Bronco Engine

[brando__32]

I have a 79 FOrd Bronco with a 400m, i've looked for up grades that are half affordable....headers, exhaust, heads, cam, carb, intake...and that's all i can really find and understand. But would it be worth swapping in a straight 6, or a 460...or should i just stick with te stock 400m and do what i can do to it...i want some what half decent gas mialge so i can drive it more.

 

[Yardape]

Im biased to 460. So I recommend swapping to one. I have owned 300 6's and 460's and almost every engine in between. I find the 460 to actually be better on fuel as long as you can keep your foot out of it. I have never known the 400m or 351m to be very good on fuel in fact I believe them to be the worse engines fuel mileage wise that ford made.

 

[Broncobill78]

Yup, my experience has been the same. Twice I went from a tired 351M/400 to a freshly built (1 was a mild build headers, intake, carb & cam while the other used a larger cam, headwork & a predator carb) 460 and in both cases my mileage didn't suffer a bit. It was actually a bit better with the mild 460 and stayed the same with the other one. With the 460 you don't have to get your foot into it nearly as far to get better performance than the smallblocks provided.

Having said that you CAN do a decent rebuild on a 400, I've just never bothered because it didn't cost much more to build the 460 and a had so much more power for weekends that it was worth it (for me anyways)

If mileage is your primary concern then the 300 or a 302 will be your best bet but a 6000lb truck always seemed a bit much to me for using those engines.

 

[J&SBroncolvrs]

Well if you go from a tired engine to a new engine obviously it will be better. Broncos will never get good gas mileage but on a 44 hour trip with mine I averaged 14.5 miles to the gallon, and that's with the first half through the mountains.460's are heavier and use more gas because they are bigger. Common sense really.

 

[rednck7736]

I have a 79 FOrd Bronco with a 400m, i've looked for up grades that are half affordable....headers, exhaust, heads, cam, carb, intake...and that's all i can really find and understand. But would it be worth swapping in a straight 6, or a 460...or should i just stick with te stock 400m and do what i can do to it...i want some what half decent gas mialge so i can drive it more.

The 460 is a much better engine than the 351m or 400.I swapped out the 351m in my 77 150 for a 460.The 351m was better on fuel but has no where the power of the 460.Mine makes around 500hp.But you can make 400 real easy out of a 460.The 460 will boult up to the trans of the 400m.You will need to buy new motor mounts which you can buy at jeffs bronco graveyard.You will need a new alternator mount and powersterring pump and brack which your can retrieve from a junkyard vehicle easlly.

They have some nice up grades now days your can do to teh 400m to pick it if you want to keep tha tyou have and not have to change anything.Headers and a came will hellp a lot.I did that to the 400 that i took out of mine.Just a 600 4bbl on the stock 351m that I had made a big difference.You could always change the piston to bring up the compression to about 10.1.

 

[Broncobill78]

460's are heavier and use more gas because they are bigger. Common sense really.

Common sense perhaps but maybe taken to an extreme. The 351M/400 engines weigh 575lbs versus the 429/460's at 635lbs. You're talking about a 60lb difference, that's the weight of a small child /emoticons/[email protected] 2x" width="20" height="20" /> if you follow that line of reasoning then you're also getting better mileage when you leave the kids at home or take off the cap and use a soft-top. Most people consider the additional horsepower & torque to be well worth the negligible weight penalty. For that matter most rebuilds involve ditching the stock cast iron intake & exhaust manifolds for headers & an aluminum intake which shaves off at *least* 30lbs. The additional HP & torque allow you to operate the 460 at a considerably smaller percentage of it's total capacity to achieve the same performance results. You're not putting your foot into it nearly as far to get the same acceleration or to maintain the same speed. To accelerate a 6000lb aerodynamic brick to 60mph in X number of seconds the 351M/400 is using maybe 80% of it's capacity while the 460 is doing the same thing with 50% of *it's* capacity. You don't have to push it as hard so even though it has a larger displacement and will use more fuel in an absolute sense, you're using the same amount of fuel to get the same level of performance and you have a LOT more performance available from the 460 because you're using much less of it's potential. Now when they're both being operated at the same percentage of their total capacity (say 80%) then sure, the 460 will use more fuel but that's because the engine is simply an air pump, the 460 has a larger displacement, it's moving a lot more air & since that air has fuel mixed in with it you're sending more fuel through the engine. Mileage has little or nothing to do with the actual weight of the engine.

 

[J&SBroncolvrs]

Common sense perhaps but maybe taken to an extreme. The 351M/400 engines weigh 575lbs versus the 429/460's at 635lbs. You're talking about a 60lb difference, that's the weight of a small child if you follow that line of reasoning then you're also getting better mileage when you leave the kids at home or take off the cap and use a soft-top

Hah, ***** good point. I think it's more like 140 pounds, but it is splitting hairs. Depends what you need I guess, 400-500 hp is an aweful ot of power for most people, and the mileage of those engines is somewhere between 6 and 8 miles per gallon. If you take a 400, zero the timing gears, put a mild cam and decent intake and carb, maybe some flat top pistons you are around 300hp and over 400 for torque. More than enough to move a bronco easily along with 33" tires and a 3" or 4" lift, and get the mileage like I described, average of 14.5 miles per gallon. And that's with stock gears. Oh, and recurve the disttributor.

