I just got my tII... it has an hks exhaust, but people tell me i should go with a 3 inch? Im assuming, 3 inch > dual? Is this true?

 

yup im a noob.

 

Watch me blow your mind.

GET A DUAL 3 INCH! AHHHHH

 

LOL! Way to be helpful.^^

When these "people" tell you to go with a 3" exhaust, that's usually from the downpipe back. RacingBeat's REV TII exhaust system is 3" from the downpipe to thepresilencer, and I think it splits off to a little larger than 2.5" from the y-pipe back to dual mufflers. Some people also go the 3" downpipe to muffler to 3" catback route.

James

 

.... thanks for clearing that up

 

full 3 inch exhaust from your down pipe all the way to your muffler, striaght through, no catz!!

 

to a dual though, twice the flames

 

or full 3 inch exhaust all the way to the end of the bumper, no mufflerz!

 

^ sure just dont live in america, or japan, or england, or canada, or......anywhere that has some sort of stable civilization

 

cat >> muffler >>>>>>>>>> pipe arrangement > pipe size

Hope that helps.

 

Do a 3" turbo-back exhaust with a high-flow 3" cat. It's the *****.

 

I have 3" from the downpipe, catless and 3" dual inlet mufflers

 

If you run a 3" from the manifold to a 3" Y inlet that goes to two 2" pipes you should be just fine, two 2.5" if you want to go crazy. Personally, I hate the way tailpipes look on the '7 if it's bigger than 3 actual inches, and in many cases it's like 4 or 5 inches. I'd think you could get good performance out of a free flowing system without having the extra weight of a dual 3" versus dual 2.5".... idk, it's up to you, but ditching the cats will do you tons more good than going to dual 3" instead of dual 2.5", and if you're talking single exhaust, yeah, you'll save more weight, but I won't get into that because I think the '7 looks terrible with single GIANT exhaust, which is what most people do with it...

 

Two 2" pipes are far more restrictive than one 3" pipe. Even two 2.25" pipes flow less. However two 2.5" pipes comfortably out-flow a single 3".

The weight difference between similarly constructed single-muffler and dual-muffler systems is well under 1% of the car's total weight, so it's barely worth considering on a street car. IMO it's certainly far less important than how loud it is, and it's much easier to keep exhaust noise reasonable with two mufflers than it is with one.

 

TOCHE (two-shey) HAHAHA

 

i had the 3 inch from the turbo to the rear bumper single exit. im now thinking of going 4 inch DP.

 

I had a stock exhaust - except for the 3.5" dump valve right behind the turbo.

Looks stock - sounds stock - until you want to play.

 

As far as dual vs single, I think the '7 looks totally sexy with dual exhaust.

 

nice welds

 

its touche... spelled just like douche

Just messin, but yea, the only reason for going with a single all the way back vs a dual would be weight vs asthetics. I have a 'vert, so its already heavy as hell, so i just went with the RB duals (got them for the car when it was NA, its now turbo, but im still running the NA Y-pipe and mufflers, no cat and no money to replace)

As for the flow, just look at the cross-sectional area of the pipe in each part (not too precise, but close enough). a 3" ID pipe will have an area of (3/2)^2 * pi = 7.07 sq in. Two 2" id pipes will be 2* (2/2)^2 * pi = 6.28 sq in. However, the exhaust doesnt flow through the entire cross section evenly. There is a boundary layer along the pipe wall thatis stopped, and it slows down the gas further inward. The profile looks like:

____________________________
____________________________
................''--,
......................';
......===>.........|
......................;'
................,,--'
----------------------------------------------
---------------------------------------------

so the center section flows a lot better than the rest of the pipe. Thus, even for a 2 pipes (2.25") that have the same cross-section as a 3" pipe, the single 3" will flow better.

 

Crude - but effective..

 

still, the smoother you can make the insides of the pipes and the more gradual you can make the twists the better it will flow.

 

I always thought dual is better, because it flows nearly the same but is more quiet, due to twice the mufflers..

 

And that's exactly why Mazda used dual exhaust on the 2nd gen.

 

Mufflers in parallel (duals) are not necessarily quieter. Two mufflers in series would quiet the car down a lot more.

Topless, you have to be an engineer (or really liked physics in school.)