We reached peak numbers with the Harrop which was a 2.3 Liter Blower. Loyd Mead calculated that while the Harrop had returned impressive results, it would not get us to our goals because the compressor just could not hold enough air. We had pushed the Harrop to about 16 consistent pounds of boost with occasionally surges to 19 psi. Steve went to the drawing board and cam up with the Custom Built Motorsports LS1 Sandrail package that included a 4.0 liter Whipple Supercharger. As far as I can tell this was the first application of the 4.0 Liter supercharger on a street driven car, certainly the first on a GTO. Most of the work required fabrication and the end result took us to a consistent 19 pounds of boost and the mid 800 rwhp range.
Whipple on the Dyno