Neither set of heads had been modified. When I was racing at 1400' I ran a 238/238/.558 solid with speed-master 2.02 heads and 9.5:1 in the dart and it was done at 5800. 101.3 on street tire in the 1/4. Low Da racing is a challenge... Hard to put enough compression in the engine on a budget. Schneider has been a big help.