NEED ADVