Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - ///// How many extra MPGs can you get driving at the best BSFC of your engine ? /////

Andyinchville1 · 10-01-2023, 12:23 AM

Hi All,

I have a 1990 F250 4x4 that I tow with (approx 9000 lbs). It has the 7.3 IDI engine (NOT Powerstroke so not alot of power but durable and cheaper to fix BOTH plusses in my book ).

Anyways unfortunately the auto trans is having issues.

With that, I plan on going to a manual tranny for better pulling power and possibly fuel economy (technically I should not say better pulling power since the factory rates the manual tranny version at less to capacity than the auto tranny BUT that is only since the factory 5 speed is not a granny low version so getting a heavy load rolling requires a bit of slipping of the clutch (not good) BUT once under way most people with the 5 speed like it more than the 4 speed auto because it has 1 more gear to keep the engine pulling better.

Anyways, since I have to change the tranny eventually anyways, I was thinking it may be better to use a big truck transmission (10 , 13 or go for broke 18 speed trans) to have lower first gear starts and more gears to keep the engine in it's "happy" BSFC zone.

My question is .... how many extra MPG's can one hope to get by keeping the engine in it's best BSFC rather than just working it haphazardly because of limited gearing ? ( I do realize there would be a weight penalty / possible frictional losses with more gears BUT I think operating the engine in a better BSFC range would or should more than offset that ..... hopefully!

Anyways ... what are your thoughts?

Thanks!

10-01-2023, 12:23 AM	#1 (permalink)
Andyinchville1 EcoModding Lurker Join Date: May 2016 Location: Virginia Posts: 44 Thanks: 2 Thanked 20 Times in 15 Posts	///// How many extra MPGs can you get driving at the best BSFC of your engine ? ///// Hi All, I have a 1990 F250 4x4 that I tow with (approx 9000 lbs). It has the 7.3 IDI engine (NOT Powerstroke so not alot of power but durable and cheaper to fix BOTH plusses in my book ). Anyways unfortunately the auto trans is having issues. With that, I plan on going to a manual tranny for better pulling power and possibly fuel economy (technically I should not say better pulling power since the factory rates the manual tranny version at less to capacity than the auto tranny BUT that is only since the factory 5 speed is not a granny low version so getting a heavy load rolling requires a bit of slipping of the clutch (not good) BUT once under way most people with the 5 speed like it more than the 4 speed auto because it has 1 more gear to keep the engine pulling better. Anyways, since I have to change the tranny eventually anyways, I was thinking it may be better to use a big truck transmission (10 , 13 or go for broke 18 speed trans) to have lower first gear starts and more gears to keep the engine in it's "happy" BSFC zone. My question is .... how many extra MPG's can one hope to get by keeping the engine in it's best BSFC rather than just working it haphazardly because of limited gearing ? ( I do realize there would be a weight penalty / possible frictional losses with more gears BUT I think operating the engine in a better BSFC range would or should more than offset that ..... hopefully! Anyways ... what are your thoughts? Thanks! __________________ 2003 Jetta TDI Wagon, 5 sp, 210K miles, Stock.....for now!