anyone thought of putting a 300cid 6 in their 78-79 bronco? and if so how did it fair for daily driving? thought of this with an adaptor plate from tci...400.00, and a well built 700r4 or 4l60 and lighter transfercase. don't ever use the 4x4 and the 203 case is wore out, and c6 is a pig on gas.
or i might just redue the 351m in truck and change to a 400 for bettert running,,, just desperatly needs an overdrive, and it runs hot.
so any thought?

 

I remember reading a writeup or two over on fullsizebronco about someone putting a 300 into a 78/79 Bronco. Nothing difficult about it, since they came stock in trucks of that year (which share the same front end). But, I think the bottom line is, in STOCK form, the 300 is a little small for the beast of a vehicle that that year Bronco is. Those things are heavy (like 6k+). It'll do it just fine, but it's a little sluggish, and is why those only came with the big block 351 and 400 V8s.
But, if you do some work to the 300, like the common upgrades such as exhaust, some headwork, and a 4bbl carb, it'll pull that thing around just fine, and would probably make a nice runner.

 

Doesnt matter what motor you put in a 2nd generation Bronco. It is 1 heavy sumbitch. Its not gonna get much more than 12 MPG if you can squeeze that much out of it. Unless you go with a diesel. And then unless you go with a small diesel, they are so heavy, I personally believe you lose alot of "real" off road capability. Try running an extra 3 to 4 hundred pounds over the front axle in the gumbo mud around here and you get buried quick. That is real life observations from someone who has been 4 wheelin since the early 70's. If you are trying to get good fuel mileage, sell the Bronco and buy an early straight axled toyota 4x4. Then let someone in a 78 Bronco pull you out of the mud hole you hit with your 38" mudders you cant turn over with the 22r 4 banger in it.

 

Blasphemy!!


With a 300 in front if it? Hardly.. if overall gearing is reasonable... it'll certainly be a lot better on gas than a smog era 351m or 400.


Go find a 5.0/AOD combo from a Mustang.

 

The C-6 is probably one of the worst transmissions for parasitic drag. Meaning it robs a lot of horsepower to work. the good news is it probably the easiest to remedy.....an upgraded pump. Personally, I love the C-6. It can be built almost bullet proof for an off road truck. I don't know about putting a 300 six banger in a 6000+ lb truck. Not sure if you're going to gain anything at all. A buddy down here has a 78 F-150 shortbed with 5:13 gears and 44 Boggers with a granny low 4 speed. He doesn't get anywhere fast.....but he gets there. Off road he is almost unstoppable!! He goes though some pretty bad stuff! He's got a header, some hot ignition and a Holley 2 barrel. He said if he gets into some really thick stuff, the engine will just stall and he gets out the winch........and it's easy on the drivetrain!

 

If you are going to buy a trans adaptor, I would say get one to put od behind the 400, or swap in a 460 and get an e4od and trans controller for the 460 or 400.
A 300 is a dumb swap. Sorry but it is. Find a complete explorer v8 and put the whole motor, fuel injection and trans in, the 5liter and 4r70 will have more power and mpg than the 351m and c6.

 

I would hook bumpers with any 302 swapped 78-79 bronco and pull it all over the woods with my "underpowered gas guzzlin" 358 and c6. Aint no way in hell an explorer runnin gear will outpull original Bronco runnin gear. Not runnin down Fords 302 but it just aint happenin. I am extremely doubtful about much of a fuel mileage gain. The old sayin "there aint no replacement for displacement" still goes. Stock 351 outpowers stock 302, built 351 outpowers built 302. That is a fact you cant change.

 

I never said swap the running gear. But if you want to get all huffy, the d35 reverse cut front end is equally as strong as a regular cut d44 diff, the cv shafts are the only thing Id be concerned about, but I've broken hundreds of d44 axles and ujoints, and zero cv shafts.
Bronco 9" is tried and true, but the 31spline disk brake 8.8 is a pretty stout piece as well.

I was only saying swap the motor, efi and trans. It will be a very reliable setup, with more power than the 300-6 I was comparing it to. The engine in your bronco isn't stock by your sig, so your comparison isn't very good. A stock 351m is a great truck motor for longevity, but I liked my 400 and c6 at least 5x better than my 351m with 4spd.

Ill still say no 300, do something better.

 

I dont post on here to get in an on-line pissin contest with anyone. When I said runnin gear I was refering to the explorer v-8,and trans. I do agree about swapping to the 300. It is a fine engine for torque and I have driven f-250 flat beds with a 300,4 speed. Great work truck. Will pull a load, just dont be in any hurry to get anywhere. And it didnt get any mpg either. I personally think its a downgrade from any of fords v-8's in a truck. And I am NOT trying to **** in anyones wheaties here. I love all things Ford. Been driving and owning them since 1975. But having said that , the second generation Bronco is too heavy and shaped like a brick stickin out of a shoe box. If you want gas mileage dont ever think about buying 1. You will be disappointed. My old gal gets 8.5 mpg. Period. Dont matter how you baby it. 8.5. I think I got 9 once with a tailwind runnin 60 on hiway 231. Maybe.

 

There's no replacement for displacement when you're looking for power, but there are other factors to consider in what one wants out of a vehicle.

There's something to be said for the multitude of people, myself included, who've regularly gotten 20 - 23mpg with a 300 I6, and that includes 70s era pickup trucks. Granted, tire, gearing, and transmission combos come in to play with that, but you're simply never going to see those numbers out of a V8 in the same vehicle. When driven properly, and with the right setup, the 300 I6 will simply outperform V8s in gas mileage every time. I get around 16 - 18mpg regularly in mine at 75mph with the same brick-like aerodynamics and average 13 - 15 around town. A 78/79 probably wouldn't see quite those numbers due to the extra weight, but I don't see it being that drastic of a difference unless you've got a C6 or something. On the flip side, I've known 80 - 96 Bronco owners who've swapped in 400s and 460s V8s and still only got 8 - 9 mpg, so the less weight didn't help them in that direction either. Some engines just use more gas than others.

Unfortunately, in the end, it's hard to tell how it would do because a 300 in those era Broncos is very rare due to the fact they just didn't come with them. You'd have to track down someone who's done the swap and ask them how it is to get any real world numbers. Also, the vehicle would be a different animal once it was done since you wouldn't have a big block V8 pushing it around.

Ultimately, though, if it's just for gas mileage, it comes down to how much its going to cost you to do a swap. How long would a few mpg take in fuel to add up to the cost of the swap? But, if you're just curious, have the engine, and want to do it for you, then by all means.