I have an 89 F250 4WD that has a 351W and 5 speed. I'm hearing some noise on the passenger side engine compartment. I think it may be a lifter, wrist pin, or rod bearing. It may travel down the road for a long time, but I'm still a bit worried. I have a 76 351W in a 71 F150 with a definite knock. I'm looking around at options I may have. I'm hoping to get an engine on the stand and ready to drop in quickly when the time comes. Would building an older 351W be okay for my EFI in the 89? My main objective is to have a reliable engine. Pulling and towing is what I'll do. I don't need to go fast.

 

Any year 351 will work in your truck as long as you use an EFI friendly camshaft, all the EFI components will transfer over and there are several aftermarket cams that qualify and will also produce more power than stock. That said a '94+ truck motor would be the best replacement candidate simply because of how it's equipped from the factory... it has a roller cam and higher compression than everything between about 1975 and 1986.

 

If your going to replace it, why not just rebuild? I had an 88' Bronco with the 351W, had a buddy that kept begging me to let him turn it into a 408 Stroker

 

When/if you rebuild the '76 351W, pay attention to the pistons and the heads. I don't remember when Ford went to the small valve/big chamber 302 heads on the 351W, but I think it was around that time ('76 or '77...you may have the good early ones). Watch the dish volume on the pistons and the compression height if you buy new ones or re-use any old ones. Bottom line is make sure you know exactly what you have and calculate the compression. The last thing that you want is an 8:1 compression 351W....especially with small valves and open chambers. The older heads with 60-ish cc quench chambers, 1.84/1.54 valves and bigger ports, combined with a good piston, will yield 9:1 or better compression and run like a 351 should.

 

not sure what your budget is but after lockin up the 351w in my 92, i bought a reman from oreillys for 1200 with the core taken off3 year unlimited mile warrany this thing is a really good motor. but like they said go with like a 94, you may have to swap PCM's for that year but that shouldnt be too bad if you do

 

What is the logic behind that statement?

 

No he shouldn't have to swap PCM's because he has a manual and I don't believe the roller setup has any impact on the PCM.

 

How would the compression affect my ability to run on cheaper 87 octane gas? Some may say that I'm thrifty, economical, or even cheap!

Budget? Cheap as possible. My 89 cost $1100, I think. My 71/72 was only $800. I hate to sink a bunch of money into something that can be bought for those prices!

Both engines seem to have the problems isolated to the bottom end. 71 is a definite solid knock. 89 is more of a slap sound. What does a slap sound indicate. I'm assuming a wrist pin, cracked piston, or a collapsed lifter. The sound goes away under heavy load. It is most noticeable in part throttle conditions when the load isn't great and RPM is between 1200 and 2000.

 

I just used an early 80s 351 block no issues

 

Generally, as you already seem to understand, bearings problems are "knocks", pistons are "slaps", and collapsed lifters are "taps".
Irs hard to diagnose anything like this over the internet, but sounds like a piston/wrist pin issue. Reason I say this, if load is increased without an increase in rpm and the noise goes away, then its not a problem that reacts to oil pressure. If you could sit and rev the motor and the problem ceased then a piston could almost be ruled out, as the increased oil pressure can someti.es hide bad bearings or collapsed lifters. The increased cylinder pressure associated with higher load can effect Ethe symptoms of worn piston components by "holding" the piston down and not allowing anything to slap.

Have you gotten out the stethoscope or a screwdriver to try to pinpoint the location?

 

As far as compression vs fuel costs, you'll ultimately spend the same amount on fuel whether you run a hugh compression motor requiring the use of 93, or a low compression motor that will run on 87. The higher comp motor will achieve better mileag, and a cleaner burn (less gunk in motor), but of course costs more per gallon.

 

^^ What he said.
An 8:1 compression 351W will be a real pooch, and end up using more fuel....especially if you do any towing. Any time you can increase the efficiency of the motor, it's a "win-win". The higher compression will extract more power out of the same amount of fuel and end up providing better fuel economy as a result. You'll notice that most modern engines are at least 9:1 compression if not higher. Advancements in combustion chamber design and computer controlled fuel & spark has allowed the manufacturers to take advantage of higher compression and still operate on today's fuel.

