Just the facts, please
I think, we all generally agree. What I am trying to point it is that we are dealing with a lot of myth and marketing hype, here.
What do we want to determine:
1. What is the best architecture for a road racing engine and why.
2. Above would imply: high power to weight ration, reliability, comapct design, flexible torque curve.
We have established:
1. Airflow determines ultimate power output and flexiblity.
2. Airflow is dependent on volumetric efficiency and RPM (and size/displacement of the motor).
Some interesting facts:
1. Smokey Y. (read his book) did a study for GM on a 4-vlave head for a small block. It did not outflow a 2-valve head at high (racing) valve lift. The project was abandoned. This was a long time ago. Maybe things have changed. everything is 4-vlave, now.
2. I could not find any reference to a 4-valve Ferrari 1.5L v-12. Colombo engines were 2-vlave. Later, bigger V6, V8 and V10 had many valves
3. The big advantage of a multi-valve head is that in racing conditions, it can be revved higher, since the valve-train (moving parts) is lighter.
4. F1 engines of turbo era were made of cast iron. They probably weighed a lot.
5. A BMW cast iron 4 or even aluminum straight 6 weighs as much as a GM LS motor. An aluminum 4-cylinder is not that much lighter than an LS (should be only half the weight, right?), because the crank and camshafts (steel) are very heavy.
6. The only light production engines are Subaru flat 4, Hartly (Hyabusa-based) motor and GM LS V8. Everything else is pretty chunky. See engine weights on the internet.
7. Bespoke race engines and F1 engines are in a diffeent league and price range
8. consider a NASCAR motor and an F1 motor. NASCAR has higher piston speed at 10,000RPM that it runs for hours. The power output is similar. the displacement is 2:1, but the rev range is 2:1 in the other direction. therefore, poser per displacement per RPM is the same!!! i.e. torque per displacement and BMEP is the same, even if not a little in NASCAR's favor. A big V8 is still havier than a 3L with pneumatic valves, though!
9. F1 V10 engines were legislated not engineered. The rule bok said 3L, V10 less than 4 valves per cylinder. I am sure there was some engineering consensus to keep the F1 show on the road i.e. achieve the desired power levels.
Therefore, we arrive at the following:
1. The motor necessary for most road racing use is under 700hp
.
2. A high-revving turbo 4-cyl is sufficient to provide this.
3. To rev it up, we need 4-vlaves. Valve lift is less important with turbo's, so 4-valves work great.
4. Next best choice is an LS7. But it is so hard to fit it into a Lotus
5. 4-valves is not always better than 2.
6. Engine displacement is just empty space and does not weigh much.
Anton