What mpg could I expect?

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ebutlerfj40

ebutlerfj40

Joined
Jun 30, 2005
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Location
Mayview, MO
I am considering a diesel swap in my fj40 for better fuel mileage.
I have a FJ40 with a spring over, 4.10's, 35 AT's, & H55 trans. I have found a place to get a good deal on a used 4bt cummins. With my setup, any thoughts on the mpg? Thanks, Eric
 
If it's geared low enough(meaning low rpms)..... or would that be high gearing...I dunno.

One guy on here had a 60 done at profitts. he claimed over 20 mpg US gallons.

Go for it. Then you can burn veg oil or bio diesel. Even cheaper.
 
Yeah, I would really like to run bio diesel. I don't have time to go the svo route though. I was thinking with the 35's, 4.10 gears and overdrive in the H55, that the highway rpms would be reasonably low which would help the mileage. Any one out there with a similar setup?
 
The MPG your truck gets will depend on the cruise speed RPMs you choose. On the 13B-T if I keep the RPMs around 2500, MPGs in the mid 20s are possible.
 
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4BT is gonna want to run much less than 2500 for mileage. i have 4.10 and 37's, with 5 speed i do about 1800 at 65mph.
 
I can't say much about the 4BT.

My BJ60 got as high as 28mpg on stock tires and gears running full out on the freeway with PetroD -- 3300rpms. That was before I had the H55 installed. (Still on my first tank of B99 since the swap.) I expect about 24mpg mixed driving with the H55, 31"s and BioD.

With your setup you'll be running at 2400 rpms at 75, which you probably already know. RPMs aren't everything though as you'll have a lot more drag than my rig with the lift and tires.
 
Best rpm for economy on a 4BT is around the 1700 range. Unlike toyota, cummins publish fuel consumption curves for their engines.

Head over to www.4btswaps.com and take a look. It's another website run by Dieselcruiserhead.
 
So would 3.70's be a better choice for the 4bt with H55 & 35's? My dodge truck has 3.73's and 31-32" tires and seems quite happy. It is a 05 which may be happier at the higher revs. Though the older 12 valve 6bt motors were available with 4.10's though they surely were limited on speed.
 
start with what you have and go from there.
 
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