#1 reason is that points/gap lose spark at 4500 drastically. I had points/gap on my truck and did a top speed run and the revs stopped at 4500rpm cause my spark got too weak to push it further. (got it to the P in MPH though
) You will not regret going to HEI.
Happy Trucking.
CoryM
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1970 heavy duty C-10 fleetside sport truck. Vancouver B.C. Canada
http://www.geocities.com/chevroletc1070
"Take up our quarrel with the foe:
To you from failing hands we throw
The torch; be yours to hold it high."
Lieutenant Colonel John McCrae, Canadian Army