Shift points for TDI

[Mustang Dave]

Originally Posted by redpoint5

... Accelerating at peak torque is most efficient. Shifting earlier would be less efficient.

For anyone wondering what is the most efficient way to accelerate, just find the peak torque and try to keep the engine RPM in that range during acceleration. Once up to cruising speed, bring the RPM way down.

I must be doing it all wrong with my Mustang. I shift between 1500 and 2500 RPM, depending on driving conditions. Peak torque is @ 3500 RPM. I rarely see 3500 RPM on the tach.

[Varn]

If on the flat, I usually let the clutch out at idle without the throttle, shifting so that I have the car in top at 30 mph. I don't skip gears but let each ratio do their job, to let the engine work efficiency. My car is an IDI with only 68 hp, doesn't have a tach YMMV.

[amdown]

Originally Posted by AndyBees

The Turbo can be "exercised" for working purposes without taking the engine up to 4000 or more RPMs. If you get on it (above 2100 RPM) with a steady push on the pedal taking the RPMs up to 3000 ..........the boost will max for an instant!..... shift and do it in the next gear. That means the Turbo actuator went full range. I've practiced that method and have never had any issues with my Turbo (still original). I do take the RPMs up to 3600 to 4000 at least once per tank of fuel.

You do not have t o accelerate rpm up to 4000 to "exercise" turbo actuator. it makes full movement already up to 1900 rpm, when ecu is "asking" full boost from turbo. when you rev up engine higher, the actuator acualy decreases turbo pressure. The exhaust gas flow and heat is what actualy cleans vanes of vnt turbo. when you realy want to clear a turbo vanes drive for a mile or two with rpm at about 3000-3500, then the heat an lean burning from the engine will burn up all the ash in turbo and exhaust system.

[AndyBees]

Originally Posted by amdown

You do not have t o accelerate rpm up to 4000 to "exercise" turbo actuator. it makes full movement already up to 1900 rpm, when ecu is "asking" full boost from turbo. when you rev up engine higher, the actuator acualy decreases turbo pressure. The exhaust gas flow and heat is what actualy cleans vanes of vnt turbo. when you realy want to clear a turbo vanes drive for a mile or two with rpm at about 3000-3500, then the heat an lean burning from the engine will burn up all the ash in turbo and exhaust system.

That's a new one on me!

So, the little old lady driving style (babying it) isn't what causes the VNT15 to stopping working?...........Hmmmm

Well, I've disassembled "numerous" VNT15s for cleaning. I've yet to find one with the VANES all clogged up! The ACTUATOR operates the internal levers that in turn move the VANES in the path of the Exhaust blast coming out of the manifold. Soot gets blown back into the "internal" working parts of the VNT15 away from the exhaust gas blast. That soot, along with moisture, during slow warmup will eventually restrict the movement of those parts. I've seen VNT15s that the ACTUATOR would not move but the VANES were perfectly clean! After disassembly, cleaning and re-assemble, the ACTUATOR had full movement with no restriction at all!

There's a "ton" of info about the VNT turbos on the net and specifically at the TDIclub.

The ACTUATOR operates per the N75 valve which is re-acting to ECU demand. As demand for more power (during acceleration) the angle of the VANES is changed by demand of the ECU to direct the exhaust gas on to/across the blades of the Turbine for additional boost. I run a ScanGauge and have never seen maximum boost at 1900 RPM, quite the contrary!

I repectfully disagree with your assesment of the operation of a VNT15! Reading and hands-on are quite different.

[euromodder]

Originally Posted by Mustang Dave

I must be doing it all wrong with my Mustang. I shift between 1500 and 2500 RPM, depending on driving conditions. Peak torque is @ 3500 RPM. I rarely see 3500 RPM on the tach.

Nah, just driving different engine technology.
You're using those cubic inches as they pump out more than enough power, and keep the rpm low.

With petrol engines you can't shift at peak torque for economy because it's usually far too high up in the rev range - but that's changing on downsized, turbocharged petrol engines like the newish Beemer 20i, 25i and 28i.They have their max torque from way down on the charts.

[amdown]

Originally Posted by AndyBees

T

I repectfully disagree with your assesment of the operation of a VNT15! Reading and hands-on are quite different.

I have rebuilt turbo on my car myself.

when I start my car turbo actuator right away pulls vanes into position to max boost. for my car it is 20% PWM signal for n75 valve. While driving when turbo spools up and boost rises, the actuator moves back an turn vanes to reduce boost up to 99% PWM signal for n75.

The only car i have seen which at idle is not pulling actuator for max boost is lupo 3L.

A lot of times I have seen that cloging of VNT vanes is due to bad (cloged) catalytic converter.

