper pushrod length using a length checker.
