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4.0L vs 2.9L


jkufen

jkufen

Well-Known Member
Joined
Mar 29, 2012
Messages
528
City
Charleston, SC
Vehicle Year
1986, 1991
Transmission
Manual
I have an 86 B2 4x4 2.9 and my dad has a 90 Ranger 2x4 4.0 and both of our motors have high mileage so we are gonna pull them out and rebuild them. My question is he agreed that if I wanted to we could swap motors because he just wants decent gas mileage and Id like a little more power for some bigger tires. I already have a thread related to the gears but I am curious for everyone out there is there a significant difference between the motors? Is it worth the swap or is my 2.9 just as good? Thanks for the help!
 
it's worth it if your not buying the motor and if your having it completely rebuilt have it punched 30 or 40 over then it'll be hella worth it
 
and have the heads port and polished its not much more money.
and the cyclenders being pucnch dosen't cost any more just the pistons are a lil bit more but honestly not much
 
The difference in mileage between the two motors is not enough to make that swap worth it. I would either just rebuild them where they are, or even better, swap the 2.9L for a 4.0 at the same time (so you both will have 4.0Ls).
You'd also need to source a 4WD 4.0L transmission for your BII as well (a 4.0L will cook anything that had a 2.9L in front of it in fairly short order if you try to get on it at all, the M5OD being the lone exception).

Just as a reference, I get about 22 MPG (maybe occasionally touching 23) with my 2.9L in my BII, about 21 MPG with the 4.0L in my Ranger (both trucks are lifted, motors are in healthy condition). The 2.9L's lack of low end torque (forcing you to rev it out more) makes it seem like it's always straining harder, even though the HP difference between them is only 20 HP.
 
Last edited:
well if thats its going to require another transmission and everything I wont do it. My dads truck is 2wd with the 4.0 motor and tranny but if i got to get another tranny its not worth it to me. We were rebuilding the motors anyway so figured it be an easy swap but i guess not
 
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