Compression vs CFM ??
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Teching In
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Compression vs CFM ?? what would be better off a higher compression and less flow or less compression and better flow. example- lq4 stock bottom with 243 heads has a more compression but less flow or a lq4 stock bottom end with l92 heads less compression but better flow which combination will work best..
TECH Senior Member
Joined: Mar 2004
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From: BFE
Actualy, both 
It really depands what you are trying to achieve. A 10:1 LQ4/L92 with small duration/high lift cam (.600 or so) would do real well as all around street performer.
But if you are going for big numbers, right size cam and compression will surely surpass it.
It really depands what you are trying to achieve. A 10:1 LQ4/L92 with small duration/high lift cam (.600 or so) would do real well as all around street performer.
But if you are going for big numbers, right size cam and compression will surely surpass it.
+1
The application makes a big difference here. Those L92 heads can move a lot of air, but they have some large ports, and resulting lower velocity on the same size engine. Adding 243 heads to a mild-medium 6.0 is a great way to improve power and drivability. If you are after big numbers, airflow will take you there, but you need to be sure that you create the right combination of parts to get there. Big ports and a big cam make for great top end performance with less than stellar results down low, especially if the compression is lower to boot.
The application makes a big difference here. Those L92 heads can move a lot of air, but they have some large ports, and resulting lower velocity on the same size engine. Adding 243 heads to a mild-medium 6.0 is a great way to improve power and drivability. If you are after big numbers, airflow will take you there, but you need to be sure that you create the right combination of parts to get there. Big ports and a big cam make for great top end performance with less than stellar results down low, especially if the compression is lower to boot.
If it's a track only car, then your gears and converter will take care of any problems on the low end. A good breathing setup that makes power from 4000 - 7000 rpms is perfect for that. If you are building a street/strip car, then your mix of driving will ultimately decide for you. The more time you plan to spend on the road when you are not pushing the car full tilt, the more you should lean towards velocity and streetable power.
Assuming the suspension and gearing are optimal, you're looking for 480-500 flywheel HP. That is certainly achievable with either head.
Assuming the suspension and gearing are optimal, you're looking for 480-500 flywheel HP. That is certainly achievable with either head.
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Thread Starter
Teching In
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If it's a track only car, then your gears and converter will take care of any problems on the low end. A good breathing setup that makes power from 4000 - 7000 rpms is perfect for that. If you are building a street/strip car, then your mix of driving will ultimately decide for you. The more time you plan to spend on the road when you are not pushing the car full tilt, the more you should lean towards velocity and streetable power.
Assuming the suspension and gearing are optimal, you're looking for 480-500 flywheel HP. That is certainly achievable with either head.
Assuming the suspension and gearing are optimal, you're looking for 480-500 flywheel HP. That is certainly achievable with either head.
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CFM - Air in and air out = power. You can have all the cam and compression in the world and its not going to help if you dont have the ablilty to flow air (see sig).
Compression and cam are important also, just not as important as heads because with better heads, you get a better cam. Its about making a grea combination that makes a great running engine.
I just went through this exercise myself. I have an LQ9, with Lingenfelter CNC L92/LS3 heads. I went with a Comp LSR cam 219/235 .607/.621 113+5. Its their LS3 (single bolt) cam, and I had them grind it on a three bolt core for me.
It pulls like a freight train and is extremely drivable, and Im still learning to tune driveability, so its getting better and better on the drivability side.
Note: I milled my heads .030 and this cam is about as big as I could go, even though I wouldnt have gone any bigger. My piston to valve clearance was about .070"s on the intake and .080"s on the exhaust. All my buddys talked me out of the 215/223 .604/.614 LSR cam that I originally wanted.
Compression and cam are important also, just not as important as heads because with better heads, you get a better cam. Its about making a grea combination that makes a great running engine.
I just went through this exercise myself. I have an LQ9, with Lingenfelter CNC L92/LS3 heads. I went with a Comp LSR cam 219/235 .607/.621 113+5. Its their LS3 (single bolt) cam, and I had them grind it on a three bolt core for me.
It pulls like a freight train and is extremely drivable, and Im still learning to tune driveability, so its getting better and better on the drivability side.
Note: I milled my heads .030 and this cam is about as big as I could go, even though I wouldnt have gone any bigger. My piston to valve clearance was about .070"s on the intake and .080"s on the exhaust. All my buddys talked me out of the 215/223 .604/.614 LSR cam that I originally wanted.
Last edited by SweetS10V8; Oct 19, 2009 at 03:23 AM.
Thread Starter
Teching In
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no one has given me a direct on which heads would be better to use. the 317 or the 243's they flow the same numbers but the chambers in the 243's are smaller which will make more compression. im guessing these are the better of the two.
From what I understand, the #317s and the #243s have the same ports. So the #243s will make a little more power because of the small combustion chamber giving you more compression.
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Joined: Sep 2009
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From: Frozen Tundra, WI
The flow data I have seen shows the 317's flowing slightly more on the intake than the 243...while the 243's flow slightly more on the exhaust than the 317's. The numbers weren't significantly different...both have the same port and valve size.
This is why I was hesitant to suggest these heads for the smallest street driven engine that they will fit. Heavy hitters and L92 heads
The reason we stay away from them is that when you Cam them up the midrange turns to crap. The heads flow good enough to make 900rwhp which is great for a pure drag car but not for what we build 99% of the time.Then add on the intake selection.
I prefer a nice TFS,AFR type of head for a strong average power.
I prefer a nice TFS,AFR type of head for a strong average power.