 

[92broncomann]

Common sense perhaps but maybe taken to an extreme. The 351M/400 engines weigh 575lbs versus the 429/460's at 635lbs. You're talking about a 60lb difference, that's the weight of a small child if you follow that line of reasoning then you're also getting better mileage when you leave the kids at home or take off the cap and use a soft-top

Hah, ***** good point. I think it's more like 140 pounds, but it is splitting hairs. Depends what you need I guess, 400-500 hp is an aweful ot of power for most people, and the mileage of those engines is somewhere between 6 and 8 miles per gallon. If you take a 400, zero the timing gears, put a mild cam and decent intake and carb, maybe some flat top pistons you are around 300hp and over 400 for torque. More than enough to move a bronco easily along with 33" tires and a 3" or 4" lift, and get the mileage like I described, average of 14.5 miles per gallon. And that's with stock gears. Oh, and recurve the disttributor.

Bad math ROFLMAO.........lol

635

-575

60

Idk i may be wrong lol

sincerley

92BM

p.s. on the topic, just do a 460 and stroke it out to a 496 and just demolish everything anytime and anywhere =D

 

[Bronc76]

Brando- everyone made good points about the engine that they would pick. theyre not gonna get great gas mileage no matter what you drop in.(maybe some better than others) If youre still thinking about what to do, you can always work off of what you already got because its already there!

 

[Broncobill78]

Hah, ***** good point. I think it's more like 140 pounds, but it is splitting hairs. Depends what you need I guess, 400-500 hp is an aweful ot of power for most people, and the mileage of those engines is somewhere between 6 and 8 miles per gallon. If you take a 400, zero the timing gears, put a mild cam and decent intake and carb, maybe some flat top pistons you are around 300hp and over 400 for torque. More than enough to move a bronco easily along with 33" tires and a 3" or 4" lift, and get the mileage like I described, average of 14.5 miles per gallon. And that's with stock gears. Oh, and recurve the disttributor.

Well, the shipping weight for a 400 long block is is 475lbs

http://flitelineenginesupply.com/index.php...;products_id=28

and the 460 is 530lbs

http://flitelineenginesupply.com/index.php...;products_id=55

add in another 100lbs or so for the intake & exhaust manifolds plus carb & distributor.

You're right of course, it's all about what you want. A large percentage of people who post are enthusiasts looking for the ability to goof around and play off-road without getting stuck or left behind. My original point was simply that most guys who do the 460 swap comment that their mileage improved over what they were getting before. 6 to 8 mpg simply isn't a realistic big block figure unless you've set the thing up for ******** competition and just happen to also drive it on the street. The last one I built ran the L&L headers, dual plane aluminum intake, a fairly high lift Erson cam, ported heads w/larger valves and a Predator carb cam'd to about 800CFM for daily driving (changed to the 950cfm cam on wkends), 4.56 gears w/36" Ground Hawgs and it got about 10mpg. I gave up a lot of my mileage with the tires, running BFG all-terrains it averaged 12. The same tires & gears on the more mildly built engine still came in around 12mpg. Admittedly both work & home were right there by the on-ramps so almost all my miles were highway.

Some guys have gone the other way and swapped in the 300. It actually has a few more pounds of torque than the 302 and if you don't need/want to cruise at 70 it's a fine engine. Except for mudrunning most off-roading is done at very low speed and the 300 works well at low speeds. I used to see a guy in a local club with a 78' set up that way & he never had any problems on the group trail rides & was content to lope along at 60mph traveling to & from the trailhead.

It's really just a matter of prioritizing what's important and building your engine/truck to suit your needs. If improving the current mileage is at the top of the list then a smaller engine will be better.

 

[J&SBroncolvrs]

Interesting to hear that a 300 worked well. I've always wondered about that. 12 sounds optimistic for mileage to me imho. I've owned both a 77 f250 camper special with a 460 and a 79 f150 with a 351M and 2 78 broncos, one with the 351m and one with a 400. The 460 did much worse for gas mileage at least for me.

 

[Broncobill78]

I remember the 12mpg figure because it was a bone of contention with the first wife because she complained about it. I recorded miles driven & gallons purchased for 3 months & ran the numbers then invited her to ck my math. it averaged 11.8 over the 3 months I kept track. A month into it I picked up a set of BFG AT's and swapped them out for the Ground Hawgs I'd been running. Usage is a big factor, mileage dropped to 10 or so around town but up on the highway it was getting 12.

I'm getting ready to build another one & this time around I'm going with fuel injection specifically to help out with mileage and I expect getting 12mpg again won't be a problem.

 

[Krafty]

my 81 bronco I had had the 300 with a 4 spd, in no ways would it win any races but it got the job done, and for the weigh and size of the truck no bad mileage. once you get into the 302's 351's and up if you go with more than a 2 bbl you're just giving yourself a kick in the pants as far as mileage goes.

but here is my v8 comparison from my 79 thunderbird project.

302 at lets say 200 somthing hp ( maybe ) 2 bbl tops out at 150km/h and on a 5 hour drive uses just over half a tank of gas with 60 liter tank

429 dyno'd at 380 hp 2 bbl tops out at 200+ km/h, on same 5 hour drive half a tank of gas, same tank

300 in bronco with 1bbl on same 5 hour drive with a 90liter tank used 3/4 of a tank of gas

and for carb comparison

camero 305 with holley 4bbl 700 cfm with 60 liter tank on the very same 5 hour drive uses almost a full tank of gas.

so bigger power with small cfm = better mileage

for the 429 I used the same carb from the 302