Sub8

Hi all - for those with experience on these engines, for a 468 LS build, which headgasket would you pick (93RON, expert mapping, track use):

0.084 gasket: Static CR 11.24, dynamic ~ CR 8.93. Quench: 0.073
0.051 gasket: Static CR 12.13, dynamic ~CR 9.63. Quench: 0.040
0.065 gasket: Static CR 11.74, dynamic ~CR 9.31. Quench: 0.054

Thanks.

bthomas

iTrader: (1)

.051

gives the tightest quench, which does more for anti knock vs the minor compression change the thicker ones do.

Btw.. my most recent build had the pistons .011-.012 out of the hole as well, and I’m running a .045 gasket.


edit: You sure on the dynamic #’s? Must be a pretty small cam your trying to run with that engine.

Sub8

249 / 265 / 114.5 seperation 0.68lift with 1.8 rockers.

Its torque vs timing vs knock that is of course of interest. A prior build had 0.084 gasket and wouldn't take as much timing as I would expect 5.5K and up. Something around 4-7 deg shy.

bthomas

iTrader: (1)

What’s the duration @ .006 numbers on the cam?

Sub8

Dont have them.

IGN-1A

Hi SUB8, the AL Crankcase will "grow" more than an Iron Crankcase AND will have LESS Squish when hot ?
Which do you have ?
Lance

Sub8

RED sleeved ls3. Ls7 heads.

IGN-1A

Hi (8) I would print MY NAME on the top of a piston, backward.
THEN, after the race, I would freshen the engine.
When I could read my name on the head the squish was correct.
Lance

Che70velle

iTrader: (6)

You have to input the .006” duration numbers to figure the dynamic compression. .005 numbers aren’t accurate and will be high. I’d have no problem setting that engine up with a .032-.035 quench…which will greatly reduce knock while aiding combustion and also open up tuning options with timing. I’m at 12.42:1 running strictly pump 93 with the 434 in my Chevelle at 26 degrees timing with zero knock ever at WOT. I tried 28 and 29 degrees at WOT but it picked up nothing (still zero knock) so we settled on 26. It’s a very efficient chamber head so it doesn’t want more than 26.
​​​​​​…edit… Im ASSuming here that you have adequate cooling AND oil cooling in the vehicle under race conditions to control thermals. This factors in to how much heat (compression) you can put in the chambers at race speeds and it actually live. If this is a drag race deal, scratch the cooling comments. I’m thinking road race type build, but it’s a 468, so idk…

Sub8

Hi - yes cooling fully addressed. Vented hood. Ron Davis rad. Laid flat IP large oil cooler. Understood ref cam assessment. Its not the most aggressive profile.

Prior build was 19-21 uptop. And would still pick-up odd knock spikes fairly often. This has led me too believe that perhaps too high a quench clearance in the build.