exhaust questions regarding max performance.

[dieselsnowmobile]

Nope, just PhotoShop.  Sorry there is no "complemented with some technical backup" with that picture that carrizog60 wanted.  I just took an exhaust off of a Pro-Stock Tractor at a NTPA Tractor Pull and pasted it on my hood.

I do have what I have been told is real technical data though.  I have heard that with diesel pickup trucks, i.e. Chevy Duramax Diesel, Dodge Cummins Diesel, and Ford PowerStroke Diesel, that when you straight pipe these trucks, you gain about 25 hp.  This is gained, as others have said here in this post, by allowing the turbo to spin more freely which in turn pumps more air in the engine for more power.  So, I would imagine that straight piping a VW TD that you would gain some horsepower.  Stock, these trucks run about 250 hp, 25 hp to that would adding about 1/10th more hp to it.  So, adding 1/10th to a VW TD would be about 7 hp.  This is a rough estimation tough, but still some technical data and there are many other variables that could make this estimation total inacturate when trying to compare it to a VW TD.

[foxracer1]

I would say you could easily gain ponies just from dumpin the factory exhaust and runnin some larger pipe. I personaly think the turbo is more than enough of a silencer so straight pipe here i come.

[935racer]

You can easily gain 10 whp and 20ft lbs of torque with a vw diesel engine from upgrading the downpipe, the power figures however dirrectly relate to your current state of tune (read: fuel).

[speedy]

I read this thread with interest as I am trying to decide what size exhaust to run on my turbobus conversion.  I was more or less down to 2.25" or 2.5".  I went to a roundy-round shop today and they had a good selection of 2.25" mandrel bent pipe so I went with that.  My gut feeling is that 2.25" is plenty for a 1.6TD, especially since the exit from the turbo is barely over 2" diameter, and the 2.25" is going to be much easier to fit than the 2.5".  If I am wrong, well... I suppose I may lose a couple of hp but I think I can live with it.

Now I have to pick a muffler - straight pipe is not an option for me, I need it Q U I E T but I think I can still get plenty of flow with a low-restriction, big bore muffler.  Is there any difference in mufflers for gas vs. diesel applications?

-Dave

[935racer]

The turbine outlet size has NOTHING to do with pipe sizing for a turbo diesel engine, mass flow does and remember that the exhaust gas is still EXPANDING after the turbine housing.

As for mufflers get a muffler you can see straight through, kind of like a glasspack.

[speedy]

Dave,

Now come on, the turbine outlet size has *something* to do with pipe sizing.     I broke out the vernier caliper and the turbine outlet size on the KKK K24 turbo is exactly 2.0" in diameter.  Not to mention that some of that diameter is displaced by the turbine itself so it is effectively less.

Yes I know that the exhaust gas is still expanding and that I *might* lose a couple of peak hp by using the smaller pipe but like I said, I'm okay with that.  I do not have a lot of space behind (well, in front in my application) of the turbine outlet which also factored into my decision.

When I think about the factory pipe which is what, 1-7/8" and crimped like mad at the turbine outlet for firewall clearance, going to 2-1/4" with mandrel bends ought to get me the vast majority of gains that are possible from a larger exhaust, wouldn't you agree?

-Dave

[935racer]

No actually the turbine outlet really doesn't have anything to do with the pipe sizing, if that was true the stock 1.9tdi should have a 1.5" downpipe... 2.25" mandrel bent will be fine for most applications still, you'll be fine.