to much timming and CR will kick the nose off the starter. i run a switch to turn on the ignition. this is separate from the key switch you have now .i used the old key switch to turn the engine over. but first i get the engine spinning and then turn the ignition with the new switch . i have some verry hi CR big block and this works the best for me and the starters had a 548 14.8 cr big block that i used a stock gm starter work fine. find a iron nose for the starter gm used this nose on beet trucks 366/427 and stick cars to