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2.5" is plenty as the guys in the fast series are running 2.5" and running in the 9's

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fixed

I think 3" would be too much on a 360 ... then again they put 5" on a 5.9 cummins

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Don't bother with 3" unless you plan on over 500hp. Also, don't negect the muffler selection.


Dave

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Don't bother with 3" unless you plan on over 500hp. Also, don't negect the muffler selection.


Dave

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I went through this same thing last summer with
my Duster! I have a mild 360 currently as well.
I debated and went back and forth for weeks...
deciding on what to do. Since mine is just a
weekend summer cruiser (car show/cruise nite/ice cream runner type Mopar)...I went with a header back Jegs(Pypes) full 2-1/2 inch kit which is a nice kit IMO.

All aluminized mandrel pre-bent tubing with
(optional H-pipe) which I got.

I wanted to go the full exhaust route, with 2.5" stainless steel tips. I had a local
muffler shop do the work,because I wanted everything welded properly. They had an easy time until they assembled the 2.5" tailpipes next to the factory gas tank. It took them quite awhile to get the fitment just right on the pass. side pipe...between the tank and leaf spring.
IT'S TIGHT THERE! The system turned out great though,sounds awesome with Flowmaster 2 chambers.

So....if you are thinking of going with a 3 inch system out the back...think twice about the gas tank issue! Good Luck!

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I read an article a couple years ago and i'll try to relay what it said even though I may be using the wrong scientific terms. But basically what its said was the by the time the exhaust gets through the mufflers, a large portion of the heat energy has been disapated, or maybe it was back pressure, anyway, it stated that you could do like 3" pipes from the headers to the mufflers, and then go 2.5" from the muffers out the back tailpipes and you wouldn't really be creating any extra back pressure by having the smaller tailpipes. But the car would be quieter with the smaller tailpipes.
Wish I could find the article, I'm sure its explains it better than I did.

Anyway, I would stick with 2.5" pipes if the car sees any amount of street use, just to keep the noise down.

Good luck

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Have read similar articles and his summation is not far off.

Tailpipes are an oft-overlooked key in noise control. Size and location of the turndown are key.

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3" is just silly for a 408, even more stupid for a 360 in a dart!!

You guys are a riot.

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Call me silly. I get a kick out of some of your stuff too .

My 340 was about 450 hp, hydraulic cam and pump gas. It had 2 1/2" with flowmaster 40s with turn downs at the rear end. I bracket race the car some and had always run it with the exhaust off and deciced to leave it on one night to see what it would do. It was late in the fall and the air was great, in the first round of open time trials all of my friends ran near their best times. I went out and the car ran 7.45 when it should've been in the 7.20s. When I pulled into my pit I put the ramps on tha trailer and pulled the car on them and took the exhaust off. Went right back out and ran 7.26, the best it had ever ran was 7.24. Now keep in mind that my exhaust turned down before the rear end, no bends over the rear end. This was real back to back runs 10 minutes apart, not some keyboard B.S.

The 408 in my car now is around 550 hp on pump 93 and has 3" exhaust turned down at the rear end, it has gone 6.70 with the exhaust and 6.57 without. Not on the same night so I can't say it's holding it back. I drive this car a lot in the summer, there is no resonance at any rpm and it's only loud inside when I gouge on it.

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3" is just silly for a 408, even more stupid for a 360 in a dart!!

You guys are a riot.

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Call me silly. I get a kick out of some of your stuff too .

My 340 was about 450 hp, hydraulic cam and pump gas. It had 2 1/2" with flowmaster 40s with turn downs at the rear end. I bracket race the car some and had always run it with the exhaust off and deciced to leave it on one night to see what it would do. It was late in the fall and the air was great, in the first round of open time trials all of my friends ran near their best times. I went out and the car ran 7.45 when it should've been in the 7.20s. When I pulled into my pit I put the ramps on tha trailer and pulled the car on them and took the exhaust off. Went right back out and ran 7.26, the best it had ever ran was 7.24. Now keep in mind that my exhaust turned down before the rear end, no bends over the rear end. This was real back to back runs 10 minutes apart, not some keyboard B.S.

The 408 in my car now is around 550 hp on pump 93 and has 3" exhaust turned down at the rear end, it has gone 6.70 with the exhaust and 6.57 without. Not on the same night so I can't say it's holding it back. I drive this car a lot in the summer, there is no resonance at any rpm and it's only loud inside when I gouge on it.

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He said his was street car, not a race car. 3" system is heavier than a 2.5" pipe. A dart is a smaller car than my challenger with 3" and it's tight under my E body. I don't care for my 3" X pipe TTI system and my 2.5" H pipe TTI pipes sound way better than the 3" X pipe, way better. I have BB in my 3" car, not a little wimpy 408.

Bigger is not always better is my point, especially for street car. Been there, done it.

