511" FE Valve Float Condition, HP, Tq, and Airflow

When the 511" FE engine was first put together, Comp Cams provided the cam and the springs. Two choices were offered, and the 919 springs were the higher pressure option, so these were selected. However, on the dyno the engine's output became irregular after 6000 RPM with these springs. Although the engine still pulled to 6800 RPM in this condition, the torque and horsepower curves clearly showed a problem.

While the engine was on the dyno, a set of Comp Cams 943 springs were substituted for the 919s. These springs had substantially more seat and open pressure, but it was felt that the Erson rockers and Smith Brothers pushrods would handle this additional pressure with no problem. The first pull on the dyno proved that the 919 springs were indeed the problem.

The two graphs at right show the differences in torque, horsepower, and airflow with these two springs. This is classic behavior for a valve float problem; if you see this during your dyno sessions, its a good bet that you need more valvespring.

511" Airflow - Valvespring Change

511" HP and Tq with Valvespring Change