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Old 12-18-2005, 01:42 AM
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351m questions

Hey guys, im new to the forums and just purchased a 1953 ford sedan with a 351m inside of it. It has a holley carb and an edelbrock intake manifold. From research i have figured out on my own that the 351m is pretty much a crappy engine. But for now i need something getting a little better gas milege. YES i know im not looking for GOOD milege, but this thing is running RICH and i personally dislike holley carbs. While watching for 351Cs in the seattle area i have some questions about the 351m. They use the same intake and such as the 351c, so they should be interchangable up there? I LOVE weber carbs and am wondering if you guys know of anyone that makes weber kits/carbs/intake manifolds for these engines? It has new plugs and wires too, just looking for some way to fix this retarded (as in timing) emission controlled horsepower robbing beast. thanks.

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Old 12-18-2005, 02:56 AM
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Oh yes, the mighty 351"M". The absolute worst of the worst engines I ever owned. In terms of Webers, http://www.redlineweber.com/html/for...plete_kits.htm

Good Luck
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Old 12-18-2005, 10:27 AM
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351m

I don't think the 351c and 351m intakes interchange.I had the 400 and I think the 351m and 400 have the same intake while the 351c is different for a shorter deck height.I'm pretty sure you only have a couple of choices for intakes,I ended up with the Weiand and a Carter carb.I think someone makes an adapter plate to use the 351c intakes on the wider deck block if you need a better intake.Why is it running rich now though?
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Old 12-18-2005, 12:48 PM
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I had a 75 M FMX and a 76 W C-4 at the same time in identical cars. A W will get 10 % better mileage.... 14 and 15.5

The M got a bad rap because it is a smog era engine and uses big block mounts and transmissions. It might as well become a 400 if rebuilt. Not much of anything interchanges M to C. The C bolts in like a small block, the M like a big block, so if you go C you will be changing transmissions also... and you can do AOD/E etc.

If mileage is a concern, your best bet is 5.0 HO SFI. It should do 20 without overdrive and 24 with. Carb will be 2-3 less. A SFI CrownVic 160 hp is no better, just less power, but can be upgraded but not cost effective.

Putting out a lot of $ for some additional mileage is not productive. I would suggest- in this specific order:
1) fix/replace your bad carb.
2) 195* thermostat
3) replace the retarded cam timing gear with a '71 version
4) full distributor recurve timing with agressive vacuum advance
5) as good of headers as you can get
6) consider a good RV or 4x4 cam... The compression is very low so keep those pressures up there. The stock cam has minimal lift.

A bigger carburetor will be counter productive on this engine.

Personally I would never consider a C. If I were swapping engine and transmission I would do a 5.0 HO fuelie. Been there, done that.... in my 63.

Simple and easy.


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Last edited by xntrik; 12-18-2005 at 12:58 PM.
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Old 12-18-2005, 02:13 PM
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351 M block

There is nothing wrong with the M block, as was mentioned, they, along with the 400, have gotten a bad rap because they were produced during the smog era and theres not a lot out there available for them.
While they do share some charactoristics with the Cleveland, such as having common heads, exhaust, camshafts, timing assembly, and distributor, the M block is 1.10 inches taller in deck height and about 25 lbs. heavier. The M block intake is wider because of this.
Wieand and Edelbrock both make aftermarket intakes for the M block, which are rated for 0-5500-6000 RPM.
They do not share common crankshafts, the M block having 3 inch main journals vs 2.75 inch, for the Cleveland. You can put a Cleveland crank in an M block by using spacers in the mains, as is done with crankshaft swaps in some of the Small Block Chevies.
To switch to a Cleveland, or a Winsor, you will have to use a different transmission as the M block shares it bellhousing bolt pattern with the Lima Block (429/460). The M block also uses the same engine mounts as the Lima.
Carburetion choice, as I see it is pretty much up to the individual. While I do have a preferance for Holley carbs, there is nothing wrong with the Carter/Edelbrock carbs, just dont have that much experience with them.

The stock cam in the 351M is the same grind as was used in the 2 bbl cleveland block, and is pretty mild. The 400 cam is slightly larger, and very close in grind to the 4 bbl hydraulic cleveland cam.
I would recommend going with a cam that has a wide lobe separation, at least 110-112 degrees. Crane has a variety of these in the Power Max series.
The wider lobe separation, keeps the cylinder pressure higher at lower and mid RPM, which would be a definate advantage for street driving. I would also stay below 210 degrees duration as well.
You didnt mention what year your 351 M is, so its hard to know the advertised compression ratio. Gettting your compression up around 9-9.5:1 would be a help in both fuel mileage and a small boost in overall power as well. and you should be able to run it quite easily on 89 octane gas.
For timing, I would recommend starting at 12 degrees initial, and if your stock distributor has points, increase the centrifical advance as well.
This is done by removing the breaker plate and pulling out the centrifical stop rod plate on the shaft and turning it 180 degrees and reassembling. The two posts will have a number stamped next to them. One may have a number like 11 and the other will be something like 13 or 14. Set the stop post plate so that your distributor is using the one with the higher number. You can also pick up a degree or two of centrifical advance by removing the little rubber bumper off of the post.
You should come up with a centrifical advance of around 26-28 degrees, and thisw with the 12 degrees initial will put you at 38-40 degrees total advance. If you have access to some other Ford point distributors, see if you can rob the counterweight springs out of them. Ford used 3 different tensions of springs, at least, that I know of. Putting in two of the lightest springs will give you full advance at around 3000 rpm. These simple mods on your stock distributor wont put it in the same league as a Mallory or Accel, but since you are dealing with a basically stock setup, it will definately improve your performance, and help your gas mileage as well.
This distributor trick can also be used on any of the Ford Electronic ignitions that use centrifical weights for advance.
2 bbl.Cleveland headers will bolt onto your M block since they use the same head, and you probably wont run into any block clearance problems due to the higher deck height of the M block. You may however, run into firewall clearance problems. IF you dont have headers yet, and are thinking about using them, contact the header maker of your choice and discuss clearance problems.
I would recommend not going larger than a 600 CFM carburetor, and if you dont plan to turn the engine over 5000 RPM, a 500 CFM would do the job quite well, and make it a vacuum secondary carb, so you can adjust the RPM at which the secondaries start coming open. There are a lot of other things you can do to your M block to improve its liveability as well as enhance performance. Send me a PM and Ill give you a few more tips on it.
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Old 12-18-2005, 04:16 PM
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xntrik and Max covered it all,

only additional small bucks item for milage/performance I thought of is a 4 hole carb spacer cause your intake is flat as a pancake

change the timing chain and dist curve makes a world of difference

2.80 gears and "big" tires if it's mostly hwy miles?
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Old 12-18-2005, 05:59 PM
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My reasons for not liking this engine is that they dont seem to go far without having to throw a crank kit and oil pump at them. 100,000 miles on an engine that has been maintained flawlessly and is in need of a crank kit is in my opinion junk from an engineering standpoint. There are many examples of this same problem on 351 "m" s. I got 14 mpg with mine in a F 250 4 wheel drive. A friend had a half ton with a stock 302 in it and it would eat that 351 anytime.
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Old 12-19-2005, 12:17 AM
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Quote:
Originally Posted by 56Maynard
My reasons for not liking this engine is that they dont seem to go far without having to throw a crank kit and oil pump at them. 100,000 miles on an engine that has been maintained flawlessly and is in need of a crank kit is in my opinion junk from an engineering standpoint. There are many examples of this same problem on 351 "m" s. I got 14 mpg with mine in a F 250 4 wheel drive. A friend had a half ton with a stock 302 in it and it would eat that 351 anytime.

Maynard,
That engine and its technology is 35 years old. And oil today is far superior to oil of just 10 years ago.... 3 decades ago 100,000 miles would have been excellent. 5 1/2 decades ago.. 100,000 miles was extremely rare indeed.

Today's snugger fitting (.002) hypereutectic pistons, new moly steel rings, modern bearing materials, cylinder finishing techniques, and the new additives in multi-vis oils.... (not to mention synthetics).... a rebuilt M today should do 150,000 plus easily.

I have a synthetic 5.0 with 237,000 and going strong.

Just food for thought.
x
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Old 12-19-2005, 12:18 AM
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Hey guys thanks for the help a ton! I already have a holley carb and edelbrock intake manifold. They came with the engine. From what i can tell, it looks like its a 1977 m block. Is there a site with pics or something that can show me my way around the holley carbs? It idles around 1100 RPM and for the life of me i cannot lower it or find an air mix screw. What kind of engines will bolt up to my tranny besides my M block?
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Old 12-19-2005, 12:24 AM
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Quote:
Originally Posted by elvisjer

What kind of engines will bolt up to my tranny besides my M block?
351M/400, 429, 460.
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Old 12-19-2005, 12:30 AM
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Okay maybe I am all wet with what I expected from this motor. I guess that running (Beating) 283s for 300,000 miles 30+ yrs ago was merely good fortune then. I just wasnt happy with it (351) at all and I did buy it brand new and babied it. I guess I shoulda layed into it some lol. A friend of mine that has run a shop for years told me that if it wasn't for Chrysler mini vans and crank kits in 351 "M"s he wouldn't be the sucessful business man that he is. Maybe he was just joking and I thought he was serious.

And Elvis, if that thing does puke a crank, come back and tell us.
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Old 12-19-2005, 06:39 AM
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1100rpm-check simple first
check the linkage travel:motor off, disconnect the linkage at the carb to be sure it's not stopping the carb linkage from going full travel-off (then have somebody hold the pedal to the floor and check for carb full open)

I'm in favor of saying keep the M, because IT'S DIFFERENT! Better (?) defines your 50's "hot rod"....started with a clunker and made it purr and scream (well....ok, not scream....how about "roar")
hell, nobody else can cook a pizza on their 2'x2' intake!

Last edited by red65mustang; 12-19-2005 at 07:14 AM.
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Old 12-19-2005, 02:26 PM
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As usual the above posts are excellent, but you may want to try this site:

http://home.earthlink.net/~bubbaf250/index.html

He has a lot of good M-block reference. Those engines really weren't that bad, my wife had a decent one, my kids' friend has a nice one in a 78 bird passed down from his mom just about original, and my dad's old 400 sedan was pretty neat too.
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Old 12-20-2005, 07:09 PM
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http://www.projectbronco.com/Technic...the_rumors.htm


http://www.projectbronco.com/Technic...ical_index.htm

Last edited by xntrik; 12-20-2005 at 07:21 PM.
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Old 12-21-2005, 06:08 AM
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I would also add a set of 351C Aussie heads. These have the same port sizes and locations so no worries about exhaust or intake. The big difference is the Aussie heads have a smaller chamber that's very similar to the 4V 351C heads. This will boost compression and also are suppose to be a more efficient combustion chamber design.
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