In reading the post about the 360 carnage i began to wonder what is a good safe maximum rpm for a 390? i ready to build mine in a few monthes and was curious as to how much beatin the stock cast crank and rods can handle, i plan on useing hyper-whatever pistons or some forged ones. i'll probably go with something like a 270-280 duration hydraulic cam. initially i'll be useing plain ol' stock heads and intake until finances allow the purchase of a good aluminum intake and carb, and eventually some heads that flow better. anyway, how much CAN stock crank and rods handle without self-destructing?

 

tough question. A lot depends on how the engine is built. You can do a standard rebuild and go up to 5000~5500 and you should be ok. With upgraded rod bolts, proper clearance on bearings, oiling mods, and all the lower end done with quality parts and carefully checked (read blueprinted), the lower end should go to 6000~6500.

That's not talking about the valve train, FE's tend to bend shafts.

the best bet is to build the engine to run strong in the 2500~5000 range and get 150,000 miles from it. But FE's can get into the 7000 range IF your wallet is strong enough.

 

The stock crank and rods are generally considered to be plenty strong on the FE. The valvetrain and heads tend to be the limiting factors on high rpm performance. That said, you can do three things if you really want to beef up the bottom of your FE to tolerate big power. First, get the best balance job you can. Find the guy with the best reputation and pay him whatever he asks. Nothing destroys a bottom end quicker than vibration at high revs. Second, have a machinist experienced with FEs do all of the oiling mods to your block. You need a steady flow of oil to the bearings to operate in the high rpm range. Restrict the flow to the heads, enlarge the main oil passages, and align and chamfer all the bearing holes.

Finally, if you're really concerned about the bottom end, you can use a forged steel crank from an FT 391 in place of the nodular iron crank from the 390. You'll need to have the snout turned down to 390 dimensions, but any machine shop can do it. The 391 crank weighs more, but it is stronger. Still, I've never heard of a 390 crank being the cause of an engine failure, so I think your money is better spent elsewhere.

 

[updated:LAST EDITED ON 12-Mar-02 AT 00:19 AM (EST)] karljay, whats the best bottom end parts, bearings and such?

karlsd, when you say "restrict the flow to the heads" are you saying "restrict OIL FLOW to the heads"? and if so how do you do that?

i am currently laid off so my wallet is quite weak, my plan is to build a good bottom end for now. i will be needing the truck for transportation to work when i find some and i figure i can add intake and heads later.

6500-7000 RPM. i don't know if i'll be hitting that mark or not. i just bought a 4 speed for the truck to replace the auto tranny. i like to put the thing in the mud to play around and when i do i tend to put my foot on the floor and let it (the motor) scream at the top of it's lungs to get through the hole i'm in. i know they say that it's better to have the auto so you don't lose wheelspeed when you shift gears but i have wheeled with both and prefer the 4 speed tranny. previously the motor had the original 600 holley on it and it didn't self-destruct with that amount of carberation but i want as much rpm as possible without embarassing myself in front of my friends when the motor throws a rod after i just built it. when things get better around here and i have some cash i can always add aftermarket ignition and restrict my rpm that way but then again we are talking about cubic dollars now.

also i now have no carb for it so i was also wondering what would be a good size carb when i do buy one.

thanks for the advice.

oh, also a friend suggested that since the motor was strong when i took it apart that i should just put a decent cam in it and go, i would consider this as i do have a 360 that i can build bigger later. my question there is what do i have to do to go that route? i think if i put a good oil pump, timing chain, water pump and hone the top of the cylinder wall to get the ring groove out then i should be ok, right? the motor is on the stand with the crank and pistons still in it, the cam is still there but the lifters and push rods got round filed. if i could put a cam in it i would be content for now. i just have never done this before and don't want to waste my time/money. if the motor would get me by for a couple years i'd be happy i think 'cause when things get better (and they will) i can really take my time and build another motor.

what of the motor currently in the truck? well it leaves a smoke trail everywhere i go, and goes through oil like it does gas, even so it is pretty peppy for a 360.

thanks again.

Brian

 

As for the size of carb, 600 is a good start, 700 might be better for the higher rpms.

As for the bottom end of a 390, many like the Clevite 77's just make sure the clearance is within the desired spec. The Ford Performance book should help here.

Oil mods for the FE are considered a given for a performance engine. It's not that tough to do. I matched the main bearing to the saddles with a die grinder and drilled the passage from the oil pump to the oil filter adapter from 3/8" to 1/2". Just be careful as you can drill thru the block and ruin it, I spent several hours drilling 2 holes, trying to be exactly straight. Round off the sharp edges with a die grinder. I also run a HV/HP oil pump and ARP pump shaft.

the reason to restrict oil to the heads is that it gives more to the crank and less flooding of the heads. Most use a Holley carb jet (see the book for more info)

As for the cam, the FE responds VERY well to a cam upgrade. Better ones are dual pattern (more exhaust than intake lift and dur) Do it as a set, new cam new lifters.

Check the book section for Ford Performance and how to rebuild Big Block Ford both well worth the money.

 

 

Great!!! thanks you guys!

I think for now, considering my moolah situation, i'm just gonna put a cam in the 390. i can build the 360 later with a stroker crank (hopefully). but i'll worry about the 360/stroker later. i'm getting ready right now to call about a cam, any suggestions as to the max lift i can use with the stock 390? i sure don't want my pistons smashing my valves. i'll be putting in a 4 speed when i swap the motor in also.

check this out, i got the NP435 for 25 bucks, the guy got in a crash and the tranny was stuck in 3rd gear, i had an extra parts tranny so i figured i could fix it. when i took the top off the tranny i realized that the end of the stick that goes into the tranny was simply jammed in the wrong spot, so i unjammed it and it appears to be working great. what a deal, we'll see how it does IN THE TRUCK hopefully early next week.

thanks for the help gentlemen.

Brian

 

Don't you just love when you get a deal like that...

I would look into a cam in that range of 210/225 @ 50 dur and .5 to .530 lift. Most like the dual pattern type, more on the exhaust side.

Most of the cam companies have a tech line, or description of the rpm range and you really should consider the long term usage of the truck and other mods you'll be making. I'd rather buy a long-term cam than a temp one that'll be swapped at the next upgrade.

the up side is that most cams are cheap, I got my Crower for < $100 but install is a bit of work.