i was wondering if i could down size my 351 to a 302 in my 78 bronco with out having to totaly replace every thing from front to rear in my drive line just looking to get better gas milage

 

351M or 351W? The stock 351M is a dog, a sick one with heartworms, at that. But..... with an intake, 4bbl. carb, cam, and opened up exhaust, it may give you the same or better MPG as a 302. (plus more torque). Ditto for a massaged 400M. Consider this if you're not dead-set on downsizing.

 

yea, your truck has a 351M if its a 351, or a 400M. only two motors avail in 78-79 broncos. 'Downsizing it would be a lot of work, as your current motor using big block bolt pattern, so it would require a trans and motor mounts etc to get a 302 in there. I would stick with it, as they are fairly torquey motors, which is needed for that big bronco. We have built some up for relativly low money, with intake and RV cam with good results. If you want a lot more power, just throw a different crank and pistons in it, and you got a 400. Yes, thats the only difference. Only reason i could see to swap to a Windsor motor would be if y ou wanted to go to a factory fuel injection setup. I think an M motor would be a great motor with an aftermarket injection setup.

ok, i think i went beyond my 2 cents

 

Guys, it is a 351M or a 400. There is no such motor as a 400M.

 

not 100% sure on this one but i believe a 300 six will bolt right up pretty much, after that i suppose there would be some linkage issues not to mention the exhaust.

i imagine the six would get a little better mileage and the 300's are known for their low end grunt but you would sacrifice the v8 rumble and top end power.

my 2 bits

see ya

Bob

 

The 300-6 would bolt up if a 351W was in the truck. He probably has a 351M which has a different bolt pattern than the 300-6, 351W or 302. A 400 or 460 would bolt up where a 351M was. Swaps usually require a donor vehicle so you can get all of those little brackets and pieces you need.

 

Ford introduced a 400m in 1972. Don't always assume that a vehicle that old has the original motor, tranny rear etc unless you know its history real well...I have seen more than one guy ****** an engine out thinking it was one thing and it was another!

The 400m blocks were very heavy beasts. The 351m and 400m were spinoffs of the **** kicking 351c which has very little in common with the 351w. The 351c is hard to come by realitively speaking but if built right would be a good engine for the 78 Bronco. The last year of the 351c was 1974 but it was a small block that acted like a big block. So my point is to check the numbers on the block because sometimes you just get lucky!

P.S. the 351w has more in common with the 302 than it does the 351c or 351m or 400m.

 

Again there was no 400M and the 400 was introduced in 1971. The 400 is not that much heavier than a 351W and not near as heavy as the 429-460's. The only engine that ford uses a letter as part of the designation was the three 351's, the 351C/W/M's. The engines are commonly referred to as M-block, Cleveland, or 335 series engines. You can read more about the 400's history here: http://home.earthlink.net/~bubbaf250/

 

I disagree with you on that. The 351 c or better known as the 351 Cleveland doesn't have anything to do with a 351w or Windsor. The 351m and 400m were spinoffs of the 351c and technically the 400m was a small block is why its not as heavy as the 429 or 460 which are 385-series big blocks.

Even if you drop the "M" off the 400, it is still a 335-series small block which includes the 351c and 351m but not the 351w.

 

Read it again. I didn't say the 351W had anything to do with the 335 series.

I DID say that "The only engine that ford uses a letter as part of the designation was the three 351's, the 351C/W/M's." They do this because there are three 351's and they had to differentiate the engines. There is only one 400, or 352, or 429, or 427, or 428, or 460, or 289, or 302 etc etc... Except for the Boss 302 ond some other variants.

 

The transition years on engines is a gray zone at best. The M blocks are often undervalued by many people when it comes to building an engine for Bronco use. The M blocks especially the 400 have potential because they can be overbored more than the 302 or 351w is what I was alluding to before we got into the argument over symantics. You may be right, but the 400 is refered to by many including in literature as the 400m but it is in the very least an "M" block. I'm not sure what caused the confusion, (block numbering?) but its not really a problem until peopls start confusing the 351m and 351w because of bellhousings etc. Thats where we were coming from.

 

I was driving 400's when they came out in 1971. It was the only year that the 400 was a good motor. It was a screamer with 9:1 compression and a straight up cam. I suggest you read the history in the link I gave above and if you missed it I will repeat it here: http://home.earthlink.net/~bubbaf250/
The gentleman that wrote that site is considered to be an expert on the 351C/M and 400. You can also check in the Cleveland engine forum and ask Bill Beyer, the moderator, about them. He is also an expert. There is a lot of misinformation in magazines and literature.

Now as far as the original poster's question... I came in and saw the engine designator errors and later misinformation. I did not want a new user starting off on the wrong foot. You can refer back to my post: "The 300-6 would bolt up if a 351w was in the truck. He probably has a 351m which has a different bolt pattern than the 300-6, 351w or 302. A 400 or 460 would bolt up where a 351m was. Swaps usually require a donor vehicle so you can get all of those little brackets and pieces you need." I hope the user has the correct information now.

 

i stand corrected for some reason i thought the six had the same bolt pattern as the 400 (no M)

see ya

Bob

 

M or not, that 400, which i am going to call an M, has the exact same block as a 351M. The only parts on a 351M or 400 that are different, is the crank and the pistons. The rods are the same, the block is the same, the heads are the same etc. The pistons on a 351M were made extremely long with really low mounted pins, so that the shorter crank of the 351M could still be used with the 400 'M' Block. so weather or not you put the M on the 400, it is the exact same motor as a 351M. The 351 cleveland was the origin of this motor series, being a performance motor derived from the heads used on the boss 302 1969 mustang, and a motor built to use them. Then, the block was basically stretched up another inch to build room for more stroke and a torquier setup, and became the 351M (M for modified cleveland design), though ford sold it under the Clevlancd name in some applications for a few more years. The 400 followed shortly thereafter utilizing a longer crank and bumping the cubes up accordingly. The interesting parts of the motors was their factory designed in emmisions equipment, such as the egr.

These are the only two motors put in broncos by ford in 78/79, which i believe we are in agreeance on. Their main problem was the factory 4 degree retarded cam shaft, which is retarded. It didnt gain either the emmisions control or the fuel economy that was intended, it in fact hurt both of them. The best modifications to these motors are an adjustable timeing chain to bring it back up to straight up, ... not much more expensive then a stock replacement chain that they probably need by now anyhow, and maybe a better cam. Edlebrock also makes a nice manifold for a 4 barrel, and you drop about 50 lbs by swithing to aluminum. I used to have a link to a website that declared all this information as well as having build several knowni this info first hand. Also, factory high flow manifolds or headers are a nice addition

 

Amen Iskybantilus! First car I ever had was an LTD 2door with a 351 Cleveland! It had 400,000 miles on it when I sold it. Just for grins , there was an Australian 302 that ford made in the early 70s that was actually a destroked 351 cleveland.

I saw some numbers from ford once claiming that about 25% of the 78/79 Broncos got 400s while the rest got 351m.