The first thing after getting the engine in proper tune ought to be more fuel and the boost to burn it- not boost sooner. That means IP adjustment not changing the turbo. A VGT is great option- but let's let the folks here know that you have more fingers attached to you than 617's have VGT attached to them.

Spoken as somebody who truly has never had the pleasurable experience of driving a VNT equipped car.

A VNT is a far more noticeable change in performance than 20hp from the rack limiter. The rack adjustment and torque capsule will have no significant effect on low end torque since power is limited by the same air availability and the stock turbo's poor response time.

The graph curves tell all. The only difference between the two graphs is time and a GT2256V instead of a K26. There is no difference in fueling, only air.


Which curves would you rather have?

JDmills wants low end torque over anything else so clearly a VNT should be priority, if not a supercharger.
The GTA2056V from a Jeep Liberty or M90 supercharger from a Buick or Ford would be about ideal for his needs.

EDIT: Here is the video I was talking about earlier. Right is exhaust pressure, left is boost. http://www.youtube.com/watch?v=eM7SNOc3nMY Its interesting to watch the exhaust gauge, you can see how the vanes open and close to control boost through exhaust velocity (exhaust pressure). Try doing that with your T3!

Those are some nice looking graphs! I think they would look even better if you'd make the TC adjustment. I think bang for the buck wise and effort invested you get a better return from making IP and stock turbo adjustments first. Then once you catch the bug you'll have the motivation to design and execute a clean VGT tubo install like you have. I swear this summer I'm going to get that liberty turbo installed on my OM616 powered Unimog

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Bob D.
Parrish, FL
1 SDL, 1 D, 1 TD, 1 Mog

Its not a matter of what should be done first. Gaskets for adjusting the pump are under $5 and the IP takes 1/2 an afternoon to remove the rack limiter and about an hour or two to adjust the torque capsule. It can be done at any time, its not "one or the other".

Forced,

This graph shows output at the rear wheels, correct? If that is so, then a VNT would be just about all I am asking for. as your car has got to be close to 250 at the flywheel..

Is this after a bunch of fueling modifications? I am guessing that it must be?



...amazing how the low end is totally tranformed by a modern turbo.. I cannot imagine what a difference it makes when driving the car... but it has got to make a HUGE difference...

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46 WDX Power Wagon

84 300TDT daily driver

FI, how can torque with VNT (~195) be that much higher over the stock one (~137)? You're only supplying air earlier. Also the VNT HP is about 10hp higher over the stock one. Air alone can't do that.

The HP graph looks nice and smooth . Over 100 hp starting from 2900 rpm if I'm not wrong .

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1992 Mercedes 190D 2.5 turbo 5sp manual. EGT+boost gauges. Boost controller set to ~14.5 psi. 1 1/4 turns on full load adjustment. LPG injection. Next in the list is water injection.

The IP will limit fuel based on RPM, pedal position, and boost pressure. FI has increased boost pressure and therefore the IP should be allowing more fuel (thus more power).

For more power, get a 603. You're already 195lb-ft @ 2400rpm stock, and with close to 150hp and a higher RPM range, you can hold low gear longer for pulling or climbing.

If the 617 is free or already installed I understand.

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Gone to the dark side

- Jeff

But there's only so much fuel that the IP can provide, so only by increasing boost it doesn't necessarily mean you'll have more power (unless you're not burning all the fuel that is injected).

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1992 Mercedes 190D 2.5 turbo 5sp manual. EGT+boost gauges. Boost controller set to ~14.5 psi. 1 1/4 turns on full load adjustment. LPG injection. Next in the list is water injection.

I didn't increase boost, I made it build boost much sooner.

No, just the turbo change. Fueling is as stock for both runs (except the ALDA which was adjusted a long time ago).

Starting with 7psi of boost @ 2000rpm instead of 1psi. The engine has 30% more air available at the same RPM and boost builds much more rapidly from there. Notice the boost curves are opposite in profile, the K26 is concave while the VNT is convex.

You're somewhat right, but flowing that air more efficiently does. The compressor wheel is much more efficient at compressing air (72% for the T3 vs 80% for the 2256 at the same flow and pressure ratio), all the exhaust is flowing through the turbine instead of most being wasted bypassing it and the rotating mass is much lighter. All of that means less exhaust manifold backpressure, horsepower, is needed to drive the turbo.