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limited budget 390 build
building a limited budget 390, aluminum heads to get weight down for sure, but which ones.
Would I get better results using stock crank, Cranes Hyd roller cam and roller lifter, roller rockers and largest safe bore size? Or buy a longer stroke crank and use coventional cam and valve train? |
Edelbrocks are really the only budget aluminum head option. And even with minimal mods they'll work OK on a 390 based piece
If it were me I'd try to find a usable 428 crank - in a budget, moderate power deal it really don't matter if the crank is 20-20, or 30-30... and they sell for less - much less. Stock rods with bolts and recon. Probe sells a pretty inexpensive .030 over "410" forged piston. You will need a balance job. Assuming you already need pistons and rod reconditioning, we just got 20+ extra cubes for somewhere well under a grand. A solid or hydraulic flat tappet will take care of things just fine - and cam/lifter combos are under $150. You dont even need roller rockers on something mild - but I'd recommend some sort of end stand support or quality shafts at the very least. Now - take all the money we've saved - and spend it to get somebody to do some port work on those heads! Other than the added displacement, head work is the best way to make power without any rumpity cam or poor driveability downsides. Go out and have fun! It should be a great street cruiser and good for some occassional wide open blasts. Just don't treat it like a max effort race piece 'cuz it will give up on you if you do.... |
I've built up several 390 HP engines and just completed one done like this:
390 block bored to 428 std. , sonic tested with all cyl. wall specs meet. 72 cc edlbk heads, mild polish and port with oil mods done. Ferara valves. 390 rods, shotpeened, ARP 190,000 psi rod bolts. Comp cams 280, hyd. cam, pusrods. Harland sharp roller rockers( Spend the money here! Buy direct, the edlbk heads have the valves on a slight offset and harland bolts on right the frst time) 428 crank shaft speed pro forged pistons, 428 std., (you can run uo to 11:1 comp. with no detonation on 93 octane pump fuel) Holley 750 cfm or Speed Demon 750 ( Dyno showed aprox 18 hp more with the Demon) Canton oil pan Precision oil pump, Modesto CA(only pump and shaft to use!) This motor will give up 425 hp + or - @ 4800 rpms, and about the same in torque. $$$? depends on how much work you do do on your own ...aprox 4,500.00 Good luck MD |
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I would probably spend the extra $500 and use hydraulic rollers. I believe they have better lobe choices. In any event, with the big cubes this would make your performance targets with fewer revs and longer resulting life. Barry could probably sell you the balanced rotating assembly. The heads are trickier. Fully CNC's are out side of your budget ($3k). So either stock, or with a once over and some bowl work...which would probably be a stage 1 or 2. Keith Craft or Barry could probably help here, as could some better local shops. Even stock, the heads would probably be ok. I would spend the few hundred more for a carb from one of the better carb builders, one (I think Pro-Systems) used to advertise here. |
So, it sounds like your suggestions are for increasing cubic inch with stroke and bore changes. if my price only allows for this would you still go this route with standard cam and stock heads? I guess I was hoping heads and roller cam would compensate equally for power gain , $$ for $$ ?????
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I'd stick with the 390 crank, otherwise do as Enginetime says. You should be out the door for well under $4k.
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I recently converted a 390 to a 428...it's not a budget engine...costs rack up quickly. To stay within a tight budget, keep the 390 crank & rods, just go with good bolts. Put your money into the heads and intake if you have it, if not, a good set of stock heads with oversized valves and a good Comp Cams Magnum hyd grind with a vacuum secondary 750 cfm carb will give you plenty of street power...keep the comp. at 10.0:1 and you're in business. Make sure to keep it simple, and you can't go wrong.
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The question is what you are spending. On a rebuild, you should be using new pistons and rings. Honing the cylinders. New bearings. Rebalancing the crank. New valves, valve springs, retainers, keepers, and seals. new timing chain and oil pump.Probably a new cam, lifters and maybe pushrods. A new valve job, maybe decking the block, head and align honing the mains.
You could just rebuild the 390. The Edelbrock heads are around $1300 or so in stock form. The intake is another $300. An off-the-shelf carb could be another $300. However, the Scat crank and rods are not expensive at $750. The BBC rods are $430, or $520 with better bolts. Boring the cylinders is around $300 I believe. So for $1500 the motor is increased in size 15%. If the block can handle the extra bore, going to a 428 would be a couple of hundred more. A Stage III head would cost an extra $1700. A hydraulic roller over a flat tappet would add around $500. A well done Cobra replica is more exotic and expensive than a '66 Galaxie...does it deserve a better motor? |
Is the scat 428 crank internaly balanced like my 390 is now? Iv'e been told all 428s were external balnce. why BBC rods instead of 428 rods?
THanks everyone for all the input . |
Internal. Don't the exact reason, but possibly because they existed, were longer, and had smaller rod journals. Somebody may have used them to handle an offset ground 428 or 427 crank.
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The 428 Scat crank uses normal FE sized rods.
The 4.125 and 4.250 use the BBC based 6.700 or 6.800 rods The BBC versions are cheaper - offsetting the cost of the longer stroke crank by a bit... The most recent 428 engine/428 Scat crank I sold used a 428 flexplate with the weight on it, and iut fell in between things when balanced. He needed to either drill a slew of holes in the rear counterweight - or lose the flexplate weight altogether and add a slug of mallory in the crank. The customer chose the mallory. |
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