I figured I would start asking questions since I'm coming to the end of my build. I picked up a set of 243 heads from an 08 silverado, and got new seals and Z06 springs put in. Even though these are already from a 5.3, do they need to be milled 0.030" like everyone does with the ones from a Z06? Would it hurt my performance? I know the machine shop wanted to mill them to true them up, but they want to know how much to take off. I'm running a 212/218 114 cam, and had the block bored 0.020" over. Let me know what you think. Thanks.

 

What pistons are you running o your 5.3 build? If you have flattops your compression should be 10:1 or close to it. If you have the stock dish pistons you need to mill .030" off to get your compression back due to the larger cc chambers.

Personally I would mill them .050" if you have dished pistons and take advantage of the low end torque and free horsepower. If I had flattops I would mill them around .030" again for the nice gain.

Hope this helps!

 

I've milled .055 on 243's , on flat top piston , on .581 lift on 113lsa, and had no problems with PVC

 

Mill, I have done some on an engine that was dished pistons (03) and milled .045. Cams love compression, will really help the dcr. I would mill at least .030. You won't have any fitment issues

 

I definately have dish topped pistons. I'm Just hoping the heads come back in good order. I got them in the mail and almost died when I saw the castech logo on them. The whole reason I've built a motor from scratch is because of that little battery shaped logo came on the heads of both of my 5.3's, and I have two sets of castech 706's with one head cracked out of each set. Was the issue fixed with the NNBS? I sure hope so.

 

i cut mine .040

 

I would have but I use the truck a lot, I still want to get away with running regular 87 octane. Plus being in Canada I would like to maintain reliability in the winter time. Cold starts are very hard on the engines when it's -40, I'm scared of cracking another head. What is the different between the z06 243's and the ones from a 5.3? I assume the castings are the same.

 

Valves and springs.

 

u need to cut them .032 to return to stock compression i cut mine .030 but i was on a flat piston 5.3 so i pulled my compression up form 9.9-10.5... i say cut them .035-.040

 

i run mine on cheap fuel all the time with no issues
28* total timing and no spark knock on 87