Engine/Transmission (1994 - 1998) Ways to Acheive better mileage

[Hillbilly Hotrodder]

Hey, I got a question. I got a 98 dodge a while ago. Its got the 12 valve with 5 speed and 3. 55's with 90k miles. Right now the truck has a complete 4 inch exhaust on it and 300hp injectors. Now, im not after anymore power and wont be in this truck. But i am after more mileage. ive been sifting thru the forums and read up on most things. I am going to bump up the pump timing to about 15. 25 degrees. I think thats a happy medium. But right now the afc housing hasnt been tampered and the camplate for the injector pump is a stock 215hp. Im wondering what number plate would help with my mileage if any. I plan on changing the rear/front end fluid to syn and probably the transmission and t/case. Also, it just had a new stock DC clutch put in it. So its good, but not for 1000 ft/lbs.



awesome site!

 

[Forrest]

Order up a #11 plate. It's pretty mild on the low/mid end ... for your every day easy driving.



http://www.dieselpage.com/tstpk.htm



I had exactly your setup, only with the #8 plate as a starter. Mild low/mid end in the 215 pump like ours & crazy fast acceleration on the high end. It helped with mileage. Gotta watch EGT with it though. I actually ordered a #12 & got the #8 by mistake & didn't check the #.

 

[Cooker]

Do not expect synthetic fluids or the mild timing bump to help MPG's much. JMHO

 

[Forrest Nearing]

put a mild plate in it, tweak the AFC to yield better acceleration without smoke, and slow down on the highway



forrest

 

[sewman]

So what kind of mileage are you getting?

Bob

 

[Vaughn MacKenzie]

Bumping my timing from 13. 3 to 15. 25 kicked my mileage up a solid . 5 to 1. 0 MPG. The first two full tanks afterwards netted me 17. 4 with 90% of it running around town, then 19. 7 on a highway trip at 70mph, the best I've ever gotten with this truck. Previous best was 18. 7.



My injection pump is overdue for a real tune-up and going through, and I'm hoping that will improve my mileage as well.



Vaughn

 

[Cooker]

I wish I could do something to get better mileage Timing didn't help me much but I sure don't drive with fuel mileage in mind



I think mileage on these 12v's is all about the driver. My fathers can get 23. 5 on the highway with his truck (1998, 2500, 12v, quad cab, 4x4, auto, bone stock) I have taken his truck on a couple highway trips and I get just over 20. I must have a heavier right foot



Maybe a list of things that hurt mileage will be easier, larger delivery valves and driving over 2000 RPMS on the experssway.

 

[Hillbilly Hotrodder]

Thanks for the replies so far fellows,



First off Im not complaining about what I get. For a 7000 lb monster its good IMO. With mixed freeway driving for the last 600 miles at speeds from 65 - 75 I got ~19. 5. Thats with a 6% increase I added from the 285 tires. I dont expect to get alot more milage.



But I think its enough to warrent me making some changes. Im also thinking about moving down to 265/75/16s and putting a gear vendors overdrive on it. I havent looked far enough into this for an overdrive ratio, but i estimated 20%, which would put me at 80 at like 1800-1900 revs. Nice I thought.



Forrest's, do you think adding the plate without the G/V will actually help with milage if I run the same speed? If I put the G/V in, I would probably do the plate. Also assume, that i would buy a used g/v on the cheap.



Right now im trying to stay away from a camplate if its not going to help with milage. Cause as many of you know. At least once in a while, if you have it youll use it.



Any other suggestions?

 

[Mad Bomber]

Gv

Thanks for the replies so far fellows,



putting a gear vendors overdrive on it. I havent looked far enough into this for an overdrive ratio,

Any other suggestions?

Some people that work in a local shop have alot of problems with the GV. Robert who also drives for a living and delivers trailers all over the US HAD a GV and said that they are a POS and our trucks have too much torque for them. Come over to www.nwbombers.com and ask about them.

 

[Forrest Nearing]

reducing engine speed a couple hundred rpm isn't going to do much... the engine still has to generate the same horsepower to push the truck against the wind resistance...



I bet if you dropped out of overdrive and just ran it in 4th gear at 65, you probably wouldn't see a 1mpg difference by running the same test in 5th at 65.



engine rpm isn't the big killer... wind resistance is... (and rolling resistance/etc. ) that's why slowing down nets better fuel mileage, not because of the reduced engine RPM.



Forrest

 

[Cooker]

engine rpm isn't the big killer... wind resistance is... (and rolling resistance/etc. ) that's why slowing down nets better fuel mileage, not because of the reduced engine RPM.

I'm not sure I completely agree with this statement. Certainly wind resistance/rolling resistance plays a factor in MPG's but there is a reason the guys with 4. 10's net lower MPG's than those of us with 3. 55's, they are turning higher RPM's for any given speed.

 

[pwerwagn]

I have a 98, 12V 5-speed, 3. 55's and 285's with a #11 plate. My mileage went from a best of 19 when stock to my new best of 20. 5 with the #11 about . 030 foward, afc full foward, starwheel 7clicks from loose, and I drive for mileage. I rarely ever exceed 5psi when accelerating, (yes, its hard to do) and try to stay below 65 on the freeway (that one doesnt happen to much, 65 is to slow).

 

[DieselMinded]

http://list.priceweber.com/cummins/turbo_oct04/economy.html



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