calmed down !
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calmed down !
i was getting all worked up and wanted to go crazy rebuilding my 390 after it spun a rod bearing ! well after thinking it through here's what i've decided to do. i'm getting a 391 steel crank from dscmotorsport, getting my rods checked, keeping my forged pistons, after randy b12 told me my comp ratio !, getting arp main studs, dual quad set-up w/ 2 600 edel carbs, and getting another plate for my nos. and basically cleaning out all the oil galleries in my motor to get any metal left over. it already had a nice comp cam in it with adjustables and eddy heads. hope to have it running by fall ! not in a hurry though, taking my time and doing it right !
Post Fiend
Joined: Feb 2001
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From: Missouri
Why the steel crank? How big of N2O shots are you planning? A cast iron 390 crank is good for well over 600HP. The block won't take too much more than the cast iron cranks without some modifications.
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i was running 125 i'm planning on 200. i wanted to go with the steel crank as an insurance policy. i have forged pistons and rods. i just wanted the bottom end to be somewhat " bullet proof " the steel crank isn't much more then the cast crank. i was told to open up the rear oil passage in the head, is this true?
Post Fiend
Joined: Feb 2001
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From: Missouri
A 361/391 block would even be better. Which block do you have? The thing you need to figure out is why the bearings spun. I would guess that there was most likely not enough clearance. You should have at least .0025 on the rods and mains. That is the minimum. It is also possible they were very worn and got very loose. A standard 390 block is liable to break before the crank would give. Of course crankshaft flex may aid in the demise of the block too so maybe the steel is better. Just throwing some stuff out in the air here.
Steel cranks actually tug at the bearings harder than cast cranks do and require bearing replacement a little more often. Cast iron bonds with oil a little better.
Scouder's crank is made of the same cast iron that your 390 crank is and he is pushing about 1000HP at sea level with a 250HP shot of N20. His block on the other hand is several times stronger than a standard 390 block.
It also depends at which RPM you plan on hitting the nitrous. With a lower stall spped you will be putting excruciating stress on the bottom end. At 3,500 rpm it won't be near as much.
Steel cranks actually tug at the bearings harder than cast cranks do and require bearing replacement a little more often. Cast iron bonds with oil a little better.
Scouder's crank is made of the same cast iron that your 390 crank is and he is pushing about 1000HP at sea level with a 250HP shot of N20. His block on the other hand is several times stronger than a standard 390 block.
It also depends at which RPM you plan on hitting the nitrous. With a lower stall spped you will be putting excruciating stress on the bottom end. At 3,500 rpm it won't be near as much.
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egoman it is the turned down 391 truck crank, i have 10-1 comp. ratsmoker,i plan on using the nitrous off the line, so is the steel crank a wise investment or really not needed? the motor had maybe 4000 miles on it if i was lucky !! i know the motor was assembled right. why it failed i'm not sure of yet, i will find out very soon though.
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Post Fiend
Joined: Jan 2003
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From: Iowa
I would look for a block with the mirror 105 where the 352 should be. It should have extra main webbing reinforcement, and the metal should be tougher. That's what you want with nitrous. Look for D3TE or D4TE on the block, and look in '73 - '76 trucks with 360's. Those should have the reinforcement webs.
DSC has 'em too, they call it the 390 truck block.
DSC has 'em too, they call it the 390 truck block.
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cool ! thanks for the input ! if i can't find one i found main stud girdles there suppose to hold the bottom end together better. i really don't think i'll be pushing too much power to worry about block failure, i hope !
