The cam has to be within 1% of the factory lift and 2% of the duration. Cylinder heads can't be ported, no bowl work, no 3 angle valve job or back cutting of the valve's. Stock exhaust manifolds. Pistons can have a small dome as a compression ratio of 1.5 points over advertised is allowed. No aftermarket rods, crankshaft. Electronic ignition is allowed, curve kit is allowed, high output coil is allowed but it has to be the same size and shape and color as the factory coil also it has to be mounted in the factory location. No aftermarket ignition boxs. No electric fuel pumps or pressure regulators allowed. Any gear ratio is allowed. Blueprinting is allowed and balancing too. All that's left is dyno tuning and you can see that these guys are running "stock " engines.