LSXSeven

iTrader: (1)

Hey guys, working on my exhaust for my 406 LS3 build. This is in a 93 Mazda RX7. Already have JTR 1.75" headers with 3" collectors. I need to design/make a single exhaust that will net me as much horsepower as possible while being street-able. I want a full exhaust with no cutouts. I have been reading this article by David Vizard.

http://www.popularhotrodding.com/eng...re/0505em_exh/

Some of the points worth noting:

1) 2.2 cfm per HP necessary for no loss in HP vs optimum Header/collector design.
2) Pipe flows approx 115 cfm per square inch.
3) Collectors should be designed to proper length and terminate into Pressure wave termination box or atmosphere(open collector)
4) muffler must flow minimum of the equivalent pipe diameter.
5) straight through designs like Magnaflow do not induce pressure drop and are considered the same as straight pipe and have to be included in collector length calculations. Using this style muffler essentially makes your collector length the entire exhaust length and you get no scavenging wave. I need a chambered style muffler that has high flow.

so as you can see, these design parameters are going to be very hard to incorporate into a single exhaust setup as dictated by the FD. Doing the math; 600FwHP x 2.2 cfm = 1320 cfm. So I need 4" pipe just to take care of flow. Since we cant run duals and any mufflers (as far as I can tell) need to be installed in series, I need 4" in/out that handle 1320 cfm. I can fit one in the rear and will most likely need a 2nd in center. The issue is that the center muffler is also where the wave termination box needs to go so I can't use a Magnaflow style muffler. It needs to be a chamber style muffler with enough internal volume to simulate dumping the exhaust to atmosphere without also limiting flow as compared to 4" pipe. The ideal volume is 8-10 times one cylinder for each bank. The means I need a center muffler with approx. 850 cu in. internal volume that flows 1320 cfm. This is so much easier to pull off in a dual setup as you can run (2) 3" pipes and each muffler can flow 550 cfm and be run in parallel.

So, whats the real world advantage of designing such a complicated exhaust when I'm sure plenty of people have just thrown x muffler on with good results. well from what I read, the scavenging wave created by having the correct length of collector pipe, can fill the cylinder with about 70cc more air. On a 350 cu in motor, this turns it into a 383 in the tuning band. This is not a trivial amount. Some of the questions I have though are: 1) do I need 4" all the way back or can it drop to 3.5 near the differential since the exhaust is cooling. 2) how loud do you think a 4" exhaust will be if I just make a hollow chamber (5x9 x20) in center using a gutted muffler case and then just use something like a 4" magnaflow in rear.

Here are a few mufflers I have looked at to try and come up with a dual purpose center design.

1) Cherry Bomb Vortex Dual 3" in single 3.5" out( I would have to redo exit to increase size
2) Aeroturbine 4" in/out 6" round
3) flowmaster (they are chamber style but flow #'s suck)

I know camaro guys have similar setup issues. They have room for a larger rear muffler. I am limited to one 5x9x12 in rear.

Mike

Irish350

iTrader: (14)

Sounds like youve given this way more thought than i gave my exhaust setup ('trueduals w xr1s sounds good but scrapes too much, time to go to a y-pipe with a good merge and a catback.. might as well add a cutout'). That being said, I also have no experience with FDs, although i wish i had one instead of my ta.

Really what im trying to get to is that maybe spintech is your best option. Tell them the specs you've come up with. Try it out. Enjoy your badass car.

i figure quasi-helpful input is better than none

Verz

iTrader: (21)

Longtubes, mandrel bends, flowmaster y-pipe borla 4in xr1 and be good. that aeroturbine is not a mufler more like a giant canister to echo the sound, trust me i had one and it was like running an open ypipe so go with something that has some sound reduction.