2009 Mustang GT, rebuilt short block (all forged), Whipple Supercharger, Tremec 6 speed with 2.66 1st/0.5 6th. Currently has 3.55 gears. Should I go 3.73 or 4.10 with new rear axle build? All street/highway driving right now. No definite plans to track. Thoughts please.
Without knowing how you cammed your motor or what your power band looks like, it is a guess (probably a guess anyway being internet advice), but I would stay with the 3.55. The blower ought to yield plenty of low end torque for anything you are doing as a "street" car, while maintaining civil highway driving. I'm don't think a 3.73 will provide enough seat of the pants difference to warrant the bother and expense, and a 4.10 may begin to press the bounds of street tire adhesion.
Sorry it took so long to reply. All good points and thank you. Stock cams and heads. The reason I am considering gear change is I will most likely be purchasing the Brenspeed rear axle upgrade kit to better handle the new found hp. 3.55, 3.73 and 4.10 are options with the kit. The 3.55 actually an extra $20. With this in mind I am leaning toward the 3.73. Thanks again