There is an interesting blurb on SIRs in the recent issue of Road and Track entitled “Formula For Power”. The short article discusses evening up the playing field for the Le Mans race. I quote:


To give cars of different engine capacities an approximate equal chance, the maximum power obtainable is limited by one (or equivalent two) air restrictors limiting the flow of the engine’s intake air.

When the speed of the airflow through the restrictor reaches the speed of sound, the flow cannot be increased, limiting the engine’s power. Roughly speaking, if the diameter of the restrictor is such that the airflow reaches the speed of sound for a 4 liter engine revving at 5000 RPM, it will also be reached by a 2 liter engine revving at 10000 RPM, both engines theoretically making the same power.

In practice, however, the car with the bigger engine will have an advantage because the air restrictor hardly affects the engine’s maximum torque, which is higher for the bigger engine. Consequently, to equalize the changes of cars using different size engines, smaller capacity engines are allowed a slightly larger restrictor than those of higher capacity, which compensates for their lower torque with slightly more power. In the case of turbocharged engines, smaller engines are allowed a higher boost.

This is in fact a sort of handicap formula, but is has been established by a component engineering formula and has worked quite well over several years. As an incentive to technical development, the formula is surely less interesting than, for example, a fuel consumption limitation. But when the maximum intake airflow speed has been reached, improvements in the combustion efficiency and reduction of friction losses can still yield more power.

So, to make these things work for IT, a lot of R&D will have to be done with engines of various sizes to make sure they are appropriate and account for torque of larger motors. Is the ITAC and CRB ready for this and willing to handle the process? There is still plenty of debate and changes in SIRs at the professional level. Is club racing ready for this? (probably no worse than the debates we're having, right?).

SIRs don't belong in IT. The recent discussion with the BMW and SIRs really does not sound like IT racing to me. IT was/is, I thought, about racing at a grassroots level and is an entry form of racing in the SCCA. Incorporating SIRs into a regional level racing program seems like overkill and does not offer any advantages to good old tried and true lead.

R