Is 3" exhaust too much?

Thanks.

I think that 2.5" is plenty for a 400 hp engine. It should be quieter, have less drone and package better than 3". Also the extra velocity and heat in the exhaust gas should help keep the exhaust from rusting out from condensation, without being too restrictive. And many mufflers that have 3" in/outlets actually are 2.5" cores with the tubes swedged out, and don't really flow any more.

Hmmm...

Ideally, you would run open exhaust with optimized length collectors. Generally speaking, the less restrictive the system, the better.

Sometimes Low-end torque is slightly improved by a more restrictive system. There are systems I have read about the purportedly produce more power with X-Pipes and optimized, tuned mufflers, etc.

Still, less restrictive is typically the better way to go.

I own a '79 Jeep CJ5 with AMC 304 V8. I run 3-inch pipes and Dynomax Mufflers on it. It's not quiet, but not overly loud either.

I also own a '71 Charger. When I upgraded from 2 1/2-inch to 3 1/2-inch exhaust on the 440 in it, 1/4-mile ET performance improved by 7/10-second.

I'm happy with mine.

Here is a page from Magnaflows web site. One thing to consider also is the difference in mandrel bends and the typical exhaust shop bends that have the wrinkles in the bends. A 3" system that has kinks and wrinkles in the bends will not outflow a good mandrel bent 2.5" system.

On my 512 challenger motor I have 2" TTI headers and 3" pipe into flowmaster 40's that dump just before the rearend. My neighbor complained saying that when I idle my car it vibrates stuff off of his walls in his house 75 feet away. If he wasn't such a jerk I would care but I think he needs to insulate his house better. My other 4 neighbors say they can hear it but it doesn't bother them they love the way it sounds. I haven't been pulled over for it yet but I know I will after all I live in Idaho. In Idaho if it's fun or free it's illegal.

I'm gonna go out on a limb here and specutate that you are making more than the 400 HP that the original poster asked about

I'd just hate to mess up this engine by over heating valves and so on. You guys are right about the horse power tho, I haven't upgraded the intake, carb or the heads so I do have room to grow. However, it's a street car and I'd like to build it to be durable.

just a touch more than 400. I will post my build info and see if anybody can figure out how much HP it should be making

if you are buying a new system anyway, i'd go 3" as they cost the same from places like tti. 440's like to breathe

I run 3" on mine with 2 1/2" flowmasters dumped in front of the axle behind a mild built 318 with a .528 cam and i like it, makes the garage floor vibrate

the only issue i have with the 3" systems is it limits your muffler choices to mostly performance mufflers, with the 2.5" system you can get quieter (but more restrictive) mufflers.
If you want performance go 3", if you want to hear the radio, the 2-1/2" may be better.

There is a huge difference in the 3" TTI with Ultraflows (best flow and quiet) than the Flow Bastards. Load rattly and not as good of flow and neighbors hate them!!

2.5 inch exhaust is fine...even to 500 hp...I have 2.5 TTI on My bee...440/030 over...6 pack with stock high performance manifolds and it works well...I have 3 inch on My 67 GTX with a 498 stroker and fitting th tailpipes and over the axel pipes is a Pain.....I have headers on the GTX and get the drone....The bee has no drone...I attribute it to headers....both have crossover pipes..one thought...the first hemi's rated at 425 hp and were grossly underrated..had less than 2.5 inch exhaust systems.

2.5" MANDREL BENT won't be much of any restriction to a car up to 500-550 HP. it'll be much quieter, too. another option is to go 3" to the mufflers and then 2.5" muffs and tails, as by then the exhaust gasses has contracted and cooled enough to not need all the volume.

a good article:

http://www.pontiacstreetperformance.com/psp/exhaust.html

pg. 2, they only lost like .05 ET going from 3" tails to 2.25" tails....

I would highly recommend an X pipe over an H pipe setup. Major difference in noise & I think a bit more power also. As said MANDREL bends no matter what system and no neckdown in the muffs.

I run 3" pipes with dumps from the headers to 3" custom mufflers into 2 1/2 tail pipes with factory like stainless tips on my '70 duster..no restrictions what so ever,car has run the same numbers through the exhaust or opening the dumps..