3" exhaust opinions?

[not so famous bob]

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?
Thanks!

I had dual 3'' dumped on both my 400sbc , worked perfectly , slowed with full exhaust !
Have 3 1/2'' dumped on my 68 505'' fastback...

 

[gtx6970]

IMO in anything but a big inch motors 3inch is a waste

This is a car I did for a client a few years back. 493 stroker . I dont remember the specs.
But behind it,,,,It sounded like it was beating on the wall

 

[icetech]

IMO in anything but a big inch motors 3inch is a waste

This is a car I did for a client a few years back. 493 stroker . I dont remember the specs.
But behind it,,,,It sounded like it was beating on the wall

Bad video link

 

[not so famous bob]

IMO in anything but a big inch motors 3inch is a waste

This is a car I did for a client a few years back. 493 stroker . I dont remember the specs.
But behind it,,,,It sounded like it was beating on the wall

sure choked down a real hot 406 sbc !!!

I think it was (summit?) that had a video of exhaust sizes per cubic in. , anything with 400 cubes or 500 h.p. needed 3''.
might have been someone else , 3 1/2'' dual is/was perfect for 500 c.i. engines.
engine masters did an exhaust test on the dyno and confirmed 3'' over 2 1/2 chokers ...

 

[Myasylum]

Yes, I've been doing a lot of reading. It seems my engine being a 400ci is pretty much on the fence as far as 3" exhaust. With having a mild cam and aluminum heads it could go either way.
One article I read said it was all in the headers. After that, the exhaust just wants to get out, regardless of size. A YouTube video I watched did show 3" exhaust flowed better, and any theory on needed back pressure was just a myth.

 

[33 IMP]

425(or more) hp 426 hemi had 2 1/2" headpipes, and 2 1/4" tailpipes from the factory. I DO believe headers and a three inch system would help.
I built a 3 1/2 system for my 440, in anticipation of the nitroused 522 in process. I used some left over pieces, and short cheap 3 1/2 mufflers on my 406 small block. Ran nines thru the mufflers, couldn't have been too bad a choice.
(Ran 3 1/2 to simulate collector extensions off of my 3 1/2 header collectors).

 

[RemCharger]

425(or more) hp 426 hemi had 2 1/2" headpipes, and 2 1/4" tailpipes from the factory.

This was what I was thinking reading through the thread.
And to add; my ol 67 newyorker had the 350 horse 440.... with just one of those exhaust pipes..

 

[33 IMP]

This was what I was thinking reading through the thread.
And to add; my ol 67 newyorker had the 350 horse 440.... with just one of those exhaust pipes..

Yikes!

 

[Myasylum]

Also stated...

I DO believe headers and a three inch system would help.

 

[DeltaV]

2-1/4" pipes and Imperial mufflers!

 

[33 IMP]

Also stated...

I meant the Hemi, lol. If you WANT the three inch system, go for it!
Just know it's gonna be louder, more expensive, and harder to work around.
(And probably not necessary. My car? It gets the 3", with big long quiet mufflers.)

 

[33 IMP]

2-1/4" pipes and Imperial mufflers!

From this?

 

[DeltaV]

From this?

View attachment 1497350

Nice car!, but no. I was referring to those enormous Imperial mufflers used in the early 70's.

 

[gtx6970]

Bad video link

I'll go in later and see if I can fix that

 

[BSB67]

This was what I was thinking reading through the thread.
And to add; my ol 67 newyorker had the 350 horse 440.... with just one of those exhaust pipes..

Me too. Mine was a 67 Chrysler 300. Ran great.

To the OP - I don’t know what to say other than to put on what ever exhaust you want. But to think your motor needs 3” exhaust is silly. 2.25” is probably the right size.

 

[not so famous bob]

true but

425(or more) hp 426 hemi had 2 1/2" headpipes, and 2 1/4" tailpipes from the factory. I DO believe headers and a three inch system would help.
I built a 3 1/2 system for my 440, in anticipation of the nitroused 522 in process. I used some left over pieces, and short cheap 3 1/2 mufflers on my 406 small block. Ran nines thru the mufflers, couldn't have been too bad a choice.
(Ran 3 1/2 to simulate collector extensions off of my 3 1/2 header collectors).

you should what see the diff getting rid of the factory small exhaust on a street hemi did .
The factory didnt install bigger exhausts because of room and expense ...

 

[440 4 speed]

I think that I read somewhere that if you have to much exhaust, you can lose performance. This would be in a ordinary street car I believe.

 

[12icer]

For a RB with built heads, 300+ cam, pistons, rods, a good fuel setup and some serious flow
2" stainless headers, 2.5 stainless exhaust H pipe at the right place and good quiet mufflers. If you want less pressure go for the 3" mufflers and back then oval the tailpipes to past the bumper. Good for a full on street wheel pulling superstock build.

 

[Black_Sheep]

Enginemasters did a dyno comparison between open headers, 2.5” and 3” full exhaust systems, 3” made better HP and torque.

 

[Myasylum]

Yes, I have to say. I installed the 3" exhaust with an H-Pipe and I didn't lose any HP at all. Matter of fact I may have gained. Since I never tried 2 1/2" I guess I have nothing to compare it too, however anyone that says that you lose HP just isn't true. I have the smaller 1 3/4" TTI header that goes out the 3" exhaust and I think that may be what the trick is.