The 3L Challenge: 79.9 MPG US over 615 miles in a Jetta TDI

[G60ING]

I hope you did not block the driverside lower grill as its for the intercooler. 20 hours driving 47mpg, wow I know I could not do a challenge like that I'd probably shoot for 56mpg and get there in 12-13 hours but then again I have a lead foot in comparison.

[vtec-e]

Best of luck Tasdrouille. Can that u-bolt not rotate a little so the bolts are horizontal, or even on top? I know, it would make then harder to get a spanner or socket on but might be worth a try. You could even try a large jubilee clip. (is that what you guys call them?!) That would be clean and the bolt on that would be most accessible when on the side of the exhaust.

ollie

[tasdrouille]

Originally Posted by G60ING

I hope you did not block the driverside lower grill as its for the intercooler.

Yes I did, and I knew what it was for. I wanted the aero advantage, and I also like the side effect of warmer air. I was a bit deceived by the result on the IAT increase from the block though. Last week it was 85 F when I did an hour of highway testing logging stuff with vag-com, including IAT. Even with the intercooler fully blocked, I could not get IAT to go higher than 115 F with the kind of driving I do. I would like something closer to 150 F. I removed the snorkel between the fender and the airbox to help with that, but haven't looked at the IAT again yet.

[G60ING]

Originally Posted by tasdrouille

Yes I did, and I knew what it was for. I wanted the aero advantage, and I also like the side effect of warmer air. I was a bit deceived by the result on the IAT increase from the block though. Last week it was 85 F when I did an hour of highway testing logging stuff with vag-com, including IAT. Even with the intercooler fully blocked, I could not get IAT to go higher than 115 F with the kind of driving I do. I would like something closer to 150 F. I removed the snorkel between the fender and the airbox to help with that, but haven't looked at the IAT again yet.

If you want to pump hotter air into the engine then just bypass the IC.

[tasdrouille]

That's an option, airflow in the intake would also benefit from IC removal. But it was easier just to block external airflow to it and remove the snorkel. Plus it's fast to put it back stock if I need to.

[tasdrouille]

The first weekend's over, and it did not go as well as I hoped it would. I had to do a bit of city driving while in Montreal. I drove 400 miles and I'm a bit short of the half tank mark, which should come around 450 miles.

I'm over 70 MPG so far, but it's not quite the 3L/100 km (78 MPG) I was shooting for.

Back roads have some disadvantages. The quality of the rolling surface is frequently not nearly as good as highways, which can have a significant impact on rolling resistance. And every small town you go through have a stop sign or two.

On the other hand, I would totally fall asleep on the highway at that speed, but on back roads there are so many things to look at. I've seen a lot of nice places, and even if it took me nearly twice as long as if I had taken the highway, I feel it was worth it.

With 600 miles remainning next weekend, we'll see how far I'll make it on the tank.

[vtec-e]

Time to pull out all the stops! Best of luck.

ollie

[tasdrouille]

Success!

991.4 km and...2.94L/100 km that's 79.9 MPG over 615 miles!!!

Average speed for the tank as per scangauge was 40 mph. Max speed was 81 mph coasting down a mountain.

Here's the car with the wheel covers on.



I used mostly DWL, but climbed the hills at best bsfc and coasted down with the engine on all the time.

I should really get rid of my winter tires...lol

[ChrstphrR]

Congrats on breaking the 3L/100km barrier, tasdrouille!

I can't deny I'm quite envious. My TDI's having problems breaking 50mpg steadily, mostly, I think, due to the (once again) bad Mass Air Fuel sensor.

Your pictures show well enough what you've done aerodynamically, but, can you give more specifics about the driving techniques?

What sort of engine load do you try to maintain while accelerating to cruising speed?

Do you use cruise control to maintain your steady speed, or do you rely on your foot mainly, to hold a smoother cruising speed?

Is your speedometer slow compared to Scanguage's kph output, like mine?

---

I'm asking these questions given that most of the TDI engined VWs tend to behave similarily.

And in my case, the only difference between our cars are the level of aero modifications, the one year different model year (2000 A4 vs. your 1999 A3), and my full sized spare is on, so I only have three winter tires right now.

[tasdrouille]

Originally Posted by ChrstphrR

What sort of engine load do you try to maintain while accelerating to cruising speed?

I accelerate at 85% load to get up to speed. When I have to climb up a big hill I do whatever it takes to maintain the engine at 1750-1800 rpm, up to 90% load. If it's a big hill and I reach 90% load I will just let rpm decrease progressively to 1500 while maintainning 90% load and then downshift at this point.

Do you use cruise control to maintain your steady speed, or do you rely on your foot mainly, to hold a smoother cruising speed?

I seldom use the cruise control. I use it only so I can move my left leg around a bit as it's starting to stiffen after some time of only playing with the go pedal.

Even on totally flat ground I don't like the cruise control at low speeds (40 mph) as it have a hard time finding its speed and the car is kinda jerking back and forth. I will usually just pick a load and stick with it as much as I can, playing with the pedal to adjust the speed so I maintain a steady load.

Is your speedometer slow compared to Scanguage's kph output, like mine?

My speedo is faster than the sg output. SG speed it 5 kph slower than the speedo. The speedo is off.

I'm asking these questions given that most of the TDI engined VWs tend to behave similarily.

And in my case, the only difference between our cars are the level of aero modifications, the one year different model year (2000 A4 vs. your 1999 A3), and my full sized spare is on, so I only have three winter tires right now.

Yup, our engines are pretty much the same up to 2003 model yeay. Your car is heavier and have a bigger frontal area unless I'm mistaken, but the impact should not be all that great.