Lettuce Discuss exhaust design

[AudiOn19s]

Scenerio: My car is extremely quiet...like can't hear it over other cars at the track quiet. It's also heavy in it's stock configuration.

 

Problem: When you run muffler bypass pipes (common) or even loud aftermarket mufflers on the 996 cars they sound like a busted ass truck from the late 70's. You know the ones that have that horrible BLAT sound but make no power and take forever to build revs. You all know you've heard a small block that makes < 200hp with a loud exhaust for no reason and that's what the 996 cars sound like with performance mufflers on them. Not a good sound at all.

 

Solution: The solution to making the car sound like a real 6 cylinder and to hear it scream all the way up to it's 8200rpm redline is to add an x-pipe in the exhaust system. This is where I'd like some input on design.

 

Stock exhaust travels across the back of the car, through a muffler then out. Banks don't merge ever in the OEM system. Picture of the OEM system:

http://www.porschepassion.com/996/99634engine.jpg

 

There are a couple of companies that make x-pipes for the car, only one of them has a reasonably priced product. Problem is I'm not completely sold on the design. Below is a picture of their design. Basically 2 U-bends with an open area in the middle. To me the primary flow here is going to be doing a 180 degree turn in the middle of the exhaust path. I'll get the sound I want but I'm not sold on this design. Am I worried over nothing, will the exhaust just follow the path of least resistance and I'm overthinking this? I want the car to sound better but I don't want to give up power in the process. Picture of x-pipe in question

http://www.fabspeed.com/images/996_GT3_54_1.jpg

 

Here is what I feel is a better design. Bigger cross section area, More of a true x-pipe with cross flow characteristics instead of a big u-turn with a cross section open in the middle. Problem is this company wants a REDICULOUS amount of money for it. (Porsche tax to the extreme).

http://www.gmgracing.com/products/porsche/exhaust/996/3.jpg

http://www.gmgracing.com/products/porsche/exhaust/996/1.jpg

 

So am I over thinking this. Is the first design inferior? Will they both still perform about the same? Or is the second one really better as I suspect?

 

I think in either case I can likely find someone local to build me what I want for less money than either, but I'm curious to hear thoughts on my questions above.

 

Thanks,

Andy

[Franchi]

To be honest, I have no idea. But subbed for interest!

[gbracing81]

I'm no expert on this stuff, but it looks like on the second pipe the exhaust will cross through from one bank to the other. In other words it looks as if the exgaust from one bank will "crash" into the exhaust from the other bank. I would think that would kill your power, especially in the upper RPM rang where exhaust pulses will be shorter. I like the first one better. I would think the area where both pipes bend and are joined together would help equalize exhaust pulses and help your power in the upper RPM. Just my thoughts, but I could be way off. I am very interested in what you find out about this.

[gbracing81]

Holy bejesus!!!!!!!!! That header is $5100 for SS or $6400 for titanium!!!!!!! The one in the second picture.

[greg1647545532]

^^^ that was my first thought as well. There's nothing wrong with a 90 or 180 degree turn in an exhaust system - it takes surprisingly little energy to change the direction of flow, as long as it's smooth. The second, more expensive design looks like it's more of an abrupt turn, where the exhaust then has to figure out which way to go and fight the other exhaust stream for the ability to get there.

[AudiOn19s]

aftermarket exhaust with no x-pipe

 

aftermarket exhaust WITH x-pipe...hold onto your panties at the 1:00 mark

[AudiOn19s]

Holy bejesus!!!!!!!!! That header is $5100 for SS or $6400 for titanium!!!!!!! The one in the second picture.

 

The center section alone is $2700

 

Their mufflers are $1700

 

The funny thing is, despite the fact that the stock exhaust is 2 1/4 diameter on a 380hp car there's maybe 15 hp MAX to be had from even the most expensive exhaust on the market for the car. It's really about shedding weight and adding noise.

[RyM3rC]

They both sound pretty secksy to me man. For that much money couldn't you have someone fab something up for much cheaper?

[AudiOn19s]

I plan on having something custom fabbed, it's a matter of which is the better design to use.

[Patterson]

Without even looking at price, both would exhibit scavenging properties. I woyld lean towards the second design with a true x fashion looking for power. And the wail from the exhaust would undoubtedly be sexy.

[AudiOn19s]

So the more I try to rationalize maybe the two U bends with the blend area would be better.

 

I think of a traditional x-pipe from my V8 days like this

http://s7d4.scene7.com/is/image/Turn5/48005?$s7product$

 

In the picture above exhaust flow is all going from right to left though.

 

I see what GBracing is saying though. In my case with the exhaust flowing across the car the two flow paths would be effectively running into each other at opposite angles as they flow into the true x design. Maybe the U bends with a common scavange area is better

 

Now I'm really cornfused and thinking out loud.

