Fuel Economy

[jelag]

For a number of years I sold and install test equipment including dyno's... .



Fuel economy always came up... . even the 100 mpg carb that the oil companies bought up to keep off the market...



After a few shorts months of working with a couple of engineers and now having a mechanical engineer for a son... let me share a few things especially since the latest issue of the TDR focused on Placobo's... . (did I spell that right)



I taught that it took a certain amount of HP to over come rolling resistance, vehicle drag through the air etc... . we used to go out and set base standards while driving on the road and come back and connect to the dyno and duplicate those standards... . and with fuel senors we could monitor the fuel used... .



I learned that as the speed doubled. . the wind resistance to the front of the vehicle was a X4 factor... . so from 10 to 20 mph the wind resistance was 4 times harder to push through than at 10... . so you see why gains of 20 to 30 mph at the Salt Flats are hard earned speed..... 20 to 40 is again X4 now 8 times the 10 mph standard... .



I would never expect these trucks to ever get more than say 5% better fuel economy than they now do... . you'd get that 5% by finding the sweet spot for each truck... . any more than that is just plain hog wash... ..... The physics of what it takes to get there tells you it can't be done.....



Remember that each maker of truck has to meet CAFE standards. . as outlined by the FED's and covered in this issue of the TDR... . it means that if you look at each of the car companies their giving away the little cracker box... at cost or close to it... . for each one they can sell means they get to sell 2 or 3 big PU's... . who knows maybe 4..... The crux of all this is that don't expect any improvements from the things we might do to bomb our trucks... ... nothing is really going to change and my personal guess is that your mileage is going to go down..... as you try to go faster. . or faster from a stop sign or light..... if the makers of our truck or engine could sqeek another 5% out of the fuel... . in extra mileage they'd do it in a heart beat... .



It was said in the TDR that if you want mileage, keep the EGT to below 600-700* and the boost below 10 psi... . like running with a vacuum gauge in a car... ...



Now if you want to just go fast... pull that hill... and just have fun. . bomb the *ell out of it... but don't expect more MPG... its just not in the cards... .



Jim

 

[RACE427]

fuel mileage

If you could advance the injector pump timing a couple of degrees I am certain the fuel mpg would increase. Keeping the tires inflated to their maximum recommended pressures would help some along with streamlining the body, example; remove those tow mirrors, mud flaps etc.



Just a thought!

 

[jsimpson]

You might want to add the best scenario/worst scenario factor: Those who brag about their fuel economy are likely giving a figure they get running unloaded on long downhill stretches on cool mornings with 85 pounds of air in every tire and the wind at their back. Those who like to complain about their fuel mileage are likely giving the worst figure they ever recorded, and are just disappointed because their mileage isn't as good as it was on their old Dodge with half the power. Somewhere in between is what you should expect. Of course there are exceptions and some trucks just plain do everything better than other, identical, trucks for no discernable reason. But I get fourteen and a half on the average with my 03 HO quad cab 4WD automatic, and that's better than my wife's Tundra gets. It's not what my 94 got, but the 94 was a single cab, five speed 2WD with half the power! And when someone with the same vehicle as mine but a 600 engine claims he's getting better milegae than me, I just congratulate him : he's getting his money's worth!

 

[WStoops]

I just got back from a 2,000 mile vacation trip with my 04. 5. On the way out I drove 1,255 miles and used 60. 3 gals which equals 20. 8 MPG. On the first leg I went 655 miles on 29. 1 gal. s, second leg used 31. 2 gals for 600 miles. Second leg included some extended dashes to 75 mph, sometimes for 10 to 15 miles until the vibes made me crazy. All the news is not good though. I have that nasty vibration at 70 MPH and above. It actually starts around 62 MPH but there is a spot at 67 mph where is seems to be a little better. So I drove all the way at 67 MPH. Also the roads were flat going south from CT. My A/C, which seems ok here in the NE was definitely not ok in Georgia, stuck in traffic, at 95 degrees. Didn't cool much below 1500 rpms. At idle the air came out at about 80 degrees. Also have the hard pull to the right. Some good some bad. Also those MPG figures were for 95% hwy, 5% in town. I get 16. 5 around our towns which have few stops. In bigger towns with lights and more stops, speeds in the 30's. I have been getting 15.

 

[Badunit]

if the makers of our truck or engine could sqeek another 5% out of the fuel... . in extra mileage they'd do it in a heart beat... .

Jim

I've heard that said before and I don't believe it's exactly true. They would do a cost/benefit analysis and do what is best for the bottom line. If they can sell all the trucks the public will buy and still meet their overall mpg standards, there's no reason for them to increase mpg if it also adds cost. If Dodge can shave just $1 off the cost of the truck, that adds around $500K additional to the bottom line. Do that a few times and you're talking some real money.



I can say with all confidence that adding a Banks Monster exhaust and synthetic oil has increased my highway (70+ mph) mileage by at least one mpg and probably two. I can't say how much I got from either separately because I did them at about the same time but I attribute most of it to the freer flowing exhaust. I never saw the mileage I'm now getting (20+ mpg) before this mod.



You would think Dodge would do the no-cost mods such as advancing the timing (assuming that would add mpg) unless there is a downside. The only reasons I can think of that they wouldn't do that are 1) it creates additional power that increases the failure rate of other parts under warranty, 2) there is a downside related to drivability and they feel their programming is the best all-around compromise or 3) they aren't that smart (which I think is unlikely).

 

[jsimpson]

The only reasons I can think of that they wouldn't do that are 1) it creates additional power that increases the failure rate of other parts under warranty, 2) there is a downside related to drivability and they feel their programming is the best all-around compromise or 3) they aren't that smart (which I think is unlikely).

I don't know about diesels, but on gas engines you'll definitely get some really higher EGT's by advancing the timing. Not good if you have no guage, and the average driver won't watch the guage anyway. I'm planning on a Donaldson muffler next. I'm assuming my HO 03 already has a 4" exhaust all the way back.

 

[Badunit]

I wouldn't make that assumption for an '03. That may be true for an '04. 5 but I think '03's are not 4" the whole way. Mine wasn't.

 

[klenger]

4" exhaust started in 04. 5 with the 600 engine.

 

[jelag]

On a gas engine, the air and fuel are in the combustion chamber as the piston comes up to during the compression stroke... because of the time delay to creat the spark and get the flame to move across the combustion chamber the spark starts before TDC (top dead center). Based on the octane of the fuel it might be as much as 40* of crand rotation..... higher octane means longer burning fuel... . less chance for knocks. .



On a diesel combustion starts as soon as fuel is injected into the cylinder... If the fuel starts to inject before TDC than this combustion will have an ill effect on the outcome, or the work that this cylinder is doing... as the combustion before TDC actually reduces HP... . So diesel injection starts at TDC and continues after TDC. . and in some cases you retard the injection to improve it... Higher cetane rated diesel fuel burns faster..... the faster it burns with the piston at the top after TDC the more power produced... ... ...



Often we hear the word advace used when were talking about our fuel injection pumps... and I'm sure that the user means to advance the timing of the pump to increase performance... . however adjusting the pump into the advance direction. . where injection occurs before TDC will create knock and piston damage... .



Jim