Generation IV External Engine - 4" Single or 3" dua exhaust

Right now I'm debating on two different exhaust systems to use for my ride. I currently have a 3" flow master exhaust system that is holding me back 70rwhp and 84rwtrq (see dyno graph) Setup is a 427LSX with LS7 heads, smallish cam in my 01' TA. I'm looking to maximize the power output of my exhaust, as I'm sure as it sits even with the 3" cutout open, I'm still losing power.


I'm currently struggling with two options:

Option one, build my own 3" true dual system utilizing two Magnaflow Mufflers 12619 at the back. This will be a full dual exhaust, no dumps, with the mufflers on each side at the rear of the vehicle, exiting to 3.5" corsa clone tips. I am thinking about x-pipe, and doing this by utilizing a second 2-1 merge welded to the end of the ARH y-pipe. See the picture attached that illustrates what I'm talking about.

My main concern with the x-pipe is the center will be 3", will this be a restriction to the exhaust? Or will it be a non-issue?


The other option would be to just run a single 4" exhaust system with a 4" elec cutout ready to be opened up. Not sure on the muffler selection, but would probably just run a 2-1 merge at the over the axle portion of the exhaust (4" inlet - 2x3" outlet) and run the same muffler selection like above.

Both systems would cost about the same for me, which one would make more power?

Thanks for any help in advance!

4" has more area than 2x3"

I'm doing single 4" on my 454. i've got 2" Kooks headers with 3.5" collectors. i'm going to run 3.5" pipe off the headers into a 3.5"x4" Flowmaster Merge collector with a 4" bullet muffler shortly thereafter, dumped. it will weigh less and flow better than just about anything. From what i've seen and read, that Y-merge is the only thing flowmaster does right. I love their single chambers too, but i'd NEVER run one of their catbacks on anything i own.

How does the 4 inch have more volume than 2 3inch pipes? The Area of the pipe for the first, Area=pi*radius^2, is 4*pi ....each of the two pipes is 2.25*pi, so you multiply that by 2, and it is 4.5 pi for the cross sections of both. Also with two straight pipes there will be less bends = more flow, right? If both pipes are equal length then the same volume is there for the four inch and the 2 3 inch pipes. I am not trying to be rude here, just wondering how it works, please do not leave negative comments.

One thing that must also be taken into account is a properly designed Y-Merge will scavenge so efficiently that the Y-pipe setup will outflow the TD's all day long, and Flowmaster's Y-Merge is nicely designed, hence my reasoning for my setup.

In building my TA, I wanted true duals also.

I bought a 3" X pipe and had 2 flowmaster over the axle pipes.

Finding someone to make it up was impossible in the Kansas City area. Everyone said impossible, but I'm sure it is if someone wants to tackle it.

With ARH 1 7/8 headers and 3" Y to a 4" outlet, I went with a Mufflex 4 inch Magnaflow. Fit like a glove.

In building my TA, I wanted true duals also.

I bought a 3" X pipe and had 2 flowmaster over the axle pipes.

Finding someone to make it up was impossible in the Kansas City area. Everyone said impossible, but I'm sure it is if someone wants to tackle it.

With ARH 1 7/8 headers and 3" Y to a 4" outlet, I went with a Mufflex 4 inch Magnaflow. Fit like a glove.

I would love to do that, only if it had dual out for the rear. I have a guy who will fab the dual exhaust up for me (know the owner of a shop) and I'll even help him out. Maybe I could get a 2-1 4" merge, and run 4" pipe with two mufflers 4" magnaflow diesel 7" round x 14" body length the rest of the way out on the mufflex system? This would be after axle. Interesting thought...

Is anyone able to find a 4" 2-1 collector?

Mufflex has a single 4 ich cat back that may help. I wouldent dare us the muffler tho.

Mufflex has a single 4 ich cat back that may help. I wouldent dare us the muffler tho.

Yea, i know they have it, and that the muffler blows. That's part of the reason why I'm probably leaning away from it. I don't want to have to purchase the whole deal, and then spend another 700 on a cutout, mufflers, piping, labor on top of the 600 it already costs.

either one will give you great power.... but i am partial to the 4" on f-bodies

i would only run a 4'' as long as it was in a cat back style. thatt dumped under the axle crap gets old fast. no more radio

Dual 3" with Borla XR1's right before the axle. If you dont dump it (no turn down), it wont drone nearly as bad. A single 4" will either have to be louder to move the same airflow or will have to go over the axle and lose it's ass in a rear mount muffler.

either one will give you great power.... but i am partial to the 4" on f-bodies


That's about what I figured, just wanted to see what everyone thought. I would be more partial to the 4" but it's just not quite what I need as far as setup and would just cost too much to setup right. Plus I already have the panhard relocation setup and perfect piping already for it. I'll post up a new thread with what I had used for it as I'll have a stainless system for under 1000 all the way out the back! Pm sent.

