Yes i did searching but i never really found an answer that i was looking for.

What i have is a 82 with a 12a street port with a Weber 48 IDA and i'm planning on redoing the exhaust this winter.

it has a RB header with 2" tubes going into a 3" flange and running 3" all the way back to into a 3" magnaflow with no cats.

what i use the car for is rally racing, pretty much rapped out all the time on stage.

So my question is, how small is to small? I'm thinking of replacing the 3" with 2.5" for some better ground clearance, but it seems with all i am reading the norm for racing is 3".

But then I have had guys tell me 3" is over kill on anything NA.

What says you?

 

I'm no rotary exhaust expert but I know that a single 3" exhaust on my 5.7L camaro is plenty to support 300hp+. A lot of high horsepower 3rd & 4th gen camaros run a single 4" system. I've been debating on what size exhaust to put on my stock 12a and Im thinking 2.25" is plenty, for you 2.5" is probably more then enough with your mods. Velocity is better then volume and as Smokey Yunik said (paraphrase) "Anyone who tells you they know anything about exhaust is full of it, nobody knows anything about exhaust, but I will tell you that too small is better then too big".

 

yeah, my thoughts were the 3" is over kill, but they rotarys really move some air and spinning 7000+ rpms on a somewhat normal bases i didn't want to choke it.

i'm going to run one more event with the 3" and then redo it this winter. but i'm hoping to get some good input about what is to big and what is to small.

 

with a port and a carb, you're right at the power level where it might matter. if it was stock port, 2.5" would be fine, bridgeport needs the 3"

streetport? dunno. i suspect you'd loose a minimal amount of power, like 2-5hp, but i could be wrong

 

Run a pair of 2" long primary tubes. Put the collector just behind the rear axle, and then your 3" muffler.
This will give you more ground clearance, and it makes good power too.

On my road racer, I cut out and raised the floor on the right side, roughly from the passenger seat front mount on back. This let me tuck my pipes up higher and get more clearance.

 

i'm assuming you are talking to run the 2 2" pipes under the rear axle. if so, no can do, that sucker would be torn off after the first stage.

although this does give me some ideas. i'm happy with how the 3" runs over the rear axle i'm just not happy with the from the header to the rear axle section. so i might do something like a double 2" to the rear axle and then the 3" over the axle and out the back.

thanks

 

For what it is worth I have not seen a 12A or 13B street port SCCA E Production car with less than a 3" exhaust. These cars also run a Weber 48 IDA. We have 6 of these cars in the KC area and I have studied the all of the first gens at the Runoffs when they were in Topeka.

When Mandeville dyno'd my friends street port 13B he recomended a 25" primary with a Burns merge into a 3" exhaust.

With a close ratio box these cars are rarely below 6500 and most are redlining at 9500.

Have you thought about using oval tubing for ground clearance?

 

well that's good stuff to know.

no i haven't really even given a thought to oval tubing, i wouldn't even know where the heck to get the stuff

 

My local Circle Track speedshop sells it - straights and bends. Googled and dr. gas came up - aluminized mild steel and stainless. He also has a conversion chart from round to oval. Dr. Gas invented the x-pipe crossover that is used in NASCAR.

www.drgas.com

There are probably other sources.

 

wow that's pretty spendy stuff.

i think with how much you have to replace an exhaust on a rally car i'm going to go a different approach, i cheaper approach.

thanks anyways.

 

you could do the 2x2" pipes, go to 3 and up and over the axle...

the 2x2 can tuck in pretty close, and 3" over the axle minimizes the power loss from the bends, but since its over, should clear everything?