Why does my 1992 Mazda Protege LX with correct tires , have such a high RPM at any speed , especially 75 mph it is at 4000 RPM.? My 1994 DX model could run 125 mph at 4800 RPM.

I believe the dx is a model that focused on good gas mileage. Just because it's the same car doesn't mean it has the same transmission gear ratio or it may have overdrive making it a 4 speed where your other could have been a 3 speed. Just 2 possibilities for you. A lot can change in 2 years. Good luck, J

My '93 has about the same ratio. I think the lower final gears is what gives it the "Zoom Zoom". The little car is quick! If you "Short Shift" it, the mileage gets even better but it isn't as fast. Another factor to the engine/trans being such a high- rev setup is that a 4 valve engine doesn't have great low-end torque. Even though Mazda put vacuum actuated secondary runners in the intake, these engines perform best at higher RPMs.