Why do LS6 heads perform better?
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From: Port Tobacco, MD
Why do LS6 heads perform better? I guess its kinda a stupid question but what makes a ported LS6 head perform better than a Ported 5.7 or 4.8? Runner size? Shape? Combustion chamber?
Phillip
Phillip
The stock LS6 head has a larger intake and exhaust port volume than a stock 5.7 or 4.8 head. Also the LS6 combustion chamber is smaller than a 5.7 head, yielding a higher compression. Keep in mind these are stock comparisons, but this is what you have to work with when beginning to modify the stock castings. The 4.8 head will have to have larger valves put into it to make it even considerable as an upgrade.
TECH Apprentice
Joined: Jan 2004
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From: Frisco TX (Dallas Area)
If you look at the two together, you'll see that the LS1 has an oval port and the LS6 has a "D" shaped port (fatter opening on the bottom than the top. The shape is similar to the old BB Chevys, the "D" port supported better high volume, bigger inch, flow while the "oval" ports produced better torque from lower RPM. Now I don't know all the particulars, but I bet that the port shape gives you a better short-side radius on the LS6 and more power potential. GM probably did all they could to increase the CFM of the heads over the LS1 during the design too. Just my opinion. HTH 
I am still wondering the same thing, but I hear that LS6 heads are better than 6.0L heads when looking for peak horsepower. I hear this is the case even if the compression is the same. I am talking about ported LS6 vs 6.0L. Not trying to steal the thread, but this should be on the same lines.
I think some of the biggest reasons that the LS6 heads ported make so much more power then a similar size ported LS1 head, with all other things being equal (compression, etc) , is
1. Short side radius of the LS6 vs LS1, this is something that I have discussed in detail with Judson, and also why we think we have some LS1 heads that flow on the bench but don't make the power they are supposed to. As this short side radius is cut down, it will still flow air on the bench, but does not make the power that it is supposed to.
2. Chamber shape, the LS6 chamber is more "scooped" right off the seat and then has the flat wall across the quench side of the chamber. I have seen pro stock heads that had this same "flat wall" of sorts and I think this may also be why they make more power.
3. The LS6 vs 6.0L with the same CNC program and all other things being equal, the LS6 will flow more air, due to the chamber shape.
4. LS6 vs 6.0L vs LS1, the LS1 heads have water behind the mixture motion dam, where the LS6/6.0l heads do not, and can be ported to have a better shape around the intake valve boss.
I think it is also interesting how when we put the nitrous exhaust port on these heads they make more mid range torque and less top end HP then the smaller exh ports.
1. Short side radius of the LS6 vs LS1, this is something that I have discussed in detail with Judson, and also why we think we have some LS1 heads that flow on the bench but don't make the power they are supposed to. As this short side radius is cut down, it will still flow air on the bench, but does not make the power that it is supposed to.
2. Chamber shape, the LS6 chamber is more "scooped" right off the seat and then has the flat wall across the quench side of the chamber. I have seen pro stock heads that had this same "flat wall" of sorts and I think this may also be why they make more power.
3. The LS6 vs 6.0L with the same CNC program and all other things being equal, the LS6 will flow more air, due to the chamber shape.
4. LS6 vs 6.0L vs LS1, the LS1 heads have water behind the mixture motion dam, where the LS6/6.0l heads do not, and can be ported to have a better shape around the intake valve boss.
I think it is also interesting how when we put the nitrous exhaust port on these heads they make more mid range torque and less top end HP then the smaller exh ports.
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Joined: Jun 2002
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From: Forced Induction Heaven
It was my understanding that it was the Port design. I think Brian explained it very well. By the way I should know this week if my LS6 heads were able to be taken out to 75cc safely. I know if anybody can do it with a CNC it is the head porter I am using.
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