IMSA Roar test leads to new Rolex 24 At Daytona BoP adjustments - Prototypes

IMSA Roar test leads to new Rolex 24 At Daytona BoP adjustments - Prototypes


IMSA Roar test leads to new Rolex 24 At Daytona BoP adjustments - Prototypes


Data from the test gave IMSA the numbers it needed to make some hard calls. (Marshall Pruett photos)

The TUDOR United SportsCar Championship’s dress rehearsal last week at the Roar Before The 24 has helped IMSA tech boss Scot Elkins to gather the final data points needed to lock down Balance of Performance adjustments.Now, with practice set to begin in two weeks for the January 25-26 Rolex 24 At Daytona race, the TUDOR Championship paddock, starting with the Prototype class, will undergo more adjustments to bring the DPs and P2s closer together.

Read about the GT class adjustments HERE.


To the surprise of no one, the powerful, slippery DPs dominated the three-day Roar test, posting a best lap 1.1 seconds clear of the fastest P2 entry. The DPs have received a 10 percent increase in horsepower for 2014, accounting for an extra 50-60hp and some of the speed differential to the P2s, and as Elkins told RACER after the test, some of that increase could be pulled back for Daytona.

“The gap got closer, but it’s not close enough yet,” he said. “And I think we talked about it earlier, I can’t remember, we’ve got the DP motors on the dyno at the NASCAR facility this week. We’re doing a validation test on them because we haven’t had them on the dyno with the sonic restrictors yet. So we’re validating that and making sure everything is where it is and we’ve worked with the manufacturers to the point of saying, ‘All right, guys, build the engines to 600hp and here’s where the restrictor needs to be at 600 and we’re just going to go validate that, check it to see where we are.’ Truthfully, yeah, I think we probably are going to have to reduce the power of the DP a little bit to get back into that area. And by reducing power, hopefully it will do two things: It’ll get us a little closer in top speed and also reduce the lap time difference.”

P2 cars underwent a few different spec changes during testing last November and December, with weight being added and later removed, and more power being allotted through bigger restrictors. IMSA only had turbocharged P2s at its disposal for those tests, with Extreme Speed Motorsports’ HPD ARX-03b doing the majority of the baseline work for the sanctioning body. With two new P2s at the Roar, and both using Nissan’s naturally-aspirated 4.5-liter V8 engine, IMSA came away with the missing data points it needed to set the restrictor sizes for the Morgan and ORECA chassis that carry the NISMO powerplants.

“I don’t really see much changing on the P2 engine side because we’ve done what we can do in terms of getting everything spooled up,” Elkins continued. “The P2 engines, as you well know, are totally based on production stuff and pretty closely regulated. And we don’t really have much more room than a five percent bigger restrictor to go there. So while a little bit more power would help, there’s just no room to do it.”Elkins’ note about P2 restrictor is based off of the input received during the Roar from teams that were asked to evaluate different inlet restrictor sizes.

“Everybody was doing a little bit of different work for IMSA at the test,” he confirmed. “Honda had a couple different restrictor sizes that were a little bit bigger. I think we had one that was plus six percent and one I think it ended up being a plus 11 percent restrictor, trying to get some data points there. The Morgan Nissan that was run by the OAK Racing guys, that car was full-on pretty much the spec that we expected. It was the right weight, had the Le Mans kit on it, plus five percent restrictor. The Muscle Milk guys actually didn’t get their restrictor. They were running the standard ACO restrictor, so they didn’t have the plus five percent power.

“So we got three or four data points on the P2s that we didn’t have previously, which helps us in the analysis to try and figure out what to do. But in terms of Nissan versus Honda, I think the position that we’re at is everything pretty much needs to stay consistent across the board. We don’t want to do a bunch of getting involved in a balancing between the P2s because that’s not really the spirit of what they are the whole purpose of the homologated car. If we apply five percent bigger restrictor to one it should be equivalent to the other.”

Asked if the exceptionally large 11-percent Honda P2 restrictor was tested as a possible option for the brand’s rumored DP engine (at present, P2 engines are much less powerful than their DP counterparts), Elkins offered a non-committal “That’s an interesting question” in response.

Continuing with the Prototype BoP workload, Mazda’s new SkyActiv diesel P2 cars were 10 seconds shy of the 1:38.6 set by Action Express Racing at the Roar, and as Elkins explains, IMSA has given Mazda and its factory partner SpeedSource Race Engineering enough room to bridge the gap.

“It’s a totally new package, there’s nothing to baseline from; a diesel P2 doesn’t exist,” he said. “So we’re pretty much giving those guys all the latitude they need to try to accomplish what they need to accomplish. I think they’ve got reliability as a higher target than performance and I think that’s my opinion, I’m not saying that that’s exactly what their case is I think they’re focusing on that as a target. And then once they get that squared away then I think they’ll start ratcheting things up.

“In terms of restrictor and boost and everything that’s there, we’ve pretty much given them the ability to do what they need to do in terms of development. And then we’ll keep working with them very, very closely, and once they pass the targets and goals that they want to, then we’ll start tweaking on it and make sure that it matches up with everything else. We’re fully aware of everything they do but we’re kind of giving them a little bit of leeway to make things happen in the order that they want it to happen.”Fuel mileage and capacity is another topic IMSA will address for the Prototype class at the Rolex 24. Other than the Mazda diesels, E10 fuel is the standard for the class, and with a variety of changes having been made to the DPs and P2s since they ran in Grand-Am and the ALMS, respectively, fuel consumption rates have gone up.

The extra DP power, coupled with an increase in downforce and drag, saw an approximate 15 percent increase in fuel usage per lap, bringing the fairly normal figure of 27 laps per tank in 2013 down to 24 or so during the Roar, and as one engineer pointed out, those figures were produced while dealing with heavy traffic each lap. As attrition reduces the car count during the race, it’s likely the MPG figures will worsen.

The mix of restrictor sizes being used by P2 cars at the Roar makes it hard to establish an exact MPG estimation, but with the extra five percent restrictors in place, teams can expect increased consumption rates, albeit at a rate that is superior to the DP cars, thanks to the lower P2 power output.

With IMSA planning to reduce DP power for the Rolex 24, another variable awaits those teams to monitor when they return for the race. Their fuel consumption rates should improve, but they won’t know by how much until they start practice.Despite the question marks on how long the various cars in the Prototype class can run, Elkins is working on a fuel tank BoP of sorts to keep the cars working within a similar fuel window. DPs and P2s have 75-liter fuel cells (19.8 gallons), and through the use of softball-sized hollow plastic balls placed inside the cells, look for IMSA to bring P2 capacities down.

“Right now it’s consistent because with them both being at a similar power output, it should be pretty close,” said Elkins of the turbo vs. naturally-aspirated DP engine MPG. “All the data that we’ve gotten so far in terms of stint length and the mileage that they’re getting seems to be pretty consistent between the Ford and Chevy. So the 75 liters is pretty much where they’re maxed out.

“We are obviously going to have to do some tweaks to the capacity of the P2 cars because they can run a little bit longer. I think the numbers right now, it looks like DP can go about 37, 38 minutes and a P2 car can go almost close to 50. So we’ll have to make an adjustment on the capacity there and reduce the capacity for the P2 car before we get back to Daytona. But, again, we’re going through and gathering information and getting stints and looking at the actual fuel use numbers there to make a good solid BoP, you could say.”


Other than slight bodywork modifications to solve a tire rubbing issue, the PC class will race at the Roar with no major chances, according to Elkins.”We added the air extractors to the PC car this year and we started seeing a little tire wear on the front (wheel arch) extractors because it’s got a fill piece on it,” he said. “So we’re looking at tweaking that in terms of letting the teams make a little bubble there to keep that from happening. But in terms of performance, it’s a single specification class so there’s really not anything for us to do. The differences that we see are coming from the driver pairings and the teams. A lot of drivers were there for the first time. So there’s nothing to be done to PC other than tweak I mentioned.”

Click here for GT class BoP adjustments