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TDI Power Enhancements Discussions about increasing the power of your TDI engine. i.e. chips, injectors, powerboxes, clutches, etc. Handling, suspensions, wheels, type discussion should be put into the "Upgrades (non TDI Engine related)" forum. Non TDI vehicle related postings will be moved or removed. Please note the Performance Disclaimer.

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Old May 16th, 2018, 08:49   #1
4WDrift
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TDI(s): Jetta PD Mk4
Unhappy Where's the Power?

I need advice on what to do now.
Injectors?
Chip?
Tune?

I have very little bottom end power after a VNT17 swap. Is that normal?
The engine is getting old so I don't want to have to rap it out every gear shift. Even with the stronger boost on the top end this car is much slower getting to speed because of the loss of the bottom end.

If I were to guess I would say I went from
180 down to 80 ft.lb at 1800RPM on WOT.
and from 90 to 100 hp at 3200 RPM. Hard boost way up high at a higher point than where I used to shift...

I kinda hate the way it drives now.

Car:
2004 PD BEW Jetta TDI with 335,000 miles.
Original injectors.
no deletes.

I have not checked my compression.
I do not have intake buildup.
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Old May 16th, 2018, 09:14   #2
QuickTD
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Should have a tune for the larger turbo. I would also check the vane position lever stop screw. Run the charge pressure control test in basic settings, block 14. Set the stop screw to get a differential of 80-100millibar from vanes open to vanes closed.
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Old May 16th, 2018, 09:51   #3
Nevada_TDI
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You have increased the compressing volume with the vnt-17, but you have not introduced more fuel to feed it. Remember, "No Fuel, No Spool" that is the rule. A tune is required to remove the lag caused by the larger turbo in this case. Checking the movement of the turbo as mentioned above is a good idea as a start, as a maladjusted turbo cannot be fixed by the addition of a tune.
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Old May 16th, 2018, 10:04   #4
Vince Waldon
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A tune will wake your VNT-17 right up.

You may need/want to change to a 3 bar MAP as well... good discussion to have with your tuner, since that decision will be based on the maps used.
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Old May 16th, 2018, 17:34   #5
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You raised air capacity with the VNT-17, but haven't raised fueling one bit.

Fuel makes power. Air by itself does not.

You need to raise fueling, and provide enough air to burn it entirely. It doesn't matter if you provide this extra air from a turbo, supercharger, or a compressed air tank. It all raises charge air pressure, from which the engine suctions a dose of. Yes it suctions even the compressed air. It's a transfer of air from a region of higher pressure to a region of lower pressure.

Power comes exclusively from burned fuel pushing down a piston.

In addition to this, you didn't actually raise boost, as the ecu will try to get the same amount of boost from this turbo, as best as it can with corrective calculations.
Basically all that was done is introduced some lag, which the ecu does not expect.
You're ready for a tune now.
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Last edited by Enabled; May 16th, 2018 at 18:00.
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Old May 16th, 2018, 23:20   #6
[486]
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aren't smokemaps all MAF based on ALH and later?
there's more fuel going in just by virtue of the more airflow, though it's not much more because it's not much more turbo

another vote of check vane travel, spool sucks when they can't close down enough
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Old May 17th, 2018, 04:35   #7
oilhammer
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The OP has a BEW, not an ALH. The VNT17 is not a huge size change over the original BW unit.

However, if you do not do the VNT Basic Settings sometimes they will feel a bit laggy on the bottom end. And even then, they may not have the same bottom end as before, just depends on how you drive them I suppose. I find them to be fine, but I am not a "lugger", I rarely operate the engine below 2000 RPMs and never ever hammer it below that, I tend to roll into the power.

In any case, a tune will wake it up for sure. I mild tune on a VNT17 equipped BEW is a great combo.
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Old May 17th, 2018, 10:00   #8
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Quote:
Originally Posted by [486] View Post
aren't smokemaps all MAF based on ALH and later?
there's more fuel going in just by virtue of the more airflow, though it's not much more because it's not much more turbo

another vote of check vane travel, spool sucks when they can't close down enough
The MAF is used as negative feedback (smoke limiter), not positive feedback in ALH and BEW, CR too.

