that helps thanks, i just put a 16cm on my 93 I C , wondering if i shud have gone smaller

 

i would say 12cm is best for manual and 14cm is best for auto.

 

My ears must have been burning

I have the 89...Gear Vendors wasn't on there with the 47rh OD trans, but it is light, 2wd, with lots of timing, and a 3.07 rear. Also the 29mpg was at 60mph. At 70-75, more like 24-26, which I still consider good. Unfortunately mud tires, different gearing, less timing, more weight, etc, etc will ruin that mpg figure. It just so happened that my drag truck theme coincided with mileage.

 

We also had a gent on here,went by crabbelle, been several years now.

He was the king of MPG with the Cummins.

https://www.dieseltruckresource.com/...33-mpg-206843/

https://www.dieseltruckresource.com/...n-drag-192608/

 

Crabbelle was the king, he ended up getting 35mpg I think before he sold the truck. Went further than I did for sure. half-ton suspension, lowered, air dam, double overdrive, etc.

 

All I can say is 4bt in a 79 w150 5speed 3.54 gearing is getting 26 , so I dont think running 2 more cylinders will get better MPH

 

5 speed and 3.54 -vs- auto and 3.07

example in numbers

60 mph x 0.77 OD x 3.54 x 31" tire = 1773 rpm
60 mph x 0.69 OD x 3.07 x 31" tire = 1378 rpm

also timing and keeping the cruising boost near 0 psi is huge.

 

Back in the 70's when gasoline skyrocketed to 60 cents gallon people were putting Perkins and kiki diesels in their full size pickups and claim 50 mpg.

There are ways to get exceptional mileage if you had too but it would not be fun to do so, some are 90 psi in your tires forget air conditioning and a lot of coasting.

Also probably impossible with a 4X4 because of the weight and aerodynamics.

 

I think I'm doing pretty good getting 20-21 hwy with a 2wd dually. 19.5s at 90psi, 518 non lockup with a goerand converter and 3.07s . Usually drive about 70mph.

 

Don't know about 30+ I get 23 out of 91 d250 518 trans and 3.07 gears. That's at 70-75 mph My friend gets 27-28 out of a 95 3/4 ton 5 speed at 60-65 mph Those are real numbers. If I drove the d250 at 60-65 I am sure those numbers would go up. We drive 100 miles to work 5 days a week, so we do a lot of testing.

 

That's crazy mileage for a p pump 5 speed. Must have some high gears in it and drives real conservative. It really doesn't help that a 1st gen is like running into the wind with a sheet of plywood.

 

Yeah, he does drive for numbers. One thing I forgot to mention about the p pump is that it has 350K on it!

 

i have learned the secret......its parked in the driveway most of 2015 and drive my altima gets me 34 mpg..............iv'e only used about 20 gallons of diesel fuel in a year,top that! my truck has over 270000 miles and runs like new

 

ya, but you don't get the pleasure of driving a 1st gen as a daily driver. i don't drive my truck because it gets great fuel mileage. i drive my truck because i love it. It's loud, it rides like a school bus, the seat hurts my back after a couple hours, the windows aren't tinted so the sun beats on my neck and i sweat no matter how high i run the AC. yet I still manage to keep a smile on my face because i love that danged old truck.

 

Yeah, my Focus gets about 37MPG. Just can't pull 11,00lbs worth of 5th wheel though. I drive my truck every fricken day that I can. I love it to pieces and I don't give a rats a$$ what it costs me.

Cheers!

Mike