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ssullivan 08-23-2020 10:05 PM

Shifting VW TDIs below 2000RPM?
Hello fellow TDI owners,

Curious what your practices are with regards to acceleration and shift points, and how it has impacted reliability. I understand that conventional wisdom is to imagine eggshells under the pedal. I believe with a stock diesel things are different, these have peak efficiency per bshp at relatively high load (see link). Just looking at the chart, you would want to get boost to around 7 bar, I assume 60-80% throttle, continue to accelerate to ~10bar, shifting maybe 1800rpm. I have a few concerns with doing this in my car, mainly ruining the bearings (lugging). This is also fairly rapid acceleration so discipline would be required to not dump that acceleration into the brakes.

I used to shift around 3000rpm based on something I read on another forum. Recently switched to 2500rpm. The deeper sound makes me more worried about lugging but I do not actually think it is. I have read some old threads, sounds like many people are shifting below 2000rpm. My question is, how long have you been doing this? What are your acceleration patterns? Have you had any major maintenance issues?

mpg_numbers_guy 08-23-2020 10:50 PM

In terms of economy accelerating at low RPM + high load is best, but I'm not sure how a turbo affects that.

I always thought shifting at 2K RPM or lower was best for diesels anyway because of the torque provided? Most semis have a 3K redline from what I've read.

In most cars lower RPM has a deeper sound under heavier loads (more noticeable with an exhaust leak) but that doesn't mean it's being lugged. You should be able to feel it when you're lugging the car by the car jerking slightly or hesitating when being lugged at very low RPMs.

ssullivan 08-23-2020 11:36 PM

Yes, I think you are exactly right. The difference is the TDI is more light duty than a semi, can make enough torque to bend rods, and redlines at 4600rpm. My friend has one that makes 220hp and revs to 6000rpm+ so you can drive them like gasoline cars.

In terms of friction, we know it is best to keep rpms low. On the other hand, too low at too high load causes damage. I thought gas engines were better to accelerate at low load. Maybe this pertains to automatics to lower the shift points?

Leinaad 08-24-2020 03:13 AM

My brother owns an Passat 1.9 tdi, my parents bought new in 2001. It has 430000 km so far. While accelerating slow I shift below 2000 rpm otherwise below 3000 rpm. There haven't been any issues regarding shifting early.

My 2.0tdi dsg shifts at 2000 rpm while accelerating slow and between 2500-3000 rpm while accelerating uphill. The transmission usually keeps the Revs at 1500 rpm.

GreenTDI 08-24-2020 12:11 PM

With my (very) light duty 3-cylinder TDI I can shift at 1800 rpm, but you can hardly speak of an acceleration. Engine speed falls back to 1000 rpm and there is no power. Besides, the engine will give a moody humm below 1500 rpm at load. It's a small engine and it has long gears ...


Originally Posted by ssullivan (Post 630002)

Curious what your practices are with regards to acceleration and shift points, and how it has impacted reliability.

In slow-moving traffic or slightly descending road, I do switch gear at 1800 rpm. Then I see no problem in it, at light load it doesn't act so grumpy :D But, if possible, I try to achieve the desired speed quite fast, with the lowest possible rpm's. So I switch at 2200 - 2300 rpm, the speed in the next gear will drop back to 1500 rpm, and that's the moment when the turbo kicks in. Done this for 80.000 miles without any problems. Engine (software) is stock - for now. It could benefit from a good remap, making more power available at low engine speeds.

ssullivan 08-25-2020 10:22 PM

Thanks for the input. I tried it the last two days. Seems pretty natural except say 1500rpm 50% throttle or more sounds like it is lugging. Depending on the gear 1500rpm happens shifting around 1900rpm. Seems I can start from idle (903rpm they say) after a long coast in 3rd maybe 4th gear (maybe down a hill) and accelerate very slowly. Sounds similar to what GreenTDI describes. Look at the chart again though, BSFC goes high at low boost/power and pretty much the whole rpm range. Worried it is "lugging" without making the sound. Just to be clear, lugging leads to bearing damage as the force is extremely high at extreme rod angles (to make power at low rpm). Still, in terms of efficiency, we are splitting hairs as the actual hp number is tiny and the chart gives consumption per hp (brake). After multiplying the two, fuel consumption is still small.

Anyone had plugging in the VNTs? That was the logic behind shifting at higher rpms if I remember correctly. Obviously, I am a little concerned about my engine bearings too. Anyone checked their intake manifold (they commonly are fairly blocked with carbon, I read).

It seems I'll be trying to shift to land around 1500rpm and if I need more power for some reason, downshift really quick. These cars don't seem to mind shifting fast.

ssullivan 08-25-2020 10:27 PM

Oops, looks like the link to the efficiency chart did not make it. Not able to make it work in the [URL] format

mpg_numbers_guy 08-25-2020 11:43 PM

If shifting below 1500 RPM affects engine performance then don't do it.

Here is the referenced image:

ssullivan 08-26-2020 01:29 AM

Thanks for posting the image, I see the button now.

I am getting a feel for it. With less load I would feel comfortable accelerating very slowowly from 1200-1300 rpm. For higher load, higher rpm to avoid lugging. I do not plan on accelerating from idle in gear 3, 4, or 5.

That brings up a good point. The tune really reminds you it is a computer sometimes. I am convinced it could make more power at any rpm, but particularly in the low rpm you can feel the computer cutting power as rpm drops. I suspect they did this for a reason.

Still interested in whether people have experienced engine bearing failure, VNT (variable vanes in turbo) plugging, maybe surprise engine mount or DMF (dual mass flywheel)...

JSH 08-31-2020 04:49 PM

When I had my 03 TDI w/ 5 speed I would shift about 2300 - 2500 RPM which would drop the engine back down to peak torque for the next gear. I accelerated briskly but not wide open to the speed I wanted and then shifted to 5th.

That usually ended up being 1st to 2,500, 2nd to 2,500, 3rd to speed, shift to 5th. (This assumes an open road ahead without a traffic light a block ahead)

The only engine related issue I had in 240K miles was the intake manifold plugging up with soot every 100K miles.

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