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CUP RACE TECHNOLOGY VOLUME 1 2007
technology CUP race A special report
INSIDE HENDRICK NASCAR’s top Chevrolet exposed
SHOCK PROGRESS Engineering at the bump stops
CAR OF TOMORROW How to engineer it to be fast today!
PLUS
Transmission Chassis
Engine secrets USA $50, UK £20, EUROPE e35 14 00_CUPRACE_Cover FINAL FINAL *.i1 1 16/11/07 13:12:49 14-29
Hendrick.indd 14-15
PROFILE : HENDRICK CHEVROLET IMPALA SS COT
The 2007 Chase: Johnson leads Gordon, both driving for Hendrick Motorsports
What lies under the skin of the best Chevrolets in NASCAR? We asked Hendrick Motorsports’ R&D chief Rex Stump
OVERVIEW The COT is an evolution of the COY rather than a new departure. Carrying essentially the same powertrain it is fundamentally different to the COY primarily in terms of chassis safety technology and aerodynamics. The COT frame incorporates a stronger roll cage and additional reinforcement for the floor pan and the walls of the cab area with anti-penetration paneling added to the driver’s (left) side. The cab is 3.0” further back, 1.5” taller and 4.0” wider with the driver sitting that much further away from the left hand door, as close as is feasible to the central transmission tunnel. Energy absorbing material is positioned between each door and the cage, the driveshaft now has a full 360 degree containment tunnel, fuel cell protection has been enhanced and the exhaust is kept to the right side taking heat away from the driver’s side. But at the same time the
Impala Taming the
racing operation, which is based a stone’s throw from Lowes Motor Speedway in Concord, North Carolina. That strength was reflected in the way that its teams performed in the inaugural races for the
H
endrick Motorsports had, at the time of writing, two of its four Cup teams heading the 2007 Chase with just one of 36 races to run. That underlined the on going strength of this Chevrolet-equipped NASCAR
Car of Tomorrow (COT), which is now the Car of Today as in 2008 the established cars become the Car of Yesterday (COY). There could be no better example of the COT than the Hendrick Motorsports Chevrolet Impala SS, which in 2007 won the first ever COT race, at Bristol, and the first ever COT restrictor plate race, at Talladega. Happily, Rex Stump who heads R&D at Hendrick Motorsports was generous enough to take us through the car.
• ProFiLe:
tHe HenDricK cHevroLet What lies under the skin of the best Chevrolets in NASCAR? We asked Hendrick Motorsport’s Rex Stump
• Focus: cot corners The Car of Tomorrow is running on its bump stops, bringing a new challenge to shock absorber suppliers such as Penske
• Focus: cot trAnsMission Gearbox, driveshaft and rear end
• insigHt:
engineering tHe toYotA Getting to grips with the new shape of NASCAR
• Focus: cot FLuiD sYsteMs Coolers, fuel and oil systems
• Dossier: cot engines Inside NASCAR Cup engines
• griD NASCAR Techno Topics
• Ps: At tHe wHeeL From the cockpit today and yesterday
COT cab is subject to higher temperatures from the under-hood
region, particularly whenever there is significant use of the brakes. This is due to the introduction of a front splitter, which is more effective than the COY’s air dam in diverting air away from the underbody region. With these cars the underbody airflow cannot be manipulated to generate aerodynamic downforce through local acceleration of it. Rather, downforce is made by reducing as far as possible the flow to the underside so as to create the maximum possible pressure differential between the airflow over the body and that underneath. The splitter has fundamentally altered the way in which the car is set up. Clearly the horizontal splitter needs to run as close as is feasible to the track surface so as to minimize the amount of air that is able to squeeze underneath it. In consequence the nose cannot be allowed significant vertical movement while any pitch in the body will encourage the tip of the splitter to scrape the track surface and wear away. Happily NASCAR has permitted the use of suspension bump stops whereas they were banned some years ago from the COY. In essence the COT runs parallel to the ground with, in the corners its springs fully compressed and the bump stop material and the tire sidewalls absorbing any surface irregularities. At the same time the COT has a completely different body form to
the COY from splitter and new-style front bumper to rear wing, where before there was just a rear deck spoiler. As NASCAR intended when it wrote the COT rules the upshot is, in spite of the use of a splitter,
Center section of the COT frame is stronger than before. Photo: Earl Wheeler 15 7/10/10 12:06:03 “As NASCAR
intended, the upshot is comparable downforce with a higher level of drag”
a comparable overall level of downforce with a higher aerodynamic drag penalty. That additional drag is a function of the new form, which includes a flatter front end and more upright windshield and of the greater frontal area, which follows from the COT being overall 4.0” wider and 1.5” taller than the COY. The additional drag is even more pronounced at Plate Superspeedways, where the COT is mandated to run the wing in conjunction with a deck spoiler. The air sees the combination of the two as one huge shovel and protests by making excessive drag at the same time as an unnecessary amount of rear downforce. The drag level is such that for the 2007 Talladega COT race NASCAR permitted an 11% enlargement of restrictor plate opening area. At the same time it took away a carburetor concession that cost horsepower but the net gain was more than a 10% increase in top end output to maintain comparable speed in the face of the higher drag level.
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