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Even though I have a big block '71 with a lot of performance parts I seldom drive it very hard. But over the past few weeks I have been doing some 60-100 mph blasts to see how quick it will run. With it's new 3.70's it would accelerate very hard up to about 96 mph then suddenly lose power.

This morning I discovered my Proform HEI doesn't have the usual amount of mechanical advance. Rather than having 20 degrees this HEI has 25 degrees and combined with the 16 degrees of initial advance I have been running my total advance was a whopping 41 degrees!

To correct the problem I am now running just 10 degrees of initial advance; giving me a total of 35 degrees and now the sudden loss of power at 96 mph is gone. The moral of this story is never assume anything. HEI's are supposed to have 20 degrees of mechanical advance but that doesn't mean they actually do.
 
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