351M/400 Tips and Tricks

[BigBlue79]

So you've got a 351M/400 in your truck, these were found in 1977-1982 Ford Bronco's and the F-Series. These were pre-emissions smog engines, so basically they were Generation 1 of your smog. The first thing that can be done for the budget minded person is a timing gear and chain swap, what it entails is buying a 351c timing set(less than $25 for LLT Cloyes) and installing this set either(your choice) 2* degrees advanced, or straight up, now keep in mind this is for a stock engine with NO aftermaket cam. You will notice a power improvement, next I see guys replacing their stock 2bbl intake and carburetor with a 4bbl and NOT doing anything to the heads, just because it runs doesn't mean it's at it's peak, I've stalled one more with a 4bbl on it than a 2bbl, engine's are like air compressor's, make it breathe in it's gotta breathe out, so atleast port the heads, have the emissions hump in the head ground down, clean up your pushrods and rockers and check the valve springs and valve's while it's off. After you've done these(budget mindedly) then you can slap on a 4bbl and some headers, I believe Heddman are the best for Bronco's BUT you must remember, longtube headers will put the collector's right at the front of the crossmember, I DO NOT recommend running the pipes under the crossmember, that's asking for a world of problems. You probably have to make an angled turn-up to get over the crossmember then run it back. If anyone has anymore feel free to add.

[Ridgerunner]

Excellent write up.

[JSoko]

good going Blue on a side note if you can keep your foot out of it a 4bbl will give you better MPG than a 2bbl point being most 2bbls are about 550 CFM as compared to the primarys on a 4bbl at 350-400 CFM but that all goes out the window when the secondaries kick in; need a little more speed suck a little more gas

[BaltoMoJoe]

BigBlue....I don't really understand what a timing gear and chain swap will change in my 351M...I guess I mean what is the difference between what is in the motor now, compared to a new set up. I've owned my 1979 F150 for about 4 months now, and I really don't know too much about what was done, but I feel I should make it right. Also, you mention stalling with a 4 bbl carb, my truck came with a 4bbl Holley, and when I punch it, it usually stalls, or at least hesitates, as I learned to let off the gas when it begins to stall, is that what you were talking about ? Joe

[JSoko]

your right a new chain & gear with not improve performance but some gears allow a 2* advance to; something not felt on the butt dyno on your stalling first I would make absolutely sure you don't have a vacuum leak next check your timing, it may need a little advance other issues could be a improper float level clogged air filter sticking choke out of adjustment lastly if unknown mods have been done to the engine, say a cam change then stock jets need changing then there are other possibilities with the valve train/cam/push rods/lifters does it ever pop through the carb when you get on it ? also are you positive it's a 351M?

[BaltoMoJoe]

Originally Posted by JSoko lastly if unknown mods have been done to the engine, say a cam change then stock jets need changing then there are other possibilities with the valve train/cam/push rods/lifters does it ever pop through the carb when you get on it ? also are you positive it's a 351M? First off, thanks for your reply yes it does appear to be a 351 according to all the indentiyfing info I've read and the VIN and yes it has popped when I was playing with the carb with the air filter off, a brand new filter that I bought, 14" mustang 4" open element well I have lots of receipts from the previous owner, here's what the engine work reads cylinder head surface install cam bearings fit pins valve job (the following is hard to read, I'll do my best, some may not make sense) rebore block? hone cylinders recondition rods? clean motor and parts install f plug pc heads? Knwl valve guides? and as I said, its a 4bbl Holley carb, also has a Holley Electric Fuel Pump

[JSoko]

the 351M uses cleveland heads, has 8 valve cover bolts as opposed to 6 it also came with a 2 bbl carb that popping could be timing or pushrods not adjusted proper (to tight, bent or a bad spring) or it could be the carb the electric fuel pump may be putting to much pressure on the carb ( they do make an in line regulator that take the pressure down to around 7 PSI) also check the fuel filters ( i would have one befre the fuel pump and one at the carb ) what size carb is it ? a 750CFM is pushing it and an 850CFM is out of the question on your stock engine I think a 650CFM or the Holly Avenger in 670 CFM would be more than enough but carb choice has a lot to do with the type cam installed; I would think he used the same stock cam to answer some of your questions: hone cylinders= all he did was take the glaze off the wall and installed the old pistons and the old rings (if the ring gap was within specs) hopefully he installed new rings rebore block? = they line bored for new cam bearings & crank bearings (hopefully it was line bored) recondition rods? = check for cracks, bend & twist, check bore fro proper size insert pc heads? = pressure tested / surface checked Knwl valve guides? = knurling valve guides, is a quick fix as apposed to replacing or reaming for oversized stems the inside of the guide is raised, then reamed to fit your reworked old valves sounds like he did just enough to get it to stop using oil and to stop smoking on a side note if you keep this engine for some time and decide to do more work to it, it's easy to make it a 400; many of the engine parts are interchangable