Superformance Exhaust
 

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

Keep us informed. I am putting a new Roush 427 into SPF #2932 and will be following this thread to make sure I"m not dumping a hundred horses before I even start it.

I agree, please update, I need to redo the ceramic coat on mine and this would be the perfect time to modify the mufflers.

I don't know about picking up 100HP on top, but you will certainly reap a gain in RWHP. I changed the side pipes on my SPF to a set I built using the Howe Racing mufflers, 3 1/2" I.D., and Hooker Headers merge collector and netted 60 RWHP gain over the stock set up. That's on a 496 c.i. FE motor.:D:D:D

I wonder what the F5 has that makes them different?

I know mine hurts my ears when I tickle the vortech!

I have a set a of these sidepipes available in the SF Bay Area if anyone wants to try them...

Just curious... My Superformance has stock undercar exhaust. Does this make more/less/same horsepower as stock Superformance sidepipes?

Jack

i agree with the factory five being more throaty and better sounding. I ran into a guy with a 302 in his FF and it sounded more venmous than my Roush 427. That where it ended, I started walking away as soon as the light turned. I guess I could call his half fast, it sounded fast but lost the race. No shame in loosing to another Cobra though. He could have beat anything else on the street.

Louvers should point away from the headers toward the exhaust outlet!!:cool:

I found out from the "King" of glass-packs (Lucien Donofrio) that if you point them toward the headers you will effectively reduce the flow of a 3.5" muffler to a 2.5" or less at high output??:eek:

I did it his way and the power increase was very noticeable as was the NOISE!!!:D

Coosawjack**)

I started with the Roush 427R single plane intake Victor Jr. that comes on a higher HP version of the motor. The Roush bench test with Holley 750 double pumper that came on the engine was 562 corrected at the crank with Roush test headers having 2" primaries and open end collector. In the car it had the Superformance headers with 1 7/8 primaries which are pinched by width at the top to about 1.1 inches give or take to cover about 1/3 inch width of each exhaust port on the AFR 205 heads on the engine. I had the Superformance side pipes too. That set up was just a touch over 400 corrected wheel HP and would trap about 125 mph at the drag strip given about 1000 ft air. I asked the Superformance dealer what's up with the loss of 160 HP. They said that's pretty good, most are only 370 to 390 at the wheels for that motor in the same set up. This makes sense given the motor is supose to only make 550 crank HP and I had 562 crank HP.

I first changed the headers. Here are the before and after.
http://www.clubcobra.com/photopost/d...sOldAndNew.JPG

I also changed to, Pro-System mechanical secondary carb of a bit over 1000 cfm, larger surface area air filter, Aeromotive fuel filter, 1/2 inch or 8AN fuel line from tank pick up to carb and side pipes from Buckshot Racefab with 3 inch louvered cores. This set up made 475 wheel HP The car with this set up made about what the engine should in my opinion and put the car easily into the 10s a little over 130 mph.

I also changed to light weight flywheel, stronger clutch, stronger half shafts and motor mounts with less movement so the pipes don't move and destroy fiberglass were they exit the engine bay.

Lots of pics in my gallery. I had a blast with this car before I sold it. If I did another one I'd do about the same stuff because I went through many of the lessons already.

Click on the link just below to watch and hear the set up at the drags.

Change is GOOD!
 

FYI,
I changed out the stock sidepipes for a set of SS pipes, and what a difference! Much louder, and less restrictive, the muffler part is interchangable for reduced noise.
They were not cheap, and do get some blueing from the heat. But I like them. Check the SCOF forum for info on them. They are custom made for your car. The stock headers are also restrictive and should be replaced if you intend to track the car. We had a long discussion going on several years ago. There is also a place in Fla. "Stainless Specialties" (I think that's the name) who made a set for one of my Fla. buddies.
TL :MECOOL:

Greg, are you saying that Roush heads are AFR's with the Roush name on them? And, who's header did you switch to or did you have the stock ones ported tom

PS What rear tires did you use for the 10 sec run?

not sure if this is your style of head...

http://www.fireflyperformance.com/header/index.htm

Terry Lee.....what brand of headers are you using? tom

Maxum 101.....I think I'm screwed on the headers. I think the ones on my car are for a stock 351 head (small port) If that's true There's still a ton of restricted HP to find.
Superformance may use the 2" I.D. muffler because the crappy headers clog everything up anyway, so what's the use. Superformance does not offer an option. I'm still checking. tom

http://www.classicchambered.com/clas...rformance.html
I'm so impressed with them I am a Classic Chambered dealer and keep them on the shelf and have fixtured up to change the mufflers.

The Roush 427R has AFR 205 heads. They do them for Roush.

The header was from the Olthofs. I think they made them from big block headers, but not sure. The nice part was they didn't cover part of the exhaust port.

The rear tires are Mickey Thompson ET street drag radials in a 275/60 15. That pass was only a 1.7 60 ft starting from idle. The tires are awesome on the road.

Greg,

You have figured the roush 427 better than anyone. Can you list your suppliers for the headers and sidepipes you used. If the muffler in the side pipe was exchangeble which one did you use?

Thanks

Tom,
I don't know which headers you have, but Superformance at one time offered headers with less restrictive openings. They were called the "402" headers. Ask Stephen about their availability.

I'm not 100% certain, but I believe that later model SPFs come with the 402 header as standard equipment. My car (2613) which was shipped just over two years ago came with the 402 headers. Based on the info that I had at the time, my car was kind of on the cusp of the change.

I'll probably be seen as a heretic, but I'm going to go with quieter side pipes when I re-do mine. Even if that means giving up some HP. :)

See below...I screwed this reply up.