Hi everyone. I have a 1991 f150 that is a gas hog. I just wanted to know everyone's thoughts on swapping out my 351 for a 300 straight 6. I used to have one in my 95 f150 but that one was a rust bucket and didn't last(engine did though). I plan on doing this in the next year or so. I always liked the economy and torque of that engine.
Thanks, George

 

That's certainly do-able, but depending upon the gearing in the truck you may not realize much if any gain in milage. What numbers are you seeing right now?

 

persionally i dont think that it would be that great of an idea, for the simple reason of the time and money you would have to endure... you would be better off doing some minor upgrades, like an intake system, exhaust system, even maybe a diff swap... ( some higher gearing) your 351 engine has lots of power and could handle that type of upgrade... the six isnt that much better for fuel to justify a swap... most of all, ease up on the throttle... that will make you save the most fuel!!

 

my uncle had one in his truck

those engines are indistructable he ran his with a bearing knock all the way from wells maine to shelton connecticut with no problems

he tryed to blow up the engine but it wouldnt go he even did the 4th gear going 70 down the highway to first and keept it floored and it didnt blow

and he drove it bout 2 miles with no oil or coolant

totaled the truck droped a cinderblock on the engine and it fell out of the truck

sold the engine and its still runing to this day



so i say go for it

 

if your main reason is fuel milage then i wouldnt do it. the straight six is an awesome engine but sip the fuel it does not. i only get like 14mpg with it which cant be much more than you're getting with the 351. the 300 will last a lot longer than the 351 but as far as fuel milage goes theres not much difference. i can remember reading threads that talked about swapping the 300 out and putting the 302 in for fuel milage. but if its torque you're after, then look no further than the 300cid straight six.

 

I used to get 16mpg with my F350 with the 351. That was untill I did the 36's and now I get 9-10.

 

Thanks for all the input. I did some asking around and everyone has been telling me to just work with what I've got. I mainly do a lot of in town driving and only hit the highways when visiting family. More input is greatly appreciated. Thanks

 

This should be a "fairly" easy swap, if that's what you want to do. You're probably going to need the frame towers out of a truck that had a six in it to properly position the engine fore and aft in the engine bay, and unless you're going to go with a carburated engine you're most likely going to have to steal the computer from a six truck, and I have no idea what that's going to involve. Then you've got the issue of whether or not the trans will bolt up. In years gone by I would have said yes, but there's no telling what block changes have occurred with both of these engines over the years. Good Luck

 

I feel your pain I have had 19 of these truck a and never had a 351 break 13 MPG (more like 10-12 MPG as My records show. .And a well tuned 300 15 plus in same truck . (20 On trip out west 31' and 3:55 rears )

If you have the parts truck for swap go for it . Its you time and even at 2 MPG (i drive 500 a week) adds up. Just know that because of 300-6 low end torc most had 3:08 or other higher gears . But I install 3:55 on every truck I get with 300 and its a great comb