I've read a few threads about true dual exhausts and it made me think a little harder about my next set-up. Seems that just about everyone agrees that 2.25" true duals are the route to go for thes N/A trucks in order to keep some low end torque. I'm wondering what everyone thinks is the optimal single exhaust size. Sooooo......What do you think and why?

If 2.25" duals are optimal then shouldn't a single 4.5" be the best seeing as it shares the same volume? ex:

2.25"(pipe size)x 3.14= 7.065, 7.065 x 2(#of pipes)= 14.13"

4.5"x 3.14= 14.13

I'm thinking about running a single 4" which should be the same as dual 2". Anyone see any flaws in my train of thought? Am I correct or way off base here?

 

Never thought about it that way.

Flow rate = Velocity * Area
Q=VA, and Q should stay the same.
If your cross-sectional area stays constant then the velocity would remain unchanged.

and then to relate to pressure...

Dynamic pressure = 1/2 * rho * V^2
q = 1/2pv^2
The density of the exhaust gases is the same so if your velocity is the same either way then the pressure should also remain the same.


Strange...but I'm sure I screwed up relating those equations somewhere.


Waiting to hear from the exhaust gurus.

 

Let us not forget the frictional loss as well, different permitted where the gasses are touching the sides of the pipe and being slowed down. Not sure if my usual equations will help, I usually deal with filled or partially filled pipes and water. While I can appreciate the same cross sectional area, it isn't that easy. You will want to keep the velocity of the gasses similar too and enlarging the pipe to 4" might be too much to get them flowing.

 

Yeah it's hard to pick a certain equation to call this. I was trying to think of one but you can't make all the regular (simplifying) assumptions they teach, such as steady flow, incompressible, inviscous, etc...the real world sucks.

Common sense would say that a 4" pipe would cause loss of low-end torque due to the decreased back pressure, but it's hard to say. I'd like to see if anyone's actually done this.

 

Wow.....more equations than I care to deal with! What do you guys think the best single exhaust diameter would be then? The biggest I've heard of I think is 3" but it just doesm't seem optimal to me given the dual sizes that work best. I know that keeping the temps in gets things flowing faster and I will be thermo wrapping it from the y back and maybe even up to the cats. Should I just go 3"? Keep in mind that i have 4.88's and the my truck is hardly ever below 2k rpm and mostly highway driven at above 2500 rpm.

 

3" at maximum.

 

wow! all that math and equations gave me a headache.
3" max. what are you planning on running? Ill give you a dollar if you say Dynomax bullet

 

Man look at the top line in my sig. It's nothing but a headache 24/7. This website and modding my truck is like a release valve for me. Dunno why, but it works to relieve stress.

 

Why 3" maximum though? Is it becasue that's all anyone's ever tried? Has anyone ever tried bigger and epically failed?

I know you run a 3" mig...do you have a loss in low end because of it and popping when not under throttle? Do you honestly think that 3.5" or 4" is going to be big? I will be going with my beloved Dynomax again but nt with the race bullet. Going back to the ultraflow most likely in 22". Still a round cased Dynomax though.......do I get the dollar?!

 

3" max. It just seems to me that you would lose so much low end. Remember, when you have to pipes, the gases are able to split down the pipes and blow out with ample pressure. I just think a 4" would be hard for the gases to flow out of because it would be so hard to build up pressure. Just my thinking may not make sense tho.

 

Found this but I will have to take an Advil if I keep reading it

http://www.hotrodders.com/forum/exha...ula-49188.html

 

If you want to run a big 4" turbo diesel exhaust found on Cummins/Powerstroke/Duramax, go for it.

The proper exhaust size is a lot more complicated than finding the sectional area of your pipe.

A 4" exhaust from the cats back is just too big, IMHO. With our N/A V8's it's the definition of overkill. Your exhaust gas velocities will be so low, you'll hardly feel the exhaust pulsing out of the tip.

I haven't seen anyone run it (good or bad), but I doubt it will work too well. Most catbacks for these trucks are 2.5-3". Only one manufacturer that I'm aware of makes a 3.5" (and I don't know if that's actual 3.5" after the cats or just after the muffler). 2.25-2.5" for duals and 2.5-3" for single both work pretty well.




HOWEVER, you see little Hondas running around with a Folger's sized exhaust and them seem to be doing pretty well.

 

3" max because it retains the best velocity to improve low end torque, exhaust gas flow, and a little increase in sound. Anything bigger does not hold velocity and the gases do not build enough pressure to retain low end energy and the exhaust temperature remains low, the engine can run lean from working too much without receiving enough fuel, the transmission can go under stress, overall its just not healthy to go bigger, same for big true duals, even 2.5"

 

Also about the ricers... don't forget the length of those systems... smaller area to fill with gases. They may be 4", but those pipes are really short

 

plus they're always WOT racing, where a open exhaust is good to have.