I have a built 383 with the works. It should have peak power from mid to upper RPM. I got GM fastburn heads, 1 3/4" headers, and a lot of other goodies. Power is estimated at around 450 hp.
What size should the exhaust tubing be?? Is 3" too small or is anything bigger TOO big?

Thanks

 

I would go 4 inch maybe. Sounds like it will be a pretty big HP/TQ engine and it will need all the exhauling it can do. But don't get ridiculous like beyond 4"

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Eric Natzke
91 Firebird 305 TBI
"It Ain't Stock"
http://members.aol.com/j007golden/91firebird.html
For info on certain parts or mods go to the site below
http://members.aol.com/j007golden/modeval.html

 

4 inch sounds good to me too.

I always like the "bigger is better" phrase. If I had my way I'd have a pipe so big that you could fit a pigme from Borneo in it.

....but that would be weird though.

No, I think you should be fine with 4 inches.

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1987 IROC-Z Auto (LB9)
Black/grey interior with the stance of a streetfighter

Mods
Custom exhaust. 4 Inch pipe from the headders all the way back to a single muffler at the rear. No Cat.

Future mods due in March:
K&Ns
RAM Air
Air foil
AFPR

Hoping to get a couple of tenths with that lot

 

There is such a thing as too big. You generally select a strategy, either high velocity/low volume or low velocity/high volume.

TPI follows the high velocity/low volume route. The long, skinny intake runners won't move as much volume as shorter & bigger runners as in the Mini-Ram or Victor Jr. type intakes. With this setup, you go with smaller header primaries and smaller exhaust than you would with the Mini-Ram or most carb intakes.

Whichever induction path you choose, there are physics involved. Go too big for your system, and you make less power due to poor cylinder filling (fuel/air charge partially blows out the exhaust port while both valves are in overlap). Go too small, and you make less power due to charge contamination (there's still exhaust the cylinder when the fresh charge arrives).

-Kevin

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1982 Z-28

See http://www.mycar.net/mafb/registry/detail.cfm?id=276 for details

 

I need a real answer as I am torn between getting a custom system mad for me at a muffler shop for about $250-$300 or getting a mufflex 3.5" or 4" system for over $500. I just don't know if it would be worth it for the bigger exhaust.

My engine builder said to get the 1 3/4" inch headers so I got the SLP's. I am guessing I would need the bigger exhaust but who knows. If you guys can come up with a decent guess as to what would work with this combo please let me know.
I have the Accel SuperRam, 58mm TB, midrange cam, Fast Burn heads, custom prom, and I think thats about all the essential stuff that one would need to figure this out. Its a 383 so that also needs to be kept in mind.
I have Dyno 2000 that shows I should get approx 450hp/tq out of the engine but the change in exhaust on the program is quite small.