I see a lot of header companies that push smaller primaries for truck applications because of the low end torque needed. My question is, how much do the primaries and collector sizes matter for a Supercharged application. For example, how big a difference are you looking at if using a set that has 1 5/8" primaries with 2.5" collectors vs. 1 7/8" primaries with 3" collectors when used on a stock 6.0 running about 10lbs of boost? In general, I would think the more flow the better when boosted.

 

I have heard the same thing. I think its a matter of finding the right combo to retain your low end as well as allowing good flow. I am about to pick up some headers for the 8.1L. They will have 2" primaries and 3" collectors with approx. 5lbs of boost. Get the bigger primaries.....you can always use a hammer to beat them smaller if the flow is too great

 

With a blower application I would use the largest set of header primaries I could find. You have to get the flow out and away, and boosted vehicles love flow. You will also need free flowing final exhuast as well.
NA trucks would rely on smaller primary to help the scavanging of the cylinder, where you have boost pushing fresh air in.

 

I had 1 7/8 primarys with a true dual 3" on mine with the radix at 8# and I was making 518 rwtq from 3000 rpm all the way across the board. I couldnt dyno any lower in the rpm range with the converter I had but low end tq with a roots blower will be there.

 

Hard to say the gain difference in the larger versus smaller primary headers. I am still using a 1 3/4 primary on some of my high boost big power cars making about 800rw. The nice thing is they make stupid TQ.

Rick

 

Both are Stainless Long Tubes, which one fits the supercharged bill? Would I even see a difference?

1 5/8" primary, 3" collector (standard collector), 3" ORY = $600
1 7/8" primary, 3" collector (Merge Collector), 3" ORY = $1200

That is the real question.

I will mod either one I get to y into 4" exhaust

 

You'd see some gains going with the larger primaries. Don't know if it would be $600 worth of gains. I'd bet they would be minute differences where you do most of your driving. The smaller tubes might even be better down low. I'd buy the smaller ones and use the savings to fund a full dual exhaust setup. If you're after max HP on a dyno and cost and street performance don't matter, go big. Otherwise......

 

New supercharger owner... I am real interested in this topic. I just purchased the Radix 112. I am running 01 2500HD CC 4x4 6.0 w/tow pkg 4.10 and G80 and P265/75. I have stock header and cats except a Magnaflow X muffler 2.5 Dual in/Dual out, then going to the stock 2.5 Y back into a single 3.5 out the tailpipe. This is my tow vehicle. What would be best to help the low to mid. I am not interested in turning over 5K. Shorty/LT... Do they make shorty 1 3/4?? Will LT hurt low end?? Would getting a different cam later change what I would buy for exhaust now??

 

One of the car mags did an article on this topic last yr (Super Chevy?), and focussed on both collector size and length. Tuned exhaust can make huge diff in performance and Nascar teams have done huge amounts of work here altering setups to match tracks. I have true 3" duals, gutted cats, and dynotech LT's.
PROB WORTH STARTING A STICKY ON EXHAUST SETUPS V MOTOR/POWER ADDER. Be a great way to compare real world results and save lots of guess work!

 

I guess what I'm thinking is that it is more critical to have a "tuned" N/A exhaust than it is a Blown exhaust, I may be wrong, but it seems that when running a blower, you should set up to get the best flow possible, ie the bigger the better. I would think that scavaging and too little backpressure concerns would be null in this situation.... I may be completely wrong though. But even if I am right, at about 500hp would stepping up from a 1 5/8 primary to a 1 7/8 primary even be noticeable