Ok, i have been searching on and off for a couple months now trying to figure out exactly what exhaust I want for my car. I have decided to go with a true dual, but I can't decide whether to do 2.5" or 3". I can't seem to find enough information comparing the two, especially for my situation. I either see it for stock cars, or extremely modified cars.

Anyway, here is my setup:

CC306
Hooker LT's Jet hot coated
Crane 1.6 rr
SLP CAI
CC Lifters
LT4 Extreme duty timing chain
Head work (p/p, multi-angle valve...)
re-program, etc.

I saw this post that kmook responded to that made me lean towards the 2.5", but it seems like most people are going with 3".

Either way I will be going with an x-pipe and the dynomax bullets. Your input is greatly appreciated!!!

-Chris

 

I have the 3" to 2.5" X-pipe system on mine.
I do believe this is a better setup to run than the 3" to 3" setup at this point in time.
When I purchased the Dr. Gas setup that is what they recommended to me. But there will come to a point in time that you will have to move to the 3" setup. Dr' Gas said that the 3" to 2.5" is good for up to 450hp.

 

i just got done fabing up a 2.5" dual setup with bullet mufflers. the reason i used the 2.5" was clearence issues. and i was able to tuck it up under the car really nice with the lowest part being the tranny mount.

i also did it with SLP shorties

 

2.5" duals flow more than a Mufflex 3.5" exhaust.

I have 2.5" duals on my 383.

I would only consider going to 3" if I was adding a blower to my setup.

 

You only need 2.5" for a true duel setup on our cars. A 3" setup is for larger engines than our 350s. You can do it but it won't help you at all.

 

I bought the exact same stuff for my 1995 z-28 m6: cc 306, hooker LT's, 1.6 rr, and stage II ported heads. I am at the same point as you are: 2.5" or 3" true duals. Let me know what you end up doing, how much it cost, and how you solved clearance problems. If I will get my car done first, I will let you know. How much hp are you looking from your set up.

Tomas

 

Thanks for all your replies. That is a big help

Ken95Z28: That is awesome you replied. I love watching your video. That time is amazing for your mods. I was actually going to refer to you in my post.

You said that Dr. Gas said 2.5" was good up to 450 HP. I do plan on doing more mods after this. Would it be a bad idea to go 3" in preparation, or would it hinder my performance too much?

It isn't very expensive to redo (~$200) so I guess I could always redo. Chances are i will screw it up somehow anyway (speedbumps, rust, etc.) and need to replace it.

tanker: That is awesome you are doing such a similar setup. I don't know how much horsepower I am looking for. As much as possible As long as I am over like 365 rwhp, i will be happy (and i HOPEFULLY shouldn't have any problem with that. This way, I will be happy no matter what )

It will probably be about a month, maybe 5 weeks before I get it done. I just took my heads into the machine shop a couple days ago, and since they are starting race season, said it would be about 3 weeks, + or - a little bit to get it back to me, then there is buildup. I will definitely keep in touch though, and so should you!! I wanna know how yours turns out, be interesting to compare.

Right when I am done, I will put up a video too (since that is my hobby) hopefully with some high quality sounds clips too.

Thanks again for the replies, I think, unless someone convinces me otherwise, I will go with 2.5".

-Chris

 

I'd go 3" and be done with it. There's no reason to go with a 2.5" unless you are looking to shed a wee bit of weight or are having a hard time with the amount of space. The freer flowing the exhaust the better, plus you won't feel any regrets further down the road when you really start putting the power down.

My .02 centavos.

-Mindgame

 

Is this actually true though?? From what I have heard, many people lose horsepower when they free up their exhaust TOO much. I do agree that a good flowing exhaust is important, but I do know that it can be overdone, and a loss of HP is the result, and I am trying to find out if 3" fits into that catagory.

I am almost temped to build two sets, and 2.5" and a 3". Dyno them both with my setup (as many people have a pretty similar setup... look above) and then sell the one I don't use.

Do you think peple would be interested in a 2.5" or 3" true dual with x-pipe and bullets for about $200 - $225??

-Chris

 

"Lose horsepower"?

I've never seen any evidence of that and I've been racing cars and building engines for better than 24 years now. What I have seen in a change to a freer flowing exhaust was in the "tuning" of the motor. Usually a slight "lean" condition as a result of freer flowing exhaust but in the scheme of things... a low backpressure exhaust is worth power. Everything I've seen on the dyno seems to back this theory pretty well. Even what I've heard and read from people I respect and trust.
It becomes a bigger deal with increases in output. The more power you put out, the more you're going to lose to a slightly restrictive exhaust. If you're running cats and everything else, you definitely want to be bigger than smaller.

-Mindgame

 

Mindgame:

What about torque?? And, i am not going to be running cats. Thanks for the help!!!

-Chris

 

I was always under the impression that an exhaust that is too big will cause a loss of exhaust velocity, in turn killing the scavenging effect gained. So you may not lose HP but you don't gain what you might with a smaller exhaust.

This all goes out the window when you get into turbochargers BTW

 

There does come to a point when you can get to big of a pipe.
Talk to the people that makes the exhaust systems for the car.
I'm sure they can set you straight one what is to big and what is to small.

 

Mindgame-correct me if im wrong, maybe you dont really loose power with a huge exhaust but you will suffer a loss of bottom end torque. im building a 396 set up now and have seen a few of them dyno better (torque) with a 2.5 in dual set up over the 3 in set up. now all three cars were under 450 hp but barely. i know atleast im going with the 2 in exhaust. well thats just my .02
Rob

 

I'd love to see true duals in 2.5" as long as they exit the rear of the car like the stock pipes do. I'd much rather have that then the catbacks on the market. Maybe someone will market them soon. There is $$$ to be made once someone designs and markets them. Later>>>>>>>>>