In a previous video, we talked about what makes a racecar a racecar. But if you watched that video, you would know that turning your car into a racecar doesn't necessarily make it fast. So what is it that makes some racecars faster than others?
If you asked class-winning ChampCar team owner Ross Shull, he would probably say something like "light weight." But then you would glance over at his team's 4th gen Honda Prelude racecar and wonder why it looks like this:
Look past the bumps and scrapes on this Prelude's battle-scarred body, and you will start to see a myriad of performance-enhancing modifications that you won't find on slower cars in ChampCar's Class B field. The reason is simple: You can only remove so much weight and add so much power before you reach the limit of what's allowed in the rulebook. After that point, it's creative ingenuity that give the frontrunners their competitive edge over the backmarkers.
Today, we'll take a closer look at the curious details that helped this car become such a dominant force in the competitive world of North American endurance racing.
The Monster in Question
Photo by AJ Allen Photography
This MGD-liveried fire breather is CMP Racing's #253 Honda Prelude Si VTEC. And on paper, it doesn't seem like it would be one of the top dogs in ChampCar's competitive racing field.
An internally stock H22 engine and a race weight of slightly under 2600 lbs seems downright modest given ChampCar's permissive rulebook. There are no exotic suspension components or expensive coilovers underpinning this car. It's even saddled by street legal, 200 treadwear tyres as mandated by the series.
And yet, this car has the pace to run a 2:13 lap around VIR's full course - Faster than many similar SCCA and NASA classed cars that have the benefit of running sticky R-compound tyres, aftermarket cams, and expensive race-tuned suspension dampers.
Let's take a look at some of the details that make this car so formidable on track, starting with those 200tw tyres.
Although the current generation of 200tw street tyres are known to be extremely sticky, they are still a step behind the 40tw R-compounds that rule American club racing. Ross's solution was to make up for the lack of grip with tread width. The CMP Racing Prelude wears 245mm wide Nankang CR-1s, stretched across massive 10" wide, zero-offset Vision Sport Star II wheels.
Of course, fitting wide tyres to the front end of a front wheel drive car is a tried and tested way of making FWD racecars fast. The real secret is in the wheels. Running a zero-offset wheel on the 4th gen Prelude has the effect of increasing the track width of the car by 110mm over the OEM +55mm offset wheels. This massive increase further improves the car's ability to grip the road while increasing stability under hard braking. The resulting increase in positive scrub radius also helps counteract the increased steering effort from running such wide tyres on the front end of the car.
In stark contrast to the fronts, the rear end of this Honda is supported by a pair of slightly undersized set of 205/50R15 CR-1's. This is also by design. The narrow tread of width of the rears helps the rears to warm up more quickly, encourages the car to rotate better through slower corners, and keeps rolling resistance to a minimum down VIR's long straights.
This unusual wheel and tyre combination gives the car the grip it needs to corner on par with R-compound shod club racing cars while running upwards of 8 hours on a single set of tyres.
Brutally Efficient Aero
ChampCar Endurance Racing rules stipulate that all wheels and tyres must be completely covered by bodywork as seen from above. While this is very important from a safety perspective, the real performance advantage comes from covering the wheels and tyres as seen from the front. The reason is simple: Spinning tyres generate tons of aerodynamic drag when exposed to the open airstream.
In order to ensure that the extra-wide Nankangs wouldn't slow the Honda down the straights, Ross and his team built a new lower bumper out of the same heavy duty Sprint Car plastic that we use for air dams and side skirts. This wider lower fascia doubles as the front air dam and is also the mounting point for the radiator and brake cooling ducts.
Because the ChampCar rules penalize the addition of any non-stock metal to the car's body, the CMP Racing crew had to be creative.
They first cut the lower portion of the stock Prelude fenders and bent them outwards as far as they could. When that wasn't enough to cover the tops of the front wheels, Ross removed the OEM exhaust heat shields from the underside of the car and used them to create weld-on fender flares. Strips of universal exhaust hanger material recovered from the car's old exhaust system give added structure and rigidity to the car's widebody front end. The resulting structure is just wide enough to shield the rotating wheel / tyre assembly from the oncoming air.
Those of us familiar with American club racing are used to seeing racecars without exterior wing mirrors. This isn't just because of all the bumping and rubbing that we do on track. It's mostly because the wing mirrors on a 90's production car account for anywhere between 7% to 15% of the drag generated by its entire body. Replacing the stock wing mirrors with smaller mirrors mounted inside the cabin makes a noticeable difference to both top speed and fuel mileage. And that can be decisive in a multi-hour endurance race.
In addition to switching out the bulky factory Honda mirrors for small roll cage-mounted convex mirrors, Ross has taken the extra step of installing a triangular block plate that extends a few inches into the window opening. Those few extra square inches of clear plastic are enough to deflect the airstream past the open windows to further cut down on drag generated by the two-door Prelude's large window openings.
At the rear end of the car sits a Nine Lives Racing wing, mounted to the chassis with endplate pylons. Even though there are many good options out there for affordable racing wings, Nine Lives Racing's wing profile still boasts one of the highest downforce-to-drag ratios of any of its competitors in the 70mph to 120 mph range. The endplate-integrated pylons are as functional as they are interesting to look at. This design is among the most efficient ways of mounting a rear wing on cars that allow for it.
