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TDI Fuel Economy Discussions about increasing the fuel economy of your TDI engine. Non TDI related postings will be moved or removed.

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Old December 13th, 2013, 22:49   #181
puntmeister
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I highly recommend the link given by Jagerbecher. Thanks again.

There are posters on it who are much more knowledgeable than I am about all of this, and have done a good job of explaining how the BSFC does, and does not, apply to MPG.

Another quote:

"The ALH engine installed in MK4 TDIs is a prime example. To achieve best (i.e. lowest) fuel consumption you should be operating in the range of 1,250 to 1,700 rpm at all times."
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Old December 14th, 2013, 08:34   #182
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Not exactly the most scientific explanation, but its along the lines of an example I was thinking of:

"You can use less energy to overcome inertia if you do it slowly. What would make you more tired: pulling a heavy wagon slowly from a stop to an all-out run, or pulling the same wagon immediately to a sprint? Pulling the wagon slowly lets you build momentum to help overcome inertia, using less energy. In your car, you should accelerate slowly from stops, allowing the car's momentum to help it accelerate."

Pulled from "Top 10 Green Driving Tips" on HowStuffWorks

I'll try to drum up more definitive evidence...
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Old December 14th, 2013, 08:55   #183
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Meanwhile, the three letters most of us manual drivers, who insist we drive manuals cuz they get better MPG than automatics, have to fear most: C....V....T

If you take a look at the line-up of cars which offer CVT transmissions, the CVT versions actually get better MPG than the manual versions.

It stands to reason - CVT transmissions offer a continuous transfer of engine-output to propulsion - there is no clutching/shifting of gears as with manuals/geared automatics.

I often why CVT wasn't offered on cars, when it has long since been a common feature of scooters....

Turns out, there was in issue applying CVT to high-torque engines (obviously not a problem with 50cc scooters).
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Old December 14th, 2013, 08:58   #184
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To boot - CVT transmissions are actually very simple in design - much simpler than geared automatics and, quite frankly, simpler than manual transmissions as well.

They are likely to be highly reliable and, in the event of a failure, more likely to be repairable by a DIYer than either manual or automatic transmissions.

Basically, they win hands down. I can see a day in the future where all cars are CVT, and manual is not even an option any more. Which blows, cuz I like shifting.
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Old December 18th, 2013, 10:04   #185
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I see the point that puntmeister is trying to make about acceleration. While BSFC chart relates to an isolated engine (let's say engine on a testbed or dyno) or the engine in stationary application, it may not mean that other physical factors that affects whole car during acceleration do not offset the engine efficiency during hard acceleration. To know the answer someone would need to calculate or experiment. But several forum members reported that according to their observation and VCDS the harder acceleration resulted better fuel economy. And I can believe that because if I just imagine "neverending" acceleration (let's say from 0 to 60 in 5 minutes, I know extreme example) I can't see how it could be more efficient then acceleration during which the rpm is kept in highest torque range.
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Old December 18th, 2013, 11:32   #186
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For what it's worth....

Going by MFD...

Cruising at 55-60mph on florida I-95 gives me 60mpg.

P&G between 50-60 gave me 85mpg for the last two days.

Same route, same distance (65 miles), Same times.

I'll hand calculate at end of tank and post back.
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Old December 19th, 2013, 04:52   #187
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Arrow the CVT is not all that in the real world....

It is not as simple as you assume, No where near as simple as your writing show you believe..........

The CVT is heavy because of the materials needed to make it work. It is a really complex build design along with needing expensive materials so it doesn't eat it self when in use. And It's really expensive to build compared to slushboxes, even the current complex offerings. And it is as much as 3 times as much as one of the currently used manual transmissions......

When compared to other transmissions used today. It is heavier than most currently offered slushboxes quite a bit than some. And it can weigh double compared to some manual transmissions. It has some fairly required costly service and repair issues. And long service lives are not the norm on the current offerings of CVTs in higher power applications. There is a lot to be worked out before they become widely used.........

In most current applications the CVTs have a really heavy big chain that is really expensive to replace when it reaches the end of it's service life or when it fails. And they do fail.!.......

When the CVT chain fails it's not just the chain but the guides and many times all of the gears. If the chain breaks it can destroy case making the transmission useless. Costs of repair can exceed the cars value.....

And I haven't even gotten to the real issue, they use more fuel in many conditions than regular high tech slushbox today! And they use a lot more fuel than a manual trans driven by a well trained driver in the real world in all driving situations.......

I have years of real world data on Nissan CVTs used in several the current applications. City used CVT applications used over rolling or hilly terrain pay the highest mpg penalty. I have seen first hand how bad these things can be in city driving..........

In a Nissan Versa side by side manual trans & CVT I have consumption numbers. For same year, same options, driven over similar terrain I have consumption numbers for ~50k miles driven around the Denver region. Records that show the manual trans version is twice as efficient as the CVT in city driving around Denver.

On average in mixed & city driving the Versa a manual trans version is seeing 35-40 mpg to low 40s max and the CVT sees high 10s to low 20s mpgs at best mixed with low 30s highway......

I also have a several of years of records for a Alitma CVT and a manual trans version. And on city loops the difference is over double on most tanks. The manual trans version can achieve on city loops above 30 mpgs, mixed low to mid 30s and all highway high 30s mpgs if speeds are kept down. IF the speeds are high on the highway it can drop to the 26-30 mpgs........

In the CVT Altima the numbers are high 10s to low 20s mpg on city only, mixed high 10s to mid 20s mpgs and on the highway consumption can get close to 25-27 mpgs if speeds are kept low enough. If You push speeds on the highway it can drop to low to mid 20s mpgs....

