Money is no object, 3.75L I6

If sticking with the AMC/VAM non-crossflow six the best bore stroke combination for a high winder would be the factory VAM 282 3.917" bore with the 199 3.00" stroke. A US spec 4.0 block should easily bore up to that size. The 199's have 12 counterweights- good for endurance racing. They could be lightened with modern piston/pin /rods.

T S

I'm going by what road racers have gone with. Modern pistons/rod sets are lighter, balancing means the counterweights can be trimmed on the outside, and the counterweight pins drilled ( less effective ) to reflect that.  You have two weights per cylinder to achieve perfect balance and just as important, to absorb secondary forces. A standard 3.00" 12 weight crank is approximately 15 lbs more than a larger stroke 3.41" 8 weight 4.0 crank. Quick revs are nice, especially for autocross or drag. A 45- 60 minute road race session, reliability is more important.

farna wrote: IKA added three main bearings, bringing it up to seven from four, in the mid 70s. I have never heard anything about a cam design change before though. I don't think it ever happened. Adding webs for mains to the block and even making a new crank would be trivial compared to adding six lobes to the cam. The cam itself wouldn't be a problem, but the entire head would have to be redesigned almost from scratch. The valve in the head are directly across from each other. There's no easy way to make two lobes work. I think getting a near perfect hemi combustion chamber by having the valve directly across each other is the whole reason for the single lobe. It just restricts cam grinding.

No, all the road racers don't use the heavy crank, I know a few who use the light one with just as good results. The ones who use the 12 CW crank cite "greater strength" more than easier balance. The ones with a lot of money in the motors balance the rotating assembly anyway, even though the six is inherently balanced. I've talked to several road racers who have built sixes. They just don't like the lighter crank because it is PERCEIVED to be weaker, and they don't want to risk finding out at 6000+ rpm. I can't really blame them for that, but the Jeepers have pretty much proven that the lighter crank is just as tough, at least in low to medium rpm applications (under 5000 rpm), even when there is a lot of torque stress on the crank. Take rock crawling -- spinning a tire in the air then suddenly getting traction usually breaks things, and on rare occasion it's a crank. From the guys I've talked to just as many 12 CW cranks break as the light ones, but both are far between.

You have some good arguments for a 12 CW crank as far as balance. Where the weight is placed around the crank is more important than the number of weights, especially with seven main bearings, but you do have valid arguments -- especially if you want to spin the thing 6000+ constantly. A short stroke built-to-the-hilt six for racing would probably need to do that. Your formula would work with existing parts and technology, would just cost a lot, and would be a "high strung" engine. Don't know if it would be very streetable, but it sure would be a lot of fun somewhere like Road Atlanta!!

lol, i have a sort-of "money no object" cylinder head .... check out this AMC part number:

http://www.wps.com/AMC/Navarro-turbo-motor/images/RD-top1.jpg

and porting....

http://www.wps.com/AMC/Navarro-turbo-motor/images/RD-combust1.jpg

and big valves...

http://www.wps.com/AMC/Navarro-turbo-motor/images/h2-wrong-valve.jpg

Alas, my money is severely limited; but I just inventoried all my parts and i'm thinking of building a < 200ci carbureted 6000rpm six cammed for 4000 - 6000. Never had an engine with a wild cam but this head is all ready for that. The block is sleeved such that with the 199 crank it's 181ci.

Will use 4.0 rods and since the cyl walls are currently an insane 0.400" thick I'll just bore it for whatever pistons I can find that work.