Downpipe Theory, It can't be too big, Right?

[AudiVWguy]

Soon I will be swapping the current turbo with a IHI Ball Bearing Turbo. I've got to custom make the down pipe again. What if the DP came out of the turbo at 3in. and then immediately went to 4in till it went down and under the car to the flex coupler then back to 3in.
This allows the hot expanded gasses to get past the turbo, then start to cool and contract on its way toward the smaller rest of the exhaust.
Does this sound reasonable, or do I just stay with the 2.5in?
I would think that even though the size of the exhaust won't be consistent, the most important part is the first 18in after the turbo.
I'm just not sure if the giant PITA is worth the benefit.
Any Thoughts??

[Christian_Finland]

Go for the 3" down pipe but make sure there isn't any sharp edges on the turbo outlet to the down pipe to avoid any unwanted turbulens.


Here's a pic of my 3" DP.

[jtanguay]

3" is probably the biggest for these motors.  bigger on a diesel is always better, but mounting a 4" pipe would be very difficult.

gassers need to limit the size of the exhaust for vacuum purposes, etc.

[Christian_Finland]

gassers need to limit the size of the exhaust for vacuum purposes, etc.

In a gasser turbo engine it's the same deal as in diesel turbo engine. Anything restrictive after the turbo is bad for the EMP's.

[jtanguay]

gassers need to limit the size of the exhaust for vacuum purposes, etc.

In a gasser turbo engine it's the same deal as in diesel turbo engine. Anything restrictive after the turbo is bad for the EMP's.

on a turbo gasser yes, because the turbo acts as a restriction.

[Smokey Eddy]

Biggest you could go would be no down pipe and exhaust at all.

You you don't like that idea i'd suggest a 6 inch (or bigger?) down pipe that comes through the hood like a zoomy.

[AudiVWguy]

I was thinking of creating a buffer area that the exhaust pressure would have to condense and then continue thru the exhaust system. Remember how the 2-stroke motorcycle exhaust had "expansion chamber" design for the exhaust pipe. I was thinking along those lines.

[saurkraut]

I was thinking of creating a buffer area that the exhaust pressure would have to condense and then continue thru the exhaust system. Remember how the 2-stroke motorcycle exhaust had "expansion chamber" design for the exhaust pipe. I was thinking along those lines.

I used to race super mod two stokes, so I know probably way too much about expansion chambers.

An Expansion chamber is a sonic supercharger for two stroke gas engines.  With out going into the whole detail of their opperation, the pipe  accutually creats a vaccum that pulls fuel air mixture out of the cylinder/crankcase and into the pipe.  Meanwhile, the blast from the exhast port reaches the rear cone of the chamber, and a sonic wave is reflected back up the pipe, pushing the fuel air mixture back into the cylinder as the piston closes the port.

In summerey, none of that stuff applies to your engine.

Upon causal inspection, there's a Wiki article that provides a good explanation: http://en.wikipedia.org/wiki/Expansion_chamber

Lots of stuff going on in one of those pipes :wink:

[AudiVWguy]

OK,
I guess that was a bad example. I guess that somebody out there who's modding the Dodge and Ford stuff would have something out there by now if there were an advantage to varying the size of the down pipe.