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VW TDI high performance and stock economy

5915 Views 11 Replies 7 Participants Last post by  BigDaddyTDI
I posted this on another TDI specific site, but I figured I would post it over here too so I could catch some other TDIers opinions :)

I have been thinking about modifying my newly acquired TDI. Diesel is a new thing to me, but I am very capable with conventional gasoline engines. I got rid of my "street" jeep to get this TDI for the sake of fuel economy but the hot-rodder inside of me has a hard time not modifying anything.

So in an attempt to heighten the performance of my Jetta while retaining the economy of it I want to ask if anyone has any experience with a dual stage set up on their car.

I am thinking the use of a dual-stage boost controller with one setting at the factory level and the other setting at a higher lever (dependent upon supporting modifications).

Accompanying the dual-stage boost controller would be a system for supplying the correct amounts of fuel for both boost setting. i.e. a factory fuel map for the factory boost and a tailored fuel map for the higher boost.

I have been doing a bit or reading but so far I have not seen anything specifically for the VW Jetta TDI that would support that? Or is there something and have I missed it? For the sake of my project I would not be against running two ECUs (one with the factory settings, or tailored to run as close to factory as possible with larger injectors, and one ECU with the custom settings) with the supporting wiring to be able to switch back and forth.

Supporting modifications would be ones that I hope (though I may be wrong) would not adversely effect the economy of the car when in factory mode and are as follows:

Better downpipe and exhaust throughout the rest of the car
Larger or more efficient intercooler
Larger injectors (which may have a negative effect on economy I hope proper ECU tuning can work out for the factory mode)

And for the sake of peace of mind, gauges to monitor boost, EGT and other functions that I may need to keep a eye on.

Thoughts? Please correct me if I am wrong in my thinking. I am actually taking this idea from a turbocharged gasoline (capri xr2) car I used to enjoy modifying.
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I'd advise against a dual setup. Stage 3-5 tunes are some of the most economical tunes availible at cruising speeds. There's no reason to switch to a lower boost map- this will only hurt mpg and defeat the purpose of modifying. Most modifications to increase power will also earn you 1-2mpg each. VNT 17/22 is a very efficient turbo- and in order to keep it clean and healthy you will need to use higher power levels somewhat regularly. With a good tune, IC upgrade, bigger injectors, and gauges.. you'll be set. Turning down the boost just decreases the amount of heat and pressure the turbo can get. This might end up doing more harm than good- a tuner can best decide how to mix fuel and boost with your exact setup.

Good luck, and have fun!
So what would be the maximum hp/tq that you can apply to the 1.9l? I want to do a serious build with mine but I need to find out what the limitations of the block and headstuds and so forth are?
There is so much involved in answering...

There are lower compression-ratio pistons and high performance rods available that let you push higher psi than head studs alone, gains to be had by modifying the intake manifold, ways to modify head to accept higher valve lift and aftermarket cams (Colt stage 2 for street or tdimeister cam for 11mm racing lift), you can buy or get a custom kit that allows bigger Merc 2260 turbos.

But what you really need is a way to go fast without snapping your axles or destroying your 3rd gear in your 02J transmission. Or maybe you need a European 6-speed meant for a diesel.. those will hold a little more torque but of course they're more expensive when they break.

I know you're looking for exact hp numbers, but those don't exist...
The torque peaks are what will break stuff, and by going to a lower compression ratio and bigger turbocharger you shift the torque peak up... raising the power and increasing redline while allowing torque levels to stay relatively low.

It's always going to be some kind of trade off in drivability vs. maximum power. My opinion is that stock internals are safe up to about 180hp. While adding more power decreases longevity, modified diesels tend to hold up very well under stress- as long as they get good maintenance.
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