On short ram engines, some of us like to control the amount of heat going to the rams.
George Riehl said completely blocking off the heat was the best way to go. Other people prefer the way Chrysler
built it (no restriction), and some people are in between.
I thought that was a good idea until I had to work on the headers installed in the car.
I learned access to the plugs is a bear.
If you choose to "dial in" some degree of manifold heat, it is easy enough to drill a hole.
At a minimum, you will need one block off shim for each ram (or two shims per car.)
If you wanted to completely isolate the ram from exhaust heat, you will need 4 shims.
Note: for long rams with thermostatic chokes, block off plates are not recommended
unless you have converted to manual chokes.
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