atm everything is stock, but i intend to run a true duel 3" at the same time i get my headers installed.

I do have plans in the future for something bigger like a blower.

But until then, how will the duel 3" perform with just headers?

anyone?
Should i just go for duel 2.5?

3 inch would be over kill. I would stick with the 2.50". See the below chart.

Hey 1989GTA, where did you find that chart at? Now I think I definatley want to upgrade to a 4" Mufflex. I have a 3" Flowmaster cat back on my car now. I'm using Hooker longtubes, with a mufflex "Y" pipe, and no cats. My new 436 engine made 500 h.p. and 570 lbs ft on the engine dyno. How much power do you think I'm choking with a 3" system?

Now offense, but I think that chart is garbage.... there's no way a 3 - 3.5 inch pipe is in the same league as a true 2.5 inch dual setup. Not even close. 4 inches might be closer... MIGHT.

To the author, go 2.5 for now, once you have the bends set up with a 2.5, copying them with 3 inch pipe in the future won't be a huge problem.

At that level, A LOT!

You might consider the chart garbage but both Walker Muffler(chart above) and Magnaflow both have a chart showing the same thing. I'm sure these two companies have many hours of dyno time on their products.

What is your basis for the chart being garbage? The math supports a 3.50" single pipe being equal to a dual 2.50" system.

Just becaue 2 2.5 inch pipes ads up to 5 dosent mean that it gives you the same internal volume that a 5 inch pipe would

It couldn't be because it's easier to package a sell a single pipe system than it would be to sell a grass roots dual setup would it?I mean - those companies aren't in the BUSINESS of selling exhausts, are they? No bias there......

Fact is, if you aren't open to making your own dual exhaust, don't try to debate me on it, because we'll both just look like idiots bashing our heads together....

... but at least my car would be faster

Correct

Flow area = pi*r^2

Dual 2.25" = ((pi*(1.125^2))*2) = 7.94 in^2 of flow area
Dual 2.5" = ((pi*(1.25^2))*2) = 9.8 in^2 of flow area
Single 3" = (pi*(1.5^2)) = 7.06 in^2 of flow area
Single 4" = (pi*(2^2)) = 12.56 in^2 of flow area
Single 5" = (pi*(2.5^2)) = 19.62 in^2 of flow area

Too make it clear before emotions get involved... that was my playing Devil's Advocate, not being an *******... hence the

Thats funny, GOY! I saw a similar chart in the Lingenfelter book. This chart soley relates to header sizes. I have Hooker Supercomps, with a 3" "Y" pipe, channeling into a 3" FM catback. It was always my understanding that if a restriction does exist, the further back, the better. I was under the ASSumtion that the smaller pipe I have, would make the exhaust flow at a higher velocity. I'm planning on checking the system with a pressure guage to see where I stand, just to be sure. Then I'll know if it is absolutley necessary to shell out $500.00 for a 4" catback from Mufflex.

Well I'll tell you want, I keep referring back to a post someone here made about gaining fairly substantial amounts of power by switching to a 4 inch exhaust FROM a 3 inch exhaust. That was on a stock long block L98, and power peaks occurred at lower RPM's with the 4 inch unit, basically destroying the theory that big exhaust = lost power down low. People always refer to the requirement of backpressure, but I think they fail to see that if their header or exhaust manifolds aren't enough pressure, the cat certainly will be.

How many cars do you see running open headers at the track? I doubt they do that by accident. But then again, there will be some that feel that backpressure is needed to optimal exhaust flow by keeping velocity high. I just don't see the point of added pressure BEHIND the cat... that cat is like I plug in the system, and savaging only occurs in front of it.

Too each his own.

Single 3.50" = 9.616 in^2

Jesus Christ - we get it, almost the same space, or near the same space. I hope you write that down on a piece of paper too keep under your pillow at night, so you sleep better.

Space is great - the forced collision of two air fronts isn't. "Balancing" crossovers are one thing, but FORCING the fronts to collide in a Y isn't! Then again... everyone seems to think their engines will blow up if they don't squeeze every bit of backpressure out of their systems that they could lately it appears. GM ditched the single exhausts after the Fbody for a reason, not by accident. Even when it was in production, did you notice the Y kept moving farther and farther back from the factory to prevent hot gases from coming to a dead stop right at the banks, like in our cars.

2 cylinders would have to fire at the same time for that to happen.

If you had equal-length headers that might be true, but with the headers that most people use it's anybody's guess what actually happens.

Also, it's not as if both headers are an equal length away from the Y. No matter how you look at it, they are BOUND to collide (do they have any other route to go?) - and the situation would become more frequent at higher engine speeds when exhaust gases begin to move slower than they are being expelled for the engine ... meaning that it turns into 2 banks fighting each other for space at the Y.

But I guess since the exhaust companies have done research, we should blindly follow them like sheep and buy what they tell us is best. By the way, did anyone specify if that was exhaust research or market research?

D/P

The purpose of the charts from the companies was to show what size exhaust whether dual or single was best for engine size and horsepower. They mainly did not want people to oversize their exhaust system. The chart was part of a dessertation on exhaust sizing. I just copied the chart portion which I thought would be beneficial to others. Magnaflow has a similiar example on their web site. Maybe other manufacturors do also.

I suggest some might want to read the whole thing instead of throwing around unfounded accusations. Sorry I only copied the chart portion and not the whole article. Allen

ShiftyCapone: Doesnt "r" mean radius. You used diameter in your calculations.

Sure looks like he used radius to me.

No I used R. Look again

sorry i must of been on crack at work today.....

crack cocaine

Sounds pretty reasonable. I''ve no smarts in the area of how air flows... if I knew how to explian what I meant properly.. it might seems a little more.. something lol

As far as exhaust pulses colliding at the 'y'... wouldn't that happen at the collector first ? And the pulse timing... why doesn't that problem occur with an x-pipe ?

Kind of stupid questions I know but, I'm better at putting the crap together instead of knowing the math and science to it.

It probably does, but zoomies aren't all that practical for street use.

twas i that posted the power gains off going to a mufflex 4 inch from the 3 inch. i just wanted to add that i had no cat on the car for either dyno.

Those tables are pretty useful, but what about a small block 383 making 523hp/482ft-lbs??? According to the table ideally I'd need a dual 3.25" to dual 3.5" setup.....is this correct??? I'm currently looking into a set of Kooks long tubes for the new engine....

- Joel

How did the power gains look across the entire power band? I know your peak value increased but did it also increase at every point in the curve? I had meant to ask you this earlier but forgot.

Realpower, I have pm'd you about the header adapter plates you ripped me off on, I would appreciate it if you would answer me.

Hey guys,I dunno if people are still posting a lot on this thread, but I am building a 91 that is going to have a 510 HP 383, and a tremec T-56. You guys have any ideas as the best way to route my pipes? I can weld and cut. I was thinkin aobut a true dual out the sides, with a crossover. Any opinions? Thanks