Hey guys I need some insight on a head swap that needs to be done. I've got an 04 Seirra LM7 with the Castech 706 heads and one or both has developed a crack. I'm looking at a new/reman set of 862s for $320 but not sure if they are Castech or not. Obviously Id like to stay away from the 706s (and anything else notorious for cracking). If I went with the 862s would it be worth it to have them milled or port/polished? I don't have a lot of time because this is my daily driver but I'd hate to do all the work and not gain anything out of it. Also is there a direct fit set of shorty headers on the market for these trucks? I have a fair amount of experience with an SBC but new to the LS platform so any insight will be appreciated.

 

Sure you could mill them, do the port and polish on the heads and install shorty headers but this kind of stuff would also require you to tune the computer for the changes.

Those two mods both change how the engine takes in air and lets air out so a custom tune would be required.

I honestly wouldn't even consider shorty headers, not worth the money for minimal power gains if any.

 

There are two brands of 706, obviously you have the castec junk. I don't think 862s were ever castec, so you should be good. You might find some on Craigslist, but they would probabaly need some cleaning at least. Lots of shorties out there, kinda torn myself on if they make HP on a standard exhaust, seen them make more power on a dyno, but not much.

 

If you can find a remanufactured set of 862 heads for $320, I'd just say go for it. But while the thing is out, I would definitely say cut them .040 and pick up some compression. May want to contact the company and see if they'll surfaced them that much.

 

Thanks for the responses guys. I pulled the trigger today on the reman 862s and they said that they are not Castech. Also pulled the trigger on a pair of Summit shortys for $200. And of course new bolts, all the gaskets, and I plan on cleaning the intake up while its out. There is a machine shop in the next town over I'm gonna call tomorrow and see what his input is on milling/port/polish but I have a feeling it will set me out too far timewise. Just bad timing cause I'd love to have some fun with it while it's apart...

So hypothetically speaking if I did have head work done, along with the shorty headers (also already have y'ed out glasspack, K&N drop in filter and a Diablosport I2 93 canned tune - mainly bought for tire size change) would I need a custom tune for this? How do I go about getting a tune?

 

Get a light mill. .020 or so maybe up to 30

go too far and you need to start messing with pushrod length and milling the intake to lay flat on the heads.

Then get a bowl blend and valve job, those are jobs any standard shop can handle and will make a good bit of difference, the bowl blend and valve job are big contributors.