Yes the 4" set up will yeild more power thru the band. Exhaust will flow thru the most unrestrictive pipe so even if you have two 3" pipes it still must travel in a smaller pipe. The 4" setup is the way to go. I had mine built by my roll cage fabricator who actually built the y pipe as a true 4" (let me know if you want pics), instead of a y pipe to a 4" set up. And I run my 4" all the way to a rear muffler and exit pipe at the bumper. Sounds cleaner, quiter, and makes more power than my old tru dual and dumped set up.

Get a y pipe that has the merge collector as a true 4" set up

I just installed a set of ARH headers on my SSS and went with the dual 3" into single 4" with the Flowmaster Y. I used a Hooker Maxflow center in/out 4" muffler dumped in front of the axle and it's actually quieter than the stock exhaust with a drop in flowmaster muffler at idle and part throttle. It does scream at WOT but thats when I actually want it to be loud. I know this is in a truck and not a car but the sound is SWEET! Also if you look at the test in the FAQ section here you will see the Hooker Maxflow was the 3rd most power and the 2nd quietest. I think it's very overlooked for power and sound...it actually flowed the same as strait pipe in the test!

I sure am confused by some of the exhaust facts/recommendations in this thread. For one, unless there is a formula for exhaust flow that I am unaware of, the dual 3" has more area for flow than a single 4" (14.13 sq in to 12.56 sq in), secondly the dual 3" has much more surface area than the single 4" (18.84 inches to 12.56 inches) which from what I have always heard may not be beneficial in helping with the scavenging affect of the headers, but once the exhaust gasses get downstream that additional surface area causes the exhaust gasses to cool and condense which means even less exhaust size is necessary for the same flow. So in theory at least, not only would the dual 3" flow more to begin with, but the gasses would cool more as well meaning that the difference in flow values would only increase the farther back the exhaust went. Of course the downside will be the dual will be much heavier, may be more complicated to route, and lastly may be overkill for the op's situation.

Not to steal the thread, rather add to it. Here's the system I'm running, its a one-off piece and it probably more then I need currently.
http://i61.photobucket.com/albums/h44/hi-po2/IMG_0256.jpg
http://i61.photobucket.com/albums/h44/hi-po2/IMG_0258-2.jpg
http://i61.photobucket.com/albums/h44/hi-po2/IMG_0137.jpg
http://i61.photobucket.com/albums/h44/hi-po2/IMG_0138-1.jpg
http://i61.photobucket.com/albums/h44/hi-po2/IMG_0673.jpg
http://i61.photobucket.com/albums/h44/hi-po2/IMG_0267.jpg

Its tight against the driveshaft only when the suspension isn't loaded. Its actually almost 2" away when loaded.

There's also a DMH 4" cutout now about 10" down the Y pipe.

Something like this could be what your looking for. On your CI, you would benefit from this 4". On my current 6.0, I don't think its helping that much. Your looking at a pretty major HP increase just from exhaust, But, lots of money tied up here with Kooks, DMH 4", and a fabbed 4" though.

I sure am confused by some of the exhaust facts/recommendations in this thread. For one, unless there is a formula for exhaust flow that I am unaware of, the dual 3" has more area for flow than a single 4" (14.13 sq in to 12.56 sq in), secondly the dual 3" has much more surface area than the single 4" (18.84 inches to 12.56 inches) which from what I have always heard may not be beneficial in helping with the scavenging affect of the headers, but once the exhaust gasses get downstream that additional surface area causes the exhaust gasses to cool and condense which means even less exhaust size is necessary for the same flow. So in theory at least, not only would the dual 3" flow more to begin with, but the gasses would cool more as well meaning that the difference in flow values would only increase the farther back the exhaust went. Of course the downside will be the dual will be much heavier, may be more complicated to route, and lastly may be overkill for the op's situation.

It definitely won't be overkill for my setup, as my engine is severely choked down on the exhaust. I do see the weight being an issue, as all of that 3" piping would be a big pain. But, I literally almost have all thats needed for the setup, and just need to get a few more pieces. But, i do like the idea of a 4" exhaust with a 4" DMH cutout. That would be SICK.

I'll start pricing out some 4" stainless piping. Anyone have any good sources for this type of exhaust pipe thats a killer price?

This is what I have to work with so far...

Two SLP intermediate 3" stainless pipes. They will plug right into the 2-1 3" collector I'll get to put on the end of the y-pipe. Then all i need is the tubing from that point and the mufflers. I already have the corsa clones as well. So far I have only about 45 dollars in that piping. The rest of the piping would cost me about 300. So thats about 380 total for the pipes.

