I've made many true dual setups on 4th gen f-bodys.

I always go 3inch off the headers and reduce it to dual 2.5 after the x-pipe.

With this setup, my car made 453rwhp naturally aspirated 383, 634rwhp with a supercharged 357.

Same setup on our Speed Inc. shop car made 720+rwhp.


Here is a link to our webpage. Go to exhaust and scroll down and you will see a pic of a true dual/ over axle setup I recently did. Everything is butt-welded and mandrel bent.

There will be more pics soon of another system I just finished today.


www.ls1speed.com

 

Yes Chris my ehaust does have an H-Pipe. The only reason I have a 2.5" exhaust rather than 3" is because it was one of the first bolt ons I did over 5 years ago. I didn't want to buy another $1,000 exhaust system or add any more weight so I just went with the cut outs instead, much cheaper and even more effective at the track Here is a video from SLP CAD a few weeks ago if you want to hear it run http://www.racingfreaks.net/videos/2_23_03/impala.wmv

Thanks Birdie, I just got a chance to reply. Yes it is a dual exhaust, all LT1 B-Bodies have duals, only the TBI/4.3 L cars had a single exhaust.

 

Going from stock dual 2.5" pipes on an Impalla to aftermarket 3" duals is also gonna give you more power because the stock exhaust is kink bent and the aftermarket system is mandrel bent.

 

Exactly.

There's no reason why you would want a restrictive exhaust or shorties with any LT1 setup. Many people are getting led into the wrong direction by some of the newer LT1 Tech posters who give bad advice.

Mike

 

Ryan

 

ROFL!

How dare you quote my post and insert words of untruth into it!

The aforementioned person knows all about LT1 Tech! Ask anyone who joined in 2003!

Mike

 

I am having true duals done this week on my Firebird. It consists of 3" duals through an X-pipe, then (2) 3" in/out bullets.
Now, heres the kicker- I am doing this with Hooker shorty headers. The guy doing it is going to modify the collectors quite a bit to make the opening larger.

 

I can help answer this next week. Going from dual 2.5" with H pipe to dual 3" with Xpipe. STOCK 350 with 175HP nitrous shot. I want the 30HP I can pickup when I use the juice.
According to my MPH I'm making 457HP at the RW.

I will dyno before and after as that's part of the price of the exhaust.

Mike

 

why does everyone dump the 3" exhaust before the rear axle or to the side? will it not fit over the axle and out the back? i've never actually seen a picture of it not to say its not there.just wondering

 

So far the only way to get 3" over the axle is to remove the upper panhard bar brace. For straightline performance this seems to be ok, but several people are still very weary.

 

I've seen some people notch the stock panhard bar.

 

I dont think that you want a restrictive exhaust, you just want a matched exhuast. I think for a close to stock motor that dual 2.5 inch would be fine. Everything I have always heard has said that dual 2.5 will support 450 hp pretty effeciently. If you are making more than that I would go bigger. I dont think that there would necisarily be losses or at least big losses by going to 3", but ground clearance can suffer. I myself have dual 2.5 inch with no cats a h pipe and bullet mufflers that dump before the rear axle. I dont think that this is very restrictive especialy since it doesnt have to make any real sharp turns like over the rear axle. If I had a fourthgen I would probably have dual 3" on my car right now though because it would have been easier to fit, but I dont think I would have gained much from it.

Ben

 

Two 2.5" dual pipes have more crossectional area than one 3.5" pipe. There will be slightly more frictional losses but as stated above, if you're dumping before the axle its still pretty free flowing.

 

Hey guys, sorry for the long delay to reply, I was installing my friends suspension on his 2001 audi a4. Anyway, thanks again for the continuing replies.

mtxpert: That would be awesome. I would love to see the dyno results. If you could either post in this thread or PM when you make a post, that would be great!!

INTMD8: That exhaust looks good. I was actually thinking about going 2.5 and going over the axel. But then there is a lot more pipe and bends (even though they would be mandrel) to inhibit flow. But i probably won't becuase of the trouble and the cost primarily.

Thanks again for your replies. Any more input would be great!!

-Chris

 

I found this article at car craft and I thought to include it since it has a strange combo--2.5 into X then 3.5 back to 3.0 which made as much power as open headers, check it out http://www.carcraft.com/techarticles/69238/