I have an 85 firebird. The spoiler doesn't seem very functional. How can I modify it to provide more down force. Has anyone added a lip to it?

 

It is functional, just not for downforce. It helps maintain laminar flow off the rear if the car, reducing drag.
Any modification to increase down force will more dramatically increase drag.
To make any noticeable downforce you need a better wing.

 

It's designed theoretically to improve fuel mileage, anything that affects performance will create more air drag for the motor to push against resulted in worse fuel mileage. Whether you will actually notice the difference or not is another thing.

 

Gas mileage isn't my primary concern. I thought that more down force would help car handle better in curves and also make it more predictable at high speeds.

 

Get a strut tower brace and the 'wonderbar' steering brace. You will notice improvement there. Also I doubt you're going to get much in terms of downforce off the rear spoiler unless you are usually flying down the road at 100mph or more. Normal driving at highway speeds or in town you will not see much benefit from the rear spoiler (other than looking cool). Work on your suspension first. Is the 85 firebird able to use the WS6 suspension package put on T/A's?

 

IMO,once you start modifying any wing or spoiler on one of our cars there's a very fine line between tasteful and TUNNER.
To each there own.


I believe High Performance tires might be what your looking for. Nice and "sticky"

 

I agree. Get a set of BF Goodrich Radial T/A's Or maybe a set of Goodyear Eagles. I to am thinking of these as well. Hehe mainly because I want the raised white letters. I think they look cool.