Optimal RPM for maximum fuel efficiency

Blue_Thunder

Veteran Member
Joined
May 22, 2004
Location
Beetle Nation
Could somebody tell me what the optimal RPM would be for my TDI-PD for maximum fuel economy? I've read 2,000 RPM and 2,500 RPM.

2,000 RPM on my TDI-PD, DSG Beetle puts me at precisely 60 miles per hour, in sixth gear.

2,500 puts me up around 65-70 mph.

So, does anyone have technical knowledge on what the most efficient RPM is for highway cruising?

Thanks.
 

tditom

Top Post Dawg
Joined
Sep 5, 2001
Location
Jackson, MI
TDI
formerly: 2001 Golf GL, '97 Passat (RIP) '98 NB, '05 B5 sedan
2000 rpm will net you better fuel economy than 2500 rpm. The max torque in the PD is supposedly available from 1800-2400 rpm. Wind resistance comes into play over 60 mph, so slower = better mileage.

hth
-tom
 

Drivbiwire

Zehntes Jahr der Veteran
Joined
Oct 13, 1998
Location
Boise, Idaho
TDI
2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI


The best range falls within the 1900-2200 rpm range give or take.

DB
 

tditom

Top Post Dawg
Joined
Sep 5, 2001
Location
Jackson, MI
TDI
formerly: 2001 Golf GL, '97 Passat (RIP) '98 NB, '05 B5 sedan
DBW- Do you have anything like that for the PD engine? The VW web site states 177 ft-lbs from 1800-2400 rpm.

-tom
 

maxforce

Veteran Member
Joined
Aug 17, 2003
Location
VA
TDI
04 Golf, 04 Jetta, 84 300SD
I will give up a couple of miles per gallon to try and keep the intake clean and have a more "spirited" drive. I shift at 3k to 3500 and have averaged 49.2 for 25000 miles. As high as 55mpg.
 

dbb635

Well-known member
Joined
Jan 28, 2004
Location
Montreal, Canada
TDI
2004 Jetta Wagon Wheat
I have a Tip with 19000km on it now, I usually get 750-800km per tank vented with about 58.5litres. If I'm not mistaken, that works out to about 30mpg us and 35 Imp MPG. I cant understand how I regularly see 50+ with these cars, I know I am in traffic for a minimu of 1hr per day, but 15 pg diff seems quite high. I'm not complaining, just confused...
 

Ramsey

Veteran Member
Joined
Jun 15, 2004
Location
Madison WI
TDI
2004 Jetta in Graphite Blue
The tiptronic is still an automatic, and they all lose efficiency in the torque converter. I rarely hear of automatics doing better than 38. main reason I didn't get the passat wagon.
 

fresheverytime

Well-known member
Joined
Dec 10, 2002
Location
Burlington ON
TDI
2004 TDI PD
My best tank so far is 901kms with the Tiptronic... 54.6l to fill (vented) -> Low fuel light came on as I was pulling into the station.
33000kms on the dial and:
Lifetime average of 6.27 l/100kms (37.54 mpg)
Best tank of 5.13 l/100kms (45.86 mpg)
 

TornadoRed

Top Post Dawg
Joined
Aug 3, 2003
Location
West Des Moines (formerly St Paul)
TDI
2003 Jetta TDI wagon, silver; 2003 Jetta TDI wagon, indigo blue; 2003 Golf GL 5-spd, red (PARTED); 2003 Golf GLS 5-spd, indigo blue (SOLD); 2003 Jetta TDI wagon, Candy White (SOLD)
I know I am in traffic for a minimum of 1hr per day, but 15 pg diff seems quite high. I'm not complaining, just confused...
I spent 90 minutes driving home this evening, about 30-35 miles. Mostly in 1st and 2nd, occasionally 3rd gear. This tank will suck for fuel mileage.

If you want to see 45-50 mpg (US), then change your job and residence so you have a nice long 55 mph drive with no stoplights or traffic.
 

