Exhaust size

Whats a good size exhaust tube ? 2.5 or 3.0 I would like to run the 3.0 inch dual all the way back, with a long tube header setup.

We'll need a lot more info like eng size, cam, hedder size, etc.

Unless your making over 500 horses, 2.5 pipe will be fine.

GM B-Body Forum wrote:Unless your making over 500 horses, 2.5 pipe will be fine.

Can it be used? - Yes.
Should it be used? - No

Actually, 2.5" dual exhaust is way too big and will kill all the low end torque on a stock or mildly modified 305 or 350.  It will also decrease the amount of cylinder scavenging and decrease your mileage which is totally counterproductive to using hedders.  Engines need a certain amount of exhaust back-pressure to work properly.  2.5 or 3" pipe used for dual exhaust is just way to big for most cars.

Rule of thumb is: On a small block when using a 4bbl carb, 1 5/8ths inch tube diameter hedders with a stock or MILDLY modded engine and dual exhaust, 2" diameter exhaust pipe is more than adequate.  Remember, the stock 2-into-1 exhaust is only what?  2.25"?  And that handles exhaust flow from both banks.  
Just adding a 4bbl carb and hedders to a SBC really doesn't increase air flow much due to the shitty little cam and restrictive heads.  Once you step up to a bigger cam, better heads, porting, etc., THAT'S when you start increasing air flow and need larger exhaust pipes.
Don't believe the hype about needing a X-over either.  It balances out the exhaust pulses, my ass, lol!  It's nonsense and defeats the purpose of dual exhaust.

Please don't be one of those people that install HUGE exhaust parts on a stock engine and afterwards wonder why their car will no longer do a burn-out, is slow off the line, and runs so poorly.  IIRC, it's also against the Bro Code.  

Exactly, thats why our cars came with 2 1/4" piping single exhaust, they were designed for low end torque. Just let us know what you got.

^^Those pics are hilarious.

Yea, like has been said dual 3" is way overkill and will kill performance of a mild small block and devastate a stock engine. I run a performance built 1962-67 327 with small journal forged steel crank, 10:1 flat tops, 325HP Corvette cam (with .455 lift), and 350 hp camel hump heads in my 82 Trans Am with flowtech headers w/2.5" collector into a SINGLE 3" primary into a single dual 2.5 inch out flowmaster muffler, which is just about perfect for my setup. Even my primary could stand to be a tad smaller, but it performs quite nicely and gets 19mpg on the highway at 55-60 mph (3-speed TH350 with 2200 stall converter at 2,400 rpm) and requires 93 octane minimum.

I agree with these fellas, When I did my exhaust I knew I was going to a bigger engine (with an idea of turbo ) so I put 3" dual exhaust on my 305. With 3" there is no way to get it over the rear axle so my duals spill out shortly after the muffler and just before the rear axel. It didnt kill the car, and low end acceleration was fine but it zapped it's power at highway speeds. With the 383 it is another story. It sounds great! load but not as load at the 305... The power band is good throughout now but I may run smaller piping someday to quiet it down and up the back pressure...

I agree too even with the 455 I plan on putting in my Imp I think 2.5" will be about it. I used to know and rode once or twice with a

guy who had punched out 400 SBC in 79 Firebird with Lakepipes(nothing but the pipes) that were about 3.5" I swear that was the

loudest vehicle I have heard  outside of a Tractor Pull. The motor was built and it screamed over 3k but it had not a lot of  low end

grunt on the street.


Mmm Lakepipes now there's a thought I  .............