[Walt Fricke]

PCA Club Racing is trying to group the 1979-1994 models into one class - 911 Cup. With some not awfully expensive adjustments (mainly weight) this seems feasible. The problem child is the US SC from 1980-1983, with the small 34mm intake port. Just how much air can you flow through that port absent forced induction?

The basis for balancing power here is use of stock engine internals - cranks, pistons, CR, heads, cams, rods, and so on all need to be stock, or where necessary permitted stock equivalents. So all engine performance modifications have to be bolt-ons, though for every model other than the small port engines very little in the way of bolt on go fasts is necessary, or in some cases has been allowed with offsetting compensation.

Boring small port heads to become large port heads doesn't meet the criteria, just as "better" cams, larger pistons, more CR don't. There are various suppositions as to what adding carbs to the small port engines will do, and what additional weight allowances will do (and will cost).

I've thought of approaching feasibility in another way: assume the internals are stock. What Volumetric Efficiency would be needed for a stock small port 3.0 to produce the hp that the late Euro 3.0 or the 3.2s, with their stock intakes and CIS/DME computer fuel injection and good race exhausts make.

Use 225 RWHP as the "standard" Dyno-Jet wheel HP for the cars currently running in this class.

Does anyone have an engine program which could do this? Enter the displacement, valve size, CR, cam, and 34mm port parameters and 225 HP, and solve for VE? The result could help in determining if allowing the best imaginable intake system (independent barrel valves, EFI, tuned, ignition, whatnot) might get these models into the ball park. Where some other parameters are needed (flow bench information?), maybe use a range if no specific data available?

There are a lot of figures out there in 911 land, but most are from guys who have modified their engines with no need to deal with rules. Debates go on about best cams, use of Max Moritz pistons, questions about how much CR you can run, the most cost efficient way to increase displacement, and so on. All that isn't directly relevant to the question here. The only real go fast on the big port 3.0s and the 3.2s is the exhaust (several out there seem to approach what is possible there, and sound levels are irrelevant), and 3.2 chips are free, which are part of the 225 WHP figure.

I have one or two somewhat simple programs which might work, but I've lost the passwords for them some while ago, and I'm not very good at this approach. I couldn't get my engine's measured RWHP to match calculations.