I don't want to start a pi##ing match here.

I have heard the M stood for just about everything that started with M. I have heard tons of "experts" spouting off on what it stood for. I'm not doubting ND, he is sharp on things Ford. If he has evidence to prove it, it would settle a long standing debate.

The only way FORD ever refered to the engine is the 351M. No modified, midland,............... If it stood for anything other than to distinguish it from the other 351 engines, don't you think it would have shown up in at least one FORD publication that someone could point to? I personally think the M stands for Million. There have been millions of people discussing what it means.

 

How did this turn into big block /small block from a gas milieage question? LETS stay on topic....

 

thats a little rude coming from a new user thats not involved in this discussion. if you had actually read the full thread then you would know that the original question was answered, and without further info from the op it couldnt be answered more specificaly. this isnt an argument and its still technical so stop criticising.

 

Owned

 

rotflmao. WOW. i LOVE this forum.....

 

Guys, in several years on this site, I have to say. This is one of the worst threads I've seen. Even the wikipedia paste has some errors, as 300 sixes were most certainly used after 1977 in Ford trucks, and the 302 was used long past 1972. There's more, but whatever.

If you stick around these Ford engines long enough, yes you will begin to know the differences between the windsor series, (351W = stroked 302 with 1" taller deck for example) and that a 300 shares the same bellhousing.

FE series, starting with 352 way back, on through to 360 and 390 versions (in trucks, far more including the big dog 428 Super Cobra Jet in 60's Ford/Merc cars) and they ended in 1977 in the trucks. This is a Y block style engine, some bores changed amongst the bigger displacements. Quite a bit larger blocks than windsor series.

385 series is the biggest of Ford Engines. 429 and it's stroked cousin the 460. Nuff said.

The 351C evolved first into the 400, then de-stroked to 351M. These have early emissions systems involving thermactor plumbing in the head, which made them problematic to EFI conversion, hence being discontinued in 1982.

351C / 351M share some things in common, but the 351M and 400M are more closely related. 351C was never in a 70's Ford truck, but lots of 351M/400's are in 1977-1982 trucks. Similar in size to the FE series, but not a Y Block.

I suggest people be patient, it's taken me 15 years to be clear on all that stuff, but I still wont tell you it's the gospel and you better believe.

Read information from a variety of sources, and actually get your hands on things. The 5 volume shop manuals are really very good items to get ahold of, and guys like numberdummy are worth asking questions.

Now as to the original poster's question:

I'm getting a consistent 14 mpg with my newest 78 F150 2WD, after putting about 1500km on it in 10 days. Someone has retarded the timing so it's at 4* with a frozen distributor (the frozen distributor I've seen on two of these engines now. Last time I smashed the old one out and replaced it, this time I'm being more patient)

It also has all the emissions junk on it, half of it not seeming to function quite right. When my thermostat opens, a ported vacuum switch is opening/closing, making my engine very unhappy. Vacuum at idle drops from 20 or so down to 15 when this happens.

Point: When these are tuned well, it's not hard to get close to 20mpg out of them, or at least 15 in a 4x4.

My 76 F250 4x4 had a 351M in it when I bought it (yes, this was a swap. Original engine in it was 360 FE) and it was in good tune, getting 15-16 mpg in a 5000lb truck with remote transfer case! (losses!).

Happy tuning, and be nice to each other. I'm stupid too, or I wouldn't be reading and responding to this thread on a friday night.

 

almost forgot. a big difference between the 351C and the later 351M/400's that are based on it:

The 351M/400 was made to share the same bellhousing as the 385 series 429/460's. There were some real early 400's that shared the 351C bellhousing, but not for long.

Here is a real good link that explains the "M" saga

https://www.ford-trucks.com/article/...00_Engine.html

Imagine that, on this same very site. Look around ya's!

 

Where do you have a ported vacuum supply? Mine comes from the carb and it runs to the vacuum advance on the distributor.

I also had crappy vacuum at idle - about 10. I read through the '76 manual and found out the previous owner of the truck had all the vacuum hoses hooked up wrong. He also had the timing retarded 6deg. and the vacuum advance on the distributor wasn't adjusted so the timing wasn't advancing

And to reinforce your point, once I got done fixing the previous owner's booboos, getting the carb tuned in, and adjusting the distributor, I get 15 on the vac. gauge and the fuel economy is WAY better. It has a 3.00 in the rear so I estimate I'm getting around 15mpg on the highway which is damn good for a 460. It's also a good compramise seeing as how it lays down 100 extra feet of rubber

 

Same in my case, I can use the one of the carb, but currently mine is set up coming out of manifold vacuum to a vacuum switch on the tstat housing.

Once the thermostat opens a couple times, my vacuum drops considerably, and I'm not sure if it's because it's suddenely receiving too much advance at idle from manifold vacuum, or if something else is malfunctioning. Same tee that the vac advance is drawn from off the manifold also supplies the vacuum canister.

I think I'm just getting rid of all of it. Run Vac Advance to carb port, and make block off plate for the EGR and ditch the rest. I can do that in my jurisdiction.

 

another pretty big factor that effects mpg is the size, type, and weight of your tires. gear ratios are important also.

 

very good article. just makes me want a 400 even more.

 

I think May '09 is more recent than Aug 07. You would be the newbie.
don't let that "senior user" thing go to your head.

 

how about we dont turn this into a pissing match. anyway conkl may have joined in 07 but didnt write anything until septemper 09. haha but it really doesnt matter, i just thought that comment wasnt necessary. so can we move on?

 

I have not wrote anything on this forum until 9/09 because it was not until 9/09 that I purchased my 1978 ford pickup. I have had my 1963 f100 stepside for 20 years, and since I would like to keep on topic the 63 has a 302 ,3 speed and gets 18/19 mpg highway and average 13 /15 driving 50 miles roundtrip to work. The 78 has not been on the road yet but will be next week, and thats why I was more interested in the original topic of this thread.

 

point conkl. lol

Just because someone hasn't made many posts doesnt mean he hasnt read them all.