These small aerodynamic enhancements add up to a big difference at speed. The CMP Racing Prelude will hit 128 mph on VIR's long back straight while maintaining the fuel economy it needs to finish at the front at the end of an 8-hour endurance race.
A Strategic Approach to Cooling
Racecars generate a lot of heat. The longer they run, the hotter they get. And the CMP Racing Prelude is no exception.
There are many ways to increase the cooling capacity of a racecar and most of these modifications come with some sort of penalty in performance, either in weight, complexity, or in aerodynamic drag. The challenge is in finding ways to achieve better cooling performance without hurting the car's performance on track.
The CMP Racing team achieves this by pulling in cooling air from as few inlets as possible, ducting it to where it is needed most, and extracting that air as quickly as possible. Take, for example, the oversized cooling vent cut into the car's hood:
This vent is absolutely gargantuan compared to what you see on most vented hoods. When viewed from above, it's the same size as the cooling inlet for the radiator. This is no coincidence.
Placing a large vent like this directly behind the radiator encourages much of the hot air to exit the engine bay before it even reaches the engine block. The 1-inch-tall Gurney flap on the leading edge of the vent forces oncoming air to flow around the vent, creating a low-pressure area directly above the opening to pull air outwards. The overhang covering the engine's valve cover ensures consistent extraction, even at low speeds.
All of these features work together to reduce the air pressure in the area directly behind the radiator, which in turn helps pull a larger volume of air through its fins without the need to cut bigger (read: drag-inducing) holes in the front bumper. As a result, this car needs nothing more than an OEM-replacement Prelude radiator to stay cool in the heat of battle.
Ross and his team applied the same philosophy to solve their brake cooling problems. The bulky radius rod front suspension setup of the 4th and 5th gen Honda Preludes make it notoriously difficult to route brake ducts from the front bumper to the brake discs. The team sidestepped this problem by stopping the brake ducts ahead of the front wheels. This results in a brake cooling setup that feeds the entire wheel well with cool ambient air, albeit at a lower velocity than if the brake ducts went all the way to the front hubs.
To compensate for this, Ross removed everything behind the front wheels to encourage the air to leave the wheel well as quickly as possible. This reduces the pressure inside the car's wheel wells and helps pull more air through the brake ducts, while simultaneously reducing the drag generated by the front wheels. Very clever.
A Faster Cockpit
With all of these creative mechanical modifications at play, it's easy to forget that it's the driver that makes a fast racecar go fast. And yes, it is possible to modify the cockpit of a racecar to make it easier for its driver to consistently punch out fast laps. Fortunately for the CMP Racing team's quartet of drivers, Ross hasn't forgotten that important detail.
The dash and gauge arrangement of the CMP Racing Prelude offers the pinnacle of distraction-free driving. The factory dashboard has been removed to give the driver a completely unobstructed view of everything in front of them. The OEM gauges have been consolidated into a single tablet mounted in the middle of the car, out of the driver's line of sight. A hard-wired shift light in the driver's peripheral vision reminds them to shift at precisely 7800 rpm every time. The sole warning light is a blindingly bright center-mounted LED, which floods the cockpit in red light in the event of a catastrophic loss of oil pressure.
All of the important buttons and switchgear are mounted on a single switch panel on the center console. The switches are spaced just far enough apart that they can be operated while wearing gloves. Indicator lights mounted directly above each switch illuminate when each switch is flipped on, and the fuses for each circuit are mounted directly below for easy troubleshooting.
Below the center mounted switch panel is the factory shifter with two small but important modifications. The first is a budget-friendly short throw adapter to make it easier to make quick, precise shifts. The second is the removal of the rubber bushings that normally hold the shifter to the chassis. The latter improves the feel and feedback of the shifter, allowing an experienced driver to make faster, more precise shifts. This does have the side effect of decreasing the height of the shifter, hence the taller shift knob.
A perforated plate of curved metal on the accelerator pedal makes it easy for the driver to roll their foot onto the throttle for precise heel & toe downshifts. The thin gauge of the metal and gentle curvature of the extension gives this throttle pedal better ergonomics than most aftermarket pedal covers. It's a brilliantly effective solution that is as popular with its drivers as it is aesthetically incongruent to the rest of the car.
A pair of NASCAR brake fans keep the windshield fog-free in the rain and the driver's helmet sweat-free in the searing summer heat. Finally, a Chillout driver cooling system keeps the driver's body temperature in the sweet spot so they can perform at their best, lap after lap after lap.
Its Last Bow
It is the combination of all of these clever details that makes the CMP Racing Prelude such a dominant force at the racetrack. Despite its successes, however, the curtain is soon set to close on the #253's competitive racing career.
Ross is planning to retire his phenomenally successful racecar at the end of the 2022 racing season. Its last race will be the VIR on the North 8+7 Enduro on December 2-4, 2022.
While we are sad to see this paragon of creative ingenuity ride off into the sunset, we wish Ross and the CMP Racing team only the best at their upcoming season finale.
If you happen to be at VIRginia International Raceway that weekend, make sure to stop by and wish the team a fast and trouble-free race. And make sure to check out the in-car live streams of their races on the CMP Racing Youtube channel here:
- Day 1 - CMP Racing VIR North 2022 Day 1 - December 3rd
- Day 2 - CMP Racing VIR North 2022 Day 2 - December 4th
See you at the track.