2.5" vs. 3" Exhaust

[Excelerater]

BBC need big pipes,my 565 and 615 uses 2.5" primary headers with 5" mufflers for track use but even my street shit had 4" Dynomax bullets...LOUD as can be,shake the ground loud ! Welcome to BigBlock world...That video was no surprise to me

For NA 5.0 2.5 is plenty but start revving it to 7500+ or add a whipple and 3" should
show better numbers.

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[v8440]

A little perspective. ..I had a '91 notchback with a 393 windsor. On a 200 shot it ran 9.80's at 137 and some change through a NON MANDREL BENT 2.5" system all the way out to the rear bumper. When I installed cutouts I picked up a whopping 6 hundredths. Yes, hundredths. True, I didn't rejet the carburetor, but you get the idea.

 

[EJS2016]

I love low-end torque too.
Am I correct in my belief that the installation of a 3" cat-back exhaust on a stock GT will slightly decrease low rpm torque and move it up higher in the rpm range?
Appreciate members insight.

 

[aschaefer]

I love low-end torque too.
Am I correct in my belief that the installation of a 3" cat-back exhaust on a stock GT will slightly decrease low rpm torque and move it up higher in the rpm range?
Appreciate members insight.

Not in any way that you'd notice while driving, however full 3" isn't really necessary unless you're running a high power FI setup

 

[BmacIL]

Not in any way that you'd notice while driving, however full 3" isn't really necessary unless you're running a high power FI setup

That and all the 3" catbacks still connect to the 2.25" neckdown, so it really doesn't matter that it's 3".

 

[aschaefer]

That and all the 3" catbacks still connect to the 2.25" neckdown, so it really doesn't matter that it's 3".

:amen:

 

[v8440]

I would be surprised if a 3" pipe after the cats affected the torque. To the extent that exhaust systems affect torque (other than through just plain excessive backpressure), it's done by complicated interactions between exhaust pulses from different cylinders, and is affected by pipe diameter and length. I think the converters are enough of a disruption to that process that no distinct pulses continue past that point.

 

[EJS2016]

Just the info I was looking for - thank you all very much!

 

[BmacIL]

I would be surprised if a 3" pipe after the cats affected the torque. To the extent that exhaust systems affect torque (other than through just plain excessive backpressure), it's done by complicated interactions between exhaust pulses from different cylinders, and is affected by pipe diameter and length. I think the converters are enough of a disruption to that process that no distinct pulses continue past that point.

It would if you were able to get rid of the 2.25" connection and make that bigger. There is legitimate restriction in the resonators and mufflers.

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