Cat-back 2.5" versus 3.0" tubing

[wildcatgoal]

3" if you have headers. 2.5" is fine without. 3" is most common in aftermarket and it's harmless to add, so just go 3".

Sponsored

 

[VinnAY]

I think I lost a little on the bottom end with a 3" and CAI but that's just the butt dyno but I thought it was noticeable. I might have preferred 2.5 like it lost too much backpressure with 3"

 

[wildcatgoal]

You lost 0 backpressure unless you removed the cats.

 

[rf_ross]

I think I lost a little on the bottom end with a 3" and CAI but that's just the butt dyno but I thought it was noticeable. I might have preferred 2.5 like it lost too much backpressure with 3"

That's always been my line of thinking, too. I mean, has exhaust technology changed so much over the years that the physics behind it has too? I don' think so. So in theory, a 2.5" should still give you better bottom end due to its faster flow rate than a 3.0".

When I originally posted this I was really curious what everyone had experienced and a couple do, in fact, suggest that a 2.5 really dishes out a better bottom end.

 

[SVT-DADDY]

That's always been my line of thinking, too. I mean, has exhaust technology changed so much over the years that the physics behind it has too? I don' think so. So in theory, a 2.5" should still give you better bottom end due to its faster flow rate than a 3.0".

When I originally posted this I was really curious what everyone had experienced and a couple do, in fact, suggest that a 2.5 really dishes out a better bottom end.

Again the cats are your restriction. If you look at your cat pipes they actually neck down to 2.25 or smaller in some sections. Your never going to flow more air then you can get by your cat pipes.

IMHO cat backs do nothing for these cars unless you are making a ton of HP.

 

[RoadCone]

I'm doing a max effort Whipple/Built motor... ported heads ect….

I have the full 3" ARH exhaust system with the 1"7/8 headers and H pipe.
I sold the headers and H pipe and just ordered 2" ARH headers and 3" X pipe.

After the X pipe the catback, even though listed as a 3" exhaust system, necks down to 2.5. This is pretty far back in the system.

It seems to be the consensus that the 2.5 will not hurt power. ARH stated as the exhaust flows out the system, it cools and slows down. The 2.5 section helps flow.

 

[v8hgt]

I'm doing a max effort Whipple/Built motor... ported heads ect….

I have the full 3" ARH exhaust system with the 1"7/8 headers and H pipe.
I sold the headers and H pipe and just ordered 2" ARH headers and 3" X pipe.

After the X pipe the catback, even though listed as a 3" exhaust system, necks down to 2.5. This is pretty far back in the system.

It seems to be the consensus that the 2.5 will not hurt power. ARH stated as the exhaust flows out the system, it cools and slows down. The 2.5 section helps flow.

I run the same ARH system as you. Physics ain’t it. As the gas cools it becomes denser and requires a smaller pipe to achieve the same flow rate. Check out the pipes on a 50’s v12 Ferrari racer. The actually get bigger as they go down. This has the effect of sucking the grass out of the system. No cats either. Makes it horrible to drive at small throttle openings and you have to be very careful about how put your foot down. No mashing the loud peddle! But it achieves the best top end power on the track (in a very narrow rev range) - think tuned pipe two stroke

Sponsored