High speed MPG - (for thoes mostly near an autobahn...)

So who has calculated MPG at "high speeds" (as compared to the slowness of the USA)

MPG @ 70 for me is 53mpg Summer fuel, round trip north and south 120miles, same pump 8 hours apart for fueling.... That was before I started to modify things. heh.

I'll get MPG up to about 80 maybe 85mph this summer for the trip I just mentioned.

However, what I'm really looking for is MPG at 100mph and faster.

I'd be amazed if anyone has data for you (beyond simple scan gauge / MFD readings). Sustaining 100 mph for an entire tank? Difficult - even on the autobahn.

I'm sure 85_305 will chime in shortly with his 50mpg at 90 mph claim, but I personally don't buy it (nothing personal dude).

Aeromods are your friend for mpg's at high speeds. They become exponentially more valuable as speed is raised. Which is primarily why I did mine - my hwy driving is always over 70. I have done entire tanks of 80+ mph cruising (sure, with some % of city on both ends of the trips / tank) and still gotten ~50. But the drag at 90 mph requires almost 50% more power to overcome than @ 80.... and from 90 to 100 is yet another 50+ % power requirement...

90 MPH gets you 30 to 35 MPG. Full tilt is about 25 MPG.

Full tilt for me on the track, running to 110 in 4th on straights, shifting at 5200+ RPM would typically get me 16-18 MPG. Obviously I'm doing a lot of hard braking, too, which uses up energy. I'd go with Bob's 25 MPG estimate.

shizzler said:

I'd be amazed if anyone has data for you (beyond simple scan gauge / MFD readings). Sustaining 100 mph for an entire tank? Difficult - even on the autobahn.

I'm sure 85_305 will chime in shortly with his 50mpg at 90 mph claim, but I personally don't buy it (nothing personal dude).

Aeromods are your friend for mpg's at high speeds. They become exponentially more valuable as speed is raised. Which is primarily why I did mine - my hwy driving is always over 70. I have done entire tanks of 80+ mph cruising (sure, with some % of city on both ends of the trips / tank) and still gotten ~50. But the drag at 90 mph requires almost 50% more power to overcome than @ 80.... and from 90 to 100 is yet another 50+ % power requirement...

Click to expand...

Indeed hard to get. So how about 6.25 hours, 584 miles, 12.1 gals or 48.26 mpg?

How about it? Are you completely serious - a 93 mph average for a full 584 miles ?!? I don't know whether I believe your speed or your mpg less.

Some people claim to have these magical TDIs, but really, no one is above the laws of physics. You can quantify the amount of fuel required to sustain 93 mph with basic data - diesel fuel energy density, and vehicle frontal area and coefficient of drag. And it's more than 1.9 gal/hr! Either you have a gross speedo / trip meter error, or are filling up at different pumps (hence bad fuel measurement). Or maybe you drove from the Johnson tunnel west of Denver (el. 11200 ft) down to sea level....?

shizzler said:

How about it? Are you completely serious - a 93 mph average for a full 584 miles ?!? I don't know whether I believe your speed or your mpg less.

Some people claim to have these magical TDIs, but really, no one is above the laws of physics. You can quantify the amount of fuel required to sustain 93 mph with basic data - diesel fuel energy density, and vehicle frontal area and coefficient of drag. And it's more than 1.9 gal/hr! Either you have a gross speedo / trip meter error, or are filling up at different pumps (hence bad fuel measurement). Or maybe you drove from the Johnson tunnel west of Denver (el. 11200 ft) down to sea level....?

Click to expand...

Durango, Co to Las Vegas NV. One fill outside of Las Vegas in the middle of no where.

No claim to a magical TDI. Just a plain one. Sounds like you are full of it.

http://en.wikipedia.org/wiki/Durango,_Colorado

http://en.wikipedia.org/wiki/Las_Vegas,_Nevada

You might think and say that, but all you have to do is map quest or google it to know that is not true, aka false. Indeed this has not been the only trip. The reason why either 12.1 gal or 584 miles is significant is that is when the low fuel lamp goes off. I've done from this area to the Santa Monica turn off @ a steady 90 mph in a driving rain and posted 50 mpg. So yes, slower gets better.

