Originally Posted by robert chilton

The washer they are talking about is a sealing washer. Similiar to that little copper washer on a brake line at the caliper. They come in different sizes. The different thickness can make the injector sit higher in the head. The reason for this is to get the fixed spray pattern of the injector to hit the optimum spot on the piston during injection. Improper hiegth can cause power problems or possible engine damage. If you look at the piston it is bowl shaped. The idea is to get the fuel to hit at the top of the bowl with out going over. When you see that 370s are designed for our motors this is why. The spray pattern is a little off but close enough that the right sealing washer will let it work safely.