16. Now that the valvetrain is fully installed, we’re going to go back in time a bit with this photo to show you an additional detail. Most modern racing engines use high-lift cams and wider 3/8-inch diameter pushrods. This can often prove to create too much pushrod movement for the pushrod holes in the cylinder head. To keep the pushrods from rubbing against the head and damaging themselves, you may need to open up the holes considerably. It can be time consuming, but opening up the pushrod holes also has the added benefit of cutting some weight off the cylinder heads. Just be careful not to cut into the intake ports.