To 2.5" or more...

[dubCanuck1]

Ok, here's an addition to the "moderate" mods on a 1.6TD I posted last year.

I'm thinking 2.5" downpipe and back, including a free-flowing muffler.

Before I give 935Racer some more money for a downpipe, I wanted to exhaust the exhaust topic (ooo that's punny).

As a review, here's what the TD project will look like

FMIC
Governor mod (only partially solid, not completely)
More fuel
Way more boost
Engine pretty much rebuilt, likely with some coated bits
Gauges, gauges, gauges (I get 10 more hp each time I use the word "gauges" )

So my first question....how to calculate air flow through an intercooler and also how to calculate air flow through the exhaust. Is this a simple matter of determining the area of the opening or is there another factor involved?

I know if you go with a 3", you will need to plumb the exhaust under the rear axle (unless you like the bumpety noises).

If going with a 3" exhaust, what are potentially negative impacts on low end power, spool time, etc....

I'm taking my time on this and want to do it intelligently, so let's hear it guys.

[dubCanuck1]

Hmmm. I did a little research and I guess it doesn't really matter with a TD what size your exhaust is over say 2.5" There doesn't seem to be any detrimental effects.

Confirmation/rejection?

[Maarten]

2-2.5" is perfect.

If you go bigger the airflow will slow down quickly (blocking the gasses behind it) and even backdraft could occur.

[zagarus]

2.5 inch from turbo back into free flowing magnaflow muffler with tdi style tip is what im doing.  what is stock size by the way?

[BlackTieTD]

2.5 is plenty. stock is under 2"

[DVST8R]

I ran 3" for a long time, its a pain to plumb, you need a good patiant (sp?) fabricator, 2.5" is a lot easier and like everyone else says will flow plenty for what you are trying to achive, the only time I would start thinking bigger is for Malone, or Andy2, as there Big turbos, exducer is 3" or bigger and so there downpipe would be 3" too match, and you would want to continue that out back.

I never tested full 2.5" exahust but spool up and egt's on my car were no different running an open 2.5" downpipe as were running a full 3" exhaust including a dynomax bullet race muffler, and you could actually drive it for more then 15min, without getting a headache from the drone.

So to some up if you are going with a bigger turbo then the stock k24 / garrett conterpart, then I would concider a 3" all the way including dp. If not go with either 2.5" PP or 2.25" TT setups. Clear as mud??  :wink:

[dubCanuck1]

The mud is clear.

[zagarus]

what kind of mud is clear?!  geeez.

[dubCanuck1]

Yeah, I better stay off the funny pills.

[stewardc]

If not go with either 2.5" PP or 2.25" TT setups.

I know TT is Techtonics. What's PP ?

[BlackTieTD]

passenger performance out in BC

[stewardc]

passenger performance out in BC

Ah, yess, but I think they only make downpipes.

[LeeG]

Is anyone familiar with muffler bender program cards?  I googled and see that Huth (aka Midas) still sells these.  Basically the card tells you how to make a specific pipe for a car, ie cut pipe X inches long bend Y degrees at specified radius at Z inches from end, rotate pipe some degrees before next bend at ....etc.  So you can start with a straight pipe, spend some time with the bender then walk up to the car with expectations that it will fit like factory.

More years ago than I like to recall I worked in a brake and muffler shop.  First choice was to order pre-bent pipe for a job as it was cheaper that rolling our own.  But if something wasnt available the program cards provided a good alternative.  More to the point, we did lots of custom work, if we recorded what we did as we bent a custom pipe, we could come back months later and reproduce it, in just a few minutes.  The factory program card was also a great starting point for building a custom system with larger pipe, usually by eyeball you could see where to slightly adjust lengths or radius to make a larger pipe fit...record the changes you made and next time was easy.

So if us diesel guys had a 'open source' program card for a 2.5" system, you could walk into any well equiped muffler shop and have the pipes bent cheaply.  Even easily make it in say 3 pieces with slip joints so it could be boxed and shipped.  

yes, the bends are not zero crush, but you dont loose much internal volume on a bend unless it is tight radius and a large bend.  It doesnt look like a mk2 or mk3 has any particularly tight bends, I doubt you would see much difference in performance between a 2.5" mandrel bent system and a 2.5" die bent system.  The mandrel exhaust guys like to say how you can loose up to 20% volume with die bends, so worst case die bent 2.5" would be like a best case mandrel bent 2.25".

Does this interest anyone?  I dont have access to do this work anymore, but I will need an exhaust system soon, so I might be up for a cost share of developing this, within reason.   Then I'll be knocking on PP's door for a downpipe!

An aside, Walker shows their factory replacement exhaust system for a 90-92 Jetta as a mix of 2" and 1.75" pipe.

[zagarus]

im deciding on weither or not to take my car to PP or get it done here at a local shop that does a really good job, he handles most of the "not so legal" parts of exhaust systems, does an awesome job.

[zagarus]

so turns out that shop can't do a 2.5 inch exhaust on a mk2 jetta cause he says not enough room between the floor and axle. So looks like im gonna be dealing with passenger performance this summer, woot!  The shop cant even do mandrel bent, i say, "haha, amateur".  Diesel already sounds nice stock, deep and loud.

http://youtube.com/watch?v=mKPgqvrt1Do