2.5" or 3" single exhaust setup?

[FSJeep13]

I've been calling local shops here becuase I'm bringing the jeep in next week. The first guy I called said that I should do 3" becuase I have the 401. The next two shops said that I should do 2.5". I honestly have no idea which one will have more benefit... Any wisemen out there?

[AlsChopShop]

3".

Al

[FSJeep13]

3".

Al

Why?

The two shops that said 2.5" were adamant about it. The other was telling most definately 3".

[Dmntxn77]

3".

Al

X2


I have put a single 3" on several SBC 350's and on my Mopar 318. The all have performed VERY well, and I have been impressed with the resultes EVERY time.

So, go with anything less with a 401, and I am sure that you would regret it.

I like a single 3" so much, I plan to pull hte true duals off my Chief and replace them with a single 3".

[Dmntxn77]

Why?

The two shops that said 2.5" were adamant about it. The other was telling most definately 3".


Probably because 3" is harder to stuff under there..

Here is what Magnaflow Performance says, and I have seen pretty much the same chart on other exhaust specialists sites.
http://www.magnaflow.com/07techtips/faq/question10.asp

[cttandy]

There are a few things to consider. Is the engine modified or stock? What convertor and muffler setup are you going to use? Is your stock Y pipe in place? What is the price difference?

If you still have the stock Y-pipe, then you will never really see any benefit to a bigger exhaust, unless your running a restrictive cat and muffler. If your not running a cat at all, the 2.5 should flow enough with a good performance muffler. If it is straight 2.5 will be plenty.

[Dmntxn77]

There are a few things to consider. Is the engine modified or stock? What convertor and muffler setup are you going to use? Is your stock Y pipe in place? What is the price difference?

If you still have the stock Y-pipe, then you will never really see any benefit to a bigger exhaust, unless your running a restrictive cat and muffler. If your not running a cat at all, the 2.5 should flow enough with a good performance muffler. If it is straight 2.5 will be plenty.

Are you basing that on the assumption that the exhaust shop will not modifiy the Y pipe to fit the new 3" pipe?

All you do is hammer one end of the 3" pipe until it flares out, slide it up your Y pipe, mark a cut line, remove, cut and then weld it on. No decent exhaust shop would even consider just flaring your factory pipe up to 3"s, start new pipe from there and calling it good.


Also, check out the chart that I linked to. You dont need any engine mods to run a 3" exhaust on a 401...

[FSJeep13]

There are a few things to consider. Is the engine modified or stock? What convertor and muffler setup are you going to use? Is your stock Y pipe in place? What is the price difference?

If you still have the stock Y-pipe, then you will never really see any benefit to a bigger exhaust, unless your running a restrictive cat and muffler. If your not running a cat at all, the 2.5 should flow enough with a good performance muffler. If it is straight 2.5 will be plenty.
Engine is stock, carter 4 bl carb.
no converter
I have a flowmaster super 40
stock y-pipe I cut off for SOA to fit driveshaft in.

Price difference:
1st guy said 2.5 with everything $600, so not doing that.
2nd guy said 2.5" total $406
3rd guy said 3" total $ 425

[Dmntxn77]

Engine is stock, carter 4 bl carb.
no converter
I have a flowmaster super 40
stock y-pipe I cut off for SOA to fit driveshaft in.

Price difference:
1st guy said 2.5 with everything $600, so not doing that.
2nd guy said 2.5" total $406
3rd guy said 3" total $ 425


Looks like a no-brainer to me... :D

[FSJeep13]

Probably because 3" is harder to stuff under there..

Here is what Magnaflow Performance says, and I have seen pretty much the same chart on other exhaust specialists sites.
http://www.magnaflow.com/07techtips/faq/question10.asp

Thanks for the link! The one thing that doesnt work out in the chart is the HP for the 401. I remember reading in the maual that I had about 190 HP with the 401.
The chart says for 350-400 CID, HP = 250-550.So that could be a point for the 2.5" side...

[Dmntxn77]

Thanks for the link! The one thing that doesnt work out in the chart is the HP for the 401. I remember reading in the maual that I had about 190 HP with the 401.
The chart says for 350-400 CID, HP = 250-550.So that could be a point for the 2.5" side...

There is a lot of back and forth regarding how AMC rated their horsepower. Notice that the old 360's show higher numbers than the newest 360's

[AlsChopShop]

yeah, especially with that 4 bbl carb sucking in all that air, go 3".

Al

[cttandy]

Are you basing that on the assumption that the exhaust shop will not modifiy the Y pipe to fit the new 3" pipe?

Thats assuming alot for about 98% of all the muffler shops I have ever dealt with. Cheapest easiest way out, is what you get most of the time anymore.

They changed the horsepower rating system a few times through the years. I think the last one was in the late 80's. My 89 chevy 350 is rated at 180, the same motor few years later is rated at 255 hp. Go figure.

[cttandy]

Given the small price difference, and the fact that engine needs no back pressure per say to run, go with the 3 inch. It will sound better.

[fulsizjeep]

Let that 401 breath.

[FSJeep13]

Ok, now I'm thinking 3". Thanks guys:cool:

[FSJeep13]

I went to www.flowmaster.com to see what the Super 40 might sound like on the wagoneer, but the sound links dont work for me. Do they work for any of you? Could be my computer restricting something...

[cttandy]

I have used lots of flowmasters, I personally think you get about the same quality sound from a turbo muffler. If you want a good sound go with a magnaflow. Excellent sound, weither they are quiet or loud, they still sound excellent.

[Dmntxn77]

Im a big flowmaster fan. IMO the only muffler that sounds better is a Borla, but I dont generally drop the coin for Borla. To me, cheap turbo mufflers sound just that... cheap...

I think that a 3" Super 40 would sound great. The fact that it is 3" will ensure that it has a nice deep throaty sound. Thats probably what I will go with on my Chief, and I already have a 3" 40 series to put on my J20 (just need to get it on).

[cttandy]

Some people are huge flowmaster fans. I was once, until I saw flow charts from many different independant companies. Really surprised me. Not all turbo mufflers are the same. I kinda like the sound from a thrush turbo muffler. I currently have a cherry bomb on my jeep, only because it was $19. I have gotten several compliments about how good it sounds. Surprised me, I have to admit.

[Wagonforever]

There is a lot of back and forth regarding how AMC rated their horsepower. Notice that the old 360's show higher numbers than the newest 360's



Pretty sure that was due to smogging down the later engines. I for one can tell you that the 360 in my 86GW is pretty wimpy, especially noticeable when towing. My 90GW was noticeably better, and it was even listed to have a few more ponies, probably due to lower production numbers. Though in the end it sucked towing too. I'm sure you can really open up a 360 though.

http://www.ifsja.org/tech/figures/engines.html

[TexTJ209]

I have 4" stock on my Chebby. :p

[mark j]

I have a single 3 inch with a magnaflow on my '89 with a moderately built 401. The sound is great and so far I am more impressed with it than I am the dual exhaust on my '72. The shop that did mine did a new system including Y-pipe, high flow cat, magnaflow for $600.

[cttandy]

I think the best sounding truck I have heard is the nieghbors 454 feeding 2 cats, x-pipe, and 2 magnaflow mufflers in his 99 chevy 2500. All pipe is 2.5 inch. Third vehicle I have had done with magnaflow, first with a x-pipe. Man it sounds sweet. Wish I had something better then my phone to record it on, doesn't have good sound quality.

ttp://myspacetv.com/index.cfm?fuseaction=vids.individual&videoid=20483289

Truck sounds wicked in life. He gets at least one person a week asking what is under the hood.