Milling ls6 heads to 11:1

[K99Raptor]

First off, I couldn't find what I was looking for with the search, so please don't give me a hard time about the search button!:D Although, if you happen to be better at it than me and find a link that will be just as well.

I'm wanting to raise the compression of the new ls6 heads from 10.5:1 to ~11.0:1. It's not expensive to raise compression and I'm looking at getting some nice tf heads or afr's in the future so I don't want to spend much now. I'm basically bartering for the heads so I won't be spending that much. Now the cam being used with this set up is a 227/228 .568/.570 111+4 with xe-r lobes. Now this car is a DD, so if 11:1 on 93 octane with a good tune will be impossible to keep from detonating, please deter me now. I talked with a shop and he said that with the ls6, I'll need to take .00030" off to get the chamber volume down. :dontknow:

Is there a "magic" formula to see how much you need to take off to get a certain compression?

Is there a formula to make sure that there will be plenty of piston to valve clearance?

Will this set up be good for dd?

Thanks for the help!

[SStrokerAce]

Kermit,

Actually for what it's worth we do race quality LS6 heads a lot around here and as a bolt on compared to your stock 853 heads the stock 243's are upgrade for sure.

The easiest way to bump compression would be to run a thinner head gasket like a .030" thick Cometic that you can reuse when you do a head swap later. That will get you 11.25:1 or more on a stock LS6 (243) chamber.

FWIW actually the most economical upgrade for cheap heads that run is a good valve job on a set of 243 castings. The heads out of the box from GM move 250-255cfm @ .600" lift, with a valve job they can move 285cfm @ .600" lift. Now this is not something your average shop can do but for a budget performance gain that will easily out power the cheap 5.3L CNC heads out there from Patriot or TSP. I have a mid sized cam that is very drivable that with the VJ 243 heads could put down 460rwhp easy.

We also have race CNC programs for the 243 heads that move 315cfm and can make 500rwhp on a stock bottom end. I would put money on them in a race against AFR 205's or the TFS 215's anyday and not break a sweat.

Bret

[K99Raptor]

Thanks a ton for the reply! it's exactly what I was looking for!

If u don't mind pm me a couple of quotes . One for just the valve job. one for the cnc'd heads. I will provide new heads.

So these numbers were at the rear wheel on a medium cam? That's amazing if so! 500 is a hard mark to make with ported aftermarket heads port matched to a fast 90mm manifold, and a large cam. My original goal was 450rwhp with plenty of power under the curve, but around 430 was my more realistic goal with the 243s. If u could help me get over that mark I would be more than happy.

[SStrokerAce]

Yeah I have a nice cam in the low 230's that makes good numbers (420-440rwhp on a 241 heads) and a bunch of smaller cams if you want something tamer below that.

The heads have a lot of direct racing experience in them from professional racing classes. Lots of dyno time in making them run not just making good flow bench numbers out of them. The valve job only stuff we do is because of some racing classes where that is all you can do to the heads. We have applied that to a few things that really work well like the VJ 243's or even Dart 225's with a VJ and CNC chamber that work AWESOME on a 402 LS motor.

450rwhp is not going to be hard with proper install and good tuning even with a small cam.

Bret