Dual exhaust vs. single pipe?

[RedMisted]

I've got a dual catback system on my car that was originally equipped with a single exhaust pipe. Yeah, I know. Racing with a street system....

Obviously, I want to dish the converters and swap out the stock exhaust manifolds for long tube headers.

Question: Should I retain the dual exhaust or switch back to a single pipe? My engine is a 3.8L V6 putting out about 190rwhp. It has yet to be opened and prepared to the full limit of IT.

Really confused as to which way to go.

[ITA_honda]

I say single pipe:026:

but what do I know, Im just one of those Honda drivers...

You'll figure it out one way or another, Chris

[JeffYoung]

You probably should wait on a full tilt exhaust program until you get the motor "IT built" (and 190 rwhp before doing so is damn good), but my guess is the following:

1. You will find that way smaller primaries than you expect on the headers will make more useable power.

2. You will find that for your motor, 4 into 1 short tubes (30-40" range) will make the most power.

3. You will find that a merge into a single side exit of tuned lengthy will make the most power.

Start with www.headerdesign.com (it's free) and then talk to the guys at Burns Stainless. Most of the off the shelf stuff for street cars in exhaust world is done wrong when it comes to racing.

[joeg]

Jeff- "4 into 1" ? How many cylinders.

[Tristan Smith]

Jeff- "4 into 1" ? How many cylinders.

He thinks everyone drives a V8.

[betamotorsports]

Here's what I'm planning on building for the 3.5L V6 in my Nissan 350Z:

30 to 32" primaries (don't know the diameter yet) grouped 3 into 2. The first collector will have a 15 degree merge to a 2" outlet. Secondary pipes will be 6 to 8" to the final merge collector with 15 degree merge, 2.5" outlet, 7 degree cone to a 3" final end. 3" exhaust all the way out the back with a Borla XR-1 Raceline muffler and room to mount a 3" SuperTrapp for the tracks with noise restrictions.

[JeffYoung]

That's funny - you got me Tristan...lol...

Red, sorry man, I saw Mustang and assumed you had a V8.....not sure the proper primary arrangement in a V6.

He thinks everyone drives a V8.

[RedMisted]

That's funny - you got me Tristan...lol...

Red, sorry man, I saw Mustang and assumed you had a V8.....not sure the proper primary arrangement in a V6.

Apologies accepted. At first I thought maybe I wasn't getting something!

It sounds to me like I'd better do my homework thoroughly before I plan any further exhaust mods. The common assumption is that long tubes mated to duals is the way to go, but not always. Of course, the cats should go because they are needless weight, but the remainder of exhaust science remains somewhat of a mystery for me.

It's interesting...Somebody pointed out in this thread that I should wait to prep my engine to IT specs before I plan the exhaust system. I thought it would make more sense to do the simple stuff first, but the complexities of engine modding may demand otherwise.

[Tristan Smith]

For the new ZX I am running dual exhaust with an x pipe. Believe it is 2.25 in diameter pipe. I found a complete exhaust cheap, with headers (I won't even speculate about how good the design is on the headers) so it is easy for now. Of course I plan on running the stock motor this year. I may change things up when I finally build a race motor.

[billf]

Chris,

I too have pondered this question. My original thoughts were to end the exhaust into a single pipe (3 in) open until it proves to be too loud.

If I could point out, the exhaust pulses of the V 6 are even on each bank, which is different from V 8's, therefore the equalizer pipe is probably not needed. If you merge to primarys into a common pipe, the equalizer (balance) pipe is created, anyway.

When I actually get the car project started, I will go this route for the simplicity of it.

I'll remain curious which option you choose.

Bill

[JeffYoung]

It's going to be a while before I even look at my ZX. I have a set of Stillen headers, not sure what they are worth, but would sell them to you for a fair price. If you aren't interested, understand.

Red, if I were you, I wouldn't spend big bucks on headers and exhaust until the motor is built. Then talk to Burns.

For the new ZX I am running dual exhaust with an x pipe. Believe it is 2.25 in diameter pipe. I found a complete exhaust cheap, with headers (I won't even speculate about how good the design is on the headers) so it is easy for now. Of course I plan on running the stock motor this year. I may change things up when I finally build a race motor.

[RedMisted]

Red, if I were you, I wouldn't spend big bucks on headers and exhaust until the motor is built.

Why is it critical to have the motor built first?

[planet6racing]

There is a great article in this month's Racecar Engineering regarding exhaust design. I'd recommend reading it, running through some of the calculations, and making a decision from there.

[JeffYoung]

A "built" IT motor will breathe differently than a stock one, and the exhaust should be built (in a perfect world) to account for that. Check out the spreadsheet on the Burns Stainless page and see some of the parameters they use to build a custom set of headers and exhaust -- some of those parameters can change with an IT build.

Why is it critical to have the motor built first?

[RedMisted]

A "built" IT motor will breathe differently than a stock one, and the exhaust should be built (in a perfect world) to account for that. Check out the spreadsheet on the Burns Stainless page and see some of the parameters they use to build a custom set of headers and exhaust -- some of those parameters can change with an IT build.

Jeff:
That sounds about right. But where I am now with money, I couldn't afford to do the IT engine build. In the meantime, I'd still like to modify my exhaust for any gains that can be realized.

[JeffYoung]

Understood. Then, what I would do is buy some off the shelf headers, and have an exhaust shop with some race experience build you a "rough" no cat straight exhaust, and run that for a few years until you build an all out IT motor.

[RedMisted]

Understood. Then, what I would do is buy some off the shelf headers, and have an exhaust shop with some race experience build you a "rough" no cat straight exhaust, and run that for a few years until you build an all out IT motor.

That's what I'm thinking. Just keep it simple until I can really go to work on the motor. Thanks for the help. I'll do my research for when that day comes.

[planet6racing]

Using the information from Racecar engineering, you could build a pretty good system for your current motor for pretty cheap. I don't have the article in front of me, but it has a lot to do with where you put the transitions (i.e. 2 into 1 collectors, etc) and the volume of gas exhausted from the motor. It is worth the read and the time to build the spreadsheet and figure it out (imho, anyway). It will also help with selecting off the shelf components because you'll understand the advantages and disadvantages of each design.

[Tristan Smith]

It's going to be a while before I even look at my ZX. I have a set of Stillen headers, not sure what they are worth, but would sell them to you for a fair price. If you aren't interested, understand.

Thanks, but the ones I have seem to be a Stillen knock off. As a matter of fact, just about every aftermarket header I have seen looks the same. Like a Stillen knockoff. Maybe it's "THE" design, and maybe custom headers will need to be fabricated down the road. All problems for later. Hopefully the cage will be completed by next Saturday and the build can finally start to move forward.