When do heads lift?
Le Mans Master
Joined: Oct 2003
Posts: 8,863
Likes: 86
From: PA
St. Jude Donor '08
Originally Posted by Shinobi'sZ
The focus on head gaskets is not to effect that which is sacred. That being sacred is the quench or squish area. The other is to not effect the shape of the head. Both can lead to detonation. Quench is also determined by deck height. FI applications can use more quench area. Normally, the quench should not be below .027 or exceed .058. So do your deck height and head gasket thickness calcs and you can determine when too much or not enough head gasket is bad. You have to consider the application too...whether it be NA or FI.
If average (ls1) deck height is .007" (out of the hole), and stock GM MLS head gasket thickness is .054", we are talking about a quench area of .047". My deck height with 6.125" rods and 3.905" Diamond Pistons ended up being .014". With .065" gaskets my quench area is .051" (my Cometics are MLS). So you see the difference is only .004" between the two. Even using a stock deck height (.007) with .065" MLS the quench area would be .058" still OK. There is a Turbo FBody LS1 over on LS1tech running .072" Head Gaskets making all sorts of power and no problems reported. Its different for NA cars where I have seen the quench as low as .027" with milled heads and fly cut pistons.
If average (ls1) deck height is .007" (out of the hole), and stock GM MLS head gasket thickness is .054", we are talking about a quench area of .047". My deck height with 6.125" rods and 3.905" Diamond Pistons ended up being .014". With .065" gaskets my quench area is .051" (my Cometics are MLS). So you see the difference is only .004" between the two. Even using a stock deck height (.007) with .065" MLS the quench area would be .058" still OK. There is a Turbo FBody LS1 over on LS1tech running .072" Head Gaskets making all sorts of power and no problems reported. Its different for NA cars where I have seen the quench as low as .027" with milled heads and fly cut pistons.
if i was to switch heads( only as far as cc) and run the same gasket the quench will stay unchanged?
kevin my short block has stock crank manley h beam clevitt bearings comp 228 224 580 582 115 cam and lunati off shelf FI pistons w/-21cc. these pistons work well with 59cc patriot ls6 heads as w/.054 mls compression 8.75. small chamber head will not affect quench? i was possible thinking of sending heads back to patriot and having them cnc to either 63cc or 69cc. i think 63cc equals 8.4 69cc not sure. i dont want off boost response to be to soft.
Melting Slicks
Joined: Mar 2003
Posts: 3,116
Likes: 10
From: Macomb MI
Originally Posted by Shinobi'sZ
Harlan's car was/is awesome. Does it still run?? 
. Working on Derty Monster now, will have 2 crazy F-bodys to deal with next year..hehePhil
Melting Slicks
Joined: Mar 2002
Posts: 2,931
Likes: 2
From: Tx
Originally Posted by RoadRebel
On Harlans we use Ported GM truck heads with GM MLS gaskets and regular ARP head studs..no issues up to 25psi and 8.50s.
Phil
Phil
So I guess I'll start worrying about the heads when I start running 170mph traps
Le Mans Master
Joined: Sep 2000
Posts: 6,976
Likes: 527
From: Clouds Over California
Originally Posted by NICK YOSKIN
if i was to switch heads( only as far as cc) and run the same gasket the quench will stay unchanged?
kevin my short block has stock crank manley h beam clevitt bearings comp 228 224 580 582 115 cam and lunati off shelf FI pistons w/-21cc. these pistons work well with 59cc patriot ls6 heads as w/.054 mls compression 8.75. small chamber head will not affect quench? i was possible thinking of sending heads back to patriot and having them cnc to either 63cc or 69cc. i think 63cc equals 8.4 69cc not sure. i dont want off boost response to be to soft.
kevin my short block has stock crank manley h beam clevitt bearings comp 228 224 580 582 115 cam and lunati off shelf FI pistons w/-21cc. these pistons work well with 59cc patriot ls6 heads as w/.054 mls compression 8.75. small chamber head will not affect quench? i was possible thinking of sending heads back to patriot and having them cnc to either 63cc or 69cc. i think 63cc equals 8.4 69cc not sure. i dont want off boost response to be to soft.
Yes. As for off boost response (maybe Roadrebel can expand upon) from what I have read keeping the CR above 8.1 still provides off boost response. If you keep your car between 8.5-9:1 CR you will be doing fine. There is a lot of material that can be taken out of the LS6 heads. West Coast Racing Cylinder Heads CNC'd and hand ported mine to 77ccs. The best way to build a FI motor is (I believe) the way you are doing it. However it is certainly not the only way. You can see from Roadrebel and my motor setups that we used only -2cc dish on the piston and accomplished the rest with the cc size and gaskets. Its just got be right when you start modifiying the chambers....when not done correctly it can actually cause more detonation than if you had a higher cr motor w/stock heads.
Le Mans Master
Joined: Oct 2003
Posts: 8,863
Likes: 86
From: PA
St. Jude Donor '08
Originally Posted by Shinobi'sZ
Yes. As for off boost response (maybe Roadrebel can expand upon) from what I have read keeping the CR above 8.1 still provides off boost response. If you keep your car between 8.5-9:1 CR you will be doing fine. There is a lot of material that can be taken out of the LS6 heads. West Coast Racing Cylinder Heads CNC'd and hand ported mine to 77ccs. The best way to build a FI motor is (I believe) the way you are doing it. However it is certainly not the only way. You can see from Roadrebel and my motor setups that we used only -2cc dish on the piston and accomplished the rest with the cc size and gaskets. Its just got be right when you start modifiying the chambers....when not done correctly it can actually cause more detonation than if you had a higher cr motor w/stock heads.
kevin ....
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