TDI at 75MPH

MPBsr

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What's up with this high rev at 75mph (2500rpm)

I think it should be around 1750rpm at most. Not sure I would do anything, but can something be done to lower the rpm's at a higher speed, which would also increase fuel mileage?

09 TDI
 

Diesel lifer

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I'm not sure the engine can generate enough power to sustain that speed/drag at that low RPM without significant blow by and excessive wear on the engine. The engine is quite happy to turn at 2500 RPM and the fuel scheduler may lean it out to save fuel when not under load.
But thats a complete shot in the dark. I'm also interested in this hypothetical.
 

JSWTDI09

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MPBsr said:
What's up with this high rev at 75mph (2500rpm)

I think it should be around 1750rpm at most. Not sure I would do anything, but can something be done to lower the rpm's at a higher speed, which would also increase fuel mileage?

09 TDI
That's pretty normal. They made 6th gear a little higher in the 2010 models, but in a 2009, that's what you get. It's the way VW decided to gear it, and we just have to live with it (unless you want to spend big money and replace your transmission with a 2010 model's gearbox). There are several threads here about the changed gear ratios in the 2010 models.

Have Fun!

Don
 

ruking

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2003 VW Jetta, 5 M, Reflex Silver: 09 Jetta, 6 Sp DSG, Candy White: 12 VW Touareg, 8 Sp A/T, Flint Gray
JSWTDI09 said:
That's pretty normal. They made 6th gear a little higher in the 2010 models, but in a 2009, that's what you get. It's the way VW decided to gear it, and we just have to live with it (unless you want to spend big money and replace your transmission with a 2010 model's gearbox). There are several threads here about the changed gear ratios in the 2010 models.

Have Fun!

Don
When all is said and done, it would seem that if you are @ 2,500 rpm and @ 75 mph, that your car has been "optimized" for that speed aka America. SPEED wise, it would be senseless to gear in such a way as to have 2500 rpm @ for example 95 to 100 mph. !!?? ( upper max torque range).

First off check your '10 VW owners manual technical page. My 2009 TDI gives max torque @ between 1,750 to 2,500 rpm. Gear ratios are slightly different from DSG to 6 speed manual and from 2009 to 2010.
 
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btcost

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My thoughts were that they did it for emissions. Keep the exhaust hotter. . etc..

I was surprised at the high rpm in my Dad's '09 DSG TDI

it seemed same as a stock 5 speed ALH car. . .
 

ruking

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Well no as the 2010 gear for the 6 speed manual are higher (taller) than for the 2009. I have read in passing the DSG gearing is a tad more aggressive than the 6 speed manual.
 

btcost

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ruking said:
Well no as the 2010 gear for the 6 speed manual are higher (taller) than for the 2009. I have read in passing the DSG gearing is a tad more aggressive than the 6 speed manual.

yes but the catalyst has also changed. . the '09 will IMHOP will turn out to be a true odd ball. like the 99.5 ALH engine cars are. in fact VW has already changed the engine code, from CBEA (09) to I think CBAA or CBJA. . .for '10
 

ruking

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Again, it gets back to the 09 VW oem owners manual technical page. 1,750 to 2,500 rpm max torque with 4,000 rpm max hp!! So what does the 2010 version say? We already know what the op says it is (2,500 rpm @ 75 mph for his 09 TDI (6 speed manual/DSG?). I guess I should care what the rpm is for the 2009 TDI @ 75 mph, but in truth, I don't know nor care. However I will take the op er's word for it.
 
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rix337

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You're not going to get optimal fuel mileage at 75mph anyway. The air drag is too high. I have noticed, even in 5th gear at 55, I get better mileage than 6th and 70mph.
 

TwoTone

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Funny, I always gave VW credit for the gearing. We travel to Cumberland, Maryland a lot and I love that I don't have to downshift to climb the mountains
 

Pelican18TQA4

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TwoTone said:
Funny, I always gave VW credit for the gearing. We travel to Cumberland, Maryland a lot and I love that I don't have to downshift to climb the mountains
x2!! I like the slightly shorter gearing found in the '09 MTs better because it allows you to use all 6 gears just about all the time, urban/suburban/highway, whereas the taller gearing in the '10 MTs pretty much locks out 6th gear for all but highway driving. Also, 6th in the '09 MTs is taller than 5th in the ALHs; verified that with my dad's car multiple times.

