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Help me design a 390!
Okay guys,
I've been tossing this around for a long time, but the "winter" has got me bored and I'm ready to plunge. My Shell Valley currently had a very potent 289. The thing is a rocket with 4.57 gears and a Tremec 5-spd. A buddy of mine has about a DOZEN 390's and is willing to GIVE them all to me. Some are runners and some are parts. I really think that the Cobra should have an FE in it, so I'm finally going to do it. So what do I want to build? I'm already in the aluminum heads/manifold mode just to shave some weight. I'd like to keep the rear gears, and I currently cruise at 70 MPH at about 2,750 RPM. I don't care about mileage, as this is a fun-only car. So what would be the best 390-starting-point combination for my 2400# (with driver and 289) car? C.R.?, Cam? Rods, crank, etc? I don't want to start calling engine builders and wasting their time with questions since I won't be spending money on their parts. I figure there are plenty of 390-guys here with some free time that can give me some advice. Thanks, Tom. |
With the aluminum heads you could go to 11:1 compression as they dissipate heat better and you have better gas there than we do here. I run 11:1 in both my stroker and the BB with the iron heads. Just can't get on them hard with our crappy pump gas. But if you just drive it mostlyI would say around 10 1/2 compression would be good. As for cams, that would depend on what you like. High end power or a more level power band. The possibilities are endless. Get the Desktop 2000 Dyno program and play with it. That will give you a darn good idea of what different setups will give you. Normally when I got everything entered into it correctly, it was within 5 horsepower and a few pounds of torque of what the real dyno readings were. And it was righ on at the RPM they occured at.
Ron :) |
See if you can find a set of C6AE U heads, small combustion chamber, good heat, good burn and cheap. They are also high compression but, you can have a torque cam ground to bleed off a little, C7 rods, well balanced cast crank and the rest is your choice. If aluminum heads were so much better, I would have had them long ago......
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I would like to see what a 390 , 428 crank , solid lift rides like .
I had a 390 , ballanced with 406 iron head ( 56 cc ?) 10.5 to 1 , hyd cam , made 315 at wheel . Good combo for a cobra ! I seem to wonder what more power would be like so I went to 427 with solid cam in my case the 390 described would have been more than fine for me ! |
Thanks for the replys so far. I guess I should be more specific, eh? I'm looking to rev the piss out of this thing, much like the 289 does. I know I'll not see 9k RPM like the 289, but I really like the gears I've got and want an engine that will survive occasional trips into at least the upper 6k's and cruise well in the 2,500 to 3,000 range. Since the 289 is such a small-displacement high-RPM engine, it doesn't have squat down low, but to it's credit, it sounds great at an idle. Like I said before, this is a fun-only car and part of the fun (to me) is a lumpy idle.
Can I even hope to cam a 390 for top-end performance and expect it to stay together at an RPM level that will compliment that choice? I know NOTHING about FE's except the few things I've read here. Thanks, Tom |
A big block FE is a very different animal than that 289 you’ve been beating on. With the FE, you’re going to get loads of low end torque and some real nice hp numbers without having to turn the thing over 6K. I have my rev limiter set to 6K which also suits my cam’s power band.
If you want a lumpy idle, you can sure get one with an FE. How much hp are you looking to build? I’m expecting 375hp (I hope for more) out of it. It’s a basic 390 build. Here are my specs: 390 .030 over short block with stock bottom end Oiling mods (chamfered oil feed holes) 10:1 compression Federal Mogul SpeedPro forged pistons (TRW-L2291F) HV oil pump CraneCam Part# 343801 Grind# H-278-2 Edelbrock RPM heads 72cc Edelbrock RPM intake Ductile Iron 1.76 rocker arm kit adjustable Crane CRN-34772-16 Pushrods Crane Cam CRN-34645-16 stock 3/8 diameter, 9.234 in. long MSD “ready to run FE” distributor # 8595 MSD coil and 8.5mm wires MSD 6AL ignition box Holley Street Avenger 770 cfm ARP bolts throughout Hooker Super Comp headers Tim |
I am also building a 390FE. 30 over w/ 390-428 Eledbrock Alum. Stock Heads #6006. Pistons TRW#2291F30. I had a Comp 280H in my last 390FE 2000rpms to 6000rpms. I am going up a little to a Comp Cam 286AH-10. 2500 to 6500 rpms.The 286AH-10 from Summit CCA-33-315-4 $119.
