Doing a 6.1 swap into a B-body and wondered if a 2.5 inch or a 3" would be best? Currently going to run normally aspirated but may go supercharger in the future.

Thanks
-C

When I did that swap on my '71 Cuda I already had a 2.5" TTi exhaust with x pipe and it ran like scalded cat. That being said the SRT comes with 2.75" exhaust and I run 3" on my SRT. You'll be perfectly fine with 2.5" and avoid drone with that size.

A 440, even a stock-ish one, likes a good 3" system. A 6.1 will make more power than even most serious 440's. I'd think 3" would be the minimum, especially if the (usually conservative) factory spec's a 2.75" system.

For what it's worth........ I have a '66 Coronet with a heavily built 383 BB and I just put a new 3" stainless system on. I went from a 2" to a 3" with a cross over pipe and my car really liked it!

Seemed to have better response and a little more power.........

I am currently gathering parts to do a 5.7 swap and will go with my new 3"

mine is 2.5" from tti front to back. No drone. x pipe. More than enough flow, the motor is only 370 cu in.

my 5.7 hemi in the bcuda has 3" TTI front to rear. it has a little more drone than I would like sometimes.

they are flowmasters though.

As for cats killing power, my understanding is high flow cats are efficient. There is a late model Super Bee running a Procharger F1D on a stock displacement 6.1 running through full exhaust of course LT headers and clicking 9.2's through cats, so I don't think they are that restrictive. One thing is for sure, it is LOUDER without cats

Oh yeah, trust me, 2.5" is PLENTY! I'm not kidding you, my Cuda runs UNREAL fast with a "lowly" 2.5" exhaust

just a note here,alot of people seem to think that exhuast size is all dependent on enginesize,this is not true,far from it.

sure engine size has a place in the equation but its not all important what is important is the power the engine makes,remember horsepower is basicly a function of flow thru the engine and its related components, a stock 440 making 375hp may live happily with a dual 2½" system while a little mean 350ish cube motor making 800hp may not be happy at all with dual 3" pipes,mufflers have a big part in the exhaust systems capability to suport big flow aswell.

on a 370cube gen3 hemi i would build 3" duals with good freeflowing mufflers. a stock 370cube gen3 hemi is at the end of what 2½ will suport add a few speedparts and you will get to the level where 3" start to make more power.
only drawbacks with 3" over 2½" is weight and it gets alitle harder to get the tone down especialy at idle and at full power.

Yeah the new engines are more volumetrically efficient generally but you still need a certain amount of air to make a HP number, it doesn't matter what the efficiency is, it just needs the right size pipe to move how much air its moving (cu inches X efficiency). I look at it like this, theoretically, HP is soley dependant on CFM of a head, cubic inches just determine what RPM it happens at. Most exhaust size calculators I look at peg a dual 2.5" system at 500 hp (gross), which a good stock 6.1 is very close to. I would go 3" and give yourself some room to breath