[Tommy]

AL427SBF - My BA degree is in aerospace engineering, but I have not used it regularly for many years. I mention that so you'll have a better idea of how much weight to give the opinion I'm about to offer. Unless you have a supercomputer and very bright people to program it (e.g., a Formula 1 team), it would be very difficult to derive an accurate horsepower required for speed curve for your specific car using just the formulae you have seen so far. If you had such a curve, you could plot your horsepower available for speed curve on the same graph. The point where the two curves crossed would be your maximum speed. ... Attaining your maximum speed would likely require a very long straight track - likely longer than any track you could actually access. Running on a curved track (e.g., Talladega Speedway) would increase drag and likely reduce your maximum speed. .... The bottom line is this. Unless you have enough money for some very expensive computer time and some very expensive track time, it is unlikely you will ever need or use the information you seek. That being the case, why not do what engineers have long done. Pick a top speed that sounds reasonable to you (e.g., 180 MPH) and select gearing that would theoretically give you that speed at 6500 RPM. No one including you will ever know if the car can actually go that fast.