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FE Specialties said my 390FE should have approx. 420hp with my set up. A 390Fe revs a little more freely with a 390 or 427 crank but a 428 crank has more low end tork with .
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Keith Craft has a bottom end girdle you'll be interested in if you want it to stay together, He would be a good source for ported aluminum heads and advice.
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my receipe for a mild/hot 390
later (or any) 390 block that will pass a sonic check to allow .075" overbore. I have sonic checked dozens of 390 blocks that will go .075".
install main studs oil mods to block off the shelf Ross 4.125" forged pistons (Doug at Precision Oil Pumps can get them, and all the other parts you need for a good price.) 9.9 to 1 to 10.1 to 1 compression Scat 4.125" stroke crank BBChevy rod journals Scat 6.700" Rods BBChevy rod journals Speed Pro or Sealed Power moly rings for a 400 Chevy (4.125") Hydraulic cam around 240 degree duration @.050", .570" to .580" lift, 110 lobe centers. If you really want to rev the crap out of it:confused: run a mechanical flat tappet with 255 to 260 deg @.050" .620 or so lift should get you to 6200/6400 rpm. If you want more, buy a 427 :D good roller rocker arm set (Erson, Crane, Precision Oil Pumps, Harland Sharp, etc.) Stage II ported Edelbrock heads (upgrade the valve springs) Performer RPM intake 750 to 850 Holley Vacuum or DP MSD billet Dist with timing set at 14 to 18 initial, 36 total. 442 cubic inches idles at 850 rpm runs great on pump gas 450 to 480 hp at 5800 rpm Should be able to build this combo for 7 to 9 grand depending on who does the work. HTH, --Mike |
I have a set of cherry C4AE big port heads if anyone is looking for some vintage factory performance pieces. $300.00 for the pair.
scotfox@earthlink.net |
Steelcomp, if those C4AE you mention end in 6090F, their worth far more than $300, providing their workable.
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Thanks for the input. |
Thanks for the help so far. Now more specifically, what can I expect for a reasonable red-line for a 390? If I were to improve on the stock rods & crank, how much of an improvement would I see?
Is it nuts to think I could (VERY OCCASIONALLY) spin it up to, say, 7k, with regular acceleration trips into the 6.5k ring? Or could I exceed those numbers? I expect to spend good money on heads & valvetrain, but my big concern is in building a bottom end to handle whatever I decide to throw at it. SFFiredog had a lot of good information, but I'm wondering just how strong the stock bottom end is and how much money I should throw at it other than just better studs/bolts. Thanks, Tom |
Tom,
I think you have been given some very good advise especially with the Ross pistons, alum H-beam rods, solid lifter cam 600 lift/ 250 dur, roller rockers, heads, and intake will be your fastest way to HP (don't scrimp), do it right. MSD is always a good way to go. In my opinion you don't need the 4.57 gears. I would go with 3.50 and not more than 3.73. You may want to find a good toploader or TKO 600 tranny (the T-5 won't last). The 390 is a good work horse and should make you very happy. Clois |
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Aluminum rods are hand grenades waiting to happen in a street engine!
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Trying to compare a 289 and 390FE is an apples-oranges comparison. Trying to get these revs from a passenger car FE block is asking for it. And tweaking this motor on a "Fun Car" to these kinds of revs will get you lots of tire smoke, and more money spend in legal fees defending your drivers license than machine shop fees building your engine.
If it doesn't have to look like an FE, a more reliable way to 427CI that will make HP and live would be a new aftermarket, 4 bolt Windsor block, forged rotating components (4.125 x 4.0), aluminum canted valve heads, solid lifter cam. Have your fun at the track. |
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Why??? Because that's how you did it?? Have your fun anyway you want to, but don't preach. 6500 from a "passanger car" 390 is no sweat. Traction problems are inherant with Cobras since most of their suspensions suck. Besides, what other "practical" purpose is there for a freeekin Cobra anyway? Four bolt block, forged internals and canted valve alum heads, and you're squawking about practical???? BBWWWAAAAAHHHHHHHHAAAAAAAAA!!!!!! Lets see..you're a lawyer. No, a doctor...wait, a dentist.:3DSMILE: |
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