Engine/Transmission (1998.5 - 2002) Mileage--has anyone really improved it?

[geusterman]

Wiredog, what's the mpg on the new ride? I had a little relapse this a. m. thinking I gotta get into this VP44 at 12K miles to see if it is what is doing the number on my mpg and started thinking about the fuel system on the 2003. Started to head to the dealer but stopped for a cooling off period so when I got back on the road my common sense returned. Just irritating to have to deal with this. I ssooo like my truck, bone simple, Kelderman Air (like a 90's Chevy ride), GV, 19. 5's,EZ,Ranchos and my Darin's Stabilizer, throttle cable and quieting stuff laying in the shop to put in. Add to that a megga list of nifty things to do. But do I quit here, strip it, cut my losses and go 2003? Not yet. Gotta check out the VP. Bill Heath told me yesterday he made some special TurboMasters on twin turbos for the guy who just rear-wheeled 685 hp and squirted some nitro and hit like 770 or so. MAN! That's a 1000 flywheel hp! I guess the fellow (you guys probably know who he is) drove to the TDR function and back home to CA (?). That was a VP44. So, maybe there is a little hope for us 24V's. George

 

[geusterman]

Slo-ryde! The light just came on re-reading your post! You have a 2 wheel drive. I have a 4 wheel drive. Not only that but it was made in April 2002 and does not have the front end disconnect. Does WireDawg have a disconnect? Smokin Joes has mileage like mine. Does he have a disconnect? I just went through this string again and there may be something here. I am going to start a new string survey regarding this. If this is the case I NEED HUBS!!!! George

 

[Wiredawg]

I'm Happy w/ Results

geusterman:



03 is getting around 16. 7 MPG. My 02 unfortunately does not have the front disconnect. I had a 00 2500 QC 4X4 LB w/3. 54s that all I got was around 17 MPG. My driving habits prevent me from getting higher mileage. I've tried to drive easy before, but can't seem to make it through a single tank. I've quit trying to see what the best I can get.



BTW, the 3. 73s in our 03 are turning the same RPMs that my 00 turned w/ 3. 54s. I guess the 17" tires are taller than the 265s on my 00, thus making up for the difference in the gain in the ratios.



I'm only getty 1. 3 to 1. 7 MPG better on my 03 2500 weighing probably around 7,500 lbs and my 3500 weighs 10,100 with both fuel tanks topped off.



Finally, I've pretty much decided I'm not going to do anything else to my 3500. I goes like a raped ape, pulls like 20 mule team borax and sounds soooo sweet. For all that, 15 ain't so bad. If your truck meets the above criteria, You might not be as bad off as you think.



Wiredawg

 

[Hohn]

Sorry, George-- I don't think the manual hubs are the cure-all you seek. They certainly won't hurt anything, though.



I have a late-build '02 that also lacks that central axle disconnect, but I still get mileage comparable to what others are getting WITH it.



I just don't want you to spend a bunch of moeny in hopes of getting big mileage gains and then be disappointed.



If you wish, put on the manual hubs and then report back to us what results you get. You just MIGHT see a significant difference.



HOHN

 

[Hemiville]

dd2s

I have an ez on the truck 01,, stock rear at 3. 54. You talk about adding dd2s at $500. Do you now have to change things in the auto trans ? More $, Can you ever justify the $500 as far as saving a little fuel? Do you have to have the dd2s installed by a shop? More $?? I haven't noticed any change in mileage since the EZ, A lot of diff. in the power , though. I'm afraid of doing any more to the truck, in the pursuit of better mileage?? I think not, as it always seems like you pay a lot to get very little back in mileage. Remember the old days,, Mallory, Edelbrock, dual exhaust ?? You NEVER got the mileage boosts they claimed you would. Want more power? O. K. but don't chase the mileage fairy!!

 

[WadePatton]

I've been holding out on this discussion.



Porsche (that's PORE-SHA) used to (and may still) include a graph in the Drivers Manual for the 911 of the power/efficiency curve for each variation of the engine (three that year). I forget the X and Y, but it showed where the engine was making the most power on the least fuel. It was a higher RPM than you would think.



Anyway, that's just an engine on a stand. When you throw it in a vehicle and try to get MPG, a couple of variables come into play.



Boost gauge tells me when I'm getting good/bad MPG!

 

[athompson]

This discussion has been quite entertaining. Everyone is make the assumption that the power curve peaks are the same RPMs for all throttle positions. I would be very surprised if this were true.



I'm sure that if all of our driving were at WOT, we would get our best mileage at over 2000 rpm. But, I rarely drive at WOT, and when I do it is for very short periods. My "real life experience" indicates that my best mileage is found between idle and about 1250 RPM. Sure, I can get 19 MPG at just under 2000RPM at 75MPH, but I can get 35 MPG at 1250 RPM at 35MPH using the same gear. If I down shift to get the RPMs back up to about 2000 RPM, my mileage reduces to about 22 MPG.



I would like to see power curves charted at real world throttle positions. That would be of greater value than WOT when discussing fuel economy.

 

[tbrudder]

Originally posted by Hohn

It is HIGHLY improbable that the decrease in BSFC at 2000 rpm offsets that HUGE increase in drag as you go faster. Remember, BFSC is in tiny amounts, and if it decreases from, say . 510 @ 1700 RPM to, say, . 490 @ 2000 RPM, then this is not that big a difference.



However, the difference in power required to maintain a certain constant speed (road horsepower) goes WAY up from 60 mph to 70 mph, which represents the approximate increase from 1700 to 2000 RPM.



The bottom line is that a small decrease in BSFC is GREATLY offset by the large increase in road horsepower, thus you WILL have lower mileage. There's nothing academic about it-- it's fact.

That's the point I was trying to make--if I didn't quite make that clear, well, what can I say--I'm an engineer, and if something can be said in ten words, a few hundred words must be better, right?



Anyway, I figured the BSFC would not change enough to make a significant difference. If the BSFC only changes by ~5%, but the BHP required goes up by ~60% (to used the numbers above)... well, we can see which term is the dominant one.



To translate that from engineer speak, go slower=higher mpg. Almost unilaterally.



And if any of you were curious, this isn't necessarily the case in airplanes. Since the wing lift also creates drag, there comes a point where your MPG (though we don't use that wording) will actually decrease the slower you go. Our trucks do generate some lift, but it's insignificant, compared to the drag. These trucks are not at all aerodynamically efficient, as I'm sure most of you know.



Maybe if we put a big bubble on the nose, and tapered from the roofline and the sides back to a point, like an ice cream cone shape. Yeah, we'd definitely get more MPG, then...



Oh, and on the fuel flow gauge:

I thought about the lubrication and bypass fuel, too. The only way to figure out the real flowrate to the engine would be to either put sending units on the high-pressure side (which would be problematic), or get it from the VP44. I would think that it would have to know what the flowrate to the engine is. There's a computer on the pump that talks to the engine computer, right? So it delivers the amount of fuel needed for the throttle position?

 

[John Berger]

After reading this thread last week, I decided to try the tried and true method to increase fuel method: Lighten foot. I shifted at a lower rpm through all gears, fastest speed attained was 62 mph, but in almost all instances I kept it at 60 or under. I also coasted to stops instead of downshifting. I reduced the amount of time I ran 45 mph in 4th gear considerably. I went from 15. 6 mpg on the previous tank to 16. 9 mpg on half of this tank. I want to try this when I don't have any planned trips towing the 5'ver, that way I can run it down to a quarter of a tank and see what the mileage is, but I really don't expect much of a difference. Funny thing is, I don't hot rod the truck. I really didn't slow down that much, but the difference is incredible. FWIW.