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Discussion Starter #1
when ever i search this i keep comming up with swaps, and write up "how to do"
but im not that far into this idea to consider an engine swap.
while making a few changes on my 90 FSB. my mother has been thinking about her 79 FSB she parked in my grandfathers garage about 5 yrs ago. she parked it simply because it did horrible with mpg, and gas price hikes didnt help either. so my questions are:

*what is the mpg on a 351M
*mpg on 351w
*which is easier to modify to help increase mpg
*scale of 1-10 (10=hardest) how difficult is it convert 79 351M carb FSB to a 94-96 351w EFI (i like the rollers)

now im not looking for tips or links on how to do the swap, just curious how much of a pain in the arse it would be on a scale. i already insisted a 4.9 swap, but she likes 8 cyl.
 

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The "Dim"olitioner....
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1: 8-10 maybe 12 if your lucky
2: I'm seeing 13-15 in my 86 w/ H.O. but 2bbl carb
3: 351w
4: MO is 5 maybe even less if your good at wiring and know what your doing.

Good luck!
 

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Discussion Starter #3
wow thats a bigger dif. then i expected from M to W. so i would assume UDP, CAI, and headers w/wrap would help the output along with MSD box and ignition setup. wow is all i keep thinking, for answers 1 and 2. no wonder its been parked. thanks for the quick reply. i just might consider this a future project after, my 84 EXP turbo, and 1970 fastback.
 

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The "Dim"olitioner....
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351m's and 400's are first gen "smog" motors, there is ways around the smog timing like swapping in 351c timing chain and gears, headers will help flow the exhaust bump up HP and increase MPG's a little, a little head work to help flow the air. My old 79 bronco with 351m ate a little less gas then a 460 but they were pretty close, of course it was a worn out old ass engine that got us from point A to B for a while not long after we sold it it was back on craigslist being sold for parts or scrap as it blew up. The windsor blocks can make some good power and still have "good" economy, when I got the 86 it had a High-rise 4bbl intake and carb, I told my dad it was coming off and I located a 2bbl intake at a pull a part and now have gone from 7-8 mpg's to 13-15 mpg's I haven't noticed a difference in power at all, it'll probably increase a little once headers are added to it.

Don't get me wrong though, the 335 series(351c, 351m and 400) can make stupid power it just costs more for the parts, search for 351m engine parts like Pistons Vs. a 351w piston and you'll probably see what I'm talking about.
 

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The "Dim"olitioner....
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Oh and the 300 is a pulling little motor 6 cylinder economy with V8 power, hell you could get an easy 18-20 maybe more out of it even a carbed engine, It seemed like we could fill up the 19 gallon tank in our old pickup and drive for 2 weeks and only hit the half a tank mark, and we live about 20 miles from the closest city.
 

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Discussion Starter #6
yeah, i dont doubt those motors can make incredible power, but for the app. there isnt a need for power, if she can enjoy driving her 79 "green beast" again, much like my 70 build, i dont plan to seek out power if it means sacrificing gas. i cant stand it when people brag about how fast it goes but then refer to it as a weekend warrior due to the 6 mpg. it is because of non-sense like this why import owners feel they are so superior. but anyhow. it will without a doubt be a very clean, modest, build of about 280-300whp maybe even swap out the 4spd. for a 5spd. change the gear ratio. dear lord, listen to me already mapping out an idea i dont want to get into for another yr. or 2 dammit
 

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1) With a good running 351M/400 (with cam, intake/carb)...I easily pull 12-14 mpg's hwy...10 city. Gearing and trans can also play a role.
2) I've gotten 13-15 mpg's hwy with a good running 351W...and 11 city.
3) Keep in mind the weight factor as well...you'll swap a W in for mpg's but now it has a few hundred more pounds to haul around also...and that extra dead weight can hack off 1-2mpg's pretty easily. That said...you'll top out with a 351M/400 at about 14-15mpg's hwy and that's if you're economical with gears, tires and driving style. The W...you could peak in to the 16mpg range...but again...don't forget about the added weight of the rig.

Personally...I don't think the work would be worth it for a negligible return.
 

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And the cost of that swap will buy lots of gas.......
 

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To swap an M motor for a W motor will require changing the bellhousing,or tranny. The tranny bolt patterns are different.

For the M motor, use 4bbl intake, SMALL carb (600cfm), headers and a good dual exhaust system. On my 78 F250, the alum intake and carb gained me a solid 2 mpg. Of course, that's when I don't have my foot in it!!!

My 78 Bronco, with a 429, 35" tires and 3.50 gears, would get 14 on the hiway. Of course, when I regeared to 4.56 gears, the mileage dropped big time.:banghead
 

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........

