Talked the tech support of a well-known exhaust outfit. He feels I would loose low-end torque if I were to go 3". He recommends 3" for something making like 500 RWHP. He feels 2.5 is PLENTY for a mild 454 such as mine.

Now I'm completely confused...please help me!

If you didnt get enough info in the last post, you're in trouble. Any big block with any kind of performance applications, will love 3" exhaust, plain and simple.

I second that comment 3" exhaust i believe on some chevelles are over doing it i seen a guy that had a 4" one time talking about massive personally i think he was trying to overcompensate for something else. Are you. But It like have a stock 350 motor with a holley 1000cfm carb no reason at all just looks big and get alot of ows & aws

I actually got enough info on cars that were making big power definitely liked the 3". I think my motor would serve as a starter for yours!!



If you didnt get enough info in the last post, you're in trouble. Any big block with any kind of performance applications, will love 3" exhaust, plain and simple.

FYI,
My combo runs .15 seconds quicker with it's 3" than it did with the old 2 1/2" system; 480 hp, 500 ft/lbs.

There is now no noticeable difference in 1/4 mile et between my new 3" system buttoned up or open headers, even with all the careful tuning I've tried!

I will say that the 3" system is louder than the old 2 1/2" system, but it's really not noticeable until WOT.

Boldm, not too much of a change in ET. Any mph difference?

Horsepower, E.T's, MPH....... WHO CARES!!!! IT SOUNDS COOL:D

They have gone over this again and again. The loss of torque has to deal with the size of the header primaries and collectors (to a lesser extent than the size of the exhaust. By the time those hot exhaust gases have gotten past the first few feet from the cylinder header the temperature has dropped significantly. If it really concerns you you can run a 3" with 2.5" tails so it'll look stock and you cna use regular ss tips or whatever.

i have to agree with Bob on this one. even on my little 406, i gained over 4 mph and almost 4 tenths of a second going from 2 1/2" duals to a 3" "X" pipe system, and this was just in the 1/8mi. i also dropped over 1 tenth in 60ft time. so much for losing bottomend. i do have a 10" convertor though, so dragstrip launches are a little different than cruising at 2500rpms or something, although the seat of the pants meter tells me that i lost nothing even at lower rpms.

Vince,if you went with a 3" X,Ultraflows and 2.5" tailpipes I'm willing to bet you'll be happy with both the sound and the performance.

This thread is exactly what I'm talking about. Some say good, some say bad.

How's the saying go, "Opinions are like....everybody has one".

Its seems like there's no data on a good 2.5 vs. a good 3"

Keep the feedback coming please!

Real world data:

http://www.chevelles.com/forums/showpost.php?p=739966&postcount=31

Keith..I was thinking about that very thread...here is that post:
Yes! I gained 4 mph in the 1/4 mile. 113 to 117 mph. I also have dyno results:

2.5" Flowmaster American Thunder system with H-Pipe: 430 rwhp & 481 rwtq.

3" home built with X-pipe and Dynomax 6" round welded Ultra-Flo mufflers:

466 rwhp & 506 rwtq!

Same dyno, same time of year, same weather. I lost no HP or TQ at any point on the curves from 2000 to 6500 rpms. No measurement below 2000.

But your making quite a bit more power than me. 460 RWHP translates into what kinda flywheel horse?

Vince,
Correct me if I'm wrong, but aren't you running a non-mandrel bent system on thet 454 crate motor? If so, you will gain with a good 2.5 or 3" mandrel
bent system with free flowing mufflers. My interpretation of what the
"well known" rep is telling you is that Back pressure/restriction builds torque down low. If that is true, and it may be to some small amount, how much
back pressure will there be in that system at peak HP? Bottom line is that
you need a system that will present as little resrtiction as possible at peak
HP. The confusion may be whether 2.5 or 3" is better. If you are buying new pipes anyway get the 3" headpipes with 2.5 mufflers and tails. I have such a system on my 396 you are local to me and welcome to come by listen/ride in the car ,may help you decide.
Thanks,
Dave

Yes Dave, I have a half-a@@ crimp bent 2.5 system w/50 series Delta FM's (which sound great BTW).

I'm leaning towards the 3" b/c of all the feedback I've been getting here. Looking like I will go with the Streetpro muffler. The Ultra flow type seems to mellow out the sound too much for me. My car doesn't have too much crackle as it is, so a chambered muffler will maintain the sound.

I would go with the entire 3" system though b/c I dont like the idea of an abrubt neck down right after the muffler via a reducer to 2.5 tails. I would rather get the 3" tails and reduce it to the 2.5 with the flowmaster reducers, and finish off w/SS tips.

Alright, I went and ordered the Pypes 3" system w/Street Pros. I also called Jegs up and got the Flowmaster tapered 3 to 2.5 reducers for the tips. I also spent the money and bought those stainless band clamps for the mufflers - In case I don't like the sound, I'll be able to change them out painlessly.

Lets see (and hope) I'll get a performance increase over this disaster that I have on there now.

Anybody looking for nice used set of FM 50 Delta series?

For what it is worth. I installed a Torq Tech 3" x-pipe system with Super 40 Flows on my Chevelle. I used to have a Flow Master American Thunder 2 1/2 system with 2 chamber 40's. I can feel the differance and yes it sounds meaner! I will test at the track in the spring and post the results.

By the way, no parts go to waste, the old system is on my El Camino now! :D

But your making quite a bit more power than me. 460 RWHP translates into what kinda flywheel horse? Around 548 flywheel hp using a drivetrain loss of 15%.