Help with heads, SCR, and DCR in truck application.
01-26-2005, 02:00 PM
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Help with heads, SCR, and DCR in truck application. I hope you guys don't mind me posting this question on 'this' side of the fence.
I'm looking for some help or feedback with getting my specs sorted out for a head-swap on my truck. I thought I had this figured out, but I don't.
Current/stock specs: LQ9 6.0L block. Rated at 10:1 by GM. Flat-top pistons, 4" bore, 3.622" stroke, 6.098" rods. 71.06cc chambers. .054" x 4.04" (compressed) gaskets. Deck height - 3 LQ9's speced out as the typical -0.008, out of the hole - haven't cracked mine open.
Cam: 210/218 (272/280) on a 110ICL 112LSA.
Throwing these numbers in a SCR/DCR calculator, I'm getting 10.23 static, 8.07 dynamic... stock. Not too shabby. This is showing an quench of .046.
Vehicle useage: The truck is a heavy 4x4 chassis, weighing in around 5,400lbs - maybe a little more, maybe a little less. I always run 93 octane. The truck is used to tow a 5,000lb trailer about 500 miles a year, otherwise it's a daily 50-mile commuter that visits the track every now and then.
Vehicle mods are listed below. Your usual (minimal) bolt-ons.
I'm looking to install AFR 205's to help out the "torque theme" I have going with the cam. I AM willing to go to just about any size on the cam, so long as I don't lose any of the excellent throttle responce and torque I have right off the bottom of the RPM range. I do NOT want to be "required" to run a stall with my final powerband, and I have little-to-no interest in revving much over 6,000-6,200. I don't mind moving the ICL around on this cam.
Still with me?
My options...
66cc's on stock .054 x 4.04 gaskets - 10.85 SCR - 8.55 DCR. Quench still at an alleged .046".
- Is this too high for all this bulk I'm lugging around? How about towing on those hot summer days?
- If I understand DCR correctly, the "rule of thumb" is to keep it under 8.5:1... but I heard some opinions out there saying GenIII motors are good up to 9.0 DCR. Is that only for you nice, light cars?
- Would you go tighter on the gaskets for a little better quench? If "Yes" - where is the line drawn with going too high with the CR for better quench? Is it "not drawn" if you're under, say, 11:1 static?
Just to put the "extreme" end of the spectrum up here... 66cc's on .041 gaskets, assuming 4.04" bore... 11.22 SCR - 8.83 DCR with a flirtatious (alleged) .033 squish.
- Suggestions on gasket sizes to use between these?
- Suggestions on doing the head swap in general? What you YOU do?
A final side question - I can't... or shouldn't buy head gaskets until I have the motor torn down with the deck height speced out, correct? Kind of a dumb question - but it seems like a lot of head-swaps I read about are a "bolt on in one day and go WOT" type thing. I'm seeing it as much more involved...
Thanks, I really appreciate any help...
-marc
I'm looking for some help or feedback with getting my specs sorted out for a head-swap on my truck. I thought I had this figured out, but I don't.
Current/stock specs: LQ9 6.0L block. Rated at 10:1 by GM. Flat-top pistons, 4" bore, 3.622" stroke, 6.098" rods. 71.06cc chambers. .054" x 4.04" (compressed) gaskets. Deck height - 3 LQ9's speced out as the typical -0.008, out of the hole - haven't cracked mine open.
Cam: 210/218 (272/280) on a 110ICL 112LSA.
Throwing these numbers in a SCR/DCR calculator, I'm getting 10.23 static, 8.07 dynamic... stock. Not too shabby. This is showing an quench of .046.
Vehicle useage: The truck is a heavy 4x4 chassis, weighing in around 5,400lbs - maybe a little more, maybe a little less. I always run 93 octane. The truck is used to tow a 5,000lb trailer about 500 miles a year, otherwise it's a daily 50-mile commuter that visits the track every now and then.
Vehicle mods are listed below. Your usual (minimal) bolt-ons.
I'm looking to install AFR 205's to help out the "torque theme" I have going with the cam. I AM willing to go to just about any size on the cam, so long as I don't lose any of the excellent throttle responce and torque I have right off the bottom of the RPM range. I do NOT want to be "required" to run a stall with my final powerband, and I have little-to-no interest in revving much over 6,000-6,200. I don't mind moving the ICL around on this cam.
Still with me?
My options...
66cc's on stock .054 x 4.04 gaskets - 10.85 SCR - 8.55 DCR. Quench still at an alleged .046".
- Is this too high for all this bulk I'm lugging around? How about towing on those hot summer days?
- If I understand DCR correctly, the "rule of thumb" is to keep it under 8.5:1... but I heard some opinions out there saying GenIII motors are good up to 9.0 DCR. Is that only for you nice, light cars?
- Would you go tighter on the gaskets for a little better quench? If "Yes" - where is the line drawn with going too high with the CR for better quench? Is it "not drawn" if you're under, say, 11:1 static?
Just to put the "extreme" end of the spectrum up here... 66cc's on .041 gaskets, assuming 4.04" bore... 11.22 SCR - 8.83 DCR with a flirtatious (alleged) .033 squish.
- Suggestions on gasket sizes to use between these?
- Suggestions on doing the head swap in general? What you YOU do?
A final side question - I can't... or shouldn't buy head gaskets until I have the motor torn down with the deck height speced out, correct? Kind of a dumb question - but it seems like a lot of head-swaps I read about are a "bolt on in one day and go WOT" type thing. I'm seeing it as much more involved...
Thanks, I really appreciate any help...
-marc
