I got a 2.9 for ranger 88 and I was wondering what would be the best mpg/power change over for the engine

 

Least expensive would be a another 2.9l.

Best power, at a reasonable cost, would be 1990-1994 4.0l engine swap
You need the computer and all the wiring in the engine compartment, including air filter box with MAF sensor from the 4.0l vehicle.
2.9l and 4.0l have the same block design so current transmission and motor mounts will match up.
2.9l will have slightly better MPG than 4.0l.


302(5.0l) V8 swap requires new transmission and mounts, plus all the new wiring, computer and engine compartment bits.


For better MPG in general you can change the gearing in the differentials for your needs.
Look on the drivers door label, at the bottom will be the AXLE code
Look here to see what you have: http://www.therangerstation.com/tech...le_codes.shtml

Find the RATIO, i.e. 4.10, 3.73, 3.55, ect.......
4.10 = better low RPM torque, for pulling trailers, but at 65mph RPMs are high so MPG is low
3.45 = less torque at low RPMs but higher top speed and lower RPMs at 65mph so better MPG

3.73 = the compromise Ratio, most common, can pull OK and has reasonable MPG at 65mph

The lower the number the better the MPG at speed, 3.08 is the lowest stock ratio.
4.56 is the highest stock ratio, you wouldn't drive this at 65mph, well you could drive it at 65mph but just to the next gas station, lol.
Since you have a 4x4 BOTH differentials need to be changed.

 

well I am thinking of buying a 1996 ranger with 4.0 that has been rolled I was wondering how much extra stuff I would need to get that running both manual I have 3.45 gears and I am running 33" tires

 

The 1996 will use the newer EEC-V computer with OBD II protocol, but you would have to swap wiring and computer anyway.

The '96 computer will also need a speed sensor instead of speedometer cable, on the '96 it is on the trans/transfer case and is just a removable gear with electronic sensor.
Problem is that your '88 speedometer needs the mechanical cable.
Dakota Digital makes the ECD-100, it takes the speed sensor signal and drives a motor to spin speedo cable, but at $300 it might be better to swap speedo gauge to electronic.

Fuel system on '96 is still the 40psi system so will work with your '88 system.

So outside of the speedo issue it should be fairly straight forward

 

so I sould be able to take the wiring out of the 96 and just get a new electronic speedo and the other thing is the 88 has 4x4 shifter on the floor and the 96 is a electronic switch I would like to keep it on the floor

 

Yes, keep the manual 4WD shifter.

In the '88 you will have the Mitsubishi FM146 5 speed trans and Borg Warner 1350 "Mechanical" shift transfer case, without External Front Yoke

In the '96 there will be a Mazda M50D-R1 and Borg Warner 1350 "Electric"
with External Front Yoke

The Mazda M50D-R1, IMO, would be a better transmission for the 4.0l and the Borg Warner 1350 "Mechanical" shift transfer case should just bolt onto it.

But the Mitsubishi FM146 trans will bolt up to the 4.0l, so you can use it as is.

The speed sensor from the '96 transfer case "should" just bolt onto the '88 transfer case, the '96 was just a gear for speedo cable but had a sensor added to it.

As far as I know the transmission/transfer case length will be the same on both so swapping to the '88 transfer case would mean the '88 drive shafts would just bolt back on since that's the transfer case they came off of.
But I have never done that specific swap.


One other thing I forgot, the OBD II system needs a "downstream" O2 sensor, to check if Cat converter is working.
I doubt the whole '96 4.0l exhaust system will fit under the '88 as is, but you will need most of it, and the wires to the Speed sensor and the back O2 sensor

 

I was also thinking of instead of buying the 4.0 and just going straight to a 302 but not sure on what I am going to do yet I am just not sure if the 4.0 will have enough power to turn my 33"s

 

2.9l rates 140hp @ 4600rpm
4.0l OHV rates 160hp @ 4200 RPM (1990 - 2000)

4.0l SOHC rates 207hp @ 5250 RPM (2001 - 2007)

Explorer 5.0l rates 215hp @ 4200

Swapping to a different size engine requires about the same work and cost in wiring.

The benefit in the 2.9l to 4.0l OHV swap is that the transmission/transfer case and motor mounting doesn't need to change.

For a 4.0l SOHC or 5.0l swap trans/transfer case plus drives lines and mounts need to be changed.
The '97 to '01 F-150 4.6l with trans/transfer case(manual if you can find one) might be a good choice.
4.6l(V8) rates 231hp @ 4750 RPM