2.5 vs 3" exhaust

[GoMangoBoys]

We are ready for an exhaust on the car.  I am thinking of going 3".The engine is a 383 stroked to be a 478CI.  We are running the cast iron HP exhaust manifolds.  I would also like to run an X or H pipe.  Can anyone tell me if I will have any trouble with clearances etc from running 3"?  Can anyone tell me if there are any reasons NOT to go with 3"?  I have some new Flowmaster mufflers that I picked up at a swap meet that are 3".  I don't have to use them, but I was planning to.  I am also not planning to use the resonators.  I have exhaust tips that came with the car, but they are not 3"  I don't know if I can neck down the 3" pipe to meet them or whether I would just use other ones.
Thanks.

[anlauto]

Personally I think 3" is a little much, but I  don't know much about exhaust

[Dmod1974]

What else are you doing to the engine? 478 is a decent sized motor, but running manifolds makes me lean towards just doing 2.5" since you're already choking it down and I don't think the extra weight and clearance issues are worth it.

[blown motor]

  Your restriction will be your manifolds and they will never flow enough air to require a 3" exhaust system. I have 2 1/2" on my 340 and 2 1/4" on my my 440 which was standard on a Charger. Of course the 440 makes a lot more power so exhaust size is not a limiting factor. If 2 1/4" can handle a 440 with headers then it could certainly handle a 383 with manifolds. Go with the 2 1/2".

[Racer57]

Other than the cool factor when people see it sticking out back, there isn't any reason for 3" until you got a monster engine.

[Skdmark]

No point running a 3" inch exhaust with stock manifolds.
I would go with a 2.5 inch H pipe setup. Check with TTI.

[RUNCHARGER]

478" I would go 3 inch for sure. You have manifolds for now but who is to say you don't add headers in the future? There should be no installation issues with 3 inch either. Everyone says you can't run a rear swaybar but that is false. I ran a factory rear swaybar on my Challenger, this was a 3 inch system actually bent for a B-body I had and I figured there was no harm in trying it, the system fit like a glove and only required trimming the tailpipes to work. I ran TTI in another Challenger but the fit wasn't as good as this system was.

[GoMangoBoys]

@RUNCHARGER What system is shown in your pictures?

[RUNCHARGER]

A local company in Port Coquitlam B.C. bent them. I just did an internet search and they didn't come up though. They weren't a one-off they had setups for lots of different cars GM, Ford and Mopar.
I also just went on Summit and I see they aren't easy to find anymore. I think Dynomax and a few others used to list them, not anymore.

[73Dodge]

A stroked motor that size will benefit from a 3" exhaust but if you know you never plan to move away from manifolds to headers, or if you're going to neck back down to 2.5" for those exhaust tips, then you're already restricted so you could just go with with 2.5" for more clearance everywhere. I'd go with 3" and plan to upgrade to headers as well as run 3" tips or just do turn downs. I installed a full 3" TTI system behind my 512ci with Hedman headers and went with an H-pipe over the x-pipe although I've run both. Technically the x-pipe will help scavenge the exhaust better but I love the deeper sound of the H-pipe. The TTI system fits well with no interference anywhere although at 3" it's important to get everything lined up well from back to front because you don't have a lot of extra room in some areas. That's less of a problem with 2.5" pipe. I'm running Flowmaster super 40's and they integrate well into the rest of the system. As mentioned earlier and by others in different posts, a stock design rear sway bar can work with a 3" system, I have one on the way from Firm Feel right now. Final thought, if you're building for the future and plan to go with headers and 3" tips later then definitely go with the 3" system but if you know you want to stick with manifolds and the 2.5" tips then you might as well run a 2.5" system because it's less finicky to install.

[Filthy Filbert]

Why build a stroker that presumably has heads, cam, compression, intake, and a big carb; then choke it with manifolds?  Is it a very mild cam that makes maximum torque at 1800 rpm? If so, manifolds and 2.5" is fine.

If you want performance, then you will go with headers and 3" pipes.   If you don't care about performance then 2.5" with the manifolds will be plenty. 

[chargerdon]

Im just curious.   anyone know of a calculator that gives info on how big a dual exhaust needs to be to handle, 300 HP, 400 HP, 500 HP etc?

My 74 Chally360 stroer to 408 has the exhaust that it came with....I.E Patriot headers with collector reducer down to 2 1/2 inch pipes.   Dual of course and with flowmaster 40 mufflers and no resonators.   Horsepower...never had it on a dyno, but, with 14" wheels, 3.23 suregrip i have timed it using trackaddict app on my cell phone at 4.99 0-60 and 1/8 mile in 8.6 secs and 85 mph.   A few weeks ago i had a set of tires on that were wore out, and was buying new set...so for the fun of it...on my empty cul-d-sac, i foot braked it and brought engine rpm up till rears started spinning right at 2400 rpm, then nailed it while releasing the brake and it left a twin stripe on 70ft on my asphalt.   So, so I'm guessing HP is something north of 400.   

Is the 2 1/4 pipes too restrictive?   would i actually notice any seat of the pants difference with 2 1/2 or 3 ?   

[HP_Cuda]

Quite simple really.

If you are planning on going over 600hp on that motor then you might use 3" exhaust otherwise you shouldn't worry about it and use 2.5"

[HP2]

2.5" will be lower cost and easier install than 3".

[6PKRTSE]

If dead set on manifolds I would at least port them or have them extrude honed. Not cheap, but the process does help. Look at all the pure stock cars and the times they are running.