Wee_Car

Well-known member
Joined
Jun 28, 2004
Location
Maine
TDI
2003 Jetta TDI Black
I think you will find your best fuel economy at about 1500 rpm or at 45-50 mph. My wife regularly gets high 50's with her '03 manual on a 26 mile commute with only two traffic lights and a steady 45-50 mph speed. My moms '04 tiptronic can't get out of the mid 30's and I doubt it will gain much more, even after breakin. When I drive my wifes car, I shift at least 1000 rpm higher and drive at least 10 mph faster. My fuel economy is about 45 mph, so there is a big hit on how you drive these things. BTW my Ford powerstrokes get their best fuel efficiency at about 1400 rpm according to the computer.
 

Xgaz

Veteran Member
Joined
Sep 20, 2004
Location
West of Montreal, Quebec Canada
TDI
2010 Jetta TDI Highline, 2004 Jetta TDI Sport
I've noticed the same for my Tiptronic, so now I'm driving it as if it's a manual tranny.

Anyone know if that will make a difference in the milage?
 

TDIMAXIMA

Top Post Dawg
Joined
Jul 5, 2004
Location
MARKHAM, ONTARIO, CANADA
TDI
2004 4motion Passat 5 speed 1.8t
For canadian drivers, I get between 900-950 km's a tank right around the fuel light comes on. I drive 98% on the highway of probably an average speed above what is posted. I think my mileage is ok, but not amazing, but my speed is the reason, Im regulary over 3000rpms.
 

PolarBear

Member
Joined
Sep 25, 2004
Location
St-Lazare Qc
TDI
Golf GLS 2004
My present average is 5.3L/100km on an average of 50litres fillup. My best up to date is 5.1L/100 (968.8Km on 49.4 litres). My driving is mostly highway with an avg. speed of 120Km/Hr. I shift @ 2000rpm to 2100rpm and easy on the accelerator. Heck of a difference with my previous vehicle: 1/2 ton Chevy Pick-up with 125Litre tank Ouch!
 

rickdick80

Veteran Member
Joined
Mar 16, 2004
Location
Detroit near-northern suburbs
TDI
Golf GLS 5spd, 2004, Reflex Silver
DBW-

Does that graph only represent WOT curves? I wonder if the torque peak

[edit: it is my understanding that torque peak and BSFC peak tend to be nearly on top of one another]

occurs at the same engine speed at 10% throttle, 20% throttle, etc. Does anyone know if torque peaks tend to shift due to throttle input?
 

TDI_04_Driver

Veteran Member
Joined
Sep 9, 2004
Location
Canada
TDI
Golt TDI, 2004, silver
Mid to high thirties per gallon, now low 40s per gallon.
Thanks! I'm currently getting about mid-30s and it only has 1600Km (1000 miles) on it (with a tiptronic) and mostly city driving. Since most people say that the original oil is special to break-in the engine a bit quicker on my first oil change at 8000Km (or 5000 miles) should show a good change in mileage.
 

TornadoRed

Top Post Dawg
Joined
Aug 3, 2003
Location
West Des Moines (formerly St Paul)
TDI
2003 Jetta TDI wagon, silver; 2003 Jetta TDI wagon, indigo blue; 2003 Golf GL 5-spd, red (PARTED); 2003 Golf GLS 5-spd, indigo blue (SOLD); 2003 Jetta TDI wagon, Candy White (SOLD)
Mid to high thirties per gallon, now low 40s per gallon.
FWIW, most folks should be observing better mileage numbers now than a couple months ago. Less or no AC usage, but the fuel isn't winterized yet.

So, those of you with fairly new PD TDIs should not get too excited about improving fuel economy. It might have little to do with the progress in breaking in your engine, and more to do with seasonal factors.
 

cp

Veteran Member
Joined
Jan 25, 2001
Location
usa
TDI
2006 TDI Beetle
DBW-

Does that graph only represent WOT curves? I wonder if the torque peak occurs at the same engine speed at 10% throttle, 20% throttle, etc. Does anyone know if torque peaks tend to shift due to throttle input?
The graph is at WOT. You cannot have a 'peak' torque unless you are at WOT. Anything less than full throttle (a misnomer in a diesel) produces less than peak torque.

