Originally Posted by 00Silv4.8

Well I just got off the phone with a guy who works at a machine shop specializing in LS motors (Thanks AJ!). Now to business..

What are the specs on 862 Heads off a 4.8??

Hirdlej told me that the stage 2 5.3 heads will work and that I need a 67cc combustion chamber... now Im told that the 862s have a 57cc chamber (thunder550). So with a 57cc chamber right now Im supposed to make more compression correct? (all info obtained from thread: https://www.performancetrucks.net/fo...lanning&page=2 )

Well Brent (machine shop guy) has kinda kicked me in the *** and opened my eyes a little. I need to do more research. SOMEONE HELP! Please!

Originally Posted by hirdlej

Are you the one who PM'd me asking me about patriot ls6 heads?

Originally Posted by GMCtrk

that was me

Originally Posted by hirdlej

Ehh, who are you and what conversation did we have?

Originally Posted by hirdlej

With your current combo now, you're running 9.5:1 compression ratio. To get the most out of your setup you will want to open those heads of yours up a bit. Quite frankly I see a more economical approach to your build would be taking the heads off your truck that're currently on there. Bringing them into a good local reputable LS1 performance shop, having them ported with a level or stage 1 port job, have new springs installed where they can check the installed height and adjust accordingly and then mill the deck surface down for a fresh new surface. You'll want to measure your piston height out of the hole before reassembly and then choose your head gasket accordingly. The thickness of the gasket minus the height out of the hole the pistons are = your quench. You will want to stay somewhere between .037-.042 for a street app. This way you can get your compression up, but yet squish the air fuel mixture better (like sqeezing on a tube of tooth paste) towards the center of the combustion chamber. This resists knock and provides a cleaner more efficient burn. The other option would be just to save yourself the dicking around, call up Patriot Performance, and get these heads:

Our custom 5 axis CNC machined new GM castings make these heads a must have for any performance oriented GM LS series engine. These heads provide are specifically for 97-98 LS applications. Custom designed runners flow up to 60 cfm over stock OEM versions.Based on other modifications, gains of up to 30 rwhp can be expected. These are a great choice for naturally aspirated engines and applications where 75-150hp nitrous systems will be used. The Stage II heads feature 21-4N 2.02”/1.57” stainless steel valves, our Original Patriot Gold Dual .650” Lift springs, titanium retainers, Super 7 machined locks, custom honed bronze guides, machined spring bases, and viton rubber seals.

*Sold as Pair

Technical Specs:

Combustion Chamber: 67cc
Intake Runner: 220cc
Exhaust Runner: 67cc
Intake Valve: 2.02"
Exhaust Valve: 1.57"
Max. Valve Spring Lift: 0.650"
Spring Pressure Closed: 135 lbs. @ 1.800"
Spring Pressure Open: 375 lbs. @ 1.090"
Retainer Material: Titanium
Valve Seal Material: Viton
Valve Guide Material: Manganese Bronze
Valve Job: 5-angle

All the fancy trick work is done for you, no down time on your truck and they are truly ready to bolt on. For a small 4.8L I don't see a benefit in ported 243 heads, they will flow too much and your intake and exhaust port velocity will slow down too much. Leaving you with shitty and soggy throttle response. I'm waiting for the "nay sayers" to come in here and flame me for that last comment. Been there, done that. Also since you went with a semi donkey dick cam for that 4.8L, you lost quite a bit of cylinder pressure and now you need that back. First, 243 heads have a larger combustion chamber than your 862's or patriot's 5.3L heads. 64cc for a 243 head and 67cc for a 862 head. The only logical way I see for you to regain compression would be run a thinner head gasket and mill .028 off the heads. Assuming you can run a .040 head gasket and mill the heads no more than .028, you should gain a half a compression point. Please don't put 243 heads on your combo, you won't know what you're missing out on. Never forget, when building a venomous street combo, usually less is more.