1988 Toyota 4Runner
 

I recently swapped out the engine in my 1988 Toyota 4Runner. It had a 3.0 liter V6 that got horrendous gas mileage, for a 3.0 Liter Turbo Diesel engine from a 1994 Toyota 4Runner from Japan. I had an air to water inter-cooler added and it set up to run 100% bio-diesel. We turned the fuel down a tad, and turned up the boost. I am sitting on 35 inch tires, because I love to go on offroad trails and go to the offroad park. I also have a K&N Air Filter and a 3 inch exhaust. I plan to do some more efficiency mods here soon, I am going to re-gear to 4.10 gearing, it currently has 5.29, which will mean a lower RPM at highway speeds, a belly pan / front skidplate, wakeplates off the back set at 10 degrees, possibly HHO injection, and am going to do some work to the injectors, just not sure what yet. The best mileage I have seen was on the highway at 58 miles per hour. I got 30 MPG on a flat road. My goal with the modifications will be for 34 MPG on the highway.

Nice hood ornament :) Welcome

I just added a front skid plate for protection and aerodynamics. My truck is much quieter on the freeway and at 60 mph it runs about 150 RPM lower. Here is a before and an after picture.

Just put on a Hayden Electric fan. The old clutch fan was really heavy. So we shall see what this does for my MPG. The company claims 5-10 percent better MPG.

That is awesome stuff!!! Ide kill to get even half your hwy MPG in my 88 F150!!! Good luck with it!
Matt

Oh God bless you, sir. I miss my fourwheeling days immensely. So cool that you seem to have the best of two worlds: 'froading and good mpg. Keep up the good work!

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I will have some updates here next week. I am making a 1400 mile round trip on the highway after Thanksgiving so I should have some new highway numbers. I am going from Sacramento California to Tacoma Washington and back for a business trip. I have even found enough bio-diesel stations along the way to use it the whole way and back. I love Bio-Diesel...even if you dont always get as good MPG, its made in the USA and keeps money here. That is what really matters. I can feel good about what I am buying knowing it isnt going to help somebody who wants to eventually shoot me in the head.

How does adding a skid plate lower your rpm at any given speed?

I am assuming that it is because the engine isnt working as hard to push the car through the air, so it runs at a lower RPM. However, this is an assumption, because I dont really understand the gearing as much as I wish I did. All I know is that is what my tach is reading. I have had it on and off several times and it is always the same.

The only way you would see a decrease in engine RPM is if you are changing gears or if you have a CVT transmission. I would assume you have an auto trans bolted to this engine? Most Autos have a 1:1 ratio in thier "3rd" gear with an overdrive of around .8:1 If you are not bouncing between gears then your engine speed will not change regardless of how aerodynamic your car is at a set speed. NOw the advantage to you getting the 4Runner more aerodynamic is that you can reduce your rear axle gearing as it will take less HP to move it at a set RPM. So lets say you make 120 HP at 3000rpms (diesel) and currently you are traveling at 65 mph at 3000rpms...if you make your car more efficent at speed you may only need 80 hp to maintain 65 MPH so you could re-gear your truck to 4.11 or 3.73 and drop your engine rpm down when cruising at 65 MPH. Hopefully I explained this alright.
Here's a calculator that is really fun to play with. You can enter in your gear ratio and your automatics final 'overdrive' ratio and then see how a gear swap will decrease your engine rpm at a given speed.