Newton is turning over in his grave.

Bob_Fout said:

90 MPH gets you 30 to 35 MPG. Full tilt is about 25 MPG.

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I would believe that is what you probably get if you are saying that is what you get. But for all the mods you list, shouldn't you expect better?

ruking said:

I believe that is what you probably get, but for all the mods you list shouldn't you expect better?

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I don't drive that fast, those figures are from people who do drive those speeds. There was a post some years ago about it.

Bob_Fout said:

I don't drive that fast, those figures are from people who do drive those speeds. There was a post some years ago about it.

Click to expand...

Me either ! So you have never done what you profess to know to be true? Figures !!!

Bored. Fun with numbers: I don't know top speed on a mk4 stock, but I'll guess 115mph. My mk4 runs 2400 at 70mph, so at 115 it turning about 3950. And assuming it is making full hp at that rpm, which might not be true as above 3750 (rated peak hp) ecu is probably backing off fueling a bit. So call it 90hp anyhow. Using a marine engine rule of thumb, each gallon per hour makes between 17 to 20hp, depending on engine and how close to peak bsfc is the operating point. So since this engine is nowhere near peak bsfc, I'll pick 18hp/gph. 90/18= 5gph. 115mph/5gph=23mpg.

Ruking, your originally posted trip descended over 4000 feet of elevation! Completely irrelevant data point. This is not helpful, as presumably the OP is not asking us "how good can the mileage be at high speeds, when driving downhill for an entire tank, with a tailwind and magic fairy dust in the fuel tank?"

You are not posting normal fuel economy numbers. We have a few geezers who drive at 50mph to pull off their great #s. And a few newbs who don't know how to properly evaluate fuel economy. But then there is you, repeatedly claiming mileage feats that no one else can accomplish. So yeah, either your TDI is magical, or you aren't being completely truthful with yourself and your mpg calculations.

I am an engineer... dedicated to using hard data to find truth. Not interested in exaggeration, manipulation of data, or, on the other hand, knocking people's results when I have no reason to doubt them. But I do have reason to doubt your #s here. Actually, to be honest, an odometer error makes sense for your car, since you also claim 112,000 miles from a set of goodyear tires.

Let's take another look at this situation objectively:

Have you seen an understood the BSFC map for the ALH TDI engine? Search for and read the BSFC thread if not. Below is a calculation of the load required to push a stock Mk4 Jetta down the road in top gear. Let's run some simple numbers for your stated speed of 90 mph.

A fairly basic calculation tells us we need ~42 BHP (31.5 kW) to sustain 90 mph. With stock gearing and tires, this is ~3100rpm, which means we are requesting ~71.6 lbf-ft (97 N-m) of torque. So, that puts our engine efficiency at around 245 g/kW-hr. 245 grams * 31.5 kW means you are burning 7.72 Kg (17 lbs) of fuel per hour at this speed. Divide by the density of diesel fuel (6.9 lbs/gal) and you can see we are burning 2.45 gals/hr. At 90 mph, this is 37 mpg AT BEST. And you claim 50 in the rain? Ridiculous.

By the way, the above analysis gets really interesting when you combine gear swaps and improved aerodynamics to study improvement in fuel economy. You can also throw a different WOT power curve onto the plot to roughly calculate expected top speed (when cruising load in top gear line intersects the WOT curve).

shizzler said:

I'd be amazed if anyone has data for you (beyond simple scan gauge / MFD readings). Sustaining 100 mph for an entire tank? Difficult - even on the autobahn.

I'm sure 85_305 will chime in shortly with his 50mpg at 90 mph claim, but I personally don't buy it (nothing personal dude).

Aeromods are your friend for mpg's at high speeds. They become exponentially more valuable as speed is raised. Which is primarily why I did mine - my hwy driving is always over 70. I have done entire tanks of 80+ mph cruising (sure, with some % of city on both ends of the trips / tank) and still gotten ~50. But the drag at 90 mph requires almost 50% more power to overcome than @ 80.... and from 90 to 100 is yet another 50+ % power requirement...