For the M motor, use 4bbl intake, SMALL carb (600cfm), headers and a good dual exhaust system. On my 78 F250, the alum intake and carb gained me a solid 2 mpg. Of course, that's when I don't have my foot in it!!!
Ditto. I added a better set of heads and an Edelbrock set up. I gained mileage over the factory 2 barrel but as you stated, as long as I'm not driving like an asshole from Hazard County. :rockon

..My 78 Bronco, with a 429, 35" tires and 3.50 gears, would get 14 on the hiway. Of course, when I regeared to 4.56 gears, the mileage dropped big time.:banghead
This is good to know, the stars are aligning on this matter for me and it seems more and more like the way to go.
 

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Discussion Starter #12
To swap an M motor for a W motor will require changing the bellhousing,or tranny. The tranny bolt patterns are different.

For the M motor, use 4bbl intake, SMALL carb (600cfm), headers and a good dual exhaust system. On my 78 F250, the alum intake and carb gained me a solid 2 mpg. Of course, that's when I don't have my foot in it!!!
being my family is big on fords, somewhere laying around i know i have a complete 351w, and fitted f-150/bronco tranny. the only cost in this area would be to get an overhaul/re-ring kit from rockauto or adv. auto.

as for the improvements to see 15+ mpg in the M, i could have sworn i read an article in one of my mags. that with the right mods, and tune the W could see into the 20's. that may have been the 289/302 but i still dont like the idea of making so much effort to an M to only be rewarded with an ave. of 15mpg. but i will admit im shocked the 429 could get that kind of mpg. i just sold a DOVE thunderjet 429
 

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Discussion Starter #13
Best thing you can do is put an overdrive transmission in it.
my thoughts exactly, which is why i was thinking of changing the 4spd, to a 5 spd. im surprised there isnt a MPG thread/sticky for the ones trying to use their FSB as a DD.
 

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people who buy a FSB do not care about millage.

if your concerned about fuel economy buy a honda.
 

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Discussion Starter #15
1) With a good running 351M/400 (with cam, intake/carb)...I easily pull 12-14 mpg's hwy...10 city. Gearing and trans can also play a role.
2) I've gotten 13-15 mpg's hwy with a good running 351W...and 11 city.
3) Keep in mind the weight factor as well...you'll swap a W in for mpg's but now it has a few hundred more pounds to haul around also...and that extra dead weight can hack off 1-2mpg's pretty easily. That said...you'll top out with a 351M/400 at about 14-15mpg's hwy and that's if you're economical with gears, tires and driving style. The W...you could peak in to the 16mpg range...but again...don't forget about the added weight of the rig.

Personally...I don't think the work would be worth it for a negligible return.
now this is news to me, i wasn't aware the M was lighter then the W that is odd, but im not doubting it. i think if i do get this ball rolling i will have keep tabs on my gains, (hp/mpg) the cost and list of mods to try making a thread in here but that is an easy 2 yr away project
 

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everything I seen on a w vs m was the W is about 50 lbs lighter than the M
 

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Discussion Starter #17
i rather keep with my Fords, i have an 84 EXP turbo i plan to use as a mpg saver. but this thread is more on how i could get my mothers 79 FSB back on the road, which she parked because it drinks like a fish. my FSB personally gets 18-21mpg. which im happy with.

and i can't believe you would label all people who buy FSB arn't concerned about MPG!? now the Excursion/Expedition/Bronco centurion i could under stand this. there is 7 FSB and 2 broncoII in my family, and only 1 has ever seen off roading. so tell me plz, if people, (general public) dont buy FSB for mpg, what do they buy them for? its not like they are Ford Raptors or anything? i am aware they "can" be used for offroading/trails/rock crawling. but thats not their only use
 

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now this is news to me, i wasn't aware the M was lighter then the W that is odd, but im not doubting it. i think if i do get this ball rolling i will have keep tabs on my gains, (hp/mpg) the cost and list of mods to try making a thread in here but that is an easy 2 yr away project

I was talking about the weight of the vehicle. I know the delivery weight of a 78 Bronco was 4650. And with a quick search, it looked like the 87-91 Broncos were a few hundred pounds lighter...but I'll put emphasis on quick search. That being said...the weight difference between a 335 series + trans + t-case vs. the weight of a SB + trans + tcase might be the difference in overall weight. But I still believe the returns would be negligble and not worth the work.
 

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My 400 gets 14 highway, 10 or 11 city, depending on how I drive it.

Now I have a Holley Pro-jection TBI rather than a carb, and running 37" tires with 3.55 gears. Engine is stock, newer block but stock build.

I will be going with a 4 BT next fall, 25+mpg will be nice!!
 
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Discussion Starter #20
if i can only see a true gain dif. of 5-7 mpg. i dont think it would be worth it either, but if i can see near 10, i think it would be well worth. besides who knows if the 351M in her 79FSB, is still in ok status atm, by the time i go to work on it, it will have sat for est. 8 yrs. if i have to pull it to rebuild, i might as well swap out trannys and invest in a W. but again this is more of a plan, then it is a physical project. my initial question that created this thread, was stock dif. in MPG M vs. W i havent truly looked into the labor/cost of the swap itself. just that i know i have free access to several complete 302/351 w/matching trannys
 
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