dual exhaust

[mjtjnj]

Hey guys,

rotted out more pipes and I'm going stainless. Took the truck into a muffler shop and going duals straight out, 2 1/2" from the cat back. Any recommendations on a stainless muffler for this project, from anyone who has done it?

 

 

Thanks

Tom

[Pete M]

what kind of sound are you looking for?

[mjtjnj]

Definitely not a civic fart pipe! Since it's going to be dual (and it's a 4 cylinder), a nice rumble, but not "open header" sounding. Looking at the Magnaflow stainless line..they have a lifetime warantee and the prices are reasonable.

[MJ is dead]

Not to poop in your cheerios here, but why are you going with duals? Just looks? :hmm:

[dasbulliwagen]

A stainless flowmaster 50 series would be close to the sound you want, but I don't think anything will give you the rumble you are expecting merely because its going onto a 2.5. Ive got the Flowmaster 50 on my 2.5 with a gutted cat and its still pretty queit, but has a little growl under load. A 40 series may be too loud though, but will still sound like a 4 cylinder.

[Eagle]

Hey guys,

rotted out more pipes and I'm going stainless. Took the truck into a muffler shop and going duals straight out, 2 1/2" from the cat back. Any recommendations on a stainless muffler for this project, from anyone who has done it?

 

 

Thanks

Tom

IMHO you are making a huge and expensive mistake. The stock system is 2-1/4". I once allowed my brother (who ran a Speedy Muffler shop at the time) to talk me into a 2-1/2" turbo muffler and cat-back system for the '88 XJ. It sounded great -- but the gas mileage dropped by 2 or 3 MPG and the performance at any legal speed suffered noticeably. By putting in a dual 2-1/2" system you'll be reducing back-pressure still more, which is going to cost you even more torque and fuel efficiency.

 

That was the only time in my life I ever looked forward to an exhaust system rusting out so I could justify going back to the stock configuration.

 

Oh, Gawd! Just noticed you have a 4-banger. Your stock system should be a 2". You are going to be VERY unhappy with what happens to your performance with this new setup you have in mind. And there is simply no way to make a 4-cylinder sound like a big block V8, not even if you had true dual exhaust -- which you won't, pushing it through a single cat.

[Harper]

Sorry, but the only way you're gonna get "a nice rumble" is to add four more cylinders...... :brows:

[knever3]

By putting in a dual 2-1/2" system you'll be reducing back-pressure still more, which is going to cost you even more torque and fuel efficiency.

 

:agree:

 

There is a happy medium with going to a new exhaust. I would run the stock 2" size to a single inlet and dual outlet muffler so you can have your dual exhaust at the back.

 

So you can have your cake and eat it too!!

[mjtjnj]

I appreciate all the input; the stock exhaust is 2"? I thought it was 2.25". Anyways, I don't' see as much drop in backpressure as you guys. This is a very long system, running through a cat and muffler (1 in 2 out). I like the look of the straight-out dual exhaust, and going to 2.5" after the cat shouldn't make that much difference. The motor is a freshly-rebuilt, bored-over 2.5 with roller rockers and a Clifford header.

 

I haven't picked up the muffler to deliver it to the exhaust guy, so he hasn't done any work yet. I'll have a chat with him when I bring him the muffler.

 

Thanks!

Tom

[Eagle]

I appreciate all the input; the stock exhaust is 2"? I thought it was 2.25". Anyways, I don't' see as much drop in backpressure as you guys. This is a very long system, running through a cat and muffler (1 in 2 out). I like the look of the straight-out dual exhaust, and going to 2.5" after the cat shouldn't make that much difference.

You're joking, right?

 

Let's see -- if your current muffler is a 2-1/4" inlet and outlet, the cross-sectional area is 3.98 square inches. A 2-1/2" muffler has an area of 4.91 square inches. That's an increase of 23 percent -- at the inlet and through the muffler.

 

But then you want to make it a dual outlet with two 2-1/2" exhaust pipes. So the outlet area will be 9.82 square inches, which is an increase of 5.84 square inches or 147 percent.

 

The 2.5L engine has a much "peakier" and narrower torque band than the 4.0L. Much more than the 4.0L the 2.5L needs backpressure to run efficiently. I don't know how you figure you don't "see" much drop in backpressure, but if you don't I respectfully suggest you need to have your eyes checked. It's your truck and your money, but I think you're making a mistake. And it won't get you the sound you want. The only way to make it sound good would be if the header had two independent outlets, each serving two cylinders. That way you could run two independent pipes right to the tailpipe and the exhaust pulses would be separated. The system you are considering is NOT a dual exhaust.

[mjtjnj]

No, I'm not joking. There is a lot of resistance to flow based on the length of pipe and all the turns. It's not as simple as calculating the area.

I know it's not a dual exhaust, it's dual outlet. I will speak with the exhaust guy tomorrow. I'm definitely going a one-in-two-out muffler. If I have a stock 2.25" system, which I believe WAS stock from the factory, even on 4cyl, you would keep it 2.25" and just go dual outlets?

 

I appreciate your advice and certainly your bad experience with a cat-back system, you don't have to be sanctimonious about it.

[Eagle]

I'm not being sanctimonious, I'm trying to help you not waste your money. I'm an architect/engineer by education and profession. We use flow calculations on a regular basis. I know that bends add resistance to flow, but the bottom line is that a bigger pipe carries more stuff with less resistance. You can't more than double the cross-sectional area of the pipe(s) without significantly reducing the backpressure.

 

If you are set on the dual outlet system, I would make the two outlet pipes no larger than 2" or maybe even 1-3/4" each.

[Harper]

Gee, I think I hear a "nice rumble" now............. :rotf:

[mjtjnj]

No offense intended, Eagle, just asking me if I'm kidding, or suggesting I'm blind doesn't help. I do respect your opinion, and will take your example (your Speedy Muffler experience) and learn from it. I re-ordered the muffler. I think I'm going to go with an all 2.25" (including single in dual out muffler). I think all the bends and extra pipe, and the more powerful motor than stock, are going to even things out. I spoke with the exhaust guy, a very experienced guy, and he said, "I honestly don't think it's going to make a difference either way." Then I started thinking why go bigger if it's not going to gain me anything, and could actually hurt the performance, so I settled on 2.25" with dual outs.

[one_bad_MJ]

why????? get a stock one on there glasspack and dual exhaust sound like poop

[Darren]

Sorry, but the only way you're gonna get "a nice rumble" is to add four more cylinders...... :brows:

 

True.

 

No matter how it sounds, at the end of the day it's still a 4-banger.

[glundblad]

Not to hijack this thread but :hijack:

Back in the day, I had a '75 chevy V8 that I gutted the cat on. I was really glad I did it.

 

Fast forward, when I bought the comanche with a rotted muffler and cat, I considered a straight pipe to preserve the "performance gain" I remembered from the chevy. I decided to go with a stock muffler and cat instead. I was amazed at how much torque I lost by not having a working muffler and cat. Someone said in a post long ago the 4.0 needs back pressure. I thought they were full of it. But they were right in my situation.

[streetjeep2.5]

Not the best quality, but this is the sound my 2.5 with a single in dual out Flowmaster (6 years old) with Clifford header. Two inch tail pipes, 2.25 head pipe, I think.

[mjtjnj]

Update:

 

Had the exhaust guy install a mandrel-bent, all stainless 2.25" system from the header, through a high flow cat and Magnaflow "1 in 2 out" 2.25" muffler. Sounds great, and he left enough room to wind my spare tire back up into place! It's a low rumble, quieter than I had with the cherry bomb, but I like it. It hasn't noticeably changed performance one way or the other. After I have her painted, going to install some flat black tips on there!