[wanab5150]

I’ve always felt as though the Superformance exhaust on my car sounded a little “compressor like”. I have the 550 Hp version of the 427R Roush motor, and it pretty much sounds like any other Superformance. I’ve heard a lot of 302 inch Factory Five cars that actually sound deeper with less of that “fuffff fuuuuffff fuffff fuufffff” sound that Superformance makes.

I never really gave the exhaust much thought until one of the Nor Cal guys cut out the stock mufflers and replaced them with Chambered Exhaust mufflers. He also has a big inch motor and it really came to life and now sounds great. He claims a huge HP gain and after more research, I found out why.

I found that the muffler portion of the Superformance side pipes are actually 1.875 Inside diameter. Steve at Full Throttle Performance in Reno cut the end off and I measured it myself. The end of the muffler where the collector is welded on actually has a solid steel plate with a slightly less than 2” hole through the middle. It has perforated holes all the way through but still, it’s less than 2” in diameter from one end to the other. While this may be fine for a 302 inch/350HP motor it certainly isn’t allowing a big inch motor to breathe, and you might as well put a 550 CFM Holley on in place of those 750’s and 770’s, because they cannot possibly breathe to their potential! Christ, even my Harley has 1.75 headers and 2” exhausts and that’s for each cylinder!!!

I talked to “Chambered Exhaust” and they feel that 2” is fine for 302”/350 Hp motors, 2.5” is good for up to 400”/425 HP motors, 3” is good for 450”/550 Hp motors, and for Maurice’s (Nor Cal) 511“/668 Hp Shelby motor 3.5” would be best. These are ball park and can be argued, but I also obtained similar figures from “Full Throttle” in Reno, MSI Corvette in Roseville, and “GT Auto” in Rancho Cordova.

There are a number of replacement mufflers out there and I.D. is the most important feature. With that come decibels …..Nothing is free! I’m sure that’s why Superformance doesn’t offer exhausts for small block and big block applications. A big block with 3” mufflers would scare customers away after a demo drive.

Now, along with the increase in decibels, comes Horsepower! If you run the 2” stock exhaust, you might as well have dropped a 400 Hp small block in it, because that’s probably all you’re going to be able to milk out of an estimated 550 (crank Hp) motor. “Chambered Exhaust” has a web site showing dyno runs with increases of about 30Hp at 2500 RPM and 104Hp in the upper RPM’s on a big inch motor. (I know some of you will search out different cites to prove me wrong and that’s OK, but PLEASE, these are for reference and not exact…absolute…and written in stone numbers!) Also, Dynos are like opinions, they’re all different.

Gt Auto, Full Throttle and Chambered Exhaust all report similar numbers. I DON’T OWN A DYNO! All I can attest to is what MY research revealed. Gary at Gt Auto said they did dyno a Superformance before and after an exhaust swap and DID pick up about 100Hp on top. I don’t remember which brand of muffler he said, but it was 3”I.D.

Chambered Exhaust has packed and unpacked mufflers. He said there is no difference in Hp but there is a 4 to 6 decibel difference (lower) in the packed. These also have sound deadening louvers inside which if aimed toward the header will absorb a few more decibels without Hp loss.

If you can tolerate the decibel increase (and it is up there) you can extract the Hp your engine was designed for. There’s no shame in quiet and I’m sure ear plugs will be in order, but my ego won’t let me leave this big dollar Roush plugged up. I’m going to give it a dose of Exlax and reap the benefits of having another 100 Hp that I don’t really need! I'll be here next month with an update. Tom