After running a multitude of porting designs it has become apparent that the timing of the rotors affects the balance of HP to TQ. If the duration is increased we do make more HP at the sacrifice of low RPM TQ up to a point of 3000 rpm at which the TQ increases 10 ft lbs and HP climbs on an average of 30-35 from 3000-5000.
The TQ loss at low RPM is more noticeable on an automatic vehicle than a stick shift-the manual transmission can easily be shifted at higher intervals to take full advantage of a ported blower. On the other hand, the automatic transmission is just that- it is automated thru the pcm.
To spread out your shift points to take better advantage of your ported blower you must alter the tranny tune start with a 300 rpm increase get a feel for your combination and go from there. Another rotor timing affect is the boost charge before the climb the first stage 4 had a boost charge of 8#s and then a quick climb to 16#s, the “re-clocked” stage 4 had a boost charge of 10#s and a quick climb to 16#s. The first stage 4 makes a few more HP but sacrifices a few ft #s of TQ up to 3500 rpms. The 2 lbs of increased boost charge of the update is noticeable thru the lower rpm the automatic vehicle lives in. All designs tested had a boost increase of 1 ½ #s over a non ported blower.
The best thing to come out of this was a better understanding about the Eaton Supercharger that will allow for more fine tuning of Eaton blowers for automatic Eaton vehicles. These tests were done with a stock (2.93) upper and a 6# lower pulley. If we ran these combos on a Cobra we would over spin the rotors due to the higher rpm redline of the 4 valve engine. For a 6# lower with stock upper run a 68 inch belt. For a 4# lower with stock upper run a 67 inch belt You will need to notch the tensioner. Boost charge and rise was solid on all tests, although total boost numbers varied with design. Current design charges 10 runs to 16.