What do you guys think? My build is finally getting finished, should have it running within April...so i'm getting the final items i need and don't know if I should try and cram dual 3" pipes under it. I do have the hawks double hump Xmember. Build is a pretty stout 6.0 with nitrous, around 650rwhp. I know I would gain with the 3", but would the 2.5" suffice?

Hawks 1.75" LT's, X pipe and dumped with magnaflows before the axle

 

base it off kooks true duals for the 4th gen. they run both pipes down the passenger side.

what i think would be the best compromise would be 2.5". that size flows enough for what youd want to do.

 

The goal is to have matched parts.

The cross-sectional area of a single 3.5" pipe back to muffler is about 38 inch square. The cross-sectional area of the twin 2.5" pipes is about 39 inch square. That gives equivalent flow.

Likewise, the cross-sectional area of a single 4" pipe back to muffler is about 50 inch square. And the cross-sectional area of twin 3" pipes is about 56 inch square.

 

I wonder if the added (or sharper) bends due to the complexity of a true dual setup would offset the added cross-sectional area in a 2.5" dual vs. 3" single?

 

i am pretty sure that if you are comparing a single large pipe to the same cross sectional area of duals (as in single 3.5 vs dual 2.5 above), the single pipe will flow more due to the smaller area of perimeter. the flow in the larger pipe will be more due to less drag.

thats my plan anyway. when i redo my exhaust i'm planning on an oval i pipe to use the larger single pipe flow benefits and minimize the lost ground clearance.

 

I think you need to recheck your math. Area of a circle is pi x (radius squared).

Also, don't forget that pipes are sized on OD. You need to subtract two wall thicknesses from the OD to get the actual flow area diameter (or, OD/2, minus wall thickness = flow radius).

Another factor is boundary layer effects. While the physical flow areas may be close, you will have more wall circumference with duals, which will increase the boundary layer.

 

I'm not even contemplating running a single pipe. Dual 2.5" or dual 3", and i'm not going over the axle so there's hardly any bends. Off the collectors to an X to 2 magnaflows...I just don't know if i should try and fit the dual 3" in there! With 3" in-out mufflers the OD of the mufflers is 4.5" i think.

 

DOH! I calculated on diameter by accident. Just fix it in your head by dividing everything by 4. My only point was that 2.5" pipe mates well to 3.5" single, and 3" Y-pipe mates well to to 4" single.

There was a time when I knew incompressible flow to a decent level. But like anything in life you have to use it or lose it. I lost it. And apparently I lost basic geometry skills as well.

 

Shameless sales plug: I've got 3" duals for sale in the classifieds. Mates up to Hawk's 1-3/4" primary LSx swap headers with 3" collectors. Has extra O2 bung for wide band tuning.

 

Got a pic of clearance? I'm pretty damn low...

 

Unfortunately, no. I bought it slightly used from another member here and never had it on my car. Right now my car has no engine, no trans, and no axle. And I sold my 1-3/4 inch headers so I can't even mock it up.

I can see if the previous owner has pictures.

 

That would be awesome. Going to order the stainless works headers next week, getting the 3" collector regardless of what size dual's i'll be running

 

I'm working on it... get back with you soon.

 

This has always bothered me because tubing is sold & used based on its OD and pipe is sold & used based on its ID. Why on earth couldn't the auto industry adopt a naming/sizing convention that everyone else already uses for pipe.