Differing size pipes make much difference?

Hi all,

Hoping to get feedback on this...I have Doug's headers (which I believe dumps to a 3 inch collector). The exhaust tips that I purchased from Accurate Exhaust are for 2-1/4" pipes. I believe the mufflers I have are either 2-1/4" or 2-1/2" openings.

Since I am getting the exhaust custom fabbed, would it make a difference if I go with a larger 3in pipe from the collectors to the mufflers to ultimately a 2-1/4" tailpipe (to fit the tips)? Or would I not see that much performance difference and just go with 2-1/4" all the way back?

Thanks for the help!

I'd go 2 1/2 from the collector to the tail pipe tip, I never mix and match.

i like to my own exhausts and found i like to stay the same size out of the headers with either an X or H pipe and reduce it after that. i just did 3 1/2 x pipe on my dart and reduced it to 3" before the mufflers, and i did 3" x on my duster and reduced it to 2 1/2 right before the mufflers, both with tailpipes to the bumper.

Since you didn't mention anything about your motor, I looked up a couple of your posts.

2-1/4" or 2-1/2" tailpipes won't matter much in your case for performance...the smaller tailpipes might be a bit quieter.

Smaller tailpipes used to be common to make the exhaust installation easier.

I can't find it, but a while back I read a good exhaust article on a Pontiac that ran 12.68 with 3" exhaust all the way and when switching out the tailpipes to 2-1/4" his quarter mile time changed to something like 12.71. Exhaust gases cool significantly after the muffler so larger pipes are overkill.

If you wanted to keep the exhaust tips you already bought then personally I would go with 2-1/2" pipes to the mufflers...also with an X-pipe...then 2-1/4" tailpipes out the back.

Otherwise I would run 2-1/2" pipes all the way front to back.

Paul

cjdive said:

Hi all,

Hoping to get feedback on this...I have Doug's headers (which I believe dumps to a 3 inch collector). The exhaust tips that I purchased from Accurate Exhaust are for 2-1/4" pipes. I believe the mufflers I have are either 2-1/4" or 2-1/2" openings.

Since I am getting the exhaust custom fabbed, would it make a difference if I go with a larger 3in pipe from the collectors to the mufflers to ultimately a 2-1/4" tailpipe (to fit the tips)? Or would I not see that much performance difference and just go with 2-1/4" all the way back?

Thanks for the help!

Click to expand...

1972DusterPaul said:

Since you didn't mention anything about your motor, I looked up a couple of your posts.

2-1/4" or 2-1/2" tailpipes won't matter much in your case for performance...the smaller tailpipes might be a bit quieter.

Smaller tailpipes used to be common to make the exhaust installation easier.

I can't find it, but a while back I read a good exhaust article on a Pontiac that ran 12.68 with 3" exhaust all the way and when switching out the tailpipes to 2-1/4" his quarter mile time changed to something like 12.71. Exhaust gases cool significantly after the muffler so larger pipes are overkill.

If you wanted to keep the exhaust tips you already bought then personally I would go with 2-1/2" pipes to the mufflers...also with an X-pipe...then 2-1/4" tailpipes out the back.

Otherwise I would run 2-1/2" pipes all the way front to back.

Paul

Click to expand...

there may be more variables to that pontiac, i agree to some of that thinking but i can also se how that would work on a chamberd or 3pass muffler but dont think it would work as good on a car with absorbation mufflers.
also depending on the whole car those 3" exhaust pipes may be overkill in the first place.
back on topic i like to build ehxuast the same size as the collectors all the way back but dont think a slight reduction at the tips would make much diference but thats just my thoughts since it gives abit more room for future development to have the bigger pipes already there.
alot of these things about smaller tailpipes because they are easier to bend and install is something i bet comes from lazy mufflershops that may be lacking the knowhow on how to do it once and do it right. LOTS of pontiacs had bigger tail/overtheaxlepipes than exhaustpipes already from the factory,and i think that may be for a good reason,those bigbends create restriction and by going up one tubesize some of that loss could probably be gained back.

Just remember, bigger isn't always better.

Dad's Pontiac wagon responds very well to exhaust flow (thanks for mentioning all of our earlier testing Duster 340).

Here it is with the big Goerlichs on about a year ago or so.

[ame="http://www.youtube.com/watch?v=cu4I6gfF68w&playnext=1&list=PL0024231A86C1C0C5"]YouTube - ‪71 LeMans Station Wagon at Strip, Run #9, 11.56 at 115+ mph‬‏[/ame]
[ame="http://www.youtube.com/watch?v=Ta6kP3itZx8&feature=BFa&list=PL0024231A86C1C0C5&index=3"]YouTube - ‪71 LeMans Station Wagon at Strip, Run #7, 11.60 at 115 + mph‬‏[/ame]

Dad is still playing with mufflers even today. He has been running the 3.0" Dynomax VTs with short tailpipes and doing so to see if the weight difference affected the performance much. It has been running 11.40s at 117.5 with them or the 2.5" Dynomax UltraFlos with 2.5" tailpipes on his 4100 pound car with the 474 cu. in. Pontiac engine. His mufflers are way to the back so again, we found it was not affected as much by pipe size just like running 2.5" ones on the 340s when compared to 3.0" ones. Granted, a big cubic inch engine or a little one running at high rpm will be more sensitive to this but in the grand scheme of things, the smaller tailpipes do not hurt as much as we used to think they might.

Tom Hand

I have 3" all the way and then I use 2 1/2" turndowns and it made a substantial difference at idle than the 3" turndowns. Way quieter.

Most street cars will never use the price difference between 2.5 and 3". A properly bent 2.5" system will support close to 700 HP. Although 3" does sound cool, it's usually a waste of money in most cases.

Thanks for the advice all! Going with 2.5 to the mufflers and then down to 2.25 for the tips. Will let you know how the install went next week!