EDIT: One more thing, if the tach was hitting 1,750 RPM in 6th at 75 mph, you would never be able to use 6th in normal driving circumstances and there would be a huge jump from 5th to 6th.
 
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ruking

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Well yes, but that would be a serious mis understanding/ application of our TDI engines.
 

isa540

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yes but the catalyst has also changed. . the '09 will IMHOP will turn out to be a true odd ball. like the 99.5 ALH engine cars are. in fact VW has already changed the engine code, from CBEA (09) to I think CBAA or CBJA. . .for '10

BTCOST, do you know specifically what changes to catalyst have been made? In fact, what are the differences between 09 and 10 TDI engines since they have different engine codes?
Also, higher RPM does not by default mean higher exhaust tempature.. The exhaust temp has more to do with the engine load. The heavier the load, the higher exhaust temperature, even at low RPM’s
 

JSWTDI09

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isa540 said:
yes but the catalyst has also changed. . the '09 will IMHOP will turn out to be a true odd ball. like the 99.5 ALH engine cars are. in fact VW has already changed the engine code, from CBEA (09) to I think CBAA or CBJA. . .for '10

BTCOST, do you know specifically what changes to catalyst have been made? In fact, what are the differences between 09 and 10 TDI engines since they have different engine codes?
Also, higher RPM does not by default mean higher exhaust tempature.. The exhaust temp has more to do with the engine load. The heavier the load, the higher exhaust temperature, even at low RPM’s
According to my service manual the 2010 is a CJAA engine.

As far as the catalyst, the only change I am aware of is that the DOC (Diesel Oxidation Catalyst) and the DPF (Diesel Particulate Filter) are now two separate parts instead of one combined part. Therefore one can now be replaced without replacing the other.

Have Fun!

Don
 

btcost

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JSWTDI09 said:
According to my service manual the 2010 is a CJAA engine.

As far as the catalyst, the only change I am aware of is that the DOC (Diesel Oxidation Catalyst) and the DPF (Diesel Particulate Filter) are now two separate parts instead of one combined part. Therefore one can now be replaced without replacing the other.

Have Fun!

Don

those are the differences. back when I posted I could not remember.
 

wild03

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Pelican18TQA4 said:
x2!! I like the slightly shorter gearing found in the '09 MTs better because it allows you to use all 6 gears just about all the time, urban/suburban/highway, whereas the taller gearing in the '10 MTs pretty much locks out 6th gear for all but highway driving. Also, 6th in the '09 MTs is taller than 5th in the ALHs; verified that with my dad's car multiple times.

EDIT: One more thing, if the tach was hitting 1,750 RPM in 6th at 75 mph, you would never be able to use 6th in normal driving circumstances and there would be a huge jump from 5th to 6th.
totally agree here, 6th any higher and it would be useless in the city. Maybe some people can specialize their vehicles for 75mph by swapping gears but seems right on the money for city and mild "55mph" highway speeds.
 

isa540

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thank you Don for the info. I wonder if 2010 DOC and DPF would also fit on 2009 year models without much modification? Not that any one of us needed one now, but years from now if a replacement is needed it would be better/cheaper to buy them seperately than as a whole unit.
 

JSWTDI09

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isa540 said:
thank you Don for the info. I wonder if 2010 DOC and DPF would also fit on 2009 year models without much modification? Not that any one of us needed one now, but years from now if a replacement is needed it would be better/cheaper to buy them seperately than as a whole unit.
Yes, but...(and it's a big but). read this:

http://forums.tdiclub.com/showthread.php?t=284440

Don
 

IndigoBlueWagon

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What's wrong with 2500 RPM at 75? It means you have adequate power for hills and passing, and the car will deliver excellent economy at those revs. My '02 has a very slightly taller 5th gear (.717 instead of .756) and is running right around 2450 RPM at 75. That's my usual highway speed and I can get 50 MPG going 75.
 

isa540

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I don't think any 09 TDI will deliver 50 mpg going at 75 MPH. @75 MPH, 09 TDI's engine will simply need to run at higher rpm levels. Maybe 2010 TDI's would provide better fuel economy at these high highway speeds due to taller gear ratios they have.
 

