Mark; I CANNOT SAY 200%..but i will bet Big money that the breaking up is in the HEI ignition..they are good for running around the street...but when you get to turning them over 5,000/ 5500 is will go away...You need a MSD billet distributer with a 6al box and msd blaster 3 coil and it will clear that breaking up...
thanks Brian
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Bjuice..
"I'M YOUR HUCKLEBERRY ! "