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Discussion Starter · #1 ·
Hey guys. Wondering who is boosting L92's? How much are you throwing at these heads before they lift? I hear they have thin decks?
 

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this subject has probably been covered 1000 times. over 700-750 hp they lift-this is assuming everything is correct. There will be guys that said they made 1000+ , but how long? 2 dyno pulls?

there is no free lunch on f/i engines.
 

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I think a good data point are the C6 guys. They running 130-134 in the 1/4 @ 34xx raceweight, so making 650-700 crank? That might translate into 12-15 psi. LS9 head gaskets seem to be popular too.
 

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I am not a heads guy, what is the difference between thin and thick deck heads? Why does this make a difference?

The thicker deck, typically 5/8" (or thicker) on a lot of after market heads are stronger and less prone to flexing or distorting.

Thin deck, or most production OE heads which are 1/2" or less and not all that consistant in deck across the head. Will only handle so much cylinder pressure before they move and release the head gasket.

The other thing to keep in mind is the head bolt arrangement, production LS's are only 4 bolts per cylinder were the LSX and other after market blocks have 5 or more. This will play a big roll in what they can handle for cylinder pressure as well.

Hope that helps.
 

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The thicker deck, typically 5/8" (or thicker) on a lot of after market heads are stronger and less prone to flexing or distorting.

Thin deck, or most production OE heads which are 1/2" or less and not all that consistant in deck across the head. Will only handle so much cylinder pressure before they move and release the head gasket.

The other thing to keep in mind is the head bolt arrangement, production LS's are only 4 bolts per cylinder were the LSX and other after market blocks have 5 or more. This will play a big roll in what they can handle for cylinder pressure as well.

Hope that helps.

So your more likely to lift stock heads than aftermarket? I gave seen people run both heads with success. I am sure aftermark is more reliable though
 

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So your more likely to lift stock heads than aftermarket? I gave seen people run both heads with success. I am sure aftermark is more reliable though

Thats your ass-umption of what I said. I did not say that either one was more likely to lift than the other. There is a bit more to it than that. I have also seen many guys run both with success and failer. ITS ALL IN THE SET UP.
 

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one other thing to add to the equation is that the material in aftermarket heads is much better. Better quality material-more strength.
 

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Discussion Starter · #11 ·
How thick are the L92 decks compared to lets say a set of 317's? I see more guys running those on boost than any other stock head. I have both sets of heads L92's and 317's. Just trying to decide what would be better of the two.
 

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this subject has probably been covered 1000 times. over 700-750 hp they lift-this is assuming everything is correct. There will be guys that said they made 1000+ , but how long? 2 dyno pulls?

there is no free lunch on f/i engines.
A couple good hard 1/8th mile passes. But I agree, this is a dead horse.
 

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i made 988rwhp through a loose th400, i switched over to the l92 gmpp 6 bolt heads now to go higher, they advertised a 5/8 deck but im not sure. i didnt have an issues but my motor was oringed. the heads did not have receiver grooves. id say 15psi and 15* timing on a 408 seemed to be A-ok, they make big power.
 

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This is a pic of an early L92 casting. It was among one the thinnest that has been cut and measured.

Info and pic courtesy of Dennis Wheet @ airflowdevelopment:

 

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Found this on GMPP


All LSX heads are made of 356- T6 aluminum and feature a 5/8" thick deck that allows plenty of room for builder-specified combinations.
 
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