Alright so I dropped my 78 f150 351m/400 c6 4x4 off at the shop to do some carb tuning since I was way too busy between work and school. They tuned it and stuff and tested compression. One cylinder is running 10psi and another is running 80psi. What could be wrong? The shop said possibly valves or cam but I want a second opinion. Ill do this work myself cause I can't afford them. If the motor is shot rebuild 351m get newer 351 build it up while I'm running 6 cylinders, or build a 460 and go that route id wanna spend as little as possible.

 

This is also my dd and weekend wheeler

 

Darn near anything can be brought back. What they suggested (valve work) should run you a couple hundred to have a shop do it or new cam should be a couple hundred in a kit. Could also be burnt rings and that'll involve playing in the bottom end. Hell, could be a blown head gasket as well. These just depend on how skill and money you have. Since you'll be swapping engines anyway, I'd just say go ahead and throw a 460 in there.

 

Ya my uncle has 460s lying around his ranch he buys them up no matter what but hey also rebuilds them 2. Ill probably just go with the 460 in the end. I know this will sound funny but since I'm 16 and make 8.25 an hour how will the gas mileage be, I know it will be horrible. And also can I drive on my old engine with 2 dead cylinders? I'm pretty sure I did before. Cause I bought it recently and I didn't check the pressure or nothing and its not like from sitting for a week the cylinders would die.

 

You can drive it, just dont rely on it. If you dont care about saving your dead engine........run it till it blows or quits. Just have a backup plan in place.............

 

The shop quoted me 900 for the valve work.

 

Ouch!!!!! If you dont want to swap in a 460, you might check Autozone, O'reileys and others for a reman long block. New engine and a warranty, Probably wont be much over the $900. But youd have to do the work...................

 

Also what would it take to swap to a 6 cylinder? I heard they make about the same power as a 351m.

 

You are probably going to be in it less money to just repair or replace the 351M. They arent a powerhouse, but in my experience are a good, strong reliable motor.........I dont know why they have such a bad rep........other than like I said, they never were known for being a powerhouse........

 

Do those reman long blocks come with everything I need? And doing the work myself means completely building it myself?

 

A long block consists of: Block, installed crank, installed pistons and rods, installed fully assembled heads. You will have to swap over valve covers, oil pan, intake and exhaust manifolds, carb, alternator, water pump and other accessories. You will not have to build the engine, just swap accessories.

 

They have a bad rep because of all the smog crap. The retarded cam and the pistons were crappy. Also the crankshaft was weak.

 

Tend to disagree on the crank and pistons, The cam timing can be advanced and helps A LOT. All engines of that era were loaded with smog crap................Dont' get me wrong, I'm in the process of putting together a 4bt Cummins swap to replace my 351M in my 78 F150, I'm just saying, that if all you are looking at is the $ involved you'll get by cheaper repairing/replacing your current 351. It's just been MY experience that they arent all that bad of a engine......and I've been around Fords since before the 351M even came out.

 

Typically, I'm a fan of the 335 series, and they can be woken up for pretty cheap. However, since it sounds like a swap is gonna happen anyway, I say just do whatever will be easiest on the wallet. That said, it's been my experience the 460 is 1-2mpg's lower than a 335 series...and you'll get varying opinions.

As for whether or not you can drive it...go for it...drive her til she blows. I had an old 351M once that I was gonna drive til she couldn't go anymore...I had the motor sitting on the stand that was gonna replace it. The 351 had 2 cylinders with ZERO compression and another cylinder had a busted piston skirt...the engine held 7 psi at 70mph. Two years and about 15,000 miles later, she still didn't blow, but I decided to swap. Before I pulled the 351, I dyno'd it at a buddy's shop, and it pulled 67rwhp...hahahha.

Ouch...sounds like someone getting ripped. I just had a set of head brought back to stock specs and only spent $300.


But they can be made to be relatively fun. And I think they get a bad rap because most guys get them after years of abuse and believe the 460 is the end all to be all because that's what they read on the 'net, even though they never PERSONALLY took the time to learn anything. Given that's not everybody, and I have and love both the 400 and 460. For me, the engine that is a thorn in my side is the 302, and how famed is that.

 

X 2 on what you just said............two years and 15,000 on six cylinders says something about how strong of an engine they really were.........Will a 351m pull like 460? Yeah, IF you dump some extra $ into it. Will it run like a 460 with the same amount of $ dumped into it? NO. It just sounded in the OP's first post that he was concerned about the $. And dollarwise, he's probably gonna get by cheaper repairing or replacing his 351m. And I agree 100% on the comment about the 302. The ONLY reason they have become so popular is due to the aftermarket support they have. They are like the small block Chevy of the Ford world. You can buy/or do anything you want to them for relatively cheap................Sounds to me like the OP is a kid with no experience who is afraid to do his own work. Not that there is a thing wrong with that, but, the best way to learn to do your own work is to keep things as simple as possible at first, or have someone with experince that can help you out when you build yourself into a corner. Trust me, I know, I was that kid....................A LONG TIME AGO............LOL