BlueGraphite'10TDI

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isa540 said:
I don't think any 09 TDI will deliver 50 mpg going at 75 MPH. @75 MPH, 09 TDI's engine will simply need to run at higher rpm levels. Maybe 2010 TDI's would provide better fuel economy at these high highway speeds due to taller gear ratios they have.
True. When driving home from school in Tucson, at 77 i usually get 46-47mpg. Going 68 nets about 54.

Driving to Phoenix from CG is a little downhill, and with the cruise set i can manage low 50's going 77.
 

IndigoBlueWagon

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You're probably right, but EPA highway on my '02 was 50 MPG. You should be able to achieve the EPA highway number plus a bit in an '09 or '10 because of the changes in EPA ratings. So say 41 plus 10-20%. Not bad. Sounds like right around what BlueGraphie'10TDI is getting.

My car also has a lot of mods that should eat into fuel economy, but don't seem to.
 

ruking

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isa540 said:
I don't think any 09 TDI will deliver 50 mpg going at 75 MPH. @75 MPH, 09 TDI's engine will simply need to run at higher rpm levels. Maybe 2010 TDI's would provide better fuel economy at these high highway speeds due to taller gear ratios they have.
I am a tad confused given the post. As (your) 09 oem owners manual says on the technical specifications page, max torque is delivered between a range of 1,750 to 2,500 rpm. This is the same whether you have DSG 6 spd/6 spd manual, since you can not do much about the DSG/6 speed manual gears. So one can do this for whatever " mph/speed". But for best economy, given good efficient engine operation, operate at lower range of max torque, i.e., 1,750 rpm. For efficient operation and best mpg range, albeit slight hit, operate closer to 2,500 rpm.
 
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Pelican18TQA4

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IndigoBlueWagon said:
You're probably right, but EPA highway on my '02 was 50 MPG. You should be able to achieve the EPA highway number plus a bit in an '09 or '10 because of the changes in EPA ratings. So say 41 plus 10-20%. Not bad. Sounds like right around what BlueGraphie'10TDI is getting.

My car also has a lot of mods that should eat into fuel economy, but don't seem to.
But the '09-'10 TDIs aren't as frugal as your '02 ('09s have more power, more weight, and much cleaner emissions...all mpg sappers). My dad's car ('02 5-speed) can get high 40s all day long at 75-80 mph. In order for my car ('09 6-speed) to get high 40s, I can't drive any faster than about 65 mph without resorting to pseudo-hypermiling techniques (no thanks!!). Of course, if I lived in a part of the country that was dead flat (e.g., Florida) and/or had little traffic, I'm sure I could go at least 5 mph faster and still get the same mpg, but no way a '09 is getting high 40s mpg at 75-80 mph unless it's downhill.
 

wild03

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Pelican18TQA4 said:
. Of course, if I lived in a part of the country that was dead flat (e.g., Florida)
Yeah but then you will need the AC! ask me how I know! :)
 

compu_85

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The 6 speed isn't like 5 + another gear, it's 1-2-3-4-4.5-5.5. Having such a high load at low rpm's is hard on everything in the drivetrain.

-Jason
 

Pelican18TQA4

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wild03 said:
Yeah but then you will need the AC! ask me how I know! :)
I run the A/C just about every day between June and September here!

compu_85 said:
The 6 speed isn't like 5 + another gear, it's 1-2-3-4-4.5-5.5. Having such a high load at low rpm's is hard on everything in the drivetrain.

-Jason
Correct. 6th gear in my '09 MT is only marginally taller than 5th gear in the earlier 5-speed MTs. The gears in-between are closer together, which allows greater fuel economy and better acceleration characteristics. The newest car gearboxes are 8-speed autos and they don't have a super tall 8th gear, but rather have a huge overall ratio spread and therefore can offer enhanced acceleration and fuel economy.
 

ruking

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I think that if one is talking about a DSG/6 speed manual comparo, it should be more than obvious there are a series of compromises and ever so slight differences in design goals.

The DSG is designed and specified for maximum mpg. An obvious one is the DSG shifts by programmed computer control (aka, automatically) It really behooves one to understand this and work WITH what the DSG computer is telling the car to do, not against it.

The 6 speed manual depends more on what one wants to do and how one wants/likes/has to drive. It is both easier to miss the finer points, but can be FAR easier to get the finer points spot on.
 
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