Chain Reactions: Ben Grambau’s Ever-Changing C5 Z06

The process is known to anyone who has ever developed a racecar over time. One modification begets another, and then another, and then the next, and so on.

It’s similar to a nuclear chain reaction, in which neutrons released in fission produce additional fission in one more nucleus. That next nucleus produces neutrons and the process repeats. When the process is controlled, it produces nuclear power. When it is uncontrolled, it’s a nuclear weapon, kind of like NASA Mid-Atlantic racer Ben Grambau’s Super Touring 2 and Time Trial 2 Corvette Z06.

Educated as a nuclear engineer, Grambau knows a thing or two about chain reactions, which helps explain the continuous development of his car over the years. It seems as though it changes each time you see it at the track.

He bought it in 2014 from NASA Southeast racer Mark Nunnally. It was already a caged racecar at that point, and it had a fair amount of weight reduction done to the car, but it was still riding on stock suspension, with the composite transverse leaf spring in the rear and nothing in the way of aerodynamic aids. At that time, it was classed as a PTA car, and Grambau drove it in a few events when the engine began acting up.

“I did a little bit of a rebuild on the motor myself that lasted three laps and, and blew up. So then I put a new motor in it and that kind of killed most of 2015,” he said. “But then at the same time I got a wing and a front splitter and a different hood, and a bunch of other mods that I did to it to kind of move it toward ultimately being a really cool ST2 car.”

What is remarkable about the car is how little it can be made to weigh. It’s possible to get it down to 2,950 pounds with a driver in it. That means reducing power levels according to Super Touring rules, so Grambau has settled on the 3,020- to 3,200-pound range, with around 355 to 375 horsepower depending on where it falls in that weight range.

To get the weight down, the car has been gutted fully, with removal of the factory dash, HVAC system, removal of the body control module and the removal of 40 pounds of wire, a lightweight battery. The fiberglass front fascia and extractor hood also saved weight as did, removing the bracing from the rear decklid, among other measures Grambau took.

Some of the weight the car is currently carrying is due to longevity and safety items such as dual oil coolers, a transmission cooler and two fire systems, one automatic Novec system and one manual AFFF system. Grambau also has further enhanced the previous owner’s system for strategically placed ballast, which has resulted in a 52 percent rear weight bias, which is pretty good for a front-mounted mid-engine car.

“I’ve got a spreadsheet that’s got all the different spots that I’ve got weight in it, but for the most part this year I’ve been running a little bit heavier,” Grambau said. “The new rules penalize my big tires, and I haven’t gone back and adjusted the tune, which I’m actually going to do in the next two weeks. But, you know, I’ve probably got at least 200 pounds of ballast in the car or things that I can control the weight with right now.”

He’s got lead weights on studs welded to the rear frame rails. He can access the weights through the inner taillamps. He’s also got 19 pounds of lead in the right rear of the car, 27 pounds attached to the subframe and ballast on the passenger side floor. He even had some of the subfloor chassis bracing custom made from thicker materials to get more weight as low as it can possibly be. Grambau’s goal is to be able to know what changes he needs to make to the shock settings and collar heights if or when he removes weight from different places around the car.

“I do all my own setup work. I’ve got the scales and the strings for doing alignment and all that,” he said. “So I think I could know in advance to say, ‘Hey, I’m going to test these two weight levels with the corresponding power levels, and I need to change the rear ride height by, you know, two turns on the shock collar, and that’s going to get my corner balance back to what’s ideal. So you don’t have to take the measurements of the track, but I just got notes in advance to say, here’s the things to change, to keep the balance right.”

He can add and subtract weight because he already has the tunes that correspond with those weight changes, and he can go lighter or heavier with less or more power and still remain in the ST2 class. Class rules forbid being able to switch power levels from inside the car, but with a few keystrokes on his laptop in the paddock and new paperwork submitted to the ST director at the track on a given weekend, the car is flexible and changeable.

One track where he thinks more weight and horsepower is beneficial is Virginia International Raceway, where he can pick up a bit more speed at the end of its three long straightaways. At Carolina Motorsports Park and Summit Point, he has been experimenting with lower weight and power, all with an eye toward nailing the right combination for the 2023 NASA Championships.

“I’m not convinced yet what the right setup’s going to be for Pitt Race, because looking at the data, Pitt Race has got three good straightaways, but under 140 miles an hour in all of them in my car,” Grambau said. “And Pitt Race has got plenty of little twisty stuff, so I’m going there to test the end of the month … and then there’s obviously the NASA Great Lakes event. So I’m going to try with several different setups on power and come into Nationals and figure out what the right sauce is.”

Part of that sauce will include the aero work that Grambau has been doing on the car. Not long after he bought it he added the extractor hood. To accommodate that he had to build a cradle to lay the radiator forward, then fabricate sheet metal duct work to the get the hot air out from behind the radiator and out from under the hood. Of course, that duct work interfered with the stock location of the throttle body.

Well, it would have, but Grambau removed the intake and turned it 180 degrees so the throttle body faces the rear, which meant he had to build a sealed sheet metal box to bring the firewall inward and to direct the intake air. The symmetry of the GM LS engine lets you do that, and the fuel rails still fit in the stock locations. He is continually experimenting with ways to reduce the temperature of the incoming air, and he’s current on the second or third iteration of that.

The front fascia and front under tray from ACP, which he used in conjunction with canards from AJ Hartman Aero and a rear wing from Good Aero.

“Making downforce in the front is the hard part, so I did what I could to make downforce in the front with the body panels, under tray, the canards and extractor hood, and then I just kind of dialed in the wing angle in the back to make it happy,” Grambau said. “There’s a point with the lower power level, I could go through the uphill esses of VIR and never lift until you get to Turn 10. So the aero and the suspension’s working pretty good.”

The changes didn’t stop there. Grambau has added a Sadev sequential gearbox, which was actually made for a C6 Corvette, which is similar to, but ultimately different from a C5. That meant Grambau opted for a C6 rear cradle, differential and lower control arms. He also added a C6 Z06 magnesium front cradle, which saved 10 pounds over the C5 aluminum from cradle. The current LS3 engine also is from a C6 car.

“I was kind going back and forth. I was like, ‘Man, do I want to spend the money?’ You know, is that going to take part of the fun out of this? At the end of the day it’s not a, quote, smart financial investment by any means. But then I was also kind of just like I said, you know, screw it. Let’s just go for it. You only live once and this is the main hobby of how you decide to have fun. So, go for it.”

When his brake booster failed, that meant Grambau could add the custom Tilton pedal box and dial in the brake bias to his liking, and he’s had a custom titanium exhaust made for the car, which weighs just 8 pounds. Of course, the new gearbox ushered in the need for programming the Motec ECU to dial in the no-lift upshifts and the five phases of two-pedal downshifts.

“You get this software out on your laptop, and I got some of the pre-setup help from GSpeed. But now you got all these little boxes, all these little things you can change,” Grambau said. “Every time I think I’ve done as much as you could want to do, then there’s still, you know, something else.”