Click to expand...

Yep i sure hit like 48.6 or 48.8mpg going 90mph. It wasn't a steady 90mph, though. Sometimes we'd slow down to 70, then hammer it to 100-105, then cruise at 90... it changed quite a bit. But I would say our average was 90mph.

And the story changes... was doing 70, then 100, then 90.. I'm "guessing" at 90mph average

The human brain can't not calculate averages like you think you were. I bet you were doing 80mph more often then not.

In any case, we can all agree that TDIs pull down phenomenal mileage at high speeds

shizzler said:

Ruking, your originally posted trip descended over 4000 feet of elevation! Completely irrelevant data point. This is not helpful, as presumably the OP is not asking us "how good can the mileage be at high speeds, when driving downhill for an entire tank, with a tailwind and magic fairy dust in the fuel tank?"

You are not posting normal fuel economy numbers. We have a few geezers who drive at 50mph to pull off their great #s. And a few newbs who don't know how to properly evaluate fuel economy. But then there is you, repeatedly claiming mileage feats that no one else can accomplish. So yeah, either your TDI is magical, or you aren't being completely truthful with yourself and your mpg calculations.

I am an engineer... dedicated to using hard data to find truth. Not interested in exaggeration, manipulation of data, or, on the other hand, knocking people's results when I have no reason to doubt them. But I do have reason to doubt your #s here. Actually, to be honest, an odometer error makes sense for your car, since you also claim 112,000 miles from a set of goodyear tires.

Let's take another look at this situation objectively:

Have you seen an understood the BSFC map for the ALH TDI engine? Search for and read the BSFC thread if not. Below is a calculation of the load required to push a stock Mk4 Jetta down the road in top gear. Let's run some simple numbers for your stated speed of 90 mph.

A fairly basic calculation tells us we need ~42 BHP (31.5 kW) to sustain 90 mph. With stock gearing and tires, this is ~3100rpm, which means we are requesting ~71.6 lbf-ft (97 N-m) of torque. So, that puts our engine efficiency at around 245 g/kW-hr. 245 grams * 31.5 kW means you are burning 7.72 Kg (17 lbs) of fuel per hour at this speed. Divide by the density of diesel fuel (6.9 lbs/gal) and you can see we are burning 2.45 gals/hr. At 90 mph, this is 37 mpg AT BEST. And you claim 50 in the rain? Ridiculous.

Click to expand...

You are even more full of it. All you had to do was google the route. So to you, the real world is all FLAT? Please, I gave a REAL WORLD example. Speedometer error? ALL of them do, so what? Does that mean in your line of thinking that 112,300 miles really means 40,000 miles ? Please... the BS here is getting gaseous. Your theory is interesting, but it seems you have never real world tested your theory. Are you are just scared 2 to3 real world data points presented by myself and others don't "CONFORM " to your ivory tower theory?

shizzler said:

In any case, we can all agree that TDIs pull down phenomenal mileage at high speeds

Click to expand...

Now really, how can you say that when you don't even believe people who have walked the walk?

That bsfc map with the road load curve really defines what an alh car is capable of. Using my 2001 and various road trip mpg calcs, the map fits my car extremely well. Within a few percent, and the error in picking numbers off the map.

The map also is consistent with what I have seen on other engines during many hours in a dyno lab. Consistent also with many performance charts showing gph/hp/torque/rpm I use in my business.

Individual cars will vary, same with drivers, road conditions, etc. Most probably within 10%.

But if you have an alh car that beats the bsfc map by 35%, you either have a magic car, an incredible tail wind, a magic diesel pump at tank fill....or there is some bs going on.

While I more or less believe the two accounts of phenomenal economy at high speed in this thread, I think it's clear they are not the norm. If the OP wants an no BS answer, the BSFC map is the way to go.

