For the absolute best in performance, using straight-cut cam gears will reduce the thrust load on your camshaft bearings, and produce more horsepower.  These are excellent quality gears, made of steel for longevity.  This gears are also slotted and come with special offest washers to enable you to dial in your camshaft to meet your specific needs. Adjustments can be made to run the cam at -4, -2, 0, +2 or +4 degrees, which allows the power band to be customized to your driving requirements.  Using straight cut steel gears does produce more noise from the engine, so be aware of this.  Some people really like the distinctive turbo style "whine" they produce, while others prefer a quieter engine. We use these quite often in our own in-house engine builds.  They are excellent quality.