A friend of mine with a 94 Z28, recently made the switch from a single 3" catback (borla) to a 2.5" duel exhaust which exits just before the rear axle. It's got a pair of "Bullit" mufflers, no cat's and a set of Hooker Long tubes. Last summer it dyno'es at 343hp and 360torque at the wheels through the borla (it was with the 1" opening plate).

He dynoed the car again last night with his duel exhaust and beleive it or not, made slightly less HP -339 but made more Torque - 375 than through the borla.

I have to say that I honestly wasn't very impressed. Yeah, the car sounded different (it's not often you hear a late model fbody with duel's). It did sound good, I'll give it that, but it just didn't provide the power increase I (or he) expected. He now has virtually no ground clearence and because the exhaust exits right underneith the car, it's really loud. There's a very pronouced "drone" inside the cockpit at all RPM's. After a while, it get's annoying.

Basically, I just wanted to say that in MY opinion the extra $$, the loss of ground clearence, and the annoying exhaust drone, of a duel set-up just isn't worth it. I'm willing to bet that had he kept his Borla and run it without any of the plates, he'd make more Torque (not just HP) than the duel.

My advice to everyone is to save your money and just get a single 3" catback.

It seems like every fbody owner wants duels now,. It's like the latest rage or something. Just thought I'd share my experience with you. Maybe save some of you some $$ from not getting the duel set-up

I'll try and get some pics. of his set-up soon.

 

Doing the two dyno sessions a year apart isn't the best to use as a comparison. There are other factors that could be affecting the dyno numbers... like worn plugs and shot plug wires for example Just pointing that out... it would have been better to do a dyno run, change to duals, then do another dyno run. But, since that didn't happen, it's good to provide the best data you can which is what you did

 

Your right, it would have been better (and more accurate) to do both dyno's ...say... within a day or two of each other but he had to save up the money for the Duel set-up over the winter. He installed new plugs alond with the new exhaust 'cause he had to take off the headers to send them over to get coated so he also got new wires too. I'd think that if anything, he'd get better #'s this time around for sure since it was about -4 last night and when he ran the dyno last summer it was like 35 degrees out.
Oh well. Just thought I'd share.

 

I appreciate the feedback from the dyno you provided, I know you ment well. I also agree that there are alot of variables between the two dyno sessions. I have rode in alot of diff. cars that have switched from a good cat back to true duals and I can deff. feel a seat of the pants improvement. I'm still going to stand by the true duals.

 

why wouldnt you just use true duals with 3inch pipe. i but money that will make more power than a catback. my buddy has dyno numbers to prove that and the where not a year apart either.

 

The thing is with a 3 inch pipe per bank you need to be making a serious amount of horsies to make that flow well. Velocity is a important factor here. You don't want the exhaust gas to slow down or your engine is going to have to push to get the gases out. Having 2.5 inch is more than enough for most of us and keeps the gasses flowing at a higher rate. One other thing to consider is the ground clearance.Just my thoughts but hey I might be wrong atwhich I'm sure someone will chime in.

 

Not very often do we get two dyno comparisons with changes done to the car. That being said thanks for at least coming to the board with sufficient information to make a judgement. If we had more dyno and track info with specific changes made like headers and catbacks it would solve alot of havoc and money for F-Body guys.

-Dustin-

 

I'm not really sold on true duals either. Too much of a pain. Also, did he run any kind of x or h pipe?

 

My 396:

4" Mufflex w/Dynomax Ultaflow

Not much more flow than that w/a muffler

http://www.slowwhitecar.com/kraest_396/396idle.avi
http://www.slowwhitecar.com/kraest_396/396rev.avi
http://www.slowwhitecar.com/kraest_396/396launch.avi

Mike

 

Were both dyno pulls at least mad eon the same dyno at the same shop?

Like Brent said, there are too many variables to consider to say that it isn't worth it. Temperature does play a bit of a role, but that's only a small part of it. Humidity is important, as well as overall tuning of the car.

Things have been changed on the car, so it needs to be dyno tuned for the new mods. Some of that lost power may be gained back with a good tune.

 

Yeah, both were made at the same dyno. I forgot to metion that his set-up also has an H pipe aswell. Sorry.

Still, I think that especially considering the -4 wheather last night, he'd have a huge gain but the dyno results speak for themselves.

Will everyone get the same results? Probably not. I'm not a mechanic nor am I an expert on exhaust systems. All I'm doing is sharing what I seen with my own two eyes. A dual exhaust makeing only a minimal power increase over a 3" cat-back despite the advantage of being run on the dyno in freezing (winter) whether.

You draw whatever conclusion you want from my (or should I say, my friends' experience.

Good luck to all

 

What Brent said, comparing two dyno sessions a year apart doesnt give accurate information.

Also compare the hp/trq at each 1000 rpms on both dyno charts and see what the difrence is between each 1k rpms.

Chuck's dyno comparisons show a much larger increase from duals but not at peak rpm.

 

My switch from a 3" Flowmaster cat back system to
a true dual system resulted in a 12 rwhp increase
and 8 rwtq increase. Something else is probably
wrong.

 

You're biggest gain cam from ditching the Flowmaster

 

im not really sure, but i spent about $200 installed for my true duals! i didnt have a dyno before/after.... but just the sound is enough for me!

like you said... its not everyday you see a late model camaro with true duals! thats why i did it, and it was way cheaper than a catback!!

pics in sig!!