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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 June 2nd, 2008, 09:56   #181
JettaJake
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Before I bought Jake (new, tyvm), I had visions of numerous mods including an aftermarket air handling device like a K&N. I received several strong advisories to stick with the stock air filter set-up and read ample material on the subject I found through a search, here and elsewhere.

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Originally Posted by zachmain02
"If you are running a cone filter (like K&N) you don't even have to check it, it's probably bad already. A stock air filter flows better than a K&N and it won't kill your sensor." - BleachedBora


i have read that the K&N filters flow better, not worse. dont care to argue the point, i just have a K&N and am wondering if i should take it out to save the MAF. anyone have a good pros/cons of K&N vs. stock?
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Old June 2nd, 2008, 14:52   #182
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Quote:
Originally Posted by deezulmark
Just ran across this thread. Thanks BB for the cetane #s reported by the various brands. Anybody know Walmart's supplier and cetane? They're always way cheaper than anybody else in town. Usually have been doing Flying J on trips as they're cheapest, but now I know to try BP and Shell and see.

Now if they would quit making diesel so much more expensive than gas! But then it is winter, so home heating oil demand pushes it up to some extent.
No problem--if you email Walmart and get cetane information I'll gladly add it to the list.
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Old June 3rd, 2008, 08:18   #183
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Anyone have Cetane info for RaceTrac stations in Florida? I can't even find a company website
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Old June 8th, 2008, 14:19   #184
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I'm new. I've seen somewhere in this forum that 1500-2500 rpm is the "optimal" range. I have always thought that the highest gear I can be in without the car struggling much (shaking) is the best for gas mileage. For example, I can usually be in fifth gear going between 35-40 mph, which puts me at about 1300 rpms. Would it be more fuel efficient to drive this speed in fourth gear? Is it hard on the car in any way to drive that speed in fifth gear? Thank you!

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Old June 8th, 2008, 14:42   #185
ruking
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The answer is yes.
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Old June 8th, 2008, 16:22   #186
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Quote:
Originally Posted by andrew4
I'm new. I've seen somewhere in this forum that 1500-2500 rpm is the "optimal" range. I have always thought that the highest gear I can be in without the car struggling much (shaking) is the best for gas mileage. For example, I can usually be in fifth gear going between 35-40 mph, which puts me at about 1300 rpms. Would it be more fuel efficient to drive this speed in fourth gear? Is it hard on the car in any way to drive that speed in fifth gear? Thank you!

andrew4
NO if you are not accelerating , running on flat or up or down a slight grade 1,300 is well within design spec . So staying in high gear when conditions allow is always the most efficient unless you could coast farther in "N" then just staying in gear . 1,200-2,500 rpms is exactly where these things are designed to run most efficiently .
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Old June 8th, 2008, 16:35   #187
zachmain02
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cruising at high 70s to 80 puts me at just under 3,000 rpms. anyone know the drop in fuel economy when you reach 3,000?
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Old June 9th, 2008, 19:27   #188
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Quote:
Originally Posted by andrew4
Would it be more fuel efficient to drive this speed in fourth gear?
A scangauge would show which is more fuel efficent instantly. The highest possible gear without severe lugging is allways the most efficient. The scangauge agrees also, but you have to use common sense with the scangauge... for example:

on level ground I set cruise in fifth gear at 50km/h and the engine will turn at around 1100rpm and I use 3L/100k
On my way home there is a hill where if usually drive 50km/h...
Third gear = 1900rpm = 12L/100km reported by scanguage on this hill. nice and smooth climb.
Fourth gear = <1400rpm = 10L/100km but the engine seems to be operating too close to its "lug limit" for comfort.

So is it worth saving 15 to 20 percent on fuel on steepish hills? Probably not for me. I take the hill in 3rd.

Personally use the highest possible gear as soon as possible but I don't climb real "hills" below 1500rpm.
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Old June 9th, 2008, 19:42   #189
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Quote:
Originally Posted by zachmain02
cruising at high 70s to 80 puts me at just under 3,000 rpms. anyone know the drop in fuel economy when you reach 3,000?
Its not the RPMs that get you at those speeds, its the laws of physics. Anything over 55mph or 90kph and you are wasting fuel IMO.
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Old June 9th, 2008, 20:00   #190
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Quote:
Originally Posted by NarfBLAST
Its not the RPMs that get you at those speeds, its the laws of physics. Anything over 55mph or 90kph and you are wasting fuel IMO.
It all depends on how valuable your time is.
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Old June 9th, 2008, 20:54   #191
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Quote:
Originally Posted by Gothmolly
It all depends on how valuable your time is.
No, it doesn't. If Narf had claimed that you are wasting money, then your counter-claim would be correct, but he didn't. Fuel is fuel, and its usage is strictly dictated by physics.
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Old June 9th, 2008, 22:08   #192
NarfBLAST
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Quote:
Originally Posted by nicklockard
No, it doesn't. If Narf had claimed that you are wasting money, then your counter-claim would be correct, but he didn't. Fuel is fuel, and its usage is strictly dictated by physics.
Thanks Nick, that is exactly what I was referring to: the diminishing returns that happen after a certain speed. I'm talking about fuel economy vs speed and how it generally peaks at 55 (90) for most vehicles

I just finished a rant about speed in another thread here: http://forums.tdiclub.com/showpost.p...2&postcount=18

I think I will need to make a chart to help me get to sleep tonight.
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Last edited by NarfBLAST; June 9th, 2008 at 22:52.
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Old June 12th, 2008, 23:32   #193
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Quote:
Originally Posted by Gothmolly
It all depends on how valuable your time is.
Time it takes to travel 30 miles...

55 MPH = 33 minutes
60 MPH = 30 minutes
65 MPH = 28 minutes
70 MPH = 26 minutes
75 MPH = 24 minutes

FWIW, you gain only 4 minutes traveling 70 over 60 MPH over a 30 mile distance.
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Old June 13th, 2008, 07:52   #194
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Quote:
Originally Posted by DieselAlles
Time it takes to travel 30 miles...

55 MPH = 33 minutes
60 MPH = 30 minutes
65 MPH = 28 minutes
70 MPH = 26 minutes
75 MPH = 24 minutes

FWIW, you gain only 4 minutes traveling 70 over 60 MPH over a 30 mile distance.
And for a whole day's driving...
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Old June 13th, 2008, 08:50   #195
rotarykid
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Quote:
Originally Posted by Bob_Fout
And for a whole day's driving...
you need to add 80 mph to that list .................

1,800 miles @ 75-80.................. 24-22.5 hours of travel time

................@ 55-60.................. 32.7-30 hours of travel time

10 hours saved from one extreme to the other , now that is a real cost for slowing . An extra 10 hours adds at least another day in a hotel nothing saved by this .

By the way in my Passat TDI I get a consistant ~50 mpgUS in the 75 -80 mph range during a trip like described .
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Last edited by rotarykid; June 13th, 2008 at 08:52.
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