I have an 85 F150 351W that I am going to have to pull the motor back out on due to compression issues. When I have it out I was thinking about maybe trying to convert it to fuel injection using a donor truck (if I can find one) or maybe instead going with TBI from AFI. I can get the whole TBI kit for about 2K. Any ideas as to what I should go with? I am looking for a little better fuel economy becuase I cant seem to get the carb to dial in right and no one I know has been able to get it either. I also would like the idea of you turn the key and she starts. No more pumping the fuel pedal.

 

Well im not sure i think i would go fuel injection TBI dont know if its that great never had it but its like half carb half fuel injected somewhat but if TBI is cheaper and easier why not

 

Go buy a 4bbl manifold and new Holley carb for about $400(if you don't have a factory 4bbl manifold) with a new fuel filter, and everything will be kosher.

 

I have the 4bbl manifold already im just worried about the fuel economy do you really think a new carb would do that much to improve fuel efficiency compared to TBI or FI? I have a 92 GMC Sierra with a 5.7 and TBI and when I do about 65 on the highway i get as good as 19mpg out of her and she is extended cab full size bed with almost a thousand pounds of weight in the back. DO you think the ford could do that? I would much rather drive my ford than that GMC

 

A 4bbl will get better mileage than a 2bbl. But a fuel injection system will get even better if it has the closed loop system with the oxygen sensor.

Before you demand the same fuel mileage between the two trucks, make sure they have the same final drive ratio(overdrive, rearend gears, tire size). Large tires carry large mileage penalties.

19mpg is awfully good though. It's going to be hard to get that with your truck.

 

Yes, you will get better fuel mileage out of a modern electronic fuel injection setup, simply because it is dynamicly adjustible for all driving conditions, such as humidity, air / coolant temp and altitude. There are more, but these are the basics. A carb is not dynamicly adjustable and will only be perfectly set for one air / coolant temp*, one humidity level and one altutude level. At least perfectly set. A carb will of course work in other temps, humidity and altitudes, but it is always a compromise over that "perfect set up" on the conditions that existed at that one time.

*the choke, which some people say is how a carb dynamicly adjusts, is only for starting / warm up, a very limited range of driving and once the engine is warmed up, it opens fully and will not "dynamicly" adjust for air temp, humidity or altitude changes.

Regardless of what anyone can argue, you cannot get past this law of physics with a carb. Although they have worked pretty well for many years, there time is gone, as is bias tires for the street, unless of course it is not your daily driver, then it is easier to live with the shortcoming of a carb or bias tires on the street. The newer EFI systems are more durable, more efficient and frankly just drive better.

Between the TBI or multiport EFI question, either one is a dynamicly adjustable system, however the performance nod goes to the multiport. Ford did a pretty good, but not perfect with there multiport EFI systems, if you want to do a bit of work that would be probably the cheapest retrofit as most parts are available used. Of course that is figuring your time at not a lot, more of a learning and hobby experience.

My old 1986 F150 Supercab 4x4, stock tires with the 302EFI/AOD combo, 3.55 gears retuned a high of 22.8 mpg on the hiway once on a failry long trip. It would routinly return high teens /very low 20's in hiway driving. Plus it always started right up, no choking, no pumping, just turn the key and go. Plus no stalling like when you open up the throttle on a carb'd engine when it is cold was the icing on the cake, I could pull out in traffic with assurance that the engine was not going to stall.


My two cents - David

 

Thanks David that was what I was looking for. I realize that the GMC has overdrive thus making it get a little better fuel economy but If i was able to get 15-16 out of my Ford I would be happy with it. I have the time because right now the truck is sitting anyways cause the compression issue. Do you suggest going with a donor truck and strippin the parts off of that?

 

I would start with a donor truck myself. You are going to have to go with a newer donor truck and the only EFI engine in the 80-86 model years is the mid year 1985 EFI 302 and all of the 1986 302's are EFI. Both F150's and light duty F250's got the EFI 302 in 1986. (American spec trucks, I do not know what other countries had in the way of engines) Of course you could go with a EFI 302 donor truck and then get the 351w specific EFI items. If you get a mid 85 or 86 EFI 302, then you are getting a harness that will be correct for your truck, a little eaisier and more bolt in that a later harness that is set up for the later dash style. Still, don't forget you wil need those EFI 351w specific items.

One thought - these vintage trucks used what is a speed-density system, so they are more picky to engine mods. Some of the later trucks used a mass air flow system which are less picky but still can be thrown off by engine changes from stock. You may have to have use a custom chip / ECM if you are to far away from stock.

There is a really good Ford fuel injection site that can help you out, but I can't remember its name right now, someone know it ?????

I will add that what you are contemplating is not a weekend work, it is a bit more and will involve changing the fuel delivery system as well. This is where the donor truck comes in to play. Try to get one with the same wheelbase as yours, so you can use the fuel tanks / fuel piping as needed. The EFI systems use a plastic high pressure hose, different than your existing rubber low pressure hose.

Now this said - This is one area that the aftermarket system might save you a bit of work. As it is designed to be added on and not built in at the factory, add on systems are generaly less complex to add, but if you are considering a TBI setup, then it is in my opinion, less desirable that the mutlport, but still better that a straight carb.

And one last thought, if you are looking to only pick up say 3-4 mpg on the hiway, somewhat less around town, if figured on a cost basis, NOT considering the increased driveability, then unless you drive a lot, it will be some time before you payback the cost of the conversion.

Just more food for thought - David

 

Well the thing is is that I want to be able to take it with me to college next year in Minnesota. It would handle the snow alot better than the mustang so I figure I could drive it in the winter. But its about a 10 hour drive from home to school so I really wanted something taht I could get better mileage out of the Ford with.

 

If your truck doesn't have OD then that is the big reason for it's poor milage, an EFI motor will be slightly better but not a lot. You would be further ahead by changing the gearig to 3.08 or installing an OD tranny and keep the carb.

 

The only problem with the OD tranny is that they arent quite as tough as the C6 and i need a really tough trans.

 

I found I can get the whole TBI kit from Summit for $844 that includes everything except the oxygen sensor I would need to convert this over. What if I went to a 5spd Manual trans out of a newer F150? Would that help with mileage as well?

 

As long as it has overdrive, it will help.