Question about 99 6.0L pistons
09-02-2010, 01:59 PM
#1
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Question about 99 6.0L pistons I would like to know if the pistons in a 1999 6.0L are dished or flat tops?
Are the pistons in the 1999 6.0L's different than those used in the LY6 6.0L??
Are the pistons in the 1999 6.0L's different than those used in the LY6 6.0L??
09-03-2010, 10:23 AM
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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.
09-03-2010, 01:03 PM
#4
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; 09-04-2010 at 09:49 PM. Reason: Correct SCR calcs
09-04-2010, 09:48 PM
#6
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.
