? about Piston To Valve Clearance
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TECH Junkie
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From: Minneapolis, MN
? about Piston To Valve Clearance Just wondering about this subject before I even consider running down the L92 headed road. My question to you guys is that I have a LQ4 shortblock 6L with dish pistons. I want to keep my compression as close to 10.5:1 or higher as possible with the L92 heads. Being they start with a 70cc chamber, to get the compression up there I have to figure out a way to shed about 6-7cc's of combustion volume. Either I do this with milling, or a thinner head gasket or both. The camshaft I'm running is a 224/228 .6xx/.6xx 112LSA +4 cam from Ed Curtis. I've already established while assembling my motor last year that the pistons are .012" out of the hole. That being said, I want to be able to bolt a set of L92's already milled and prepared so there's zero downtime. My truck is my daily driver so I don't want to have to put the heads on, check PTV and then send them off to get milled. What would you guys recommend I do to get my compression up while maintaining adequate piston to valve clearance and my quench between .030-.040 thousandths? I've already verified that the stock L92 head gasket is actually .056" thick from GM. So how many of you are running L92's that are milled .040" on a stock lq4 shortblock? If so, what cam are you running and what's your piston to valve clearance like? With that monster intake valve size it makes me nervous to proceed....
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TECH Junkie
iTrader: (31)
Joined: Dec 2004
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From: Minneapolis, MN
I have a few sets of pushrods and if those don't work I have a speedshop down the road that carries lots of comp pushrods. I do not want this project to stretch beyond a day.
I'm curious about this as well... I plan on milliing the L92 heads down to 64cc chambers and using the GM L92 head gasket. My planned cam will be different though... 232/236 112 LSA .650 lift .... Not sure how much my pistons stick out though as I haven't assembled my block yet...But I think you should be fine...
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From: Cairo, GA.
add me to the list also. i have a LS2 getting ready to do a 402 stroker kit. i just bought L92 heads milled to 64cc my cam is 234/236 113 LSA 600 lift . wondering what kind of problems im going to have
You wont get the compression your hoping for. I cc'd the dish of an LQ4 piston and L92 cylinder head before I ran them together. It came out to a 9.14:1 compression ratio with a stock head gasket and no milling.
As far a PTV clearance, I have an LQ9 (flat tops) stock .055" gaskets, and L92 heads that are milled .030" I tried a 223/231 .604/.607 on a 112 and had .050" PTV on the intake and .120" on the exhaust. So I had to change cams since I didn't have enough clearance.
I went to a 219/235 .607/.621 113+4 and had .085 Intake and .080 on the exhaust which I can handle. The problem is that we have pistons that stick .005-.008" out of the hole, and we have that HUGE intake valve!! If I wouldn't have milled the heads both cams would have been fine.
That's why you cant get the compression you want without different pistons, because milling or thin head gaskets will leave you with little PTV. Your piston does have a valve relief, but its for a 2.00" valve, not a 2.160".
As far a PTV clearance, I have an LQ9 (flat tops) stock .055" gaskets, and L92 heads that are milled .030" I tried a 223/231 .604/.607 on a 112 and had .050" PTV on the intake and .120" on the exhaust. So I had to change cams since I didn't have enough clearance.
I went to a 219/235 .607/.621 113+4 and had .085 Intake and .080 on the exhaust which I can handle. The problem is that we have pistons that stick .005-.008" out of the hole, and we have that HUGE intake valve!! If I wouldn't have milled the heads both cams would have been fine.
That's why you cant get the compression you want without different pistons, because milling or thin head gaskets will leave you with little PTV. Your piston does have a valve relief, but its for a 2.00" valve, not a 2.160".
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You wont get the compression your hoping for. I cc'd the dish of an LQ4 piston and L92 cylinder head before I ran them together. It came out to a 9.14:1 compression ratio with a stock head gasket and no milling.
As far a PTV clearance, I have an LQ9 (flat tops) stock .055" gaskets, and L92 heads that are milled .030" I tried a 223/231 .604/.607 on a 112 and had .050" PTV on the intake and .120" on the exhaust. So I had to change cams since I didn't have enough clearance.
I went to a 219/235 .607/.621 113+4 and had .085 Intake and .080 on the exhaust which I can handle. The problem is that we have pistons that stick .005-.008" out of the hole, and we have that HUGE intake valve!! If I wouldn't have milled the heads both cams would have been fine.
That's why you cant get the compression you want without different pistons, because milling or thin head gaskets will leave you with little PTV. Your piston does have a valve relief, but its for a 2.00" valve, not a 2.160".
As far a PTV clearance, I have an LQ9 (flat tops) stock .055" gaskets, and L92 heads that are milled .030" I tried a 223/231 .604/.607 on a 112 and had .050" PTV on the intake and .120" on the exhaust. So I had to change cams since I didn't have enough clearance.
I went to a 219/235 .607/.621 113+4 and had .085 Intake and .080 on the exhaust which I can handle. The problem is that we have pistons that stick .005-.008" out of the hole, and we have that HUGE intake valve!! If I wouldn't have milled the heads both cams would have been fine.
That's why you cant get the compression you want without different pistons, because milling or thin head gaskets will leave you with little PTV. Your piston does have a valve relief, but its for a 2.00" valve, not a 2.160".
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I had my pistons flycut, and I still have good clearance with .070 milled off the heads and compression around 10.75 with a 242/246 655 615 108 lsa cam. GMPP intake and a few other little tricks, made almost 600hp on the engine dyno
