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.

 

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.

 

No 93 octane up here. I can get 110, though, in a pinch. I'd just assume not have to mix it with every tankfull of gas to keep detonation down, though.

 

Bump it up. Trying to decide between 59cc ported LS6 and 64 cc LS6 on the LQ4 shortblock.

 

Why not get the 64cc heads and the bigger cam. Then measure PtV clearance to see what you got and have the heads milled locally.

 

I'm having the cam custom spec'd so I need to know the head specs before I have the cam spec'd.

 

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.

 

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.

 

Fly cutting isn't a big deal. I did it with my engine in the car. It took almost 2 hours. That's it. I rented the tools for $60 bucks.

 

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.

 

I'm thinking 64cc will give you 10.5 CR with stock gaskets, so 62cc should be another 1/4 point more.

 

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?

 

lq4 has dished pistons. lq9 has the flat tops.

 

I was thinking LS1, it's been a while since I looked at page 1, so forgot this was a LQ4. What pistons?

 

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 used an average out of the hole number and with my CR calculator, I also got about 10.5. That should work well for you.

 

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 have a Torquer V.2 in the shortblock now, but I'm having PatG spec me one out for my combo. I may just go with the TV.2 until winter, though.

 

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.