i have a 4.8 in my 99 silverado now. i sold off my 6.0 to help pay a medical bill i had. i got a set of 243s for free for helping a boy out with his 6.0 build off his old L33. i just dont feel like messing with building a motor and i have a 5.3 if the 4.8 ever took a dump. but my plan is to stick these heads on, a tbss intake and get the x link with a throttle body. get pat g to spec a cam for me and hopefully go ahead and do a kbracing front mount. i know these heads are going to boost my cr and i just dont want it to be TOO high...id like to just run about 5-9 psi and have some fun. what are your alls thoughts?

 

the 243s boost cr, or drop cr?

 

243 heads will lower your compression!!!
they need to milled to retain factory compression ratio
scratch that tbss intake idea also...been there done that lost performance! .5 and 4mph at the track

 

but if their milled they will flow more air though correct? and how much they need to be milled?

 

No sir, milling only changes the combustion chamber area (increases compression). You're thinking of porting, which is done to increase airflow.

 

so im better off just leaving my heads on than

 

no 243s flow better but need to be milled to gain back compression of the bigger chamber
243s are a better head

 

You sure there weren't other contributing factors to the decrease in performance?? There's multiple threads on here of folks benefiting from it, including a dyno run of a bolt-on 6.0 gaining like 20ft-lbs all across the board after the TBSS intake install.

 

They'll need to be milled roughly .025 to keep the same compression. However, if you're going to throw boost at it, maybe you'd be better off to keep them where there at and dropping your compression a bit for more boost.

 

I�m not going to say whether it would loose power or not, as I can�t say, but the air-flow requirements for a 6.0L (364cu-in) vs a 4.8L (292cu-in) will vary greatly. So what may produce good power on one engine may not on another.