[Franchi]

The center section alone is $2700

 

Their mufflers are $1700

 

The funny thing is, despite the fact that the stock exhaust is 2 1/4 diameter on a 380hp car there's maybe 15 hp MAX to be had from even the most expensive exhaust on the market for the car. It's really about shedding weight and adding noise.

 

 

I'll never complain about exhaust prices again for my Mustangs. lol

[CRed05]

APR uses the first type on their B8 S4 exhaust. They claim that it's the best way they could have possibly made the X-pipe.

 

http://www.goapr.com/includes/img/products/exhaust_b8_s4_30tfsi_crossover_mid.gif

 

Either way it looks like the exhaust gas crosses over.

[Patterson]

I don't think the exhaust pulses will block each other. The firing pulse will pull the stalled side gasses through.

[zeitgeist57]

they sound like a busted ass truck from the late 70's. You know the ones that have that horrible BLAT sound but make no power and take forever to build revs.

 

:fa:

[DavidBaustert]

APR uses the first type on their B8 S4 exhaust. They claim that it's the best way they could have possibly made the X-pipe.

 

http://www.goapr.com/includes/img/products/exhaust_b8_s4_30tfsi_crossover_mid.gif

 

Either way it looks like the exhaust gas crosses over.

 

There is so much more at play than this diagram leads on.

[Science Abuse]

Go with the first design. The actual volume is greater (that 4pc welded cross section has less area), and the equalization of the pressure is all you want for sound. The second system is inefficiently produced for ridiculous cost, intended for buyers with more money than brains. It will likely have more ground clearance than option 1, though, so if you're draggin ass that may be a consideration.

[TTQ B4U]

to hell with the sound, the cornering of the car in those vids gave me wood. good luck with the mods. can't wait to see it out.

[Science Abuse]

aftermarket exhaust with no x-pipe

 

aftermarket exhaust WITH x-pipe...hold onto your panties at the 1:00 mark

 

Proof that a Porsche flat engine can be made to sound better... but never good. Maybe Stuttgart made it quiet for a reason.

[gbracing81]

There is so much more at play than this diagram leads on.

 

I am curious to know more on this?

[DavidBaustert]

Exit losses, entrance losses, all the turbulence your going to get from exhaust gas pressure colliding in the X, high and low pressure zones. Q=VxA... Your flow rate isn't going to change unless there's a leak, so that's constant. Area of the pipes don't seem to change, so that's constant, therefore no increase in velocity in that section.

[POS VETT]

Cross-sectional area, junction design, pipe parameters, bends, thermal parameters, exhaust pulse timing, stroke-bore parameters, turbocharged or otherwise, sound attenuation - all of them aside.

 

What did the dyno say ?

[Nate1647545505]

I heard Tom's pretty good with pipes, AMIRIGHT??

[AudiOn19s]

Cross-sectional area, junction design, pipe parameters, bends, thermal parameters, exhaust pulse timing, stroke-bore parameters, turbocharged or otherwise, sound attenuation - all of them aside.

 

What did the dyno say ?

 

Both companies claim HP and torque bumps. But both claim unrealistic levels as far as I'm concerned. And both also claim ther other's product has issues. GMG claims you will LOOSE power and torque if you ditch the cats on these cars....??? really???...I think they are just trying to justify 2700 for their center section with race cats. Last time I checked 996 cup cars had no cats and made 415 hp vs. the street car's 380. The only difference intake and exhaust and raised rev limiter. The motors are otherwise identical.

 

Nate and I had a good conversation about this the other day and I think we're on the same page.

 

Honestly I don't care about power increase at all, I just don't want to loose any power. It's all about weight and sound for me.....and not spending a million bucks to get there.

[POS VETT]

I heard Tom's pretty good with pipes, AMIRIGHT??

 

Yez ...

 

Both companies claim HP and torque bumps. But both claim unrealistic levels as far as I'm concerned. And both also claim ther other's product has issues. GMG claims you will LOOSE power and torque if you ditch the cats on these cars....??? really???...I think they are just trying to justify 2700 for their center section with race cats. Last time I checked 996 cup cars had no cats and made 415 hp vs. the street car's 380. The only difference intake and exhaust and raised rev limiter. The motors are otherwise identical.

 

Nate and I had a good conversation about this the other day and I think we're on the same page.

 

Honestly I don't care about power increase at all, I just don't want to loose any power. It's all about weight and sound for me.....and not spending a million bucks to get there.

 

Lots of hearsay; hard to tell honest facts.

 

Raised rev limiter does have the effect of bumping horsepower up to a point.