Less compression and bigger cam vs more compression and smaller cam
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From: St Simons Isl, GA
That may be true...honestly I'm not sure what the deck height of either head is. I was just saying that by milling the heads, the valves become closer to the piston, thus affecting what duration cam will or won't clear. When I called TSP about their heads, they told me that the 5.3s would have more valve drop than the 243s on a 60cc head, but I assume thats just in the head design. I think another one of the advantages to running the 5.3 heads is that they are a smaller chamber to begin with...obviously, any of the heads can be milled to a given combustion chamber cc.
Last edited by -Q-; Jul 7, 2010 at 01:25 AM.
Can you get 93 octane in Alaska? Around here we can only get 91 octane. I still say compromise a little on compression, like 10.5 or so and get a bigger cam. That will make more power than high compression and smaller cam. Higher CR will be harder to tune, might have to drop timing to keep it from knocking unless you run racing fuel or have really good pump gas.
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From: St Simons Isl, GA
Can you get 93 octane in Alaska? Around here we can only get 91 octane. I still say compromise a little on compression, like 10.5 or so and get a bigger cam. That will make more power than high compression and smaller cam. Higher CR will be harder to tune, might have to drop timing to keep it from knocking unless you run racing fuel or have really good pump gas.
You really think .5 to .75 is going to make that much of a difference? Pretty much rule of thumb on compression is 1 full point = 3% to 4% in power. Your only talkin 8hp to 12Hp loss on the high end of the scale. Myself, I would have the cam spec'd for 64cc heads then check valve drop and cut the heads.
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From: St Simons Isl, GA
Yeah, you're right. I'm probably way overthinking this, but I just want to get it right the first time...especially since I have the opportunity to do all the work on the motor while its out of the car.
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From: St Simons Isl, GA
Ended up with a set of PRC Stage 2.5 LS6 heads at 62cc. Compression should be right at 10.5:1 with a stock headgasket...a little higher if I go with the .040 Cometics. Once I get my custom cam specs from PatG, I should be good to go.
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From: St Simons Isl, GA
On an LQ4? I had 64cc heads with stock head gasket calculated at 10.25:1, and 62cc at 10.55:1. It all really depends on how far out of the hole the pistons are, and the shortblock is currently on its way to me so I haven't measured yet.
Just remember that the larger the cam you run the lower your Dynamic Compression ratio too. So a big cam will actually drop your Compression ratio.
So a big ol cam and mediocre compression is going to give you poor driveability. If its a street car a MILD cam and the upper end of compression makes for the most fun and efficient.
Also are you calculating using the 4" bore size? That makes a big difference in compression.
I would think the best route would have been ported truck heads, stock gaskets and a 23x duration cam.
Does the LQ4 have flat top pistons?
So a big ol cam and mediocre compression is going to give you poor driveability. If its a street car a MILD cam and the upper end of compression makes for the most fun and efficient.
Also are you calculating using the 4" bore size? That makes a big difference in compression.
I would think the best route would have been ported truck heads, stock gaskets and a 23x duration cam.
Does the LQ4 have flat top pistons?
Last edited by 00pooterSS; Jul 12, 2010 at 06:58 PM.
Just remember that the larger the cam you run the lower your Dynamic Compression ratio too. So a big cam will actually drop your Compression ratio.
So a big ol cam and mediocre compression is going to give you poor driveability. If its a street car a MILD cam and the upper end of compression makes for the most fun and efficient.
Also are you calculating using the 4" bore size? That makes a big difference in compression.
I would think the best route would have been bored truck heads, stock gaskets and a 23x duration cam.
Does the LQ4 have flat top pistons?
So a big ol cam and mediocre compression is going to give you poor driveability. If its a street car a MILD cam and the upper end of compression makes for the most fun and efficient.
Also are you calculating using the 4" bore size? That makes a big difference in compression.
I would think the best route would have been bored truck heads, stock gaskets and a 23x duration cam.
Does the LQ4 have flat top pistons?
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From: St Simons Isl, GA
They are -6.7 dished pistons in the LQ4. The dish in the pistons combined with the additional bore size actually makes the compression ratio come out the same as a stock LS1. If you put 241 heads on the LQ4, you have 10:1 comp. 243 heads is 10.26:1 comp, and so on...
I ended up buying 62cc PRC Stage 2.5 LS6 heads. If I use the stock .051 head gasket, I'll be right at 10.55:1 comp...a little higher if I use .040 Cometics. I'll have to measure exactly how far out of the hole the pistons are when my shortblock arrives before I make that decision.
I ended up buying 62cc PRC Stage 2.5 LS6 heads. If I use the stock .051 head gasket, I'll be right at 10.55:1 comp...a little higher if I use .040 Cometics. I'll have to measure exactly how far out of the hole the pistons are when my shortblock arrives before I make that decision.
Just remember that the larger the cam you run the lower your Dynamic Compression ratio too. So a big cam will actually drop your Compression ratio.
So a big ol cam and mediocre compression is going to give you poor driveability. If its a street car a MILD cam and the upper end of compression makes for the most fun and efficient.
So a big ol cam and mediocre compression is going to give you poor driveability. If its a street car a MILD cam and the upper end of compression makes for the most fun and efficient.
Couldn't agree more. People forget that big cams bleed off compression and love small chambers if you flycut. FYI I'm at 11.5:1 and my cam (236/238) is a tad bit too big for street duty IMOP. I plan on dropping down to an F14 or Torquer v2, and upping the nitrous jet a size or 2 to compensate.
Also, flycutting is easy and well worth it. There's a good write up on here somewhere.
I bet that cam will make for a pretty fun combo actually, im sure you can get better but I imagine that one is going to be pretty close overall.
