Compression ratio for 92 octane
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Joined: Jan 2019
Posts: 72
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From: Carnation, WA
Compression ratio for 92 octane
I'm about to have my LS3 heads CNC ported and am not sure what to tell the machinist in terms of milling the heads. I would like to maximize the C/R for running 92 octane. I'm sure the shop can tell me how much to mill and what gaskets to use if I just provide them with the desired C/R. Inputs greatly appreciated.
Le Mans Master
Joined: Dec 2005
Posts: 6,999
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From: Southeast TX
You can do a lot of milling, use a narrow LSA/high duration/high lift cam and you absolutely have to mock things up and check PTV clearance. Do a little milling, don't go apeshit on the lift and duration, and use a little wider LSA and you'll be OK without checking PTV clearance.
Not sure what other shops do, but if you employ TxSpeed for the CNC work, they also do a valve job. During the valve job, they "sink" the valves into the head to the tune of .010. That increases PTV clearance by that much. I milled my heads .010 and used a .011 thinner head gasket. My static CR went to 11.2:1. Not a huge increase, but essentially free as TxSpeed will mill your heads to your spec as part of the CNC head porting/valve job package. I had to buy head gaskets anyway....thinner ones weren't any more $.
Whoever you buy the cam from can probably tell you what you can get away with milling wise.
Not sure what other shops do, but if you employ TxSpeed for the CNC work, they also do a valve job. During the valve job, they "sink" the valves into the head to the tune of .010. That increases PTV clearance by that much. I milled my heads .010 and used a .011 thinner head gasket. My static CR went to 11.2:1. Not a huge increase, but essentially free as TxSpeed will mill your heads to your spec as part of the CNC head porting/valve job package. I had to buy head gaskets anyway....thinner ones weren't any more $.
Whoever you buy the cam from can probably tell you what you can get away with milling wise.
