If your turbo has a 2" outlet, and you have a 2" exhaust with no muffler, would you see gains by adding a 3" turbo-back exhaust?

What if you have increased the boost pressure to 25psi with fuel to match?



ps-I got my post-turbo alcohol-port-injection manifold welded yesterday

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$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment

In theory, yes. The less restriction after the turbo the better.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Yep. Not by much though.

Once you get into the 20psi range, you will probably start to see a difference. That's a lot of air to try and flow through the pipe.

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My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior

Yep! Take a straw from your favorite fast food restaurant, and blow through it. Now cut it to be two inches long. Blow again.... should be a noticeable difference. Whether it makes a difference for our specific application depends on how much back pressure we actually have, etc.

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John Robbins
'05 E320 CDI - 240k
'87 300TD - 318k

Isnt the turbo housing the most restrictive thing on the exhaust?

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2004 Infiniti G35 3.5L 6mt Coupe 73K miles 25.6mpg ytd
2001 Green Audi TT 225 AWD Roadster 71K 6sp 30.9mpg >>STOLEN<<
1982 300D Turbo 231K 120hp? 28.1mpg YTD

It is(especially mine-2.25" outlet)
But the straw comparison makes sense.

How loud do you guys think a straight pipe exiting in front of the rear wheel(passenger side) would be?

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$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment

The most restrictive thing in the exhaust is the turbine itself. The really short section of the turbo exhaust housing is going to contribute to the back pressure, but, there is no reason to limit the exhaust size to the turbocharger outlet... depending on the HP demands you could very well see a benefit.

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John Robbins
'05 E320 CDI - 240k
'87 300TD - 318k

The turbine is the biggest restriction. The less restriction after the turbine, the bigger the pressure drop will be and the more efficient it will work.

I ended up going with 2.25" (Recycled alot of the existing exhaust)
Tomorrow I've got to weld in the pipe going back and out in front of the passenger wheel.
Factory exhaust: 4x90* bends, 2x15* bends, and a muffler.
My exhaust: 2x90* bends, 1x45* bend, 1x15* bend.

Here's my fancy welded downpipe

__________________
$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment