I have a friend that wants to build a 347 small block for his 68 bronco. The truck has a 4 spd from an f150 now, a 302 with a bad knock, and some valve train issues. I have built 390s, 460s, and a 545 stroker with pretty good success, that is why I was recruited to help with this project.
I know nothing of the small block ford platform, so recommended parts combos, cylinder head options, cam recommendations, rocker arm choices, cam timing settings, block casting info, and basically just looking for some useful information to get this on track. I have some pretty good local resources as well for information at the local machine shop, but more is always better. I will do some searches too, thanks guys.

 

What is the budget?
How much power is your guy looking to make?
I'm guessing this will be carbed and depending upon the answers to the above questions it may be better to just get a 351.

 

Well, for some reason the 351 idea is shut down (not sure why) budget? Well, Not in concrete yet but sounds like $3000 for heads, $1500 crank cam lifters rockers pushrods timing set studs guide plates $1000 and machine work maybe $750 and then a gasket set, bearing set, freeze plug set, we have a few intakes, but if need be there is $$$ for a new intake, carb will be an edelbrock 600 or a holley 600 or holley 750, whichever it seems to work best with, all are on hand in good working order.


power, well that one leads to a new can of worms. We are at elevation here, 6000 and up to 12000 in the mountain passes and 4wd roads, so power to us is a minute goal. I feel that if we build it to turn 5k maybe 5500 and build power above 1000 rpm, it might be fine. I will shoot for 10:1 CR if iron is used and 11:1 for aluminum. If the thermostat is a 160 or 180 and timing is limited this will still run on 85 pump gas up here and not ping so long as we achieve good quench. The headers/exhaust will probably be the limiting factor. I hate to build a cool motor and then choke it to death, so rpm may have to be limited. Time will tell.


I was more after what casting and year blocks to use or to stay away from, what parts are junk, what are good, what iron heads work well, what iron heads are bad/poor, what deck height works, what cam timing to use, just the basics as I know 460s and not 302s. thanks.

 

Well here's the thing, the 302 block is relatively weak and won't tolerate high rpms or boost without literally breaking in half and that means it's really only reliable up to the 350-400hp at sea level range, and that's not that hard to get to with a stroker. The 5.8 block in comparison is safe to 750hp and it has the displacement you want already so it makes a lot more sense to start with one of those if it will physically fit in the vehicle.. the block is a little taller and wider than a 302 but it's still smaller than a big block.

As for cylinder heads there really aren't any factory cast iron heads worth your trouble.. they're all WAAAY to small for a motor of this displacement, ideally you want something like an AFR185 or TFS 190, and use a cam with a mid 260 seat to seat duration to keep the powerband in a streetable 1500-5500rpm range.

 

Thanks for the info. I will relay, but i am afraid the 347 is a go, is / are the older blocks any different than newer castings? Are these like the 460 platform where the deck height changed 3 or 4 times, the depth of the cylinders went deeper on later castings, or were they all the same? Is there a cam timing issue like the 460s? Discounting the roller cam units, is there any difference in blocks from year to year?

 

There were some early mexican blocks they had some more meat in the mains webbing area but they aren't significantly stronger and of course aren't roller ready.

 

Thanks again Sounds like even steven on blocks then. I need to look close at what options are available for headers, induction, room for a 351 maybe? Before I start making any recommendations for now. Is there any other info like cam timing, pushrod length, oiling system mods, like 460s and 390s? On our 390s we chamfer the oil gallery in the main web and drill out a few passages in them to get better oiling, on 460s we advance the cam timing and always need longer pushrods. How far are the head bolts good for on sbf platform? Any need to budget in studs?

 

If you use heads with pedestal mount rockers you can use stock pushrods, but of course if you go to heads with stud mounts they will have to be different and exact length depends upon block machining. No oiling problems on these blocks though it never hurts to make sure everything is clean and clear. Cam timing can be straight up if you pick the right cam and there are what seems like millions of them available, this engine family enjoys almost as good aftermarket support as the SBC so you shouldn't have any problems finding what you need. Stock cam setup is straight up as well. Head bolts are not usually TTY and are good for any non boosted or sprayed application, and both of those power adders are death to the 302 block anyway so.

 

I'd think you'd be money ahead, and stronger, going with a 351. I had one in a '66 Bronco, very easy fit.

If you want to turn 5500, I'd say shoot for something like 218/224* duration, lift will depend on the head you put on it and what type of cam, but .525-.550 would be normal. You don't want to overcam at that elevation. This is also assuming properly geared for the tire size, etc.