2.5 Inch exhaust to small?

[WicKeD_SS]

I would like to know is 2.5 Inch exhaust would be to small for a 650 to 700 HP BBC? I have a Ridetech 4 link and want tail pipes and stainless works has a kit for my 4 link but its 2.5. Would 3 inch be that much better ?

[Ron Sutton]

Originally Posted by WicKeD_SS

I would like to know is 2.5 Inch exhaust would be to small for a 650 to 700 HP BBC? I have a Ridetech 4 link and want tail pipes and stainless works has a kit for my 4 link but its 2.5. Would 3 inch be that much better ?

2.5" is not optimum for 650 to 700 HP. If you want to pick a hp number & max rpm you care about, I'll run some quick calcs and post the diameter you should run.

[MarkM66]

Personally, if it was my only option, I'd rather sacrifice a few hp, and have it go over the axle.

[Twoblackmarks...]

What about loudness, is that any problem?

You can have 3 inch into the muffler and 2.5" out of the mufflers?
To help quiet it Down, and easier to fit in the rear too.

[Vegas69]

Originally Posted by MarkM66

Personally, if it was my only option, I'd rather sacrifice a few hp, and have it go over the axle.

Originally Posted by Twoblackmarks...

What about loudness, is that any problem?

You can have 3 inch into the muffler and 2.5" out of the mufflers?
To help quiet it Down, and easier to fit in the rear too.

Yep, If I had kept my car it would have 2.5" tail pipes after the muffler.

[Bsinclair]

I have a 3" stainless back to my mufflers also on my 68 camaro ride tech 4bar set up. With the muscle bar in place I do not have enough room to run even 2.5" over my axle. Ridetech recomends going under the rearend which im not a big fan of. The 48hr car is done this way and looks good but its also blacked out so you dont notice it from behind. I used vband connections on the entire system and welded the outlet of the muffler with one to later install tailpipes. I think if I run them under the rear I will end up ceramic coating them black so they are hidden.

[FETorino]

Hot gas needs more room than cool gas. Go 3" to the mufflers for sure. The restriction from the muffler back created by the 2.5" pipe won't be that bad. Of course if your 3" muffler's cfm rating (if it exists) is less that 750 each then that is your cork anyway.

From one exhaust article I read and saved a while back.

Once the available flow exceeds about 2.2 cfm per hp, the gains possible by increasing muffler capacity drop to less than 1 percent.

Knowing that 2.2 cfm per open-pipe hp means zero loss from backpressure allows us to determine how much muffler flow your engine needs. Just make a reasonable estimate of its open exhaust power potential and multiply by 2.2. For instance, a V-8 making 700 horsepower on open exhaust will require 700 x 2.2 = 1540 cfm.

A section of straight pipe the length of a typical muffler, rated at the same test pressure as a carb (10.5 inches of mercury), flows about 115 cfm per square inch. Given this flow rating, we will see about 560 cfm from a 2.5-inch pipe. Houston we have a problem.



Read more: http://www.popularhotrodding.com/eng...#ixzz2eyrgMmkk

[Ketzer]

Originally Posted by MarkM66

Personally, if it was my only option, I'd rather sacrifice a few hp, and have it go over the axle.

^^ This ^^

That being said... My car also BBC, 600+ hp has a really poorly done 2.5 exhaust (crimped in the bends). I hope to revamp this winter so interested to hear what everyone says...


Jeff-

[Ron Sutton]

Originally Posted by FETorino

Hot gas needs more room than cool gas. Go 3" to the mufflers for sure. The restriction from the muffler back created by the 2.5" pipe won't be that bad. Of course if your 3" muffler's cfm rating (if it exists) is less that 750 each then that is your cork anyway.

From one exhaust article I read and saved a while back.

Once the available flow exceeds about 2.2 cfm per hp, the gains possible by increasing muffler capacity drop to less than 1 percent.

Knowing that 2.2 cfm per open-pipe hp means zero loss from backpressure allows us to determine how much muffler flow your engine needs. Just make a reasonable estimate of its open exhaust power potential and multiply by 2.2. For instance, a V-8 making 700 horsepower on open exhaust will require 700 x 2.2 = 1540 cfm.

A section of straight pipe the length of a typical muffler, rated at the same test pressure as a carb (10.5 inches of mercury), flows about 115 cfm per square inch. Given this flow rating, we will see about 560 cfm from a 2.5-inch pipe. Houston we have a problem.



Read more: http://www.popularhotrodding.com/eng...#ixzz2eyrgMmkk

This is correct is you're looking for optimum power. If you're not looking for optimum power, what is the purpose of the question?

[Vegas69]

Drivability, dumps get old from a noise and dust perspective on a street car.

I take my previous statement back, 3" over the axle with modifications to your trunk or under with black powder coating is my pick with this hp level.