Right now I got 400 in my 78 4x4 right now being Rebuilt. now there been couple times I been wanting to get a 460. now if it was you what would you stick to for now because of Gas Price's? Then my other question is how does Valve end up Burnt with Cracks in the Valve?

 

IMO that all depends on your power needs. But in general it's easier to get power out of a smaller engine then MPG out of a bigger engine.

A burnt valve is rather easy to explain, depends on how it was burnt though, it has a burnt out notch in it? A crack however I've never seen a cracked valve, I'd be curious to see that.

 

Number 1 Valve on the Small 1 there 3 Crack Lines I don't know how that happen. Someone did machine work Valve Hole 1,3, and 4 Hole screw up the Seat Valve's on it I am wondering if thats how Valve 1 got cracks?

 

IDK hard to say, maybe someone will chime in but as I've seen valves will generally bend before they crack. If I had to guess if the valve seat wasn't installed/machined square it could apply a force to the valve that could crack it.

I'm assuming your taking your heads to a machine shop, point it out and make sure they take a good look at the seats I guess.

 

I say build up the 400, a mild cam, aluminum intake, and 4-bbl carb and headers will do a lot. The next step from there is to either mill the heads or use different pistons to bump up the compressions.

They're somewhat expensive but with the stock pistons, if you get your hands on a set of Australian closed chamber 2V heads you can bump up the compression a lot. Tmeyer makes a 434 stroker kit too...

I have nothing against 460's but the 400 reaches it's peak torque right off of idle pretty much, horsepower is never too high because they only rev to 5,000rpm or so. 4x4 Dentsides never came factory with a 385-series engine, but L&L makes kits to install them and I'm sure other people have as well. I like the 335-series engines though, torque monsters, and torque is usually what you want in a truck.

 

Which ever way you go keep in mind if as you increase compression you increase the need for 92 octane fuel to make it run .. let's say on a 100,000 mile motor you are getting 10 miles per gallon .. You will be buying 10,000 gallons of fuel for the 100,000 miles .. 10,000 x .10 (difference in price for higher octane fuel .. could be more) = $1,000 .. something to consider when weighing your options .. sometimes less is more

 

Very good point, but what if that compression bump got you a MPG bump from 10 to 11 or more? Riddle me that, Sometimes more is more

 

The majic number in this day in age of high fuel prices is the big question .. I did a calculation the other day where just a 2 mile per gallon mpg increase saved you about $6,500 on 100,00 miles at $3.75 per gallon .. That's real money

 

It would certainly seems from this math that things that can allow you to bump compression without a bump in octane needs like polishing the heads, aluminum ones if available, flat top pistons, great tuning components, etc. can really pay off in the long run.

 

Now with me rebuilding the 400. How long before I have to rebuild it again? I been told the 400 has 2 different Intake Manifolds 2 Barrel Intake and 4 Barrel Intake is that Correct?

 

If you change the oil at regular intervals and your not a thrasher easily 100,000 miles if the motor was done by a professional and timing is correctly maintained .. I have gotten 175,000 on a rebuilt 390 and it still had decent compression when I sold it ..

yes, 2 and 4 barrel intakes are available for your motor ..

 

are the 390's and the 400's almost the same motors?

 

The 400 was the replacement for the 390 ..

 

How does one define "same motor"? Are they the same number of cylinders, yes. Are they similar in displacement, yes. Are they both Ford motors, yes. Do they share many of the same parts, no. Are they visually similar, no.

If gas mileage is truly a concern for you, the answer to your question about a 400 vs. 460 is neither.

 

IMO Redroads answer was a little conservative and general. The better answer IMO is it all depends on many MANY factors. Do it right and the engine will go easily 400K up to 600Kmiles, do it cheap, half assed, and don't take care if it and you might get 100K out of it.

That would mean VERY good and complete machine work, turned/polished crank, quality rod resize, chamfered oil passages, honed with a pressure plate, Hard seats, screw in studs, full bronze guides, etc.

Very good parts, good oil pickup fitted to a high volume pan, a high volume(not high pressure) oil pump, of course good forged pistons, molly rings, positive valve seals, etc.

A few important better then stock upgrades, a roller cam, double roller timing chain, good roller rockers.

And the most important, an oil accumulator for pre-startup oiling. And a good true synthetic oil(not for break in) of the right viscosity

All that adds up though, which is cheaper all that, or replacing the motor again?



As for manifolds, of course 2bbl and 4bbl versions are available. But there is the rare "4V or 4bbl heads" those use a different manifold then 2bbl heads. Putting an aftermarket 4bbl manifold on a set of 2bbl heads is the best setup for a truck. Don't worry you don't have 4bbl heads. More info here;
https://www.ford-trucks.com/forums/8...-4v-heads.html
LOL, I was just thinking about re-opening/rebranding my shop to specialize in 80-97 Ford Trucks and Broncos.

By my understanding no problem using the Ford name as it's a descriptor of the type of word you do. But using the Ford logo in your signage would be a no no.

WOW fmc400 way to contribute nothing but attitude, 2 thumbs up.