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[He said his was street car, not a race car. 3" system is heavier than a 2.5" pipe. A dart is a smaller car than my challenger with 3" and it's tight under my E body. I don't care for my 3" X pipe TTI system and my 2.5" H pipe TTI pipes sound way better than the 3" X pipe, way better. I have BB in my 3" car, not a little wimpy 408.

Bigger is not always better is my point, especially for street car. Been there, done it.

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Mines a street car too. What does the bad big block Challenger run? 8.20?

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[He said his was street car, not a race car. 3" system is heavier than a 2.5" pipe. A dart is a smaller car than my challenger with 3" and it's tight under my E body. I don't care for my 3" X pipe TTI system and my 2.5" H pipe TTI pipes sound way better than the 3" X pipe, way better. I have BB in my 3" car, not a little wimpy 408.

Bigger is not always better is my point, especially for street car. Been there, done it.

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Mines a street car too. What does the bad big block Challenger run? 8.20?

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I have no idea what it runs because I have never taken it to the drag strip. Even a 10 second ride is not exciting to me anymore on the track. On the street is totally different story. Now it's about cruising in a reliable muscle car for me.

My 440 has eddie heads on it and a 6 pak. It'll smoke my 12" wide mickeys at 35 MPH roll.

I just got a go pro camera for Xmas and wanted to use it today but it is still too salty on the streets. I've been downtown and to work already today on separate trips checking out the streets because it's going to be 55 today and the rest of the snow will melt. It's gonna have to wait. My cars are no slouches but I'm not claiming to have the fastest car.

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you should have stayed with this post only ...

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YEAH, I know! All this talk about pea-shooter sized exhaust is quite entertaining though.

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3" is just silly for a 408, even more stupid for a 360 in a dart!!

You guys are a riot.

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Call me silly. I get a kick out of some of your stuff too .

My 340 was about 450 hp, hydraulic cam and pump gas. It had 2 1/2" with flowmaster 40s with turn downs at the rear end. I bracket race the car some and had always run it with the exhaust off and deciced to leave it on one night to see what it would do. It was late in the fall and the air was great, in the first round of open time trials all of my friends ran near their best times. I went out and the car ran 7.45 when it should've been in the 7.20s. When I pulled into my pit I put the ramps on tha trailer and pulled the car on them and took the exhaust off. Went right back out and ran 7.26, the best it had ever ran was 7.24. Now keep in mind that my exhaust turned down before the rear end, no bends over the rear end. This was real back to back runs 10 minutes apart, not some keyboard B.S.

The 408 in my car now is around 550 hp on pump 93 and has 3" exhaust turned down at the rear end, it has gone 6.70 with the exhaust and 6.57 without. Not on the same night so I can't say it's holding it back. I drive this car a lot in the summer, there is no resonance at any rpm and it's only loud inside when I gouge on it.

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I bet those crappy flowing Flowmasters cost you far more restriction than the 2.5" pipe does/did


Dave

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3" is just silly for a 408, even more stupid for a 360 in a dart!!

You guys are a riot.

---

Call me silly. I get a kick out of some of your stuff too .

My 340 was about 450 hp, hydraulic cam and pump gas. It had 2 1/2" with flowmaster 40s with turn downs at the rear end. I bracket race the car some and had always run it with the exhaust off and deciced to leave it on one night to see what it would do. It was late in the fall and the air was great, in the first round of open time trials all of my friends ran near their best times. I went out and the car ran 7.45 when it should've been in the 7.20s. When I pulled into my pit I put the ramps on tha trailer and pulled the car on them and took the exhaust off. Went right back out and ran 7.26, the best it had ever ran was 7.24. Now keep in mind that my exhaust turned down before the rear end, no bends over the rear end. This was real back to back runs 10 minutes apart, not some keyboard B.S.

The 408 in my car now is around 550 hp on pump 93 and has 3" exhaust turned down at the rear end, it has gone 6.70 with the exhaust and 6.57 without. Not on the same night so I can't say it's holding it back. I drive this car a lot in the summer, there is no resonance at any rpm and it's only loud inside when I gouge on it.

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I bet those crappy flowing Flowmasters cost you far more restriction than the 2.5" pipe does/did


Dave

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Agreed! Despite the name those things flow like there is a potato stuck up the pipe. For as much back and forth as there is regarding pipe size in this thread, muffler choice is probably more critical than 2.5" vs 3" for these power levels.

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The DynoMax tech section has some good information about calculating exhaust diameter based on C.I,D. and horse power
seems like muffler selection is also a factor in their calculations
http://www.dynomax.com/assets/2012catalog_pdf/2012_Dynomax_techsection.pdf

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As per DynoMax tech piping chart about horsepower.
It is brake horsepower or rear wheel horsepower.
Big difference...
My engine is a 451 with 373 RWH and I use 3.00 may be It's too big.