For a mid 600 fwhp solid roller 383 is the 4 inch mufflex good enough? It will have 1 7/8 Hedman headers, 3 inch mufflex y pipe.Car will shift at 7000 rpm. I read an article years back that a single 3 inch pipe would outflow 2.5 dual pipes, this info still stand? If so it would stand to reason a single 4 inch would outflow two 3 inch pipes. Or am I off base with my comparison? Has anyone with a high hp car switched between a 4 inch mufflex and 3 inch true duals with dyno or track numbers? If the Mufflex is suffiecient I will keep it, this car will see alot of street duty, If I do not need true duals I can do without the headache of dragging them over speedbumps. ANY info appreciated.


David

 

When I looked at single vs. dual pipes in detail
several months ago this is what I found:

2.5" duals flow better than a single 3"

2.5" duals flow equivalent to a single 3.4"

anything over 3.4" and the single will outflow 2.5 duals

Now 3" duals is a different story. I did not check that
out but from eyeballing my old graph I would say that
it's a wash comparing to a single 4".

 

I'm pretty sure it's just based on the area of a circle, which is found by Pi * r * r. So for 2.5" duals, it's:

3.14*1.25*1.25*2 = 9.8

Single 3":

3.14*1.5*1.5 = 7.1

Dual 3":
7.1*2 = 14.2

Single 4":

3.14*2*2 = 12.6

To get the flow of dual 3", you need

2*sqrt(14.2/3.14) = 4.25" pipe.

Hope this help, I'm not sure if other factors come into play but I think I'm pretty sure the main factor in flow is just the area, as long as there are mandrel bends and whatnot.

 

There are other factors in play, the info I remember from years ago said the area of the pipe did not equate to better flow, something about air"friction" in the pipe, the article said you could not simply multiply the area of 2 pipes vs 1 to theoretically have more flow. The article actually did flow comparison of some sort. Any more info?


David

 

George Baxter ran over 1,100flywheel HP through an exhaust that consisted of Hooker 1-3/4" LT's, a custom made 3" Mufflex Y-pipe, and a Mufflex 4" catback. In order to save weight, he removed the 4" Mufflex catback (45#) and ran with just a 3" Borla XR-1 shorty on each collector and a turndown. There was no difference in RWHP for the two systems, as measured on a chassis dyno. He did drop his ET from 9.11 to 9.04, but that was all due to weight savings (a total of 90# was removed). The 4" Mufflex can handle well over 1,000HP.

I had pretty much the same results.... 1-3/4 AS&M's into the Borla XR-1's, custom 3" Mufflex Y-pipe, 4" Mufflex catback, at a shade under 800HP. Removing the catback and the Y-pipe, and adding enough 3" pipe to get the turndowns past the back edge of the door (as required by local track rules) did not change RWHP.

You can not determine the "equivalence" of two different pipe sizes by looking only at the area of the pipes. You also have to account for the preripheral friction of the air against the wall of the pipe. Area is proportional to the square of the diameter, periphery is directly proportional to diameter. When comparing two relatively similar pipe diameters, a "short cut" is to compare the diameter raised to the 2.5 power. This is only an approximation, but it give good "real world" results.

 

YES, thanks Injuneer. EXACTLY what I needed to know.


David

 

did you mean RWHP not fwhp?

Also, with the 1 7/8 headers, don't you have to use adapter plates because that large of header actually cover up the exhaust bolts?

I'm just asking, no flame intended.
Jason

I have often wondered if going with bigger exhaust on my bird would help. I have dual 2.5's right now, I thought about going with 3inch duals or a mufflex 3.5 system. I don't know if the exhaust is really holding me back or not, but my car doesn't make anywhere near 60o RWHP. I hope it makes around 400, if I ever get it on a dyno I'll find out.

 

Yes with 1 7/8 headers you need ex port adapter plates, depending on the port size and bolt layout. I was referring to mid 600 fwhp.


David

 

Injuneer, what muffler did you and Baxter run on the mufflex, I have the Spintech dual outlet one. I called Spintech about a performance advantage going from the dual outlet to the straight through Spintech, they said no difference. I am considering a 4 inch Flowmaster top ten shootout or Borla XR1, maybe even a Bullet(maybe not) with a 4 inch turndown, if the dual outlet Spintech is equal I will leave it. Anyone make a 4 inch cutout?


David

 

ok you lost me, what are you running 600 front wheel drive horsepower in, and its front wheel drive, why do you need a the mufflex?

There's obviusly a communication problem and its probably on my end.

 

FWHP= FLYWHEEL horse power,not front wheel.

thats gotta be the miscommunication.

 

Yeah thats gotta be it, I have never seen or heard it reffered to as that.

FWHP, front wheel horsepower
RWHP, rear wheel horsepower
AWHP, all wheel horsepower
at the crank, flywheel horsepower

 

I wish it were that simple. It's actually extremely complex. You
have gas equations, laminar and turbulent flow, friction losses,
and losses for each bend, transition, etc. The calculations I did
only considered losses per foot of straight pipe. Duals will double
the bend, transition, and entry/exit losses for the overall system.

Just my 2 cents.

 

We both used the 4" Flowmaster. I didn't really like the noise level on the Flow', and went to Mufflex to look at the twin outlet SpinTech. It sounded a lot quieter. Denny, who owns Mufflex put the SpinTech on his car and ran it at E'town, and said there was no performance difference, based on ET/MPH, but I don't think his car was making big HP.

I had the standard Flowtech outlet turndown. George cut the turndown off his, and had the original "2OTL" tips that came with his 30th SS welded onto the Flowmaster.

We took the car to the track one day, and it hadn't been run in a lonnnnggggg time. On launch on the first pass, it blew a 40-foot cloud of rust out of the tailpipe...... never saw anything like that before. Maybe by that point, there was nothing left inside the Flowmaster

Cloud o' rust

 

OK this whole thread kinda has me lost.

From this quote, I assume that 3" would flow about the same as dual 2.5??

but where can I find how to calculate the actuall loss?