Aero-tuning the Championship-Winning NASCAR Dodge Trucks

reynard wind tunnelSome time ago, I talked about how I came to work in Dodge’s NASCAR Truck efforts, which ultimately were rewarded with numerous wins. One thing we did was work on aerodynamics, where we did a lot to advance the state of the art.

From the start, I worked with Paul Brown from Reynard, which did some nice work on the drag/downforce program. They did some nice calculation and some aero work on their quarter-scale moving ground plane wind tunnel at Shrivenham, which led to some interesting improvements.

The Shrivenham moving ground plane wind tunnel for many years helped develop the Reynard IndyCar winning vehicles. It was one their secret weapons, and in it they were the first to discover the high nose concept of all modern open wheel racing cars, especially Formula One (F1) cars.

Julian Randles at J&P Motorsports came up with a good idea, which was a two-pass radiator — it had two cores, one behind the other, but all in one radiator unit. You pass the water in the back part of the radiator, and then you fed that through the front part.

You took as much heat energy out of the cooling water as you could, using the minimum amount of air, so you could run a smaller radiator, which meant you were letting a lot less air into the engine bay. This meant you were not giving as much lift to the engine bay and had less frontal lift in the car. You were always struggling to achieve this with NASCAR, always looking for down-force.

Adding down-force was the golden rule of what we wanted to do in the trucks. It was crying out for front down-force.

closeup of the model

So we did the dual pass radiators and that was a success. They went to CNR Radiators to get these fabricated and manufactured, and then CNR took the design and told all the other NASCAR teams about it, so they built them for the other NASCAR teams so there’s no advantage there. But we had an advantage for a race or two.

I said to Julian, “Let’s move the radiator closer to the engine and create a ducting from the front of the cars grille,” which you’re allowed to do, “a radiator ducting from the front under the front grille facia, to the radiator to channel the air.”

We tested this out on the model. From the front of the splitter underneath the car to the backside of the radiator cowling closest to the engine, we gave it an incline, a slope up, and saw if we could crank up the front down-force up. When we put it in a wind tunnel it did, quite a bit.

We went to the race with it, with just a simple sheet of structural aluminum that faced up at the rear and gave us the required down-force improvement.

moving plane wind tunnel

We were using the Reynard’s moving ground plane wind tunnel at Shrivenham in England. I don’t believe any of the other teams had one at that time. One Chrylser manager was vehemently opposed to it, saying “you don’t need a moving ground plane” – which you obviously do, to move the ground underneath the vehicle to simulate real world conditions as best possible, to get closer to a true effect of what the vehicle’s doing on the track entraining air underneath the vehicle, as those pressure differences and rotating wheels in the wheel house, alter and interact with the pressure differences over the top of the vehicle.

His thinking was that we only needed a fixed wind tunnel, that interaction of the air underneath the car made no difference; he was only concerned with anywhere from six inches up over the vehicle.

When it was proven in-house that it was producing down-force, at the next race Ford put in a protest against us [though they were not involved in any way in the testing as that was done in the UK, and should not have known about it]. Like before, I think we had a mole within our camp that was determined to make sure that we were not successful in the work we were doing.

If you look at the NASCAR engine and rule book, one can either run a mechanical fan or an electric fan to help draw air through the radiators at low speed. We knew that extricating air from the front engine bay helped (increased) the front down-force, and would have made the car have faster lap times and improved tire life.

shakedown run

I got our fabricator, Frank Christilaw, who was really good at conceptual one-off manufacture, to make a special fan. Fans were free; you could run whatever fan you wanted. You could run electric fans if you wanted to. We just couldn’t get enough power into the electric fan.

We turned the fan blades around and put them in a cowled duct, which you’re allowed to do, and blew the air through the radiator out the front. So instead of allowing air through the radiator from the front of the car into the engine bay, we forced the air out of the engine bay, drawn through the wheel houses, and also filled in the boundary layer over the body surfaces, cutting down drag.

aerodynamics

I asked Reynard to put it on the model on the moving ground plane wind tunnel at Shrivenham, and to push compressed air down through the stinger [see photo], which is the device that holds the vehicle in relationship to the moving ground plane in the right place to blow through a simulated radiator. They made a nice little radiator on the quarter-scale model.

We blew through the radiator to the front, and that reduced the drag significantly, as well as increasing front downforce, which was the original intent. It filled in the boundary layer that was getting thick around the vehicle as it was in motion, and provided more of a laminar flow. A double bonus, and you don’t get many of those in motorsports.

wind tunnel

The problem being is we could never develop enough power from the belt drive. . . and we didn’t have time to develop it; we had a few hours of running it on the track, and it overheated the engine after a few laps of running, so we couldn’t get enough power to push through the radiator against the air pressure developed as the car went around the track. In hindsight, I think the belt was slipping; it was just a simple V-belt drive. We wanted to see what the power loss from the engine was, versus the improvements from down-force and reduction in drag, and what that did to lap times.

We could never get it to run in the few hours we tested it. I should’ve put a tooth belt on there from the crank to the fan. It might’ve thrown NASCAR into a bit of a loop seeing that, but we were within the rules and laws that you could do that; just they wouldn’t have known how extensive the modification was, blowing the air through the front of the radiator.

Ian Sharp in early Dodge NASCAR truck

“I drove the car before Lanier — I laid two black tire strips up the yard, as the guys were egging me on to open it up! So you could say I was the first NASCAR driver, when Chrysler came back to racing....”

But anyway, before we got to the first race, we were called into the NASCAR trailer and told if we were to ever do anything like that, we would never race in NASCAR again. We hadn’t even run it in the race. I think, again, somebody told NASCAR about the work we were doing, again the fifth columnist within our own Chrysler group who wanted us to fail.

Since the Jeep NASCAR office was next to the Stereolithography lab, we had a great working relationship with the lab supervisor, Tom Sorovetz. He was a good bloke who wanted us to succeed. I asked Tom if he could make some ¼ scale plastic NASCAR bodies as we had all the body data in CAD. He did and I sent 3 bodies over to Reynard to run simulated race track traffic simulations in the wind tunnel.

ted musgrave in nascar truck series

We made around four quarter-scale bodies in the end, and I got them to run different bodies in the wind tunnel at the same time to look at how we would race the car on the track, to see how the car responded with bodies running in front and behind running in traffic.

Reynard mocked up these other bodies in place, so they wouldn’t be aerodynamically impinging on the object test model. So they were a true representation of a truck in front and a truck behind. And we discovered where, in the wind tunnel, the best place to position the car if you were running second, to wear out the other guy’s tires.

We tried to bring a lot of new things in, but nearly every one was shot down by NASCAR. Eventually, with different teams, Chrysler did win two championships in the series. Still, it became clear that NASCAR was either trying to discourage innovation, or was not eager to see a new player, and a relatively small one, making too many wins.

Chrysler History and Other Bios • Jeep Grand Cherokee ZJJeep Cherokee XJ

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