I just bought my first truck which is a 1979 F150 4x4 400 with an automatic c6 transmission. I plan to swap out the 400 for a 300 I6 and I want to know what I am getting myself into. I have not bought a 300 to swap it with yet.

I have done some research and it looks like the following things will not line up if I put in a 300:
Engine mounts
Engine perches
Throttle linkage
Exhaust
Transmission
Anything else?

Can anyone verify if this information is correct? If so, does anyone have any tips to make the switch as easy as possible?

Thank you for your help!

 

You doing this in hopes of better mpgs?

Your list looks pretty good. Cooling will be ok but you may have to make your hose connections with multiple hoses or pipe sections. Check the input/output for cooling and plan accordingly.

IMO what you are getting into is a lot of work for a less powerful but still thristy vehicle. ymmv Good luck with it.

 

Yes I am hoping for better mpgs. Hoping I can get 15-20 hwy out of a 300. Much less thirsty than 10mpg

Thanks for the reply!

 

You might see 15, probably not 20. 45-55 mph for best mpgs.

What tire and gear ratio are you running?

 

Check this out. 2wd shorty, manual od trans, skinny tires, tall gears:

https://www.ford-trucks.com/forums/1...-9l-300-a.html

The 300 is a fine motor, but you need to do the math on the pay back here. If this is not a daily driver, chances are you'll never pay it back.

IMO put some higher compression slugs in that 400, put in a decent cam, and enjoy the power.

 

Thanks for all the info! I would really like to have it as my daily driver which is why I want to put in the 300.
What would you say the swap would cost?
Would it be best to get a 300 out of a donor truck so I would have everything I need?
I'm not sure what the gear ratio is. Tires are 30's I believe

 

Does this truck run good right now? All there, runs, starts, rolls, stops?

If so, sell it and go find a 300 six truck. That is your best bet.

As for trying to guess cost, well, it could be free or it could be $10,000. Depends on if you find a good running 300 six 4x4 truck. If you do, see above.

Seriously, think twice about taking a running truck apart. The scrapyards are full of projects like that.

 

It runs, but it dies when idling if you don't give it gas and the guy I bought it from said that the pistons might be worn but I wont know for sure unless I take it apart or have a mechanic look at it.

 

Simple carb adjustment or rebuild. Kits are cheap.

Yea, the pistons are worn. All pistons wear. Does it puff out big blue clouds of smoke?

Fix the carb and drive it or sell it. JMO.

 

I'm not sure about the smoke. I haven't gotten a chance to run it much yet. I will try the carb adjustment though.
Thanks for the feedback!

 

Check the engine over, it might be okay. toss a bit of money at it and have it tuned (or do it yourself) and see if it really is worn out.

Maybe find a buddy with a similar truck that might want a 400 that has a 300, then all parts needed would be right there.

or a parts truck, or shop the picknose n pull

edit: Also, maybe investigate EFi options and subsequent tuning, might help to toss in only the fuel the engine needs, instead of a sloshing spitting carb (ugh hate carbs). The 300 is easy to EFi as Ferd made them up to 96 (the 96 is highly desierable because of the Mass Airflow Sensor and sequential injection)

 

I'm looking into buying a 1978 F150 4X4 manual with an I6 as a donor truck.
My Questions:
If I bought this as a donor truck, would I have eveything that I needed to swap out the 400 in my truck for the I6 in the donor truck?
Also, how hard would it be to convert my automatic truck to a manual with the donor truck parts?

 

I consistently saw 21mpg at 65mph revving at 2,800rpm out of a 300 that desperately need some tending to. It's possible.

 

Was that a 2wd or 4wd truck?

 

It was 2WD but it was with a leaking carburetor and a slightly rich mixture.