I ran 11.0s with 3" mufflers and 2.5" compression-bent tailpipes, FWIW.

Friend of mine went from a dual 2" (86 camaro) to a single 3.5" with a 3" Y-pipe and picked up 6/10th's. No joke.

I think you won't see an ET difference with 3" to the mufflers & 3" tailpipes to 2.5" tailpipes, due to the mufflers.

Muffs are where the biggest loss is at.... and the only
reason I am saying anything is due to your statement
"DUE TO MUFFLERS"... I got way too many years testing them
and I designed the F-body police car exhaust with dual
fronts to dual muffs and a rear Y pipe... where do you
think your buddy got the idea from... it was done so the
cop cars could run a bigger fuel tank but we didnt have
the room for dual tail pipes... by the way that was
in 76

I imagine he got the 3" y-pipe into a 3.5" single idea from some chevy magazine.

I remember reading about quad 68 Cadillac mufflers on the silver bullet Plymouth. No ET difference from open headers.

Edit;
http://www.silverbulletgtx.com/index.html

Do you have a pic of this system?

No... we werent allowed to take that type of stuff
out of work.. I got a patient on it(back in those
days... well expired now)
EDIT
The left pipe went across the rear end area and
the Y was at the right side of the rear end area..
that system was only on cop cars

The video in question, they lost 20hp, gained nothing below 3200rpm. That's with a 600hp engine. Then they slanted their comments toward the larger system. I think it was a biased opinion because the sound of the larger system played into what they liked.

R.

Sure it was biased.. and they did a complete 2 1/2
vs 3" system... the OP already stated everything from
the muffs forward is staying... he wants tail pipes ONLY
and if you looked at the Pontiac data it showed just tail
pipes then muffs vs noise and hp... if I was the OP I would
put dumps on it also... on my Rampage I built the headers
to match the engine but went with a less noisey muffs and
it was still to loud.. I added resonators and elec dumps
and I see a big difference when the dumps are open(the
resonators are straight thro... they only dropped the DB
6 DB.. I was hoping for more... right now its 92DB

Guess I thought it was so obvious that I didn't have to say it. Using 2.5" to get over the rear axle won't harm performance one bit.

It'd be interesting to map temperatures during a high horsepower run on the road and find out exactly what temperatures were. Then we could calculate quite easily the decrease in volume due to cooling.

R.

I did that stuff back at work... we would run about
200 thermocouples for the length of the exhaust and
data logged all of them... do I remember the numbers..
hell no.. did it every year the exhaust changed...
that was most of the reason we moved the muffs to the
rear.. more power and less noise
EDIT
and we would read about 4 pressure readings at
different points

Don't need fancy measuring equipment. Carefully touch the exhaust pipe just before the muffler, then after. After is a lot cooler. So I revise my earlier statement.

I think a 3" exhaust to the mufflers w/ 2.5" tailpipes will be a tad faster than 3" tailpipes. Due to the cooler exhaust gasses getting a velocity increase from
the smaller pipes.

With the added bonus of better fitment & overall quieter.

Your results may vary with like 610 cid engine vs a 360 cid.

Just my

When building a car you have to be a bit closer
than... yep thats hotter than that... and temps
come into play with making power

Yeah. XX inches from the collector. A crayon will tell yah the same thing. Just without all them fancy numbers.

That is so much BS I cant believe people still believe it..
what happens if the engine is fat or lean... OH that line
changes by INCHES... and I have already proven it
EDIT
And all crayons dont melt at the same temp

How so? Crayon wax melts at 150f. You can clearly see where the melt stops on an exhaust.

But we ain't talking fat or lean.. just where the air starts to cool/slow down. Few inches fore/aft is inconsequential.

Anywho gonna go to Burger King.

"that was most of the reason we moved the muffs to the
rear.. more power and less noise"

Never heard that before.

To be honest this isnt worth my time... 34 years
in the exhaust lab at Chrysler and I've tested more
ways and tried theories that you will EVER think of..
built a ton of headers for Chrysler for competition
and all crayons dont melt any where near 150*
EDIT
Its much easier to use a program for the headers
and collectors so your right. not a guess.. its math
and I have bult headers that were different that the
math said and they didnt make as much power at any point

You want the muffs after the exhaust gases stop expanding. Gases expanding in the muffler will cause a restriction/pressure build up.

It makes sense, but again, the solution never has been discussed much here, from what I have read, nor was it mentioned that there is enough difference to make it worth the effort. I hope Mr P follows up on this . I did it with one of my cars years back, but thought it was out of the norm.

I would also be curious when he was doing non crayon tailpipe temp testing (sorry, I couldn't resist), since it sounds important enough to measure small temp differences, did outside moving air speeds and location, factor in much on effecting inside tailpipe temps, and if so, how did they account for those conditions?

yep.. and where is it coolest... at the rear
EDIT
the cooler its also easier to control noise..
all in all its way better
this is where I put my muffs