I am completely on board with your intentions here. I too like to remake the old stuff better. The issue as I see it getting enough demand to make it worthwhile. I think it would be cheaper and just as effective to have one offs of the girdle, main web beef, etc fabricated at a good race shop if you are really hell bent on acccomplishing this. Dropping the coin to re-engineer and eliminate the shortcomings of the 6.9 and then spending the money to re-cast everything is going to cost a buttload. No way I see to even get anywhere close to each motor not costing ungodly stupid amounts of money.
I would love to see it done, don't get me wrong. I just think if you want a race motor, build 1 only. I would like to know where the performance limit for the IDI style motor is. So far no one has made one with stupid power that hasn't blown up. From all I've read, Dave Sponaegle (sp?) is the only guy who's running a way above average amount of boost reliably. But we still don't know what the power levels are. (I'd really like to know too)
So with that said, what are your ideas concerning the cylinder head combustion chamber design? How do you feel the precups should be modified or should they be eliminated all together? My opinion would be to eliminate the precup and redesign the piston to move the combustion chamber there. But then it wouldn't be an IDI anymore. I really don't have any information or knowledge of the benefits and drawbacks of the precup design but it seems to me it would be the limiting factor in ultimate power output.
Maybe if you had a 2 stage injection to start the combustion in the precup and then a second injector to add additional fuel to an in piston combustion chamber after the ignition event. Timing would be a real PITA I am sure. I don't even know if it could work but that's the thought I came up with. Then, if you were cramming 50 lbs of boost in there you might be able fuel it as you would have to have a second injection pump.
I've been wondering lately if anyone has ever really attempted to significantly beef up the valvetrain on these motors. Roller rockers and improved retainers. Stiffer valve springs and better lubricating valve guides. Hell bigger valves while we're at it. With the amount of dropped, or close to, valves that the 7.3's seem to have this would be a great place to start. There might actually be a small market for a bulletproof valvetrain.
On that note, if you were to re -cast the 6.9 motor make it use 9/16" head studs and 7.3 heads/gaskets. Keep the 6.9 bore.
O.K. those are my ideas at the moment. Anyone else got any.