Why is there a dip in the torque and HP curve at 3500 RPM?
All highly tuned engines with high overlap cams will encounter good and bad tuning peaks through their RPM range. See Appendix 3 in user’s manual “Intake and Exhaust Tuning”. For header primaries from 30-40 inches long, a “bad peak” for exhaust tuning comes around 3000-5000 RPM, where you will see a “dip” in the power curves. This is NOT an indication of bad performance, just a “necessary evil” to get good tuning and performance at other RPMs. If you try to eliminate this dip (close up overlap), you will hurt performance at other RPMs. You can move where this dip occurs by changing header primary length. For example, going to longer primaries will move the dip to lower RPMs.
