Engine fuel economy

One thing to remember, while looking at lifetime economy.
Fuel has been going up for several years, but most drivers did not start to really cut back to save fuel till recently.
Find out what RPM the sweetspot is on that engine and gearing, and go that speed. Many times you will find that the last driver (prior to fuel going nuts) was probibly driving that truck too fast for optimal economy. You may have a 7 mpg truck sitting there. Also, make sure that the engine idling was taken out. May be even higher.

 

I would say mpg's would be alot higher with a 13 or 18 spd. With 336's you would need to be doing 75 mph to use 10th and I'm not sure what rpm you would be at in 9th but it could be matched alot better with 13 or 18spds. You should be able to get a good deal on the truck though because not many people looking for a truck like that want a 10 spd

 

assuming 24.5 lp's he would be around 71, 72 to put him in the 1400rpm range. Dropping back to 9th would mean he would have to do 52mph to keep it at the same 1400rpm. I'd say theres alot of milage lost between rears and gears on that truck. Unless your up around Brickman running the flatland at 75 mph all the time. A 3.58 gear would do that truck some justice or a 13/18 spd. From my studies you want your truck to be no lower than 1200 rpm at 55mph in top gear and around 1400 rpm seems to be real close on the sweet spot for most engines as far as milage is concerned. I'd love to hear back from drivers as to what RPM#MPH=MPG's for them.

 

If we split the difference and say 1300rpm would be prime sweet spot on a CAT he would be in good shape with those gears. 67mph would net him 1315RPM with either 24lp's or 22 talls.
But at 55 he would be luggin her bad at 1079rpm. Dropping to 9th would put you at 1478rpm this is were that 13 or 18 would be nice to have. Dropping to 12/17 would put her at 1271rpm 55mph. This supports my opinion of a 13/18 being able to get better milage than a 10spd.





5mouths slips away to pat himself on the back heeheeheeheeheehee!

 

I tend to be a PITA and want you to "SHOW" me. Opinions vary but numbers never lie. Unfortuantely short of putting 2 trucks on a dyno with computerized perfect shifts to compare the theory of "letting off to shift more causes worse milage" I am going to stick to my numbers. With a 13 or better yet an 18 I can keep my rpms at a specified rpm giving maximum efficiency far better than a 10spd whether its a manual or an automatic. Even the automatic cannot make up for lack of gear ratios in between the top 5 of a 10spd.

 

They are very close to each other on the low side first 5. I was considering the lower gear splits for mountanous regions really. Otherwise there would be no difference between the 13/18 (5H and up) for milage gearing.

 

really for road work the lower splits are a waste you will hardly ever use them unless you are way heavy or really do low speed work