My 12A powered autocrosser has a stock Nikki with a K&N, and a set of RB road race headers, that dump into a single 2 1/4" exhaust which goes through a resonator, then over the rear axle. I originally had a Borla straight through muffler, which sounded great but was freakin' LOUD. In the interest of not losing any autocross venues, I whacked off the Borla and put a 'turbo' muffler on it with a turndown. This obviously cured the noise problem, but introduced a new one: there is a noticeable flattening out of the power above 6000 RPM. On long straights, this is a real problem.

Anybody have any ideas on how to uncork the exhaust without making it so loud it sterilizes frogs? Rules permit me to run the exhaust out ahead of the axle, as long as it exits from under the car, but ground clearance would be affected. I was considering running dual 1 3/4" pipes to the rear, underneath the rear axle, and then through two small turbo mufflers.

 

well i'd suggest a borla pro xs muffler on ls1tech.com they had a muffler flow comparison and the xs was one of the best flowing mufflers. i have also heard that muffler on a camaro z28 and it was really quiet and deep. i'd look into these if i were u it flows good and is quiet.

 

Run an offset "turbo" muffler.
Make sure the center section is perforated and not louvered - the louvers effectively make the I.D. smaller.
The offset center passage kills the sound.
We've had good results with one center muffler (ala pre-sliencer) and another (or two for FC) in the rear.


-Ted

 

The resonator isn't doing much for you for noise reduction. I suggest replacing it with a high flow muffler. This will reduce noise, and allow you to put your old muffler back on. This worked pretty well on my 82 GSL.