So, I must be getting old, because driving around in my car that has turndowns right after the mufflers is starting to be less enjoyable. I am ready to put tailpipes on the car, and I wanted to know if anyone had any real world test results comparing 2 1/2" and 3" tailpipes? The head pipes and mufflers on the car now are 3", and they will be staying the same. I remember reading somewhere that once the exhaust gasses have cooled down, the exhaust pipe size can decrease without any horsepower loss. I would love to use 2 1/2" tailpipes, because they will be much easier to fit on the car, but I don't want to give up anything performance wise. The car is a 67 B-body with around 600 flywheel horsepower. I have a electric fuel pump, fuel filter, and braided lines coming from the gas tank sump all taking up room under the back of the car, so space is at a premium back there. Any input would be greatly appreciated!

Depending on the muffs there isnt that much of
a HP drop.. just a few HP... I did testing at work
checking the difference.. but on those engines it was 6 hp
difference... in the end your muffs can and will make a
bigger difference.... there was a article on a Pontiac that
showed what little difference there was in ET just in changing
the tail pipes... then they went back and did the same tests
with different muffs... and with certain muffs and the 2 1/2
pipes... the same muffs and the 3" gained less than .02....
I want to say they were Dynomax muffs... but part of the
test was noise also.... I cant remember all the data on it
but it was a good article... it was all at the track
EDIT
and your right the temp is less so the volume/area
is less... the longer the car the cooler it is

All I can say is 2 1/2 tailpipes are very tight but doable on a 67 B Body in a stock location. I had a set on my 67 Coronet from Don's Custom Exhaust.

Were they press bends like any muff shop or mandrel...
I'm talking all mandrel bent exhaust... press bend you
lose 15% per bend... thats why MOST all production exhaust
is mandrel bend... aftermarket... different world

This episode of Engine Masters may not look at tailpipes only, but it gives a good idea of 3" vs 2-1/2". I have 2-1/4" tailpipes on my 67. I'm not so worried about street performance though, since I don't street race. I uncork with 3" cutouts at the track.

https://www.youtube.com/watch?v=_PVXvHkr-Vs

Thats a great vid.. BUT.. he has the 3" all the way
out of the muffs... not changing from a 2.5 out the
back... he wants to change the tail pipe... and the muff
difference is a major part... so its not apples to apples

Mike was your testing on 600+ hp engines?

I was wondering the same thing when I was trying to fit my 3" tailpipes around my shocks, fuel system, and leaf springs
It seems that it would be much easier if they were 2 1/2"

Gus

i have 3" tti tail pipes on my 65 coronet. fit like a glove. very happy.

I have the Flowmaster pipes and they don't seem like they were even made for my Savoy. Ron 383man has the TTi's on his 63 and they look real nice maybe I will just sell the Flowmaster pipes and pick up some tti's.
Thanks

Gus

I very badly want tailpipes for my Duster, I have a 3" H-pipe system so I'm debating on getting TTI's 3" tailpipes or just getting the 2.5" tailpipes for ease of installation...?

No.. about 400-450hp so the percentage will change
but they were changing the complete exhaust from 2 1/2
to 3 and their muffs were straight through... if you have
a 3" muff(if its truely 3".. a lot are 2 1/2 to 3") the
data would have changed... guarantee it
EDIT
Everyone that buys what they did love what they
bought.. its always the best.... try using stuff
thats given to you to test and do it on the dyno
or the track... then say whats best... all the
stuff was given to use to test for production...
it meant MILLIONS to the companies

Yea as Gus said I use a full TTI 3" system. The tailpipes fit great as I installed the full system in my driveway with the car just jacked up about a foot at the most. It fits great and was easy to install on my 63. I do use 3" tailpipes but I have heard that the exh gasses have contracted enough by the time they hit the tailpipe that 2-1/2" tailpipes work fine on a 3" system. Ron

Google "Jim Hand exhaust system testing" and see if his results are still available online.

That's the guy that did a bunch of muffler & pipe diameter comparisons on his bb Pontiac street/strip wagon.

I had a complete three inch sytem on my old Duster, that car had coil overs on it so the exhaust shop ran the 3 inch tailpipes under and around the rear end housing and mounted the three inch by 14 inch long oval Magnaflows between the rear end and the rear bumper outside 1/4 panel and the rear subframes behind the rear end. It had a stock Gas tank also. I'm puttng a 1966 Coronet Deluxe two door sedan together right now,440 4 speed car now I bought the Summit three inch B body exhaust system for it but I haven't taken that system out of the shipping box yet . I did buy a set of 3 inch Ultra flows for the car and plan on mounting them back behind the rear end like my Duster had, I had the rear leaf springs move into the rear subframes and moved the rear end forward two inches I'm using a new stock gas tank also so it might be lots of fun routing the exhaust back there

They were not mandrel bent.

I went 13.30 at 101.75 mph with a full 2 1/2 exhaust with 1 3/4 inch headers with a lot of tuning left. Lousy 60 foot because converter was bad so only made one decent run with the combo. Lost a second the next run because of the bad converter. It would of been a solid 12 second car with a working converter and some tuning.

4000 lb car, 3.55 gears, small tire, light converter, home ported 906 heads, 9.1:1 compression and a .550 lift hyd roller cam that floated the valves on the one decent run.

I was pretty happy with the combo for a cruising street car.

Cab.

you have a picture of the 66' Deluxe Sedan? Those are some neat cars to set up ala Stahl Tuned Exhaust look.

Thanks for all the replies, and for the link to that great Pontiac exhaust testing article! My car has the larger body size 3" Dynomax Super Turbo mufflers on it, and those will be staying on the car. I will probably get the TTI tailpipes, everyone seems to say those fit the best. After reading that Pontiac article I am leaning towards the 2 1/2" tailpipes. They compared 3" to 2 1/4" and there wasn't much difference at all, so 2 1/2" should be even less of a difference. The headpipes that are on the car were done at a local exhaust shop, so they are not mandrel bends. The tailpipes will be mandrel bent.

You should have all of it mandrel bent... specially
the front where the temp is.. thats where you need
the area and the bend reduction hurts it