[powerlifter405]

Originally Posted by amdown

If i would shift ta 2500- 3000 RPM and press acelerator pedal about 70%, then it feels like I am going on drag race So there is no point off reving engine up to 2500 - 3000 when presing acelerator pedal up to 30%

All I know that driving at peak torque would kill turbo and engine a lot faster, because at that RPM engine is developing peak torque and all engine components are at maximal stress. (I am also a car mehanic and i know what I am talking about). In my lupo I already had rebuilt my engine, including new turbo.

vw also suggests that shifting early is better for MPG. And as I know, construction of PD TDI engines and new bluemotion engines are not so different either, both have direct injection and VNT turbos.

Shifting will be engine, drivetrain, terrain dependant. Anyone who says not to shift the 7.3 PSD at peak torque, when under load, doesn't understand diesels. IH and Ford recommend a shift range w/ the 7.3 and the 6spd to occur between 1800-2000 rpms, right where the peak torque is. It doesn't kill the 7.3 and it for sure wont kill the turbo.

I had an 02 7.3 PSD and I short shifted that 8k truck all the time unless I was loaded. 18 mpg for a 8k brick wasn't bad but I did well due to shifting around 1500, just under the peak torque.

OVERSPEEDING a turbo is what kills them, besides lack of oil. A stock 7.3 turbo will live forever under factory injectors and factory tuning going 250-300k miles as a pulling/hauling vehicle. However, a simple "chip" add on creates extra boost that, over time kills the turbo due to repeated over speeding, and even for the aftermarket GTP38R Garrett Ball bearing unit, they recommend not to exceed 40lbs of boost.
I know that aftermarket HO Precision and Bullesye turbos die from being oversped.

FWIW, having owned two large vehicles there is a variable that people some times forget and the 14mpg semi on this forum should be a reminder to all:

1) Keep rpms as low as possible w/o lugging the engine. It takes fuel to make revs. He's running 1200rpms @ 55. A member on another forum I frequent is getting 24mpg hand calc in his 8800lb F350, dynoed at 700Hp. He got the hwy #'s by using 3.31 vs the factory 3.73, keeping rpms low.

2) Aerodynamics. Factory cars will never get super duper mileage from the factory for now since the public as a whole doesn't want bullet cars. This also falls back w/ RPMS, it takes more fuel to push your barn door or even your small door through the air, the faster you go the more fuel that is burned.

3) Parasitic loss, poorly lubricated drivetrain components, sticking brakes, etc.. I noticed a 2 mpg drop recently and i had a caliper sticking. Fixed it and things are normal again.

I come here to pick up some ideas and its interesting to see the innovation that is made.
I truely miss the 50mpg, in stock form, mid 1980's honda civic. People get exicted about a 30 Honda accord, oh how we've forgotten what was not only possible but what was.

Really, if you are a mechanic and have experience w/ cars and diesels. You should feel comfortable and know to take advantage of the torque the TDI provides. Shift just above the lugging point so you're not having to go beyond what your current throttle position is and still provide enough power to continue at your desired rate of accelleration. I'd say there is no magic # as I mentioned before there are plenty of variables to discredit a set RPM #.

[amdown]

Complitely agree to your points. I love to have a car that is esaly capable of 66 MPG

As I see in this forum, it seems there are a lot of Americans, who has not have so much experience with TDI engines. In my opinion if some one says you must to keep your RPM at 2500 -3000 to get good MPG, then he does not know nothing about diesel engines (more over about TDI).

[powerlifter405]

Originally Posted by amdown

Complitely agree to your points. I love to have a car that is esaly capable of 70 MPG

As I see in this forum, it seems there are a lot of Americans, who has not have so much experience with TDI engines. In my opinion if some one says you must to keep your RPM at 2500 -3000 to get good MPG, then he does not know nothing about diesel engines (more over about TDI).

Anyone, American, Brit or whatnot, who claims that is a good rpm range is a fool but whatada do? The TDI is a neat little engine and I'd love to pick one. My buddy has a NA diesel in his 80 something rabbit truck and gets 45mpg. I'm trying to talk him into a small turbo to help w/ his low end torque but he's hesitant. Banks, which is over priced/over hyped, has a kit for the NA 6.2 and 6.5 chevy diesels and they see improvements in both daily mpg and a small HP jump.

Good luck w/ the 70 mpg goal . My 1st goal is a repeatable 20 mpg w/ my 600hp setup. If I can regear and start working on some aerodynamic improvements I hope i can get maybe 23-24 repeateable at hwy speeds. I have a lot of hurtles but it will be interesting to try.

[ecomodded]

With my ko3 turbo when at 1000 rpm and i give it half throttle my boost goes from 0 to 20lbs for a spike then settles at 15 lbs until i release the gas pedal.
At 1900rpm my car is making full torque, I need about 1/4 of the torque to accelerate, attempting to use the whole torque is non sensible unless you are in a race or are trying to tow a house.

Anybody with a boost gauge and vnt turbo should be aware of boost levels.

~ A health monitor for the turbo ~

A boost gauge may be the best thing you could do for your turbo, You can see over boosts and no boost problems and anything in between.