'91 F150, Straight6 300 EFI as starting platform? - Pirate4x4.Com : 4x4 and Off-Road Forum
 
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Old 07-09-2010, 06:41 PM   #1 (permalink)
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'91 F150, Straight6 300 EFI as starting platform?

Hey, I have a '91 F150 with a Striaght 6 300ci EFI engine. Manual 5-speed with 3.55 rear. I've had it for a few years, it's been a daily-driver for less than half that time, mostly just hauling firewood and other loads occassionally (2-3 days a month at most). The guy I bought it from, had it for I believe 7 years, and just used it to haul his boat to the bay now and again. Currently it has 124k on the engine (unless it rolled over once prior to him buying it) but I'm not sure.

I've been thinking about building it up for off-roading. I've spoke with a local off-road company about lifting it - they can do 6" suspension lift, a short body lift, etc. I've looked up tires sizes that'll fit with said lifts and maybe a little cutting of the fenders. Calculated the gear ratio I'd need for the larger tires, etc. All in all, I love the truck, I'm not a huge Ford guy - though the truck has been growing on me. And I know absolutely nothing about fuel injection. So here's my question(s)...

Would (could) that straight 6 put out enough power with the right gear ratios for bogging through mud and snow and mild rock climbing? I'm under the impression (perhaps because I'm new to wheeling) that the straight 6's low-end torque with some gnarly low-end gear ratio would make the thing a machine. Or would the straight 6 simply come up short in power?

I know I want to stick with a truck as my vehicle. I don't plan to do much rock crawling, with 80% of my "off-roading" being mud and snow. The rest being rock crawling and just extremely steep, loose gravel roads out in the hills.

Should I swap out the EFI for carb? If so, what are the pro's and con's to each? How hard would it be to swap out the straight 6 for a V8 like a 460?

I guess I don't know if the aim should be high RPM HP, or low RPM torque? What do you guys focus on during a build? Could this be an awesome machine or ultimately a money sink-hole w/o performance?

I realize I asked a bunch of very vague questions, but I hope I can learn a bit from you guys so I can make a wiser decision. Thanks for your time!
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Old 07-09-2010, 09:19 PM   #2 (permalink)
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The straight six can be used if you gear accordingly they are tough as nails also just dont expect to run 7.17 gears and a straight six in the mud with great results. As for a bolt on lift kit in a shop that is really money down the drain it would be better to either fab the suspension or have a shop fab suspension because you would be paying for an improvement in performance instead of looks and a little ground clearance. As far as could the truck be good or just a money pit well it can be as capable as your willing to pay for but all wheeling rigs are a money pit simply because you will never sell it for what you invest so plan on driving it till theirs nothing left if you wanna build it and not lose your ass selling it
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Old 07-29-2010, 06:52 AM   #3 (permalink)
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i have had mine for 15 years and the straight 6 has been really good for me, but i have only used it for mudding in rice fields and swamps here in louisiana. i was running some 38.5" x 14.50" tsl-sx with 1/2 ton axles loaded with 4.10. the only difference for me is that i have the t-18 granny 4-speed. it makes a hell of a difference. i always play in 4-hi with it and it has 165,000 on it. just reciently i swapped to a 3/4 ton running gear and it seems the same just will have less likelyhood to break and i was going to put 44 on it but now i just want to sell it. the 460 is an easy swap just get the computer with a motor and you will need to get a new bell housing to fit it.
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Old 07-29-2010, 07:48 PM   #4 (permalink)
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I would say that the 300 is a pretty good motor. My second truck i built was a f-150 with an inline 6, injected, and it kicked ass. the the only bad part was I could not keep motor mounts holding that motor down. I wheeled it for about 2 years, and with it being injected i was able to climb hills alot better than all the carb'd motors i had.
Secondly the front axle is fine as long as you don't abuse it. But with what you are planning on doing with it, i would say look for a d44 high pinion out of a late 70's f-150. They have coils and radius arms. Look through the Ford section, you can find many people who have dont that conversion, even on rangers.
Good luck
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Old 07-30-2010, 05:30 PM   #5 (permalink)
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Originally Posted by stynky View Post
Secondly the front axle is fine as long as you don't abuse it. But with what you are planning on doing with it, i would say look for a d44 high pinion out of a late 70's f-150. They have coils and radius arms. Look through the Ford section, you can find many people who have dont that conversion, even on rangers.
Good luck
That truck already has a high-pinion D44 under it, it's just built into two sections is all. It should hold up as well as any other D44 if you avoid the shit suspension lifts like Midwest Ford Wheeler mentioned (though unfortunately, almost everything out there is shit). Skyjacker is one of the very few with some good parts that could be used to build something out of it without having to dig near as deep into the wallet as a total full-custom buildup would normally call for.

I guess I should probably ask before going too far... What size tires are you thinking of running on it?
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Old 07-30-2010, 08:46 PM   #6 (permalink)
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That truck already has a high-pinion D44 under it, it's just built into two sections is all. It should hold up as well as any other D44 if you avoid the shit suspension lifts like Midwest Ford Wheeler mentioned (though unfortunately, almost everything out there is shit). Skyjacker is one of the very few with some good parts that could be used to build something out of it without having to dig near as deep into the wallet as a total full-custom buildup would normally call for.

I guess I should probably ask before going too far... What size tires are you thinking of running on it?
I broke the stock axle to pieces with 33'' swampers. The hubs went out a couple times, bearings went out twice, and the springs got so bad from the 'flexing'(as much as it could flex) it looked like i had an extra 1000# on the front end. Thats why i was recomending the SOLID d44. But you could always bolt on the 3/4 ton d44 or d50 out of the 250's. I do believe the only thing you would have to do is take the bottom spring block and the bottom 'all thread' with the nuts off the 1/2 ton axle and you can bolt the coils right back down. That would solve the 1/2 ton axle bearings. and as for the springs, like 4x4junkie said find an pretty good lift, alot of the lift spring won't take a whole lot of abuse before they start to sag.
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Old 07-31-2010, 08:11 PM   #7 (permalink)
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Well there certainly are times where a D44 simply isn't enough axle to support some driving styles. Time for a D60 (the -ton D50 TTB would need a fair amount of work to get it situated under a -ton truck, and is still nothing near as strong as a D60 would be).

I've had very good luck with Skyjacker's springs, as well as with many of their other components (and is why I recommended them). My experiences with both Superlift and Rancho are pretty much inline with your other comments however. Definitely avoid.
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