Now, if I could get an idea as to how much 4" piping would be?

wow that custom 1 off system looks like the y pipe is choking the crap out of that system. and think of the gas flow in a pipe as exhuast will flow together instead of gasses seperating. my fabricator put it this way. Exhaust gasses dont seperate so if it can flow in the least restrictive direction which would be the largest pipe. all i know is i made more power with 4" instead of my old 3" dumped setup and i moved from a 10 bolt to a 9".

wow that custom 1 off system looks like the y pipe is choking the crap out of that system. and think of the gas flow in a pipe as exhuast will flow together instead of gasses seperating. my fabricator put it this way. Exhaust gasses dont seperate so if it can flow in the least restrictive direction which would be the largest pipe. all i know is i made more power with 4" instead of my old 3" dumped setup and i moved from a 10 bolt to a 9".

I thought the same thing, definitely need to have a merge collector there to flow better.

Where are the pics of your system? Also, what mufflers were you running before with your dual system, and what are you running now on your 4"? Lastly, do you have the dyno sheet? What is the motor setup that you made more power with the 4" rather than the 3"? Just trying to get some more information, and a dyno sheet would be sweet.

It seems to be doing alright so far. Better then most setups so far.

Yea, i know they have it, and that the muffler blows. That's part of the reason why I'm probably leaning away from it. I don't want to have to purchase the whole deal, and then spend another 700 on a cutout, mufflers, piping, labor on top of the 600 it already costs.

Mufflex now has this:

Part# 98402CM
4 inch Catback Kit for 1998 - 2002 LS1 Camaro / Firebird
Fits 98-02 LS1 V8 cars with Dual type catalyist (or off road Y pipe form long tube headers).
This unit uses a Magnaflow ® straight through 4" race muffler.
Recommended for Turbo cars and cars with other power adders for extreme HP appilcations.
cars with other power adders for extreme HP applications

That is no different then what I have seen there. It is also a single hideaway tip, I want dual tips to the back. Thanks tho.

I love the Mufflex 4" system. I only have a 382, but was going to build a 427 or 440ish motor. Before I bought the system, they had me go to a site with a car running in the 8's with over 900HP with their 4" system. They claim their system will handle over 900HP.

I started with the Kooks 1 7/8"X3" Stainless Race Hedder and 3"ORY-Pipe. Then mated that to the 4" over the axle to the SpinTech muffler which exited to dual 3" pipes out the back, with the chrome tips they had sent. I had a friend fabricate the dual tips as I had the CME on the 02SS. It sounded great and got tons of compliments on the unique design of the exit of the tips. If I went to the bigger motors, I would definately get the 2"X3.5" hedders. I wish I had a sound clip. Cruising the tone was docile and when you nailed it, it sounded awesome. I had a convertible, so with the top down I could enjoy the sweet music, (tone). I will try to get pics as my computer crashed and am now on a laptop and I have temporarily lost all of my pics. I would recommend the BMR upper Panard bar which made much more room for the dual 3" or single 4" tubes over the axle. There were no problems, even with the factory heat sheilds intact.

Good Luck with your choice.

4" has more area than 2x3"


and how will that be ?

I thought the same thing, definitely need to have a merge collector there to flow better.

Where are the pics of your system? Also, what mufflers were you running before with your dual system, and what are you running now on your 4"? Lastly, do you have the dyno sheet? What is the motor setup that you made more power with the 4" rather than the 3"? Just trying to get some more information, and a dyno sheet would be sweet.

Sorry I have been busy but I just emailed then to you. The mufflers for the dual system were bullet mufflers but it has been so long I can't remember the make. The muffler I use now is a single chamber race flowmaster muffler that impressed me cause I hate flowmaster. I will have to look for the dyno sheets but I have the latest one if you want me to email it or put the dyno sheet on here. My motor is 100% stock short block with 243 patriot head's (small valves), T-rex cam, old flp hearders, victor jr, intake elbow with NW 90mm, and pro flow carb plate for nitrous. Nothing special lol.

Let me know if you need any more information. I can bolt the exhaust up if you want pictures on the car.

http://i154.photobucket.com/albums/s260/ssfast99/DSC02371.jpg
http://i154.photobucket.com/albums/s260/ssfast99/DSC02370.jpg

here is what i found on mufflex site


This unit is a 4" Catback Kit for The 1998 to 2001 LS1 Camaro & Firebird.

This unit features a Spintech tm Crossflow Style Muffler and Dual 3" Tailpipes along with Round to Oval Stainless Tips.