i have a 351M it runs ok but starting to leak oil. this is only a weekend driver about 200miles a month
Questions i keep pondering over is upgrade 351m to 400 or i have a 300 six that i can rebuild, or there is a 460 with a c-6 trans that supposible rebuilt 3000miles ago and hit in the rear for $750 for both

i like the simpleness of the 300 six and gas milage but i also like power
if i just put the money into the 300 six can i get good enough power??? I had never drove a 300 six in one of the pickup trucks i have only drove a dump truck with this motor and it was slow but would always get from point a-b with no issues and still running today i still see it running around it weighted 8000lbs empty

i dont do drag racing or rock crawling, but i do like it to get out of its own way. also if i go 460 what are all the componets needed and poosible cost to complete swap and will drive train be ok????

 

I'd go with the 300 .....but I'm partial........ours pulls great .....even with 3.08 gears and 33" tires....
You might jump over on the straight 6 forum on here......you will feel the love for them

 

I'll second the 300 suggestion. Gotta love an engine that hits full torque at 2300 rpm. Mighty little mills will pull your house of its foundation if you combine the low-end torque with the right gearing. Don't look for it to be a speed demon though. The 300 is the equivalent of a clydesdale as opposed to a stallion.

 

I would go 460 or rebuild what you have. The 300the is nice but the 78-79 Broncos are bigger and heavier I think then the 80+ that everyone loves the 300 in.

 

Plus the 460the will drop in. The 300 will require you to swap transmissions.

 

460 drop in....nothing to change, exhaust, cooling, accessory drives, all the same huh? NOT.

As little as I think of the 351m, the smart money here is to fix the leak on an otherwise ok running engine. 200 miles per month and you say you don't need big power--sounds like you're good right where you're at.

In stock trim without much tinkering, the 300 makes about the same power as the 351m. More to be had, of course, but a lot of your time and money will be spent changing the trans, exhaust etc.

Convert to 400? IMO the best way to decent power for the least money and hassle when you start with a 351m.

460 swap? The best way to big power if that's what you want.

 

460 is fine if you want the brute power but remember the trade off... fuel consumption!

And there is ZERO worry over the 300 being able to pull around the 78-69... the 300 was dropped into the F-250's and F-350's for many years as an OEM power plant. No 300-equipped truck was ever underpowered. Most folks who have NEVER driven a 300-equippped truck will try the old, "its only a six-cylinder so its gotta be underpowered" line on you. Just understand that they are WRONG and move on.

 

If his 351m runs ok, what's the gain going to the 300 when he only drives less than a tank full per month...???

 

The 300 is a great motor, but in his case it would be more of a hassle to swap then any of the other mentioned options. The main difference between 351m and 400 is crank/stroke length. So you could just rebuild the motor you have now and get a 400. A little drop in MPG but you gain more low end.

If you are wanting a motor to build just for fun and don't care bout MPGs then the 460 is prolly better as it has more aftermarket support. Options weren't as plentiful when I built my 351m.

 

i just bought the 460 swap kit from jbg about $1000 with 3/4 lenth l&l headers should be here in about 2 weeks [canada] i did a lot of work on the stock 400 in my 79 and am still not happy with it [intake,eddy carb,"260 tork cam",lifters,timeing chain,valve covers so for about the same milage i can have a better engine i allso enquired about installing a 302 i have on the stand but no one seems to have ever done this swap that i can buy a kit for so the 460 should give her a bit more motivation after 1 experiance with that 400 i am convinced thats not one of fords better ideas lol