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IMSA revises performance balancing rules for ALMS
IMSA, the sanctioning body for the American Le Mans Series, have revealed its revised procedure for performance balancing after all the complaints from teams last year in a series of three technical bulletins. The first outlined the new procedure which competition adjustments will be made throughout the year. Additionally, two further bulletins were issued confirming the specification of GT1 and GT2 cars at the opening race and possible new alternative fuel regulations for ethanol.

The ACO Technical Regulations are the basis for the technical regulations of all “Le Mans” branded championships. However, in order to maintain sporting balance between cars in each class IMSA reserves the right (at its discretion) to observe an adjustment method during each season. IMSA will follow the method below:

1) For adjustments within each class, IMSA may make one change, by notice no later than forty five days prior to the first race of the season. During the season IMSA may make two additional adjustments within each class, which may occur at any time during the season. Individual car types that enter late in the season, or that have not competed regularly in the series previously, may receive an additional adjustment at any time, which shall not count as a change within the class.

2) Adjustments of engine restrictor diameter and boost pressure take effect 21 days following the notice, all other adjustments take effect seven days following the notice.

3) The following maximum changes apply:
a. Minimum weight of the vehicle
  i. Up to plus 25kg and minus 50kg (“LM”P1)
  ii. Up to plus 25kg and minus 25kg (“LM”P2)
  iii. Up to plus 50kg and minus 50kg (GT1 cars)
  iv. Up to plus 50kg and minus 25kg (GT2 cars)
b. Engine restrictor / boost pressure change
  i. Up to +/- 10% restrictor area and / or 9% of absolute permitted pressure (All Cars)
c. Other parameters may be changed by IMSA as may be required.
d. The above changes are the total maximums that could be applied in the season, not the maximum change per adjustment.

a. Changes will be made to all cars of the same configuration based on the performance of the fastest (as defined below) car of that configuration, relative to the performance of the fastest cars of other configurations.

b. It is intended that during the season, changes will be made first to weight, and only if the changes required exceed the available weight changes, will Engine restrictor / boost be used.

c. During the season, the maximum single weight step for any single car shall be 25kg (plus or minus.)

5) Basis for making changes:

a. The target range is defined as:

Being within approximately 1% of the fastest average green flag race stint lap time of the reference car during each race in the evaluation period (i.e. less caution laps, in and out laps for pit stops, penalty laps, and other non-representative laps.) IMSA may filter out laps or stints that are not representative.

b. Cars that are outside the target performance range may receive adjustments such that the performance potential of the car should fall within the range.

c. Cars that have received prior adjustment advantages that consistently exceed the target performance range intended may be adjusted downwards. Such a change would count as a change within the class, and would be counted towards the maximum of two change periods in the season.

d. Otherwise changes will not be made to balance.

e. Organizer may exclude from consideration performances that are not reflective of the demonstrated potential performance of the car.

6) Changes to cars that are not of current specifications may be limited. IMSA is not responsible for ensuring that cars that do not exhibit performance representative of their class become competitive.

7) IMSA shall have the right that teams must provide any car data that they may develop at any events. Further, IMSA shall have the right to require the entrant to run an additional data gathering box, and provide inputs for such data box, at entrants cost. Providing false or intentionally misleading information is a breach of this regulation.

8) These changes are deemed to part of the sporting regulations of the series. IMSA’s decisions regarding performance balancing are not subject to protest or appeal.

The second bulletin released confirms that GT1 and GT2 cars in the 12 Hours of Sebring will run per ACO rules. It includes all annexes and air-conditioning adjustments.

1) The starting conditions for ACO homologated cars in GT1 and GT2 for the Mobil One 12 Hours of Sebring, will be as per the ACO Technical Regulations, 2007. This includes all annexes and air-conditioning adjustments, as per the ACO Technical Regulations. With respect to Bulletin 07-01 Para (1), this bulletin may not be superseded.

The third and final bulletin explains that diesel and gasoline cars should be equal and neither should show an advantage. It also explores the possibility of teams running a third type of fuel, which will become available later in the season.

IMSA has taken the position that the energy carried on-board the various cars in the series should be (approximately) equal. For the start of the 2007 season, one type of gasoline and one type of diesel fuel similar to premium types available for “highway use” will be provided at each American Le Mans Series event by IMSA for use by all competitors. During the season, a new ethanol based, blended fuel will be developed which will be similar to the “E85” ethanol blends that are becoming more commonly available across North America, and will be available as a third fuel option.


1) Prior to the start of the season IMSA, in conjunction with the ACO, shall establish the relative energy values of the fuels used in the American Le Mans Series compared to the reference fuels used by the ACO. The total energy value of the total quantity of each type of fuel carried on board each car shall be approximately the same.

a. The basic gasoline fuel system capacity shall be 90 liters, and shall remain fixed.

b. The basic diesel fuel system capacity shall be 81 liters, plus or minus an adjustment of no more than three liters to accommodate the fuel energy values between the fuels used in the differing championships.

c. The basic ethanol blended fuel system capacity is targeted to be 110 liters, plus or minus an adjustment of no more than five liters to accommodate the fuel energy values between the fuels used in the American Le Mans Series regardless of the energy content.

2) In order to ensure that the re-fueling times for a given quantity of energy are approximately equal between fuel types, IMSA may adjust the re-fueling rig restrictor diameter and re-fueling rig height prior to the season such that the time taken for the quantity of fuel to pass for a given quantity of energy shall be approximately the same for each type of fuel. IMSA shall use a standard fuel tank, restrictor and hose length to measure the time taken to pass into an open container at ground level. No adjustments shall be made under this bulletin to equalize the re-fueling performance of a particular car’s fuel system.

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