Fast355

I have Thorley 1 5/8" Tri-y headers that merge into 2" then into 2.5" pipes on a ~400 hp 350 and they work GREAT. Might be giving up a few HP upstairs but at part-throttle and WOT from idle to 6,000 rpm they work very well.

George C....

those garbage things belong on a SBC thats mild, they have no business on a LS motor that out breathes SBC

Fast355

No way in hell a stock 4.8 outbreathes a 350 SBC with aftermarket heads and a 215/220 @ .050 cam with .545" valve lift. Its not like the 4.8 is going to be living above 6,000 rpm with the stock cam and springs anyway.

George C....

depending on yr 4.8 the heads flow 240-250 cfm

Fast355

My heads flow about that, but I have 56 cubic inches on a 4.8 and pull more airflow than a 4.8 through the larger engine.

slick_sierra

Getting a lot of conflicting opinions but I appreciate all the feedback the motor never sees over 5000 so no need to worry about top end. I just don't wanna make it more of a dog down bellow 2500

Fast355

1 5/8" primary is more than enough for your setup and will help your low-midrange torque.

George C....

You'll regret small primaries
He'll stock manifolds are that size

Fast355

LMAO!! A header is no comparison to a log style manifold. I have a buddy running 7.90s 1/8, 12.80s 1/4in his stock shortblock 5.7 2003 quad cab Hemi Ram with 1 5/8" primary headers.

George C....

These aren't HEmI motors

Can't compare apples to ******

Putting a 1 5/8 header on a 4.8 is a **** up

And if OP plans to go with a health 6.0 the 1 7/8 will be choice
Now a badass 6.0 will love 1 7/8 stepped to 2"

These motors need to breathe...minimal for a 4.8 or 5.3 should be 1 3/4