Again, tailwinds: I've observed a huge bump in mileage with a strong steady tailwind in the open plains of the West. Even large elevation changes have a surprisingly small effect over long trips (I've done the math for a tank just using m*g*h, and relative to the amount of fuel you burn in a tank, extra work from elevation didn't really seem all that important) I suppose ruking could have had a nice tailwind in his run.

Is there anything wrong with estimating that a 25 mph perfect tailwind at 90 mph can net the normal mileage of 70ish (We do know that drag increases with the square of speed, but I don't know about friction with the tires and drivetrain so I "gave them" 5 mph)

Ski in NC said:

ut if you have an alh car that beats the bfsc map by 35%, you either have a magic car, an incredible tail wind, a magic diesel pump at tank fill....or there is some bs going on.

Click to expand...

Maybe he has an HOH generator on board

I suspect liquid schwartz is involved here.

^^^^ LOL, nice.

Ruking, do me a favor and stop telling me I am full of it. I am being as objective as possible (ok, maybe with some colorful doubt on the part of your #s).

I am not saying you are just making up numbers for fun. I don't see any point in that. But you need to accept that there is room in your measurements for some serious error. Just think logically for a second here. Why would your TDI be over 30% more efficient than everyone elses? If this was really true, I would recommend you take your car straight to a laboratory for a detailed analysis. Because whatever is special about your car needs to be understood and applied to all new vehicles. The other, much more plausible scenario is that you have some serious error in your calculations. Again, not intentionally.

The BSFC map posted above is not a theory. In fact, it matches my own real world results to within +/- 1 mpg. Average speeds over full tank refills. Then I changed my 5th gear ratio, plotted everything again, and it correctly predicted my increase in mpg (i.e. not much, haha). The data on this BSFC plot is straight from Volkswagen. It stems from many hours of diligent dynamometer testing under high scrutiny. It is a much more realistic starting point for correctly estimating fuel economy than to listen to one guy who claims some amazing results, and only later admits he drove all downhill.... etc.

And for 80% of Americans... the real world is pretty flat on a daily basis. I.e. the whole Midwest and almost every metropolitan area east of the Rockies. Driving 4500 ft down in one direction hardly constitutes the average driving route.

Sorry for not googling your driving route right away, my bad. But I did go back and look up the exact weather records for the exact time of your trip. You had an avg 22.7 mph tailwind at approximately a 5.3 to 6.7% angle of yaw. I used government satellite surveillance records to observe you repeatedly drafting semis as well! tsk tsk.

Where are people getting their magic fairy dust these days?

Quiksilver said:

I suspect liquid schwartz is involved here.

Click to expand...

Post of the week! Brilliant!

Agreed

shizzler said:

How about it? Are you completely serious - a 93 mph average for a full 584 miles ?!?
I don't know whether I believe your speed or your mpg less.

Some people claim to have these magical TDIs, but really, no one is above the laws of physics.
You can quantify the amount of fuel required to sustain 93 mph with basic data - diesel fuel
energy density, and vehicle frontal area and coefficient of drag. And it's more than 1.9 gal/hr! Either you have a gross speedo / trip meter error, or are filling up at different
pumps (hence bad fuel measurement).
Or maybe you drove from the Johnson tunnel west of Denver (el. 11200 ft) down to sea level. .?

Click to expand...

He posted that B/S before, and I didn't believe it then, nor do I now.

If you been in that area, some of the roads are not able to be driven at such speeds!

And where was the Highway Patrol in those three states while all this speeding was going on?

How fast do you have to go to be able to average 93 MPH for 6.25 hours?

Some of us here have been around the block a few more times than he has!
Then there's the story of his original tires lasting 112K miles also.
A person cannot have tires that last that long when a car is driven like that for any length of time.

When someone tells such woppers, nothing they say can or will be believed!

I've driven professionally all of my life and I cannot go that long
without making a rest stop to 'take care of business.'

No sir, when it comes to such astory, I'm from Missouri, you know,
The Show-Me state. Well no, I am actually a native California!

That kind of F E claim coupled with that unbelieveable time over distance just
simply could not be true. Head for the rafters fellows, it's getting too deep.
Save yourself.



D