Some of the budget priced aftermarket pistons will have a reduced compression height (distance from center of wrist pin to top of piston) which results in the piston being farther below the deck surface (top of the block) at TDC. You want the piston to be as close to the deck as feasibly possible for effective exhaust expellment as well as keeping the compression ratio up. The closed chamber design of the early model heads will have a quench effect on the combustion which will actually help reduce the tendancy for spark knock and lower the octane requirement. With good pistons that will provide about .020" deck clearance and a slight dish, you should be around 9.2:1 to 9.5:1 with the early heads. That would be about perfect for over-all power & economy, and you should still be able to run 87 or 89 Octane fuel with proper ignition timing. If you're up to it, a little mild polishing on the combustion chambers to smooth out the surface and get rid of the rough texture will also reduce the octane requirement as well as help limit carbon build-up in the conbustion chambers.

I think you're main decision at this point will depend on which engine will require the least amount of work (money) to rebuild. The "knock" in the older motor sounds like it may require some crank work. You really won't know which engine will be the cheapest to rebuild until you tear them apart. You might keep your eyes open for a good used late model truck 5.8L on Craigslist...it may be the best alternative in terms of cost, time and labor.

 

I have yet to take a stethoscope to the engine. Partly due to the fact that the slap is virtually unnoticeable (to the ear anyway) while it is at idle or revved while sitting still. I've never considered that I may be able to hear something with the 'scope that I don't notice by ear. I have thought of sticking a microphone in the engine bay while I drive to get a 'clearer image', if you will.

I've never thought of the effects of a better ignition or better fuel delivery relating to a higher compression. Points well taken. I've always heard, "higher compression=higher octane." I hadn't considered that I would also be making more power and that efficiency would improve.

If I'm stuck with "emissions" heads, say 77-85 (even though I have a 76 and 89, I have access to a couple donor engines), would polishing up the chambers gain me anything? Would shaving the heads gain anything, or be more problematic? Is there a hi-top piston that could be used in an otherwise stock engine to increase compression?

 

youd be surprised what you can hear with a stetho, or a screwdriver. it allows you to "listen past" the other sounds in the engine compartment that would otherwise mask the sound you want to hear. 9 times out of 10 i just use a screwdriver because i dont have a stetho at the time that i need to listen to a noise. plus, the stetho can get melted if you need to listen to a hot spot.

yep, if you look solely at a motors thermal efficiency, it is correlated to its compression ratio, and power output, and fuel consumption. the higher the thermal efficiency of any given motor, the greater the power output will be, and the less fuel will be required to achieve that power. in any motor, higher compression will always equate to more power w/ less fuel due to an increase in the motors thermal efficiency.

polishing of chambers, as he suggested, would help keep carbon from forming (as he suggested) and allow for a slight increase in efficiency. a rough combustion chamber "deadens" the explosion, even if its slight. think of it as an empty room that you shout in, vs a room that is completely furnished. the sound is deadened by all of the nooks and crannies from the furniture. on another thought, porting the valve bowls and the intake/exhaust runners so theyre free of casting flash and obstruction is a great way to increase efficiency.

note: theres a fine line between polishing chambers and taking out material. removing material from the combustion chamber is generally something that will result in negative performance. polish it with fine sandpaper or something of the like, removing no material.

you can mill any head (that has combustion chambers) in order to increase compression. the only problem with this; once you mill past a certain thickness (generally between .015-.030 depending on the particular setup) you also need to mill the intake manifold as well in order for the ports to match up. this can be a costly procedure, and generally the cost doesnt justify the gains. a competent machine shop will be able to tell how much material can be milled off and still be able to keep the intake manifold lined up.

 

I wouldn't waste my time on the 77 thru 86 small valve heads, but that's just me, and I have plenty of early heads stashed away. E7TE or GT40 would be acceptable. You don't need a domed piston, just a flat top or even a mild dished piston with like a 12 to 15cc dish or less...as long as the compression height is like 1.77" or so. I'd have to look in a catalog and do some quick math to give you specifics. My brother just tore apart a 351 that a guy rebuilt years ago. He complained about a lack of power. Ends up, the guy used a Set of deep dish pistons with a 1.72 CD and a set of '78 big chamber heads...if it was more than 7.5:1 he was lucky. Smothing the chambers will also eliminate "hot spots" in the chambers which lowers the octane requirement and alows more agressive ignition timing.