69 B body 3" exhaust?

[Erik Morris]

By the time the exhaust gasses reach your rear axle, it doesn't really make a difference if it's 2.5" tubing over the axle and out the tailpipe. There is a benefit to the first 2-3' of 3" exhaust, while the exhaust gasses are still very hot and expanded, but after that point, I don't see a restriction with 2.5-2.75" tubing.

We often forget that exhaust velocity is also important to take into consideration, and should be placed on a similar 'exhaust hierarchy' as flow rates. Reduction in exhaust size towards the rear end of the car, will maintain the velocity of the exhaust gasses as they cool down. I'm sure someone has done some testing on this by now, or have a more technical explanation to provide.

For example - the Hellcat has a 2.75" exhaust system, so do the 6.4/392s. The mufflers apparently even neck down to 2.5" on these cars, which never crossed my mind when I owned a 2015 SRT.

 

[33 IMP]

I have NOT read this whole thread, but summit offers their own brand of header-to-bumper 3" system for b-body 68-74, with or without turbo mufflers. $500 with, $425 without. I'll bet jegs offers the same. Sum 680141. Add NM for no muffler.

 

[moparedtn]

First thing I thought of also at the time (Fred has 3" all the way back and although it fits, it ain't much fun
to have under the car in any respect) was this episode.
This is a good watch. Very revealing video.

 

[furious70]

First thing I thought of also at the time (Fred has 3" all the way back and although it fits, it ain't much fun
to have under the car in any respect) was this episode.
This is a good watch. Very revealing video.

That's an oldie. Wish they had rejetted for both exhaust systems, would have been less difference

 

[moparedtn]

That's an oldie. Wish they had rejetted for both exhaust systems, would have been less difference

Doesn't matter how old it is; facts is facts.
In case you missed it BTW - I'm no fan of 3" exhaust on a street car and there will be a day when I yank
it off of Fred, to be replaced with 2 1/2".

 

[furious70]

Doesn't matter how old it is; facts is facts.
In case you missed it BTW - I'm no fan of 3" exhaust on a street car and there will be a day when I yank
it off of Fred, to be replaced with 2 1/2".

In newer seasons they are a lot more thorough and probably would have rejetted. And it would have shown the 2.5" didn't lose that much.
They showed in that and a couple other videos that muffler choice hurts you more than 2.5/3

 

[pnora]

In newer seasons they are a lot more thorough and probably would have rejetted. And it would have shown the 2.5" didn't lose that much.
They showed in that and a couple other videos that muffler choice hurts you more than 2.5/3

If you do not have enough motor I could see larger taking some away. No different than headers on some applications.

 

[furious70]

If you do not have enough motor I could see larger taking some away. No different than headers on some applications.

In various shows they use a 600hp and 350hp mill to test this stuff

 

[lemondana]

There aren't to many muffler shops that will bend 3 " over the rearend, hell they don't even like to bend 2 1/2 over. They usually mangle them up pretty bad. Just pay the money and get the mandrel bent system. I have a TTI 2 1/2" on my 69 Coronet R/T and my 71 Polara in my avatar. They both fit great and I'm glad I spent the money!

 

[INTMD8]

In case you missed it BTW - I'm no fan of 3" exhaust on a street car and there will be a day when I yank
it off of Fred, to be replaced with 2 1/2".

I'm curious why you dislike the 3"?

 

[moparedtn]

I'm curious why you dislike the 3"?

With the cross-sectional area difference between 2.5" and 3" being rather exponential,
that means those considerably larger diameter pipes are closer to your cars' floorpans.
Fitment becomes more of a challenge - but the real PITA with it is all the heat transmitted into the
cabin, even with the factory carpet underlayment/insulation in place.
Gets in the way more often when under the car working, too - things like accessing transmission
linkage, stuff like that.

Unless you're running over 500hp - and running it at full boogie a LOT - 2 1/2" is just a lot easier to
install and live with.