Dago Red lost an engine last year after the final race at Reno, as Skip Holm prepared to go for 500 MPH, after clocking 489 MPH earlier in the week. While the Reno unlimited class planes are W.W.II based, they are heavily modified. Only most of the very basic structure remains, the rest is either replaced or so heavily modified it is barely recognizeable. Of course, due to the events of 11 September, this year's Reno races were canceled because no VFR flights were allowed.
There are several factors restricting the piston engine prop driven planes. Horsepower really isn't one of them. Most of it is due to propellers. The technology of prop driven piston engine powered planes pretty well topped out during the war. The planes that won the trophy for the next few years were mostly P-39's with P-38 engines, and the P-39 held most records for years.
Horsepower isn't much of a problem for radial powered planes, but the radial engine creates a great deal of drag because of size and cooling needs. The Republic engineers had turned up the boost on the P-47 engine enough to make 3500 horsepower back in 1943, and run it that way for 24 hours straight.
It isn't a big problem for some inline Vee engines either. When I was working in tractor pulling, we had Allison engines making over 3000 horsepower at 60" of manifold pressure, and running with only oil and spark plug changes for an entire season. We did this with only the built in crankdriven centrifugal supercharger, and not the turbochargers like the P-38 used (the P-38 was the only Allison powered plane to use turbochargers, and that is why it ran well at high altitudes). Now I'm not as sure about the Merlin engines, we never ran them, they seemed to be less durable to me. I have no experience with the Griffon. There are still a few tractors using the Allison engine, and they are competitive, which tells me they are making well over 4000 horsepower.
Being a seriously devoted race engine builder with some Allison experience, I'd say you could get 4500 reliable horspower from an Allison set up like the P-38 installation by using normal techniques like headwork (bigger and better valves, porting and polishing), increasing the compression ratio, and using new technology camshafts. You'd need to replace the carb with fuel injection, and use a newer technology turbocharger too.
The problem is getting a prop to harness the power. You'd need at the very least a counter rotating four blade twin prop setup. Those things are terribly complex and relatively fragile. These are the problems that faced engineers after W.W.II, and caused many problems with prop driven bombers. The complex gear boxes with hollow shafts and reduction ratios just could not take the power. I'm sure that with the advances in metallurgy and engineering gear boxes and hubs could now be built. But they'd be very expensive. Another thing about those gear boxes is that they would be fairly large and heavy, creating weight and drag problems.
I'm not real sure what the rules on those things are at Reno (if I had a real warbird I'd be playing with it and not posting here, besides, I'd say it would be real hard to have a plane you could fly AND race successfully). The planes at Reno rely a great deal on donations and sponsors to keep them running, and there is very little to be won in the way of money. The only exposure a sponsor gets is at the race, and on a rare cable TV clip. Except possibly some aircraft magazines. Money is very short, so development is limited.
The critical Mach on most of the original airframes was between .67 and .80, so aerodynamics may not be a huge factor, but it does contribute. Several could be controllable in a dive approaching 600 MPH, so the basic airframes could likely get the job done. Mostly it is a matter of drag. One sure sign of how big a factor drag is would be that several of these planes were able to reach speeds of around 450 MPH in level flight at critical altitude.
Renegade Savage
[ 11-13-2001: Message edited by: Renegade Savage ]
