"Sewer Pipe" Twin Turbo Exhaust

[Herr-Kuhn]

A couple shots of my dual 3" turbo-back exhaust for the twin turbo 32V S4. This DOUBLES my pipe cross sectional area. I'm estimating earlier boost rise and major ponies out of the barn on the north end. You don't realize how much larger a 3" pipe is compared to a 2" pipe until you see them side by side. This system uses the Borla XR-1 mufflers. With a turbo car, there is no scavenging or the like after the turbo...your only goal is to "get it out" with the least restriction possible. Any back pressure aft of the turbine shows up at about double that on the head end of the turbine. This is the "devil" of turbocharging...keeping exhaust back pressure as low as possible.

[Herr-Kuhn]

[Normy]

Nice looking. What does it sound like?

N-

[Normy]

So, the 928S2 turbo system; when is it going to come out?

N!

[Herr-Kuhn]

Not totally sure on the sound just yet since I'm not done...but indications are it will have a very deep and toned note.

Normy...I could build a system for that car, but we are back to a small market again. I never set out to build masses of these things, but rather to make some very unique automobiles that would be desirable in the market.

I should have the exhaust system done by Sunday

[m21sniper]

It'll probably sound a lot like this, but with a 'whistle' effect to boot:

http://video.google.com/videoplay?docid=-8806935301358640930&q=porsche+928+rain&hl=en

[Herr-Kuhn]

Yes it is something like that Sniper.

[Herr-Kuhn]

Here is another shot from the rear of the car. I have grafted the 3" dual system into a "stock" RMB. It is a rather nice looking array of bends. The exhaust is made in three pieces, two center sections and one rear section. I was able to have the same basic bends in each side of the system and all cuts are fully tangent. All in all this was a pretty easy job. I lost three days this week due to a bad flu, but I anticipate finishing off the welding today and tomorrow and painting up tye other side.

One interesting point of note is that the turbocharged car enjoys much lower exhaust temperatures as compared to a NA car...this is becuase the turbo takes 300 or so degrees out of the exhaust temps before you make it down the downpipes.

[rhjames]

so was your RMB 3 inch diameter as well?

if so, you should state so......

personally, I would have just done away with mufflers entirely, the turbos would keep the noise level down to a liveable (for some of us) level, and there wouldn't be any back pressure at all----

(EX: a friend of mine, back in the late '70s, had a '56 Belair with a potent small block and one of the early Accel turbo kits on it. He had no mufflers at all, just the turbo--single--keeping the noise level in check. Easy on the ears until he nailed it, and then it wasn't nearly as bad as dual and glasspacks.)

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Cancel my 3 inch system ideas----Hooker header sidepipes now on order.

Benefits:

lower under car temps
less weight
easily removed inner mufflers (for race applications)
4 inch main tubes

Detractions:

not sure if I'll like the Corvette sidepipe idea, but what the heck....probably catch S*** from the 928 crowd----OH, well.


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[Herr-Kuhn]

The whole system is 3" except for the first 8" of downpipe which is 2.25" which is closer to the size of the outlet of the turbine. You never want to just place a huge pipe right after the turbine...ideally it transitions up quickly, but not in big steps...you want the flow to smoothly transition out of the turbine wheel, not have steps where transitions take place. Additionally, the downpipes are divorced, meaning the turbine and wastegate outlets have their own paths and are then re-joined. The turbine pipe goes to a full 3" before the 1.5" gate pipe joins back into the fun. The RMBs are typically 3" at the discharge and about 2.25" on the inlet. Since I had the unit already here it was easy to just cut it off with the sawz all and move forward.

The mufflers I am using are stated to flow as high as a straight pipe. Without silencers the car would be too loud.

[rhjames]

a better detailed description, thanks-----

[Herr-Kuhn]

No prob...I have it back on the road again...the turbines are more audible now for sure.

[Danglerb]

I was just looking at this site, http://www.spintechmufflers.com/ What kind of power would you need to be making to need a 5" pipe?

[Herr-Kuhn]

A lot...a dual 3" is probably good to 800 HP, maybe even more.