So more air simply allows to fuel up to the written limit for that condition. It will not add more fuel.
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-BMW 328is Manual (heavily modded 220whp, track toy)
-BMW Z3 Roadster (Fun in the sun car)
-BMW Z3 M Coupe (1 of 36)
-BMW 328d wagon (Self tuned ~230hp)
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Old May 17th, 2018, 10:47   #9
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One of the nice things about the BEW is you don't have to purchase larger nozzles for decent increase in power as there is "room" already there. Just get a tune and call it good.
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Old May 17th, 2018, 13:26   #10
4WDrift
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Quote:
Originally Posted by Nevada_TDI View Post
One of the nice things about the BEW is you don't have to purchase larger nozzles for decent increase in power as there is "room" already there. Just get a tune and call it good.
This nozzle feedback is very good information!
I was cringing at the thought of spending 400-800$ for larger PD injectors.
Just barely learned/read the PD Injectors are not DIY upgradeable as far as nozzle size.
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Passed the TDI to my daughter.
Then Blew it up, and now rebuilding him.

Last edited by 4WDrift; May 17th, 2018 at 13:29.
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Old May 17th, 2018, 17:59   #11
[486]
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Quote:
Originally Posted by oilhammer View Post
The OP has a BEW, not an ALH.
thus the "and later"
Quote:
Originally Posted by Enabled View Post
The MAF is used as negative feedback (smoke limiter), not positive feedback in ALH and BEW, CR too.
So more air simply allows to fuel up to the written limit for that condition. It will not add more fuel.
very good, you understand how a diesel is throttled, gold star.

point being, it does see the added airflow and allows the extra fuel so long as everything else is in order, without any ECU remapping
there's problems elsewhere such as it going into limp mode or the vanes not fully closing
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Old May 17th, 2018, 19:06   #12
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Woo! Got a gold star! And maybe some sarcasm too, but sarcasm makes things fun, so it's good.
Definitely not trying to contradict.

That would assume the smoke limiter is the lowest limit. Unfortunately it's not.
It's always the torque limiter.
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-2003 Jetta TDI GLS Manual (Mods: SBC II Daily, .681 5th, VNT17 & PP520, Self Tuned)
-BMW 328is Manual (heavily modded 220whp, track toy)
-BMW Z3 Roadster (Fun in the sun car)
-BMW Z3 M Coupe (1 of 36)
-BMW 328d wagon (Self tuned ~230hp)

Last edited by Enabled; May 17th, 2018 at 19:13.
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Old May 17th, 2018, 19:12   #13
[486]
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Quote:
Originally Posted by Enabled View Post
But that would assume the smoke limiter is the lowest limit. Unfortunately it's not.
It's always the torque limiter.
except when he says he's got less power than before with only a turbo change
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Old May 18th, 2018, 04:33   #14
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Quote:
Originally Posted by [486] View Post
except when he says he's got less power than before with only a turbo change
Except he didn't say that... he said the power band moved from down low to up high...at least, that's how I read it... and that has been my experience after doing this same turbo change, but not so much that I felt the car was "bad" to drive afterwards.

The Basic Settings can improve that if only just slightly, but if he is not liking the way the car drives now, that probably is not enough to make much difference. And the VNT will, eventually, learn on its own anyway.

I did one of these recently, and the guy loves it.... he spends most of his time in 5th gear on the Interstate at 70+, and he says it pulls nice now to pass someone... and he's owned the car since new. But he also said he cannot do a rolling stop through suburban stop signs in 2nd anymore as easily. So there is obviously a trade off.

But again, software will solve it... and improve it... drastically actually. The BEW has plenty of extra fueling left in it. And I know something mild like RC1 (which is what we usually do) won't make it smoke at all.
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