IMSA released a series of Balance of Performance changes on Friday night in advance of the Mobil 1 Twelve Hours of Sebring which takes place on March 15. Official practice begins on Thursday, March 13.
Prototype: The Corvette DP, which posted the fastest lap time in recent testing at the 3.7-mile Sebring circuit, has been given a pair of bigger restrictors to reduce power, moving from the 34.5 mm units used at the Rolex 24 at Daytona to openings that measure 33.8 mm. The 5.0-liter V8 Chevy engines have also had an RPM limit of 7450 established.
The 3.5-liter twin-turbo V6 Ford EcoBoost-powered DPs have received a pair of smaller restrictors in an effort to better match the naturally-aspirated Chevys, moving from 33.1 mm openings at Daytona to 33.7 for Sebring.
Honda’s 3.5-liter twin-turbo V6 DP engine, which will race for the very first time at Sebring, had its restrictors established at the same 33.7 mm size mandated for the Fords, but turbo boost for the P2-derived engine is slightly higher at 26.7 psi.An increase in turbo boost for Sebring has also been implemented, jumping from 24.6 psi to 25.6.
The biggest restrictor change went to the Dinan-prepared 5.0-liter BMW V8 which saw its pair of 76.4 mm restrictors reduced to 72.9 in an effort to bring its performance in line with the other DP motors.
GT Le Mans: IMSA made sweeping fuel capacity reductions after Daytona to shorten stint lengths for all cars. More tweaks have been made between the Sebring test and race, and comparing where the cars were at for Daytona, Porsche’s 911 RSR has moved from 110 liters to 99, Corvette’s C7.R from 110 to 96, Ferrari’s F458 from 110 to 94, Aston Martin’s V8 Vantage (which is not entered in the race) from 90 to 85, and SRT’s Viper from 120 to 103.
The V8 Vantage received a significant 30-kilo weight break from the test, reducing the Aston from 1205 kg/2657 lb to 1175 kg/2590 lb. BMW’s Z4 has been allowed to use modified door sills and has been given an extra 10 mm Gurney for its rear wing since the test BoP, an increase from 15 mm to 25.
GT Daytona: Large fuel capacity reductions were also called for in the GTD class after Daytona, but IMSA has now added most of what was taken away back to some cars and actually increased the amount others had at the Rolex 24.
Porsche’s 911 GT America will race with an 83-liter tank, down from 85 at Daytona, Ferrari’s F458 will have 92, up from 86, Audi’s R8 will have 94, up from 86, BMW’s Z4 will have 89, down from 100, Aston Martin’s V12 Vantage will have 97, up from 90, and SRT’s Viper will have 104, up from 95.
Porsche’s GT America has also been allowed to use Crawford’s spec DP rear wing.
An update posted by IMSA on Saturday further defined GTD wing and endplate heights–a point of some controversy in January–to ensure standardized downforce and drag figures are generated: “In the complete operating range, the complete wing and end plates must measure at a maximum equal to roof height and at a minimum -60 mm below the roof height and 101.5 mm maximum, 77 mm minimum rearward of the rear most perimeter of the body work when viewed from above. The operating range for the rear main plane angle as indicated by the manufacturer will be specified in the Adjustment of Performance Bulletin.”
Driver Ratings: Three status changes have taken place less than a week away from the event.
Driver Name: New Rating, (Previous Rating)
Davison, James: Gold, (Silver)
Johnson, Billy: Gold, (Silver)
Wilden, Kenny: Gold, (Silver)