Now, Nissan claims it has a new design of CVT that is 10-15 % more efficient than the current & previous CVTs. And if those claims are true it will still be 30 % less efficient than a manual trans version...
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Old December 19th, 2013, 11:06   #188
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Much appreciated post on CVT's - I admittedly am not up on all the details when it comes to CVT. Anything I wrote about CVT was either speculation, or based on the scant data provided by manufacturers (higher MPG numbers, for example, for new CVT versions of cars vs/manuals).

I do realize the drive profile has a significant impact on real-world MPG - everyone on these threads is keenly aware of that .

I find it hard to believe, however, that the MPG figures quoted for new cars are so far off - in the sense that they show CVT as (modestly) better than manual, but you claim they are actually 30% to 50% worse....however skewed the quoted numbers are, they are skewed for both manual and CVT alike, as the testing procedures would be identical. If the testing procedures aren't identical, or the numbers are skewed in some other fashion, then the manufacturers are downright guilty of fraud.

As for longevity & repair costs - pure speculation on my part. What you say does make sense - that the chain is very expensive to replace and, if/when it breaks, causes serious damage. Just the same, I'd hardly consider rebuilds of current slushboxes reasonably priced, and I wouldn't consider them durable/reliable either. CVT vs. geared automatic? A race to the bottom, its sounds like....

Last edited by puntmeister; December 19th, 2013 at 11:10.
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Old December 20th, 2013, 05:39   #189
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Arrow

Quote:
Originally Posted by puntmeister View Post
Much appreciated post on CVT's - I admittedly am not up on all the details when it comes to CVT. Anything I wrote about CVT was either speculation, or based on the scant data provided by manufacturers (higher MPG numbers, for example, for new CVT versions of cars vs/manuals).

I do realize the drive profile has a significant impact on real-world MPG - everyone on these threads is keenly aware of that .

I find it hard to believe, however, that the MPG figures quoted for new cars are so far off - in the sense that they show CVT as (modestly) better than manual, but you claim they are actually 30% to 50% worse....however skewed the quoted numbers are, they are skewed for both manual and CVT alike, as the testing procedures would be identical. If the testing procedures aren't identical, or the numbers are skewed in some other fashion, then the manufacturers are downright guilty of fraud.

As for longevity & repair costs - pure speculation on my part. What you say does make sense - that the chain is very expensive to replace and, if/when it breaks, causes serious damage. Just the same, I'd hardly consider rebuilds of current slushboxes reasonably priced, and I wouldn't consider them durable/reliable either. CVT vs. geared automatic? A race to the bottom, its sounds like....
Maybe I wasn't clear, but there are some conditions where a CVT is more efficient than a slushbox and can come close to a manuals numbers. Those conditions are over mixed route tanks over flat or almost flat terrain. There is a point when terrain becomes varied enough that those numbers flip in favor of the slushbox.

The current test procedure doesn't really give a clear picture but numbers clocked in the real world do....

The jury is somewhat in on the geared automatics, they are long lived and reliable if proper maintenance is carried out. And if issues that arise are quickly dealt with before catastrophic damage is suffered they can have similar life spans to a manual......
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Old December 20th, 2013, 11:26   #190
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rotary,

Gotcha.

Yes, I suppose its true, current automatics can be reliable, if properly maintained - I just know of so many instances of automatics going bad. Then again, that's probably because most people never bother to change the trans fluid/filters.

To be fair, clutches go bad often too (mainly due to bad shifting methods) - but, its generally much cheaper to change a clutch, than rebuild an auto trans.

In any event, even if the quoted MPGs of CVTs were representative of likely real-world driving, and did get consistently slightly better MPGs than manuals, I would still choose to drive a manual....
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Old December 29th, 2013, 11:12   #191
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Some pages back, there was a discussion on how "quick" one should get up to speed, up to fifth gear...all really depends upon where you need to be...35MPH or 55MPH.

Someone stated that they were using the LOD gauge on their Scangauge to "temper" their acceleration...my word, temper. I hadn't used the LOD gauge mode, but I turned it on to see how I was personally performing. And my acceleration was in the 80 range...I believe that LOD is basically the ECM stating what load the driver is asking from the engine given the particular RPM and throttle position. Some things to take note of with that...one can input less than 100% throttle input and that will produce 100% engine load at some engine and ground speeds.

So, back to real world... I found that in my light-ish acceleration and lower RPM shift points, I could produce pretty good MPG. Around 50MPG on my route to and from work. Using the LOD gauge, I found that often I was producing LOD in the 80 to 85 range to get myself up to speed. Not a jack rabbit at all, but it was lightly spirited.

Anyway, some pages back, someone made a statement, or maybe it was another thread even, that one should try to accelerate in the 60-70 LOD range. I think those guys that got 80MPG in the Passat used a Scangauge while driving, and this might have been one of their techniques. I think that they would try to not exceed 70% on LOD even going up long hills, which resulted in them slowing down, downshifting, and even turning on their hazzard lights.

I tried using the LOD gauge reduce my input to that 60-70 range, and I was rewarded pretty consistently with better MPG. My average increased, and my best increased. It certainly makes it to where I'm not going to be the one someone in a rush wants to be behind leaving a stop light and increasing speed to 45MPH. And if one wants to try and use that guide on the Interestate, you might certainly find that you won't always be traveling at the posted speed of 65-70MPH.
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Old January 2nd, 2014, 18:53   #192
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today,

24 mile round trip, full tank of gas 59.7

3 kids, 2400 miles on car 35 psi
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