Lq4 build
TECH Junkie
Joined: Dec 2012
Posts: 3,614
Likes: 1,326
From: Iowa
Compression distance is the distance from the center axis of the wristpin to the flat deck of the top of the piston. If yours is measured at 1.329, you're using stock length rods, and the deck is indeed 9.240 then the math is as follows
1/2 stroke=1.811
rod length=6.098
compressin height=1.329
total=9.238
That means the piston is in the hole .002
As with any factory machining process, there is variance. I would doublecheck deck height to be sure.
Most aftermarket rods are offered in 6.100 length vs the factory 6.098. In this case, this would move you up the perfect amount to fill the gap.
The best way to check actual values would be to just use a deck bridge and a degree wheel.
1/2 stroke=1.811
rod length=6.098
compressin height=1.329
total=9.238
That means the piston is in the hole .002
As with any factory machining process, there is variance. I would doublecheck deck height to be sure.
Most aftermarket rods are offered in 6.100 length vs the factory 6.098. In this case, this would move you up the perfect amount to fill the gap.
The best way to check actual values would be to just use a deck bridge and a degree wheel.
Thread Starter
Teching In
Joined: Sep 2015
Posts: 27
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Compression distance is the distance from the center axis of the wristpin to the flat deck of the top of the piston. If yours is measured at 1.329, you're using stock length rods, and the deck is indeed 9.240 then the math is as follows
1/2 stroke=1.811
rod length=6.098
compressin height=1.329
total=9.238
That means the piston is in the hole .002
As with any factory machining process, there is variance. I would doublecheck deck height to be sure.
Most aftermarket rods are offered in 6.100 length vs the factory 6.098. In this case, this would move you up the perfect amount to fill the gap.
The best way to check actual values would be to just use a deck bridge and a degree wheel.
1/2 stroke=1.811
rod length=6.098
compressin height=1.329
total=9.238
That means the piston is in the hole .002
As with any factory machining process, there is variance. I would doublecheck deck height to be sure.
Most aftermarket rods are offered in 6.100 length vs the factory 6.098. In this case, this would move you up the perfect amount to fill the gap.
The best way to check actual values would be to just use a deck bridge and a degree wheel.
6.100=rod
1.811=stroke
1.329=Compression height
TECH Junkie
Joined: Dec 2012
Posts: 3,614
Likes: 1,326
From: Iowa
Right, your math adds up. In that case, the piston would be even with the hole if you're using 6.100 rods.
I was under the impression you had measured your piston compression height and the value you measured was 1.329. If the measurement for the piston matches the spec of 1.331, then the piston will be OUT of the hole .002
I was under the impression you had measured your piston compression height and the value you measured was 1.329. If the measurement for the piston matches the spec of 1.331, then the piston will be OUT of the hole .002
I don't think the LQ4 blocks are 9.240", more like 9.230". My rotating assembly stacked up to 9.230" on my iron 6.0L block and ended up pretty much zero deck when I mocked it all up.
TECH Junkie
Joined: Dec 2012
Posts: 3,614
Likes: 1,326
From: Iowa
^^that's why i advise using a deck bridge. It's the only way to be truly confident in what you're getting. If this block wasn't exactly factory spec off the line, if it has been milled or resurfaced before,etc. you'll have different numbers.
Factory spec was 9.240 +/- .005
Factory spec was 9.240 +/- .005
^^that's why i advise using a deck bridge. It's the only way to be truly confident in what you're getting. If this block wasn't exactly factory spec off the line, if it has been milled or resurfaced before,etc. you'll have different numbers.
Factory spec was 9.240 +/- .005
Factory spec was 9.240 +/- .005
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TECH Junkie
Joined: Dec 2012
Posts: 3,614
Likes: 1,326
From: Iowa
I haven't seen enough to really disagree with you, but I'm just going off of GM spec for what it "should" be. Direct GM replacement block for lq9 says 9.240 deck. I believe every block in this family (except the LSX) share a common deck height. https://www.summitracing.com/parts/nal-12572808
I have also found that Weisco mentions the 9.230 for 6.0 iron blocks, but what I find from GM is different, and weisco is the only manufacturer I've seen that lists that outright. Lunati and others list it as 9.240.
If the iron blocks had 9.230 deck, the pistons would be WAY out of the hole wouldn't they?
I have also found that Weisco mentions the 9.230 for 6.0 iron blocks, but what I find from GM is different, and weisco is the only manufacturer I've seen that lists that outright. Lunati and others list it as 9.240.
If the iron blocks had 9.230 deck, the pistons would be WAY out of the hole wouldn't they?
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Teching In
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