Valves and seats must remain...
Valves and seats must remain stock. No trick angles or blends can be used. Proper valve seal, of course, is hugely important.
High-performance intent holds greater weight than high-performance image with us. Cars known as "sleepers" have all the intent in the world, but little image, so they're legal. (Note: Cars that come close, but don't quite meet all these criteria will be evaluated on a car-by-car basis, and acceptance is determined by the event organizers.) For example, any GTO is eligible because they show intent and image. However, the '67-'69 two-barrel-equipped cars wouldn't be eligible because they don't meet the intent criteria.
Factory lightweight cars built specifically for sanctioned drag racing, with no factory warranty, as well as dealer built/modified cars aren't eligible to participate.
Before we go into detail about the rules, I want to mention that the Pure Stock Drags does allow cloned musclecars, so long as they are 100 percent correct, inside and out, top and bottom.
No mods can be done to the...
No mods can be done to the intake ports, not even a gasket match.
After talking it over with many of our participants, Bob and I decided that since we already had an influx of NHRA-spec'd engines, we adopted the NHRA Blueprint specs as the limit that we would allow participants to machine and build their engines. These specs are available to everyone so we don't have to "play God," and decide what one can or cannot do. Plus, anyone can go onto the NHRA Web site and see what others are allowed to do. Many participants have used the NHRA to help them decide what kind of car to build for the race.
Basically, blueprinting an engine to NHRA specs raises the compression ratio anywhere from a little to a lot. We are now quite familiar with the specs for many of the engines produced in the late-'60s and early-'70s, and we made some interesting discoveries. It's fairly evident that by 1970, many manufacturers were trying to get an edge over the others by altering the specs they gave to NHRA. For example, for the '67 through '69 GTO and Firebird 400 four-barrel engines, all of the cylinder heads show the same combustion chamber volume of 65 cc's. For 1970, the cc requirement dropped to 62 for the same engines and cars, giving them a compression advantage. Buick did the same thing for its Stage I engine in 1970 by whittling 4 cc's out of its chambers, making it stronger in its particular class.
Some of the other NHRA engine rules we adopted include limiting oversized pistons to 0.070-inch, using their specs for deck clearance, head gasket thickness, piston type (with dish/dome volumes), and cam lift. What the NHRA allows its racers to do with the rest of the car is not our game.
We realize that a majority of our musclecars sacrificed their original blocks in their quest for supremacy back in the day. Also, many of our participants whose cars still retain their valuable numbers-matching block prefer to set it aside and build another to race. Therefore, engine blocks don't have to have matching numbers, or have the correct casting number, but they must be a vintage block with the correct cubic-inch displacement-no aftermarket blocks are allowed. However, the engine has to be correct for the year, make, and horsepower claimed.
Cranks And Rods
No lightweight cranks or rods are allowed, either. We want our participants to make the most of the parts the factory provided them. Anybody can spend money on aftermarket parts in order to go fast, but it's not as impressive as doing it with parts as close to factory specs as possible.