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NASCAR: Restrictor plate education tutorial

22 October 1999

Posted By Terry Callahan
Motorsports Editor, The Auto Channel
Restrictor plates reduce the amount of air intake through the carburetor by nearly 30 percent, which translates into a loss of approximately 340 horsepower.

"To understand how much horsepower engines lose to restrictor plates, imagine drinking a thick milkshake through a one-quarter inch diameter straw," Pro-Motor Engineering's Peter Guild explained. "With a straw that size, the milkshake comes up fairly easily. But when the diameter of the straw is reduced to about half that size - the 'restrictor plate' - you must draw a lot harder, but you still won't get as much milkshake."

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