I've been thinking really hard about your comment that the early T/E heads with 32 mm ports are good enough for tons of HP and the S heads being all marketing for anything less then a race engine. Here's my logic as to why I doubt that you'll be able to get more then about 175 HP from T/E heads, no matter how fast you spin a 911 motor. An also why you do need S heads to get the HP up to around 210.
Let's start with the T/E flow data that you have published previously:
Quote:
Stock 911T w 46MM intakes 42MM exhaust
intake
lift flow (cfm at 28" )
0.1 " 60
0.2 " 121
0.3 " 174
0.35" 192
0.40" 200
0.45" 200
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Note that BK911 flowed a stock T/E head and came in at about 150 CFM rather then your 200, but let's use 200 CFM at .4 inches. (Note that BK911 also flowed at least 8 S heads and they all came in at about 215+/- CFM) Let's convert 200 CFM to 5663 liters per minute.
How long is an E cam open for at it's peak HP engine speed? About 0.000105983 seconds. How much air can flow through a 32 mm port in that time?
~.4 liters. (Note that I've assumed that the flow profile is like a trapazoid with 1/3 of the time at full lift, 1/3 on the ramp up and 1/3 on the ramp down. So the flow over that time would be equal to 2/3 of the flow * time: (1/3T + .5(1/3)T + .5(1/3)T)
What is the capacity of a single 2.4 liter engine's cylinder?
.4 liters.
Hmmm....
What happens if you put an S cam into that engine? Well the extra lift of the S cam won't provide any benefit over an E cam since an E cam's lift is .408 and an S's is .459 since a 32 mm port doesn't flow any more air at .459 inches of lift then it does at .408. But it does have more duration and overlap. At the same engine speed an S cam would have the valve open for 0.000114103 seconds. Going through the same math results in .43 liters of air being available for a .4 liter cylinder. So chances are the S cam would not quite be starting to run out of air at 6500 RPM like an E cam would. If you look at 6800 RPM where an S cam seems to peak, once again the ports would allow .41 liters of air into the cylinder which is within 3% of the cylinder capacity. Since the engine will be allowing full cylinder filling at a 5% higher engine speed, I'm guessing that maybe the engine will make 5% more HP or about 8.25 HP for a total of 173 HP. Keep in mind that you will lose some flexility at the bottom end since the torque peak will increase from an E's 6200 RPM to an S's 6500 RPM.
Now I've always maintained that the 2.7RS (which uses an S cam) was also port constrained even though it was using 36 mm ports.
Repeating the analysis with a 2.7 engine results in the ports flowing .44 liters at 6800 RPM into a cylinder with a capacity of .45 liters. This might explain why 2.7 RS motors don't make proportionally more HP at then a 2.4. The answer is because at peak HP RPM the cylinders aren't getting a full charge of air, thus the BMEP (aka: torque/liter) at that engine speed is less then a 2.4S's. Incidentally at an RS's peak HP speed of 6300 RPM, the ports will flow .48 liters of air into the .45 liter cylinders.
