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3" exhaust opinions?


Well-Known Member
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12:40 AM
May 10, 2020
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Don't mean for this to be an argument thread... however I have heard 2 different opinions on this.
I have a 400 engine with aluminum RPM heads. I bought 1 3/4" TTI headers...
I've read on forums to go with 2 1/2" exhaust and H-Pipe for a lower tone. 3" is overkill and you lose low end torque.
The Mopar shop that I go to said, since I have the 1 3/4" headers I should open it up after that to 3" exhaust with an X-pipe.

I just want tti ask people on here what there experience has been and if they experienced loss of torque going to 3" exhaust.
Since this is a 400 engine, even with a small cam and RPM heads (of course I don't know for sure) but it can't be really more that 350hp.

Thoughts on this?
I think a 3 in would be a waste on your car. x pipe or h pipe is up to you.
At 350 hp, there is no reason for you to go a 3" exhaust. If you were at 550 - 600, that would be a different story.
As someone who has lived with 3" exhaust on my GTX for a dozen years....I'd advise against it.
There is a sizeable difference between it and 2 1/2" - more than you'd think, unless you had both
in your hands to directly compare - and the 3" makes for a really toasty interior (even with decent
Then there's all the fun of fitment and such....and it's gonna be louder, too, unless you muffle hell
out of it.

So...why do I have it on my car?
It came on the car when I bought it back then - and the damn stuff is all stainless and refuses to
corrode/rot, so I stubbornly refuse to rip it off of there.
You'll understand such nonsense the older you get, trust me. :)
The TTI full 2 1/2'' system. I have installed at least 30 sets on many body style Mopars.
A friend's 67 Coronet had 3'' installed and as many above stated it killed his low end torque.
i have tti 2" headers with 3" exhaust on my '65 coronet with a 440 probably making somewhere between 450-475 net horsepower. i believe a smaller exhaust would do the same numbers as long as it had good mufflers.
At the OP's power level, I wouldn't bother. 550 HP or more, I would.
Been down that road several times, up to 3.5", X, & Race Bullets on my drag car.
Never noticed any power loss on the 600+ HP cars, but that's a different deal than the OP's.
I did find that - on 2 that got tailpipes - using 2.5" tailpipes really reduced loudness & drone but didn't slow the car down.
X-pipes tend to smooth the pulses more than an H, and either will aid scavenging.
You dont need more than a 2 1/2 pipe for 350hp. Mufflers will determine sound and volume more than pipe size.
In my opinion, for best power, and a quiet exhaust? Proper size pipe for the engine combo, and the biggest longest muffler that will fit under the car.
Well, right now I have old school glass packs under the car, so loudness isn't really an issue.
I kind of like the Dynomax Ultra flows, they have a low deep tone that I like.
I guess I'll stick with the 2 1/2 pipes, but? H-Pipe or X pipe? Idk? I was going to go with the H pipe, but now, I'm not so sure?
Considerations for exhaust include scavenging, backpressure, and resonance as well as physical fit, intended rpm range, and tonal quality.
I'll just be going TTI all the way back.
I need to call them and make the order. Thats why I'm trying to figure this out. They want more for the Ultra Flows because they are a different size, and extra tubing to make them fit & Shipping sucks.
So...why do I have it on my car?
It came on the car when I bought it back then - and the damn stuff is all stainless and refuses to
corrode/rot, so I stubbornly refuse to rip it off of there.
You'll understand such nonsense the older you get, trust me. :)
I hear ya Ed, I have a 440 with mild roller cam, 1 3/4" headers and 3" stainless exhaust. Mine was on it when I bought it as well and has been for the 13 years or so since I owned it. I ain't racing and it's gonna stay until I croak!
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3" vs. 2 1/2"

I just put 3" on my GTX 440 with 1 7/8" headers, probably around 430 to the wheels. Sounds good. Still makes excellent burnouts. Haven't had a chance to take it back to the track.
I have three cars with 2" headers, 3 1/2 collectors. One has 3" with straight thru magnaflows, the other two have 3 1/2 pipe with Flowmaster or hooker aeros. All three have over 525 crank hp. Haven't noticed a lack of torque.
I still think the o.p. with a mild 400 doesn't need a three inch pipe. He does need a quality muffler with the sound characteristics he likes.
(I like the chambered muffler sound, many don't, and they are prone to drone.)
So it basically comes down to the whole "mine is bigger" concept.
I'll be proud to admit I'm only 2 1/2 inches.
Is how you use it, not the size.
my car is 101% street car. something else i noticed about a 3" system is burning the water out of it. water is a by-product of combustion and doing short trips doesn't burn the water out. i've had mufflers rot from the acidic water and noticed water clinging to the pipe walls when changing collector gaskets. i have no idea how much run time is needed to evaporate the water but i'm sure it's more than 10-12 mile hops. i think at lower rpm driving exhaust isn't moving thru the system fast enough to dry it out.
My last car was a challenger with a big block and 3" that stopped at the axle.. i have no desire to live with non stop noise again (i'm old) My plan is a single 3" exhaust with cutouts for when i do want noise.. I should do a 2.25" and try to get that commando sound.. such a great exhaust noise.. can't fit a resonator in my car though