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2.5 or 3" exhaust? 68 dart 360

Posted By: GTSDart340

2.5 or 3" exhaust? 68 dart 360 - 03/07/13 09:58 PM

Im putting exhaust on my dart, mostly stock 360. In a few years I'm planning on a 408 stroker. Should I go with 2.5 or 3" exhaust?
Posted By: rapom

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/07/13 10:45 PM

2.5" is plenty as the guys in the fast series are running 2.5" and running in the 10's
Posted By: Dodgem

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/07/13 10:55 PM

Go 3" flows 40% more!
Posted By: JohnRR

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/07/13 10:56 PM

Quote:

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




fixed

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

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/07/13 10:58 PM

HELLO IF YOU ARE GOING TO PUT NEW EXHAUST ON I WOULD GO THE THE 3" THEN WHEN YOU PUT THE 408 IN IT WILL ALREADY BE THERE . I RUN 3" ON ALL OF MY BIG ENGINE CARS THAT MY
Posted By: RapidRobert

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/07/13 11:23 PM

3". I believe any neckdown aft of the header collector restricts flow & therefore hurts power & you want no restriction & the least amount of backpressure from there rearward in a 4 stroke eng. Gas speed/scavenging is a seperate pri tube dia/length issue. But a 3" setup is going to be VERY loud & you'll need every ex trick in the book to make the noise liveable, X pipes, addit'l glasspack muffs alongside the leaf springs & maybe add some sideways capped 1.5 ft long pipes welded to the 2 bends over the axle (helmholtz resonators iirc). Ain't tried it but reportedly it is an accoustical godsend for noise reduction. Best might be those trick muffs that open up when you get on it I forget what they are called or some cable or electric operated cutouts along with restricted muffs (keep em quiet till the money is in the hands of a neutral 3rd party ). 2.5" would be troublefree. 3" would be a certain amount of gain but would be alot more work/planning. Mandrel bends everywhere.
Posted By: DPelletier

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/07/13 11:43 PM

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


Dave
Posted By: 1Fast340

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/08/13 12:01 AM

Quote:

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


Dave




whats the point in building a 408 if you are not shooting for that kind of power?

i say go for it and like said before chose the right mufflers for it!
3" usualy gives a nice deep sound
Posted By: MoparMarq

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/08/13 01:05 AM

Quote:

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


Dave




x2
Posted By: pinkduster

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/08/13 01:20 AM

Posted By: MileHighDart

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/08/13 02:01 AM

As usual the original poster didn't really indicate what his intended use for the car will be. Is it a race only drag car, or a weekend cruiser, or a daily driver.

As others have stated, 3" will be very loud inside the car. And in my opinion is overkill. But if your just racing who cares how loud it is. If its a driver or a cruiser, the loud pipes can get old very quickly.

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
Posted By: GTSDart340

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/08/13 03:02 AM

Its going to be a street car, but not a daily driver.
Posted By: Prodart440

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/08/13 04:47 AM

I see you came to ask the professionals. I think 2.5" would be plenty. You will be fast enough, and light enough, to beat all your brothers and their GM cars.
Posted By: RoadRunnerLuva

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/08/13 05:00 AM

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!
Posted By: radar

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/08/13 08:29 PM

Quote:

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!




Yep I put that kit on my 73 swinger- the passenger side over-axle isn't quite right. I had to do some surgery to get it right. Still was cheaper and easier than going to the local shop with a non-mandril bender that's going to try and sell you flowmaster 40s!
Posted By: Fury Fan

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/08/13 08:47 PM

Quote:


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



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.
Posted By: pjc360

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/08/13 10:56 PM

i'd go with dual 2 1/4 inch pipe, a dual 2 1/4 inch exhaust is enough to support 450 horse power, you dont want to lose scavenging affect.
I know a guy who runs a 408 stroker magnum thats real close to 450 hp and he runs hedman hedders 1 5/8 primary hedder tube into a dual 2 1/4 inch exhaust with an H pipe and his car runs just fine with the exhaust set up he has.
Posted By: Challenger 1

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/08/13 11:36 PM

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

You guys are a riot.
Posted By: drew72

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/09/13 01:03 AM

3" is waaay overkill. Racecar, maybe... but not on the street.
Posted By: pinkduster

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/09/13 01:42 AM

lmao!!!!



You guys should just go with something like this. I mean, you wouldn't want to disturb the neighbors with some three inch now would 'ya.
Posted By: racealittle

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/09/13 01:54 AM

When I bought my 1974 360 Challenger it had 3" pipe and flowmasters off the headers. It was loud, and gutless. I bought one of the Jegs $200 mandrel bent exhaust kits with mufflers in the 2.5" size. The car picked up quite a bit and sounded better out of the exhaust tips.

I am lowering the car, removing the headers, and putting '70-'71 high flow factory exhaust manifolds on it. I will make up the required pipe to join up to the Jegs setup and will likely add a set of electic cutouts for fun (that might exit something like the T/A pipe).
Posted By: dezduster

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/09/13 05:52 AM

I have TTI headers, had tti 2.5 H pipe set up on my duster with the 340 that went to dynomax mufflers. I swapped the 2.5 H pipe for a 3.0 DrGas X pipe when I went to the 422 stroker, that goes into "the hated flomaster delta flows" it drops back to the 2.5 after the mufflers and out the tti tail pipes to the bumper.
I like the flow masters, most on here dont. As for too loud its as quiet now as it was before, cruise wise anyway. Its not to loud while your on it and mellows quickly from behind as its driving away.
Posted By: abodyjoe

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/09/13 12:25 PM

Had 3" pipes with x-pipe and the larger 3" dynomax super turbo mufflers with 3" tail pipes to the bumper of my dart.. With the good 360 (low 12 sec. In the quarter.) Car was nice and quiet inside, no drones. Loved it.... Spun a bearing in it and put a stock 360 in it and it ran great with they big exhaust.... I wouldn't be scared of 3" exhaust with a stock motor especially if your upgrading down the road....

I have seen a couple articles saying like stated already. 3" to the muffler and 2.5" tail pipes.. It's supposed to keep the gasses flowing quickly. But who knows. Not sure if they take bends in the pipe in to account though... Not sure if anyone has done any real testing on it.. Be an interesting article for one of the magazines.
Posted By: pinkduster

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/09/13 01:35 PM

Car Craft Magazine did extensive exhaust system testing on their "Project Chevelle" several years ago. I don't know if the information would be on their website.
Posted By: Dcuda69

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/09/13 03:25 PM

Well...if you're doing the 408 I would do the 3". I have 3" on my 69 B'cuda....I have no idea why some of these guys say it will be so much louder than the 2.5"?? Use some good pieces like TTI,absolutely use tailpipes(no turn downs)an X-pipe and pick your mufflers wisely(no Flowmaster 40's)Mine is more than reasonably quiet(meaning you can talk without yelling) at highway speeds but it has a nice growl when you mat it!!
Posted By: justinp61

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/09/13 03:39 PM

Quote:

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.
Posted By: Challenger 1

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/09/13 03:51 PM

Quote:

Quote:

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.




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.
Posted By: justinp61

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/09/13 04:07 PM

Quote:

[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.




Mines a street car too. What does the bad big block Challenger run? 8.20?
Posted By: Challenger 1

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/09/13 04:18 PM

Quote:

Quote:

[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.




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




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.

Posted By: JohnRR

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/09/13 04:54 PM

Quote:






you should have stayed with this post only ...
Posted By: pinkduster

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/09/13 08:54 PM

Quote:

Quote:






you should have stayed with this post only ...




YEAH, I know! All this talk about pea-shooter sized exhaust is quite entertaining though.
Posted By: Dr-Dave2

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/10/13 01:25 AM

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
Posted By: DPelletier

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/11/13 08:47 PM

Quote:

Quote:

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.





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


Dave
Posted By: MarkZ

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/11/13 11:21 PM

Quote:

Quote:

Quote:

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.





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


Dave




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.

Posted By: Locomotion

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/12/13 01:23 PM

FWIW, years ago, after a few years of tuning with collectors, I added a 3" TTI X-pipe and Dynomax UltraFlow mufflers to their step headers on my 360 IHRA Stocker. I picked up between .05 and .10 in ET right off the bat. A number or two leaner on jetting also helped.
I figure the X-pipe helped and the Dynomax mufflers didn't hurt.
Posted By: STROKIE

Re: 2.5 or 3" exhaust? 68 dart 360 - 03/12/13 02:07 PM

Quote:

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




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.

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