I dont quite understand the concept of gear ratios. Many say they hurt your gas mileage, but yet help you get off the line. I'm new to all this, so please forgive. I'm a noob. I was curious as to if gears out of a 2000 camaro SS would fit in my 91 GTA? If so whats required to do the gear swap? Also am I wasting my time and will not feel any difference? I believe the SS has 3.42's. Or should I just jump to 3.73's?

 

It all has to do with torque multiplication and engine rpm.

A highway gear would be something like 2.73. It offers a low torque multiplication which will struggle to get a 3500 pound vehicle off the line quickly but at highway speeds, the engine rpm will be kept low to increase the fuel economy.

A deep gear would 3.73, 4.10, 4.56 etc. It offers a lot more torque multiplication to get a heavy vehicle moving quickly but will also bring the engine rpms up quickly. A fast dragstrip vehicle has a high powerband. The deep gear will get the engine up into those higher rpms quickly. On the highway however, running at those higher rpms will burn more fuel.

Typically, a good street vehicle with good fuel mileage, will cruise down the highway at less than 2000 rpm. A vehicle with deep gear in the diff may cruise at 3000-3500 rpm.

A compromise is using an OD transmission such as the 700R4. It has a low first gear so using a highway gear in the diff like 2.77, 3.27, 3.45 etc will still give a good torque multiplication to get the vehicle off the line quicker and when using the OD with the highway gears the engine rpms will be kept low for better fuel mileage.

The 700R4 however has a wide ratio spread between first and second gear making it a poor choice for dragstrip use.

The fourth gen gears and carrier (posi) will fit into your 91. Both will have 28 spline axles. I can't say how much of a change it will be since I don't know exactly what gears you currently have. There's 3 different ratios offered for a 91 GTA with a 305 depending on the transmission and if it has the G92 option or not.

 

Thanks, that pretty much summed it up. well the gears that are in the car are 2.73's. I've done little work to the engine so I figured it should be able to at least light them up a little. But I get little 6 ft. stretches then the car seems to have slowed its pace climbing its mph's. It feels week and I've been told that bigger gear's would help it out from a stop.