Hello, I am contemplating making my ss my daily driver.. I currently have a 3" X-pipe system with borla XR1's. This is just too loud to be driven every day so I am considering going to a Y-pipe setup with a corsa catback. I have been reading about exhaust sizes versus horse power ratings and with my setup I think I may be limiting the car a bit with a jethot y-pipe it collects at 3" then the corsa would be three inches back to the muffler and split. My question is if this is limiting the horsepower how much will I actually be hurting my performance by making this switch? My mods are in my signature.

 

with a h/c car...you could easily see 10-15hp peak.

might not see much difference...possibly a gain...in the lower rpm band.

 

This saddens me.

 

get better mufflers.

my magnaflow 4x9s do a GREAT job quieting my cam only LS1.

the setup:


xpipe with no mufflers:


same day with mufflers installed, never moved the camera:

 

not a great video....but same car and setup on a dyno...going to 6400rpm

 

Some people actually pick up power going from TD's to a y-pipe setup. I know someone who dynoed (same day) with TD's and a Corsa (I believe that's what it was) cat back and he actually picked up 12rwhp and like 15lbtq with the cat back over the TD's, don't remember what all was done to his car though.

 

his dual setup must have been pretty badly setup if he's making more horsepower by going to a y setup..

 

single 3in will outflow dual 2.5in. You have an X-pipe in there so I dont no if that we still be true. I wouldnt be too worried about the HP loss. It might seem slower since its not gonna be as loud but I doubt you will actually go any slower.

 

How does one three inch pipe out flow dual 2.5 inch pipes?

 

I 'did the math' and disagree- the dual 2.5 in exhaust would have a slightly larger cross-sectional area than a single 3 inch, so, at equal pressure would flow slightly more exhaust- It would probably also cost more and weigh more for a negligible gain- I remember reading somewhere that a single 3 in exhaust should be able to support around 400 hp, so good for most vehicles on the street-

area = pi x r squared
a = pi x (3.0/2) squared = pi x 2.25 = 7.068 in sq for 3" single

a = [pi x (2.5/2)squared] x 2 = [pi x 1.5625 ] x 2 = 9.817 i sq for 2.5 " duals

even 2.25 in duals have a cross-sectional area of 7.952 sq in- of course, this disregards the effects of boundary layers on the flow- a 2" dual system as a sectional area of 6.283 inches sq and would be more restrictive, all other things being equal, to a single 3" pipe-

On the other hand, with the smaller diameter pipe, the exhaust flow speed would be higher, and might lead to better scavenging, and less loss of exhaust energy (heat)- probably the difference is pretty slight in the real world unless you are pushing big displacement and high h.p. numbers-

 

I don't know how his was set up I just know the numbers difference. I personally love my TD's and X-Pipe set up.

 

its not that the exhaust pipes have a larger cross sectional area. its has to do with laminar vs turbulent flow and drag properties. When calculating flow numbers the fluid in contact with the pipe is essentially stopped. this causes drag and effects turbulence. Turbulence has more of an effect when determining the pipe diameter. The area of the single exhaust compared to the total circumference of the single exhaust is better performing. Basically a single exhaust has less area slowing down the exhaust. Plus you get the added benefit of less weight. If you dont believe me Im sure I have some professors that could explain it more clearly than me.

 

Within a range, yes, but there are other factors- Do you think a single 3-inch system would outflow a dual 3-inch system? You could express the boundary layer as a percent of area, versus the free-flow area, or calculate the total area- according to you, a dual three inch system would have twice the drag, so would flow worse- ain't gonna happen....

I would agree that there is a trade-off on weight, and cost, too. Double the clamps, hangers, maintenance parts- Depending on headers and tuning, there may or may not be some help in scavenging from the timing of the exhaust pulses, too. And, as I said earlier, the smaller diameter would flow the gasses faster- think about equal volumes of exhaust going through a 3" pipe or a 2" pipe, the 2 incher is going to have a faster flow in FPS-

Agreed, there are many considerations, not a simple one-dimensional question. OVerall length, tuning, resonant frequency, on and on- And we haven't even started talking about one muffler versus two....

 

A dual 3 inch exhaust should outflow a single 3 inch exhaust. The thing is most vehicles dont need a dual 3 inch exhaust and the exhaust is moving too slowly and has more restriction. The flow of a system is computed as the integral of the speed of a cross section (in general terms). Think of it as the area under the curve. obviously the 3 inch is going to have more area than a 2.5 inch, but when you go to duals the speed drops to under half which results in less area under the curve. There is a happy medium between exhaust size and exhaust speed, similar as heads and cam setups. This scenario neglects scavenging which your setup would do quite well due to the X-pipe. This is just in general terms and neglects cats, mufflers bends over length. Obviously its not 100% accurate and the only true way to tell you HP gain/loss will be with a dyno.

 

Troof! That is the point I was trying to make, that it is complex, and tuning is almost more of an art than a science- Like the idea of painting the exhaust pipes, and placing the cross-over where the paint burns off- and the whole H-pipe versus X-pipe thing. The best exhaust for your application is the one that works with your RPM range, gearing, driving patterns- there is no one 'fits-all' answer. Exhaust flow or speed is important, as is length in relation to resonance tuning. Sometimes it takes a little tweaking to get it just right- but then, that is part of the fun, modding your car-