I love techinical stuff.............
Horsepower is a product of heat. An EGT gauge gives you an indication of where you are in the heat curve. This is a bell curve... as you lean out the engine the temperature will increase, peak, and start down the other side. If you are on the wrong side of the curve you are in trouble.
Like all tools, you need a full tool box to do the job. The EGT is only one of the tools that you need. I think an EGT is worthwhile for long pulls like Bonneville. Even at Maxton they can provide decent information. IMO, on a short run like Maxton you can run an EGT of 1500 and get away with it.
An aluminum piston is going to melt in the 1200 range depending on the alloy. But the piston actually sees much higher temps than the EGT indicates on the power stroke... like 4800 degrees. Then it gets cooled by the incoming charge. Your gauge reads the average at the EGT probe.
The distance, type of thermocouple, open or closed tip, and other things keeps it from being an absolute tool. As a relative tool, being able to compare run-to-run helps.
At 1200 you are giving away HP. At 1300-1400 you are close. Over 1500 it better be short!
An oxygen sensor (AF meter) coupled with the EGT gives you a really good tool set. The amount of oxygen exiting the engine should be zero. In a perfect world that would be the case. In the dynamic environment of the cylinder, you can't get a perfect mix of fuel and oxygen because of the short time for that to happen. Excess fuel is required to make sure that you get peak HP.
Now we must also consider fun subjects like detonation, the effect of compression ratios on flame temperature, incoming charge temperature, and humidity.
Walt:
Horsepower and torque are a by product of the inherent heat of the combustion process. Other things like reciprocating mass need to be taken into account as well. While alloy pistons will stand temperatures above 1500 degrees for short periods. the crown area will start to deform and detonation will occur with resultant metal transfer, usually depositing itself on the plug electrode and the upper cylinder walls. You have one advantage in the R3 engine and that is it has factory under crown oilers. Oil is squirted, under pressure into the lower crown area of the piston, carrying away excess heat just like is common practice in turbocharged diesel engines. I've re-bored and re-sleeved a number of engines, both 4 stroke and 2 stroke and the result is always the same. The search for the optimum AF ratio usually leads one to the machine shop ultimately.
You are correct in the theory that the piston gets cooled by the incoming charge but if you improve the AF ratio too much on the lean side, you loose the cooling effect and meltdown will surely occur. If I were you, I'd err on the side of being slightly rich. Granted, any internal combustion engine will produce maximum horsepower and torque on the ragged edge of detonation but that edge can and will be very expensive.
No matter how fast the sampling rate is on the EGT probe, it will only give you an approximation of actual combustion chamber temperatures. The charge actually cools substantially after combustion as the actual temperature is absorbed by the mass, the piston, liner and the head and the exhaust valve....see below.
You can't control the relative humidity, or the flame front/path. You have to rely on your ECM to adjust for humidity and the flame front and path is inherent to the combustion chamber shape, valve placement and crown shape which are all inherent design aspects of the motor. Incoming charge temperature is entirely determined by the ability of the air-to-air cooler dropping the charge air temperature below the point of detonation as well as the basic compression ratio, again, adjusted by the ECM to optimum conditions.
The engine mass itself cools the combustion temperature, the heat is transferred through the liners and head to the coolant which transfers the BTU's through the air to water cooler. Problems occur when the mass of the engine cannot dissipate the inherent heat of combustion fast enough, when your incoming charge is so lean that it actually has no heat transfer effect and combustion chamber temperatures reach above what the alloy will withstand.
One thing you aren't taking into account is the exhaust side of the equation. Your exhaust valves are solid stem. If you want to explore that ragged edge (I know your pocketbook can do that, mine can't), I'd seriously consider sodium filled exhaust valves. The liquid (at exhaust temperature) sodium will carry away the searing heat from the valve head and prolong the life. There is a real chance, with solid stems, running an optimum AF ratio, to loose a valve head. Drop a valve at 6,000 rpm and you might as well use your expensive motor for an anchor. If, at Maxton at speed you drop a valve, you'd better be prepared to test your leathers. Not something I'd want to do.
You consider Maxton a short run as compared to say Bonneville, which it is. Therein lies a problem. At Maxton, you are going to stress the engine in an abrupt heat cycle whereas at Bonneville, you can stabilize the engine temperature prior to running it at WOT. The spike in temperature in the combustion chamber is very abusive. Basically, you are going to pre-warm the engine (which will not bring the combustion chamber temperature anywhere near a load condition) and then make a WOT run with a short shut down. Alloy's don't like that abuse and will move in relation to the heat. Hopefully, they won't move the wrong way.
Again, I'd stay on the side of the bell. near the top but not precisely at the top. I don't believe the engine will stand it. I've studied the R3 engine internally over some time now. Just putting a compressor on the inlet and cooling the charge air, I don't believe, will allow the engine to make 300 RWHP even with cams and porting. It may for a very short time, a very, very short time but without any reliability.
I'd also seriously consider sodium filled exhaust valves.
If I were you (and I'm not), but if I was going down the road you are traveling, I would have turbocharged with charge air cooling, maybe even compound turbocharged. You blow all the energy out the tailpipe while using a parasitic supercharger but then, I'm a turbocharger guy. You aren't.
I'm more than interested in how the beast runs at Maxton. I'm sure you will keep us apprised of any and all results whether positive or negative I'm sure.
By the way, chatting with you on this site is much better than farming or mowing the lawn. Both mundane tasks that I'd like to train my wife to do but I strongly suspect that will never happen.