Notice the slight valley in the SFC curve. Therein lies the answer to peak efficiency, but not necessarily best economy. At the lowest point of the curve, the engine produces horsepower with the least consumption of fuel. But that is not to say that a speed with a lower horsepower requirement, albeit at a less efficient SFC, will not produce better mileage. Horsepower required to overcome aerodynamic drag is a cubic function whereas the sfc only varies a few percent.
 

whitedog

Veteran Member
Joined
Jul 12, 2004
Location
Bend, Oregon
TDI
2004 Jetta that I fill by myself
"Horsepower required to overcome aerodynamic drag is a cubic function whereas the sfc only varies a few percent."

Yeah... let me run that past the guys at work and see them look at me like I had a third leg sprouting from my ear.

Not that I completely understand it, but they wouldn't have a clue.
 

TurbineTech

Veteran Member
Joined
Feb 22, 2003
Location
Burnaby, BC
TDI
2003 Jetta
DBW-

Does that graph only represent WOT curves? I wonder if the torque peak occurs at the same engine speed at 10% throttle, 20% throttle, etc. Does anyone know if torque peaks tend to shift due to throttle input?
The graph is at WOT. You cannot have a 'peak' torque unless you are at WOT. Anything less than full throttle (a misnomer in a diesel) produces less than peak torque.

Notice the slight valley in the SFC curve. Therein lies the answer to peak efficiency, but not necessarily best economy. At the lowest point of the curve, the engine produces horsepower with the least consumption of fuel. But that is not to say that a speed with a lower horsepower requirement, albeit at a less efficient SFC, will not produce better mileage. Horsepower required to overcome aerodynamic drag is a cubic function whereas the sfc only varies a few percent.
Did you not notice that the graph says engine speed at the bottom? Of course it is at WOT but only on the left part of the graph, and no, it does not make max torque only at WOT.

http://www.getfaster.com/Techtips/Physics6.html
 

Kiwi_ME

Veteran Member
Joined
Jul 3, 1999
Location
New Zealand
TDI
'18 Kona EV, ex '03 Golf TDI, '82 Rabbit Diesel
The above graph does indeed represents pedal to the metal over the full range of rpm and therefore is helpful, but not fully accurate in answering the original question.

You need the full fuel consumption map with constant power curves. I'm not sure if this is precisely for the ALH (certainly not PD) but it shows the principle.

The colored curves represent lines of constant horsepower produced by differing combinations of speed and torque (torque is proportional to the brake mean effective pressure on this chart.) Red and yellow at the top-right are presumably 100 and 90% power, and so on to the lower-left.

For a particular percent power level, work along the appropriate colored line until you find the rpm that hits the lowest possible brake specific fuel consumption.

For example, at the lowest power line (near bottom, in blue) you need to run at 1000 rpm. Your BSFC is about 235.

(The actual fuel consumption is then the BSFC multiplied by the power being produced.)

Note this engine is most efficient running at about 60% power at 1750 rpm, the line going right thru the "197".

In summary, the most efficient RPM ranges all the way from 1000 to 3750 rpm over the full power range.

 

cp

Veteran Member
Joined
Jan 25, 2001
Location
usa
TDI
2006 TDI Beetle
Did you not notice that the graph says engine speed at the bottom?
Let me go back and look again at the graph....yep, it still looks the same.

Of course it is at WOT but only on the left part of the graph, and no, it does not make max torque only at WOT.
How did you come to the conclusion that it's WOT 'only for the left part of the graph'? And I would be interested in hearing how an engine can make 'peak' torque at less than WOT.
 

TurbineTech

Veteran Member
Joined
Feb 22, 2003
Location
Burnaby, BC
TDI
2003 Jetta
Okay, I think I know what you are saying: that irrespective of engine Rpm, the throttle is being held wide open, and that max torque is made at WOT not necessarily max rpm- yes?
 

cp

Veteran Member
Joined
Jan 25, 2001
Location
usa
TDI
2006 TDI Beetle
Okay, I think I know what you are saying: that irrespective of engine Rpm, the throttle is being held wide open, and that max torque is made at WOT not necessarily max rpm- yes?
Correct.
 
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