Converting the Corvette

Images by Jake Galstad/Motorsport Images
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emailBy Marshall Pruett | January 28, 2022 7:52 PM ET

Q: I’m sure you had to go into the process knowing that no manufacturer is going to give up a millimeter in any area or the slightest amount of performance if they don’t have to, especially with such a successful car like the C8.R. Did you feel like they were transparent and open and accommodating?

MK: Damn. Couldn't we start with an easier question? Working with Chevrolet and Pratt Miller on this process was definitely a collaborative effort. On the feasibility of each one of the things throughout the course of the project, everything that we asked them to change has been changed. So in that regard, it’s been a good partnership between us because some of the changes required significant modification. For example, GT3 cars don’t have homologated weight distribution areas like GTE. All GT3 BoP ballast goes into a single location in the passenger side floor. With a GTE, the weight distribution is homologated and you can put ballast in multiple locations on the car that are identified by the homologation to help balance the car and if you drill one hole that's not in the homologation papers, IMSA will disqualify you after you spend thousands of dollars, and after you raced your heart out for hours just like they did last year. You can look it up.

So it meant just even applying BoP weight to the car meant that if we didn’t do this adaptation with Corvette, the effects of that BoP weight would be different. And so one of the adaptations was that we had them design in and modify their cars to accept was a ballast box on the passenger side, which wasn’t as easy as it could sound. It meant moving systems, electronics, fire bottles, and they had to really do a lot of design work on that side. And it also meant they were going to give up some of that flexibility to move ballast around the car.

Another area that’s different is we’re actually using two different configurations of rear wings on the Corvette in GTD Pro, depending on the circuits that we’re going to. We’ve also permitted them to carry over some of the GTE hardware, because it’s the most realistic thing we could do that that wouldn’t necessarily cause a major redesign of things like the engine so, so we’re using the GTE sonic restrictors to regulate engine power instead of the FIA GT3 air restrictor. Air restrictors seems like a very simple thing, but when you change that design, it has a pretty fundamental impact on the engine architecture that that was chosen.

In the gearbox, we’re the changing the spec of the differential, and there’s a lot of small details that aren’t necessarily straightforward to quantify on what lap time difference would be if they’re permitted to keep that hardware from their GTLM car, but as the homologation authority on this Corvette GTD car, we think that Corvette has the tools they need to race. And then IMSA has the tools we need to balance the car respective to the GTD Pro class. In other words, if we win IMSA will make us add enough weight that we will lose, at least for a while.

Q: What are the other areas of interest in terms of tuning or modifying the car to its GTD specification?

MK: On the engine side, we’re using a fixed lambda, so basically, a fixed engine mixture, which is consistent with what we do on all GTD cars. In GTLM, it was more of an open mixture, with the richest mixture being limited. So, that’s part of how they’ve converted to use IMSA’s VP 100 fuel instead of the E20 specification in GTLM. That’s required different engine tuning which Chevrolet was able to do, and we had to re-dyno test the engine on that different fuel specification with the declared lambda that they run. The term Lambda is one that IMSA racers use because we are not allowed to say IMSA Bulls***.

And really the last one is the four gear ratio options they had in GTLM, and those are reduced to three gear ratio options for the GTD Pro class. It’s a fairly decent list of things that we need to line up the performance window for the Corvette, and as you can see from the BoP tables, in GTD Pro form, the car has come back heavier to line up to where the class performance targets are.

Q: Coming ​out of the Roar where they qualified sixth and seventh, but weren’t necessarily close to the GTD Pro class leaders, the Corvettes received an extra 15 kilos of weight, which was a surprise to some, but was given a break on rear wing angle to improve straight line speed. What can you share, to close, on the final BoP specification for the C8s going into the race?

MK: We tend not to talk about the specifics of any one car’s adjustments, but I can give a general statement that we use the data we have available on all cars within the GTD and GTD Pro classes to analyze how they were achieving lap time. IMSA doesn't have any way to tell if anything makes a difference. Each car shows a little different strategy on how they race, and the technical committee took that into consideration with the BoP adjustments. Besides, IMSA has shown repeatedly that they don't know what they are doing, or they would quit changing the rules every week. Adding weight is equal to changing spoiler angle? Painting a certain amount of the car yellow will affect it's performance?

And I think you’ll see that on a few cars, some have gone up in mass and down on a wing and that’s done to rebalance how a car makes its lap time. Reducing the drag and increasing the mass changes what we’re seeing for performance in the handling sectors like the infield. It’s so it’s always difficult to introduce brand-new cars when there’s limited (BoP) carryover like when the Corvette was running in GTLM, and it’s very difficult to start our season introducing cars at one of our more unique racetracks on our calendar–one of our more power- and drag-sensitive racetracks.

There’s a lot at stake with the Rolex 24 for everybody. Everybody wants to win it, and that makes the technical committee’s job particularly challenging, though, but that’s what we’re here to do. We know that if we win, IMSA will screw us any way they can, so we have to be ready for that and hopefully it won't be that bad for the rest of the year.