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From: Minnesota
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So, yesterday I bought a 75 explorer that had a 390 with ac in it for 100 bucks. there isnt much useable as this thing is pretty rusted out. The 390 is in pieces, and it has a steel crank. My dad said the 391 truck engines had steel cranks rather than cast. He also said the heads had sodium valves, but I am not sure what the difference is. Can anybody verify these things? My dad said back in the day they used to install the sodium valve guides in the pickup heads because it gave them some more longevity. Anybody know anything about these?
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The 391 HD cranks were good to use for all out drag racing back in the 70s and 80s, but today there are so many better choices. The standard 390 crank is a high quality piece as it is. Besides the fact the 391 crank needs a lot of maching done to the snout in order to use standard balancers and pulleys which makes it un-economical. Cost for cost it makes more sense getting a stroker crank from Scat or others than it does to machine a 391 crank.
As for valves the 330/ 361 and 391 HD engines used much SMALLER valves than the standard 360/ 390 engines. Again not worth it.
FE Nascar engines used mostly sodium filled titanium Exhaust valves, but they did not last much more than a couple races. That should give you an idea of longevity.
Josh
As for valves the 330/ 361 and 391 HD engines used much SMALLER valves than the standard 360/ 390 engines. Again not worth it.
FE Nascar engines used mostly sodium filled titanium Exhaust valves, but they did not last much more than a couple races. That should give you an idea of longevity.
Josh
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From: Minnesota
I called the PO and apparently he built this engine to pull back in the day. Used to haul cattle with it. He said when the engine was new he had to keep a set of heads on hand because he would burn them out every 20K. Apparently he built a set of heads with sodium valves or guides? said it really made alot better engine out of it. Apparently the mismatched parts are because he took the bottom end out and put it in his louisville grain truck . Apparently what I have is the bottom end out of the grain truck, and the top end out of the f150. Dunno if these heads are any better than stock, but he swears by them.
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I have to confess you aren't making much sense...
But anyways... a 1975 390 will most likely have D4TE cylinder heads which are actually great for a budget build. Machine them for CJ valves and blend the bowls and it will flow quite nicely.
Ignore the sodium valve crap, they are worthless.
A 391 truck crank CANNOT be used with standard balancers, pulleys and timing cover without substantial machine work to the crank snout. Add to that the crank weighs almost twice that of the standard 390 crank. Not worth it unless UNLESS you plan on building some sort of 8000+ RPM 390. But even then the standard crank will hold up just fine. You'll throw rods or valves before the crank ever lets go.
Sounds like the PO lugged the snot out of the engine if he was replacing heads every 20 grand. The rods have got to look like spaghetti.
Josh
But anyways... a 1975 390 will most likely have D4TE cylinder heads which are actually great for a budget build. Machine them for CJ valves and blend the bowls and it will flow quite nicely.
Ignore the sodium valve crap, they are worthless.
A 391 truck crank CANNOT be used with standard balancers, pulleys and timing cover without substantial machine work to the crank snout. Add to that the crank weighs almost twice that of the standard 390 crank. Not worth it unless UNLESS you plan on building some sort of 8000+ RPM 390. But even then the standard crank will hold up just fine. You'll throw rods or valves before the crank ever lets go.
Sounds like the PO lugged the snot out of the engine if he was replacing heads every 20 grand. The rods have got to look like spaghetti.
Josh
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I know I am not making any sense, and I am not building another engine right now anyways. The crank that I have is out of a grain truck, apparently he used the 390 bottom end out of the pickup, slapped his intake heads and carb on it and put it back in the grain truck. therefore, the block, crank, pistons, etc that came in the box of this beat up explorer are all 391 and the heads, intake and holley are off the 390. He told me about the heads in an effort to convince me he was really selling me something useful. All I wanted was the big core radiator, dash pad and the ss trim around the windshield. lol..got the rest with it.
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