Mileage and Higher RPM power

[Dfeland]

Yes I know that many people have posted this topic before but here it is again. I realize that I have the worst combo for mileage I barely break 15mpg city and only get about 16 highway. Do you guys feel that this is normal. I just bought the truck it has been meticulously maintained, you sould see the engine it looks brand new, seriously. I don't know when the valves were adjusted last. Will this affect mileage? Also at higher RPM's I don't really have the poop to pull, about 75 is my top speed and I feel like it should be higher than that. Also where does everyone buy their injectors and who has the best price? Any info would be appreciated. BTW I have a factory service manual for a 93 if anyone needs info or wiring diagrams lemme know. Thanx.

 

[Matt S]

75 mph in direct with 3. 54 gears is what I get. Are you positive that it is shifting into overdrive? More power will increase your mileage too. I would give Big Don a shout about injectors, etc. Do a search of his name and it should come up.

 

[Dfeland]

Yes it is going into overdrive.

 

[Scott Elliott]

My truck is pretty much stock and I get 18-20 (usually around 18) city and highway. My top speed is also about 75 mph (in overdrive), but I try to limit it to 65 mph for rpm/mileage reasons. At 65, I am looking at about 2000 rpm's, and 2300 around at 75 mph.

 

[Bob Beauchaine]

The more I read postings concerning mileage and auto trannys the happier I am with my 5 spd. I am running 3. 54s and usually see 12. 5 to 15mpg when towing (12,500 GCW). Most of my towing has been in western mountains. When empty it's 18mpg in town and 22mpg on the highway. I have kept track of every drop of fuel I put in my '93 and after 138,000 miles, including 30,000 miles towing my average is 18. 34. As you can see by my sig. I am far from stock. Every upgrade has improved preformance and mileage. If I am not using my cruise control it will run at 80mph quite easily. The closest I have come to my top end was before my mods and that was 90mph going up a long 2% grade.

Happy Trails

 

[drturf0]

something is wrong with those trucks mine will run 95 mph @2300 rpms and is pretty much stock and i avg. 18-19 around town and have gotten as high as 23 mpg on highway . also mileage depends greatly on the weight of the drivers right foot.

 

[Midnite]

drturf0, mine is also a '92 and basically stock, and I can also hit 90 with ease. The *only* performance mods I've made are:



1. replace stock muffler with 3" straight-thru muffler

2. turn up full-power screw all the way to the shim



However, I also have almost brand new injection and lift pumps, so maybe that's helping things.



Mike

 

[AlK]

I am with Bob. I am happy that I have the 5 spd.

FWIW my truck achieved the following maximums on a flat road with the truck empty and no headwind.



2 gear = 29 miles

3 gear = 50 miles

4 gear = 75 miles

I have not yet taken it up to the maximum in 5 gear but 100 miles maybe a possibility.



Another good place for injectors and help with your truck is Piers.



http://www.piersdiesel.com

 

[Matt S]

Dfeland,

Hmmmm. I'm not an auto guy but you may want to try to get a locking torque converter if it is possible with that transmission. I think that it is slipping trying to push your truck at that speeds. Your truck should have a better top end than the 5-speeds as my ratio is . 77 and I think yours is in the . 69 range. You could also try to adjust the max RPM's to get a few more for a better top end.

 

[Jim Curry]

Hey Dfeland'



As you can see from my sig. I also have a 93 auto. Sure I am Far from stock but even when I was stock I was able to hit 90 to 95 mph unloaded with not much problem. I do not tow very often but now unloaded I can easily reach 95 + with 30 lbs of boost. I have not pushed it that hard since some of my latest mods,(timing,propane, bhaf) but I will see what effects these have had in the not to distant future. Adjusting the vaulves will peak booth power and millage including your top end speed in most cases. Particullarly if they are out of specs buy a good amount. I do not think however you will go from a top end of 75 to 90 or 95 with a vaulve adjustment unless they are way out.



PS: Unfortuneately you can not put a lock-up converter in a first gen auto. You would have to convert over to a 47rh transmission out of an early secound gen truck to have a lock-up converter. Have your 518 checked and/or overhauled, installing a shift kit and a DDT 518 TC. (89% or 91% are available)





Jim

 

[Bob Beauchaine]

I'm seeing the same speeds as AlK in each gear and also feel that 100mph is not out of line. With the NV4500HD my OD is . 74 and at 65 to 70mph it runs about 50-100 rpm slower than my old Getrag did which helps mileage slightly.

Happy Trails

 

[rdodd]

After setting my pump up to 3000 rpm my 92 auto 3. 54 will hit 100 mph. Before setting up governed speed it would make 92 mph. I have a friend with a 92 5-speed that runs 3. 07 rear and he can top 105 mph.

 

[NuttyMopar]

I am able to hit around 90 mph maybe 95 if I push it. Mostly going down the highway, downhill. LOL. I usually drive around 75 - 80 on the highway because of the hills in VT. the truck just cruises right up them without a problem, anything less and I end up putting my foot into it to pick up the speed I loose at the bottom of the hills. I usually get around 18 mpg with the best being 21 mpg when I keep my foot off the floor. I agree with all the talk though about more fuel & power = better mileage. Truck just seems to get better the more you put into it.