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Absolute Best Exhaust For 3.1 MPFI

Posted: Sun Jul 19, 2015 8:37 am
by DUBS28
OMG I'm posting in the forum! Can you believe it?
Was looking through here and found that most threads were generalized and not specific to engine type, hence subject line specifying 3.1 MPFI (none of that 3X00 crap). I suppose this would apply to the 2.8 as well because it has about the same badassary status.
Anyway, I'm looking for the best sound and performance exhaust set up out there for a 3.1 MPFI. What has been everyone's experience?
I once had a '91 3.1 with 2 1/4

Re: Absolute Best Exhaust For 3.1 MPFI

Posted: Sun Jul 19, 2015 8:52 am
by DUBS28
Stupid forum wouldn't allow me to type anymore. I shall continue here.
As I was saying I once had a '91 3.1 with 2 1/4" pipe, a MagnaFlow high flow Cat and a MagnaFlow muffler and it sounded awesome! I no longer live in an are that requires emission testing so the need for a cat is out the window. I've heard of some running just straight pipe all the way back, does that not have a negative affect on performance? Seems I remember hearing something about how you need to have some back pressure to maintain performance but that may have been a conversation about bigger V-8 engines.
Let me know what you all know.

Re: Absolute Best Exhaust For 3.1 MPFI

Posted: Sun Jul 19, 2015 11:11 am
by heavywoody
On a stock engine, I think 2.25" all the way back would suffice. If you are running headers/cam/built engine/forced induction, I would look at 2.5" for N/A build and 3" for boosted builds.

I personally wouldn't run catless on these engines just because I feel they sound weird without one.

Re: Absolute Best Exhaust For 3.1 MPFI

Posted: Sun Jul 19, 2015 2:00 pm
by 1988GTU
True duels, no cat, muffler, resonator, but must use mandrel bent tubing, would be the best in my opinion for performance. 2.5 mandrel bent with a short resonator for a cat and a chambered single in/out muffler sounds good, but again my opinion.

To obtain both is not possible.

Re: Absolute Best Exhaust For 3.1 MPFI

Posted: Mon Jul 20, 2015 1:46 pm
by 3X00-Modified
DUBS28 wrote:Stupid forum wouldn't allow me to type anymore. I shall continue here.


You always seem to be the one who find's the oddest limitations with the forum... Can you please explain more as to why it wouldn't let you type anymore? Browser your using? Device? Error message? Being the Admin and never hearing of this EVER and people making posts that are paragraphs and paragraphs long I would like to know what issue you had to possibly resolve it or get you on the right track so you don't have this problem again.

Re: Absolute Best Exhaust For 3.1 MPFI

Posted: Mon Jul 20, 2015 1:55 pm
by ronaconda
I love my exhaust that I believe you heard in Denver (can't remember if i had it then or not) - 3400 manifolds with 2-1/2" all the way to the muffler. Muffler is a Flowmaster knock-off that was given to me.

Re: Absolute Best Exhaust For 3.1 MPFI

Posted: Mon Jul 20, 2015 2:03 pm
by Stencil
GW,

We went over this years ago back in the day. 2.5", manifold back, is the best exhaust for the 2.8, 3.1 and 2.3 engines, even in stock form. It dynos more power and the car is faster at the track (both at Sea Level and 7000+) For the 3.1, you do loose a little "oomph" under 3000 RPM, but it's way more than made up for it on the mid/top end. Also, with a 5spd and a good launch you don't even notice it (it was way more of an issue with the Automatic if you were using a stock 2200RPM stall).

I would recommend the following:
2.5 from the Manifold back.
2.5 Magnaflow HighFlow CAT (car sounds odd without them, and smells, plus if the law changes you have to get it anyhow)
2.5 Magnaflow 18" high flow resonator (installed immediately behind the CAT). This keeps the sound deep and keeps the poppyness/snap out of it (it sounds terrible, trust me - I can even provide sound clips of the difference).

Now, if you want, you can run no muffler with this setup, but be warned, it's LOUD. I ran this on my 89 GT for years, and it was JUST under the tolerable limit for sound. It's really cool at low RPM's, but after a few hours on the road it started to give me headaches.

I would recommend adding a nice strait in/out 2.5 Magnaflow muffler to knock the sound down and then the tip of your choice.

Re: Absolute Best Exhaust For 3.1 MPFI

Posted: Mon Jul 20, 2015 2:10 pm
by Stencil
I would also recommend you get a downpipe from a junkyard and cut off the flange and port it out. Then you can take the flange into the exhaust shop and they can make you a TRUE 2.5 from the manifold back. I did that with my GTZ and it was noticeable. The first foot of the downpipe was like double walled and was like less than 2" at that point.

Re: Absolute Best Exhaust For 3.1 MPFI

Posted: Tue Jul 21, 2015 4:38 pm
by DUBS28
As seen on CBO FB we went with the 2 1/2" cat back and a MagnaFlow muffler for now. Once Lil Faif becomes a much more experienced driver I hope to throw the turbo kit on and that will change all the cat forward stuff so we chose not to do any of that yet.

Re: Absolute Best Exhaust For 3.1 MPFI

Posted: Wed Jul 22, 2015 1:12 am
by Cliff8928
This could be a good thing for you. If her car is modified, then all the guys might assume that "it's her boyfriends car".

Re: Absolute Best Exhaust For 3.1 MPFI

Posted: Wed Jul 22, 2015 2:19 am
by weba
I can tell you what I can't recommend from my personal experiences with 3.1:

- High flow or small universal cat converter will make it sound farty at most cases, avoid at all cost.
- DeltaFlow muffler without any soft material inside, will make it sound too metallic
- Too small muffler wont make it quiet enough, get the biggest one you can fit or go with 'turbo' style one.

I was most happy with stock cat converter + Magnaflow combo.