What speed can you drive in your 94 s10 blazer when it is 4 high before start hurting it?

The recommended speed for a 1994 S10 Blazer in 4-High is generally under 50 mph. Going faster than that significantly increases the risk of drivetrain damage, especially to the transfer case and front differential. The exact speed limit depends on several factors including road conditions (smooth pavement is better than rough terrain), tire wear, and the overall condition of your vehicle's drivetrain. It's best to err on the side of caution and stay well below 50 mph.