<P> However, restrictor plates initially were not used for Camping World Truck Series trucks . Rather, aerodynamic, air intake reduction through the use of a 390 cfm carburetor, and eventually a tapered carburetor spacer were implemented for those races . Combined with the aerodynamic disadvantage of the trucks, this allowed NASCAR to avoid the use of such equipment for the trucks until 2008 . In 2008, the Nationwide Series (now known as Xfinity Series) and Truck Series began implementation of tapered spacers in the engines to restrict power compared to Sprint Cup cars at all 35 (NNS) and 25 (NCTS) races . Both these NASCAR series now use a restrictor plate and tapered spacer at the two tracks . </P> <P> The third use came in 2000 . Following fatal crashes of Adam Petty and Kenny Irwin, Jr. at the New Hampshire International Speedway during the May Busch Series and July Winston Cup Series races, respectively, NASCAR adopted a one - inch (2.54 cm) restrictor plate to slow the cars headed towards the tight turns as part of a series of reforms to alleviate stuck throttle problems which were alleged to have caused both fatal crashes . For the Winston Cup race, it was used just once at the 2000 Dura Lube 300 . Jeff Burton led all 300 laps in the ensuing race, despite a 23 - car two - abreast battle in the first ten laps, a dramatic charge past 22 cars in 100 laps by John Andretti (who finished seventh), and two charges by Bobby Labonte in the final 50 laps where he took the lead but Burton beat him back to the stripe . The use of restrictor plates, intended as an emergency measure pending a more permanent replacement in any event, was discontinued at New Hampshire for the following race for Cup only . However, the Modifieds still use a restrictor plate because the speeds are too great for that class of racecar without them . The track has since been changed with soft walls to improve racing safety . Restrictor plates remain a permanent fixture to the Modifieds and the racing has often broken 20 official lead changes for 100--125 laps of competition . </P> <P> Rusty Wallace tested a car at Talladega Superspeedway without a restrictor plate in 2004, reaching a top speed of 228 mph (367 km / h) in the backstretch and a one - lap average of 221 mph (356 km / h). While admitting excitement at the achievement, Wallace also conceded, "There's no way we could be out there racing at those speeds...it would be insane to think we could have a pack of cars out there doing that ." </P> <P> A frequent criticism of restrictor plates is the enormousness of packs in the racing, with "Big One" wrecks as noted above singled out for condemnation despite the greater violence of "smaller" crashes on unrestricted tracks . In restrictor plate racing the packs have brought about an often - enormous increase in positional passing; at Talladega Superspeedway the Sprint Cup cars have broken 40 official lead changes sixteen times from 1988 onward, including both 2010 Sprint Cup races at Talladega, which had 87 official lead changes in the regulation 188 laps . (The 2010 Aaron's 499 had 88 lead changes, but the 88th--the race - winning pass by Kevin Harvick--was on the last lap of the third attempt at a green - white - checkered finish). Daytona International Speedway has generally been less competitive because the age of the asphalt (the track was repaved in 1978 and again in 2010) has reduced grip for the cars and thus handling has impeded passing ability to a significant extent . The 2000 New Hampshire race was condemned because Jeff Burton led wire to wire; the plates were singled out as impeding ability to pass, a criticism contradicted by the use of restrictor plates in a Busch North support race the day before where the lead changed seven times in 100 laps and by the highly competitive nature of restrictor plated Modified races; as noted above the 300 also saw a 23 - car battle for third in the first ten laps and a burst by 22 cars from John Andretti . </P>

How fast would nascar cars go without restrictor plates