I have a 1978 f150 w/351m.. I am not sure how old or how many miles are on it. However, the timing chain broke & bent some valves. I had a power issue up to this point as the result of detonation. My mechanic tells me that I should just put in a new rebuild since I don't know the past the motor. I want to put in a comp cam 265deh, dual plane intake, carb., ect. I have used Jasper in the past with much success. Jasper wants 2120.00 for a 351m. They have a 3yr/75000 mile warranty. I have also found a place that will sell me an ATK for 1575. They have a 3yr/unlimited mileage warraty. They will also sell me a 400m & take my 351m back as the core. The ATK is $545.00 less for the 400m. Anyone have any experience w/atk? Not sure what to do & looking for some opinions.

 

With an uncertain history and your desire for improved performance, replacing the engine makes the most sense. I think you should consider another alternative to buying a reman engine, though: rebuild the existing engine yourself, or have it done by a good local shop (or a little of both).

This might not be feasible if you're in a hurry, but if you can afford to have the truck down for while for engine replacement, I'd recommend rebuilding the existing engine.

If you get a local machine shop to work on your existing engine, you can ask them to document their work, and you will get exact dimensions for everything (deck and cylinder head surfacing, bore aligning, cylinder overbore and finished size, etc.). Moreover, you will have some input to the process, and by doing your own research (especially searching previous threads and asking questions in these forums), you can make intelligent decisions about what you want.

If you don't want a "stock" rebuild, you can have the shop upgrade exactly the components you want (cam, pistons, etc.), or just have them do the basic machine work, and then you do all of the bolt-it-together assembly yourself. That will save some money, and it's an excellent learning experience (by far the best way to get an understanding of how your engine really works).

There are also lots of little things that a good machine shop does routinely (careful hand cleaning on block and heads, chasing threaded holes with taps and cleaning out all of the oil galleries with wire brushes, chamfering crankshaft oil holes and micropolishing the journals, relieving the fillets on turned journals, etc.), and these can produce substantial improvements in reliability and/or longevity, long after any warranties expire. Few (if any) mass-production remanufacturers take the time or care to do these things.

I can't comment on either of the reman outfits you mentioned, as I have no direct experience with either of them. Maybe they are both great companies with great products, but to me, any mass-produced remanufactured engine is a huge unknown.

Most re-man outfits don't document how much overbore they use (some actually overbore cylinders to different sizes on the same engine to save money on piston replacement), how much cutting they do on the deck and cylinder heads (the heads on reman engines often come from different cores, with slight variations in ports and chambers from different castings, and each head might be cut differently), or how much they turn the crankshaft (some turn the journals farther down than you might want, if you had a say, and some even turn individual journals different amounts), and so on.

Unless the re-manufacturer provides complete shop specs for each individual engine, you will know a lot more about your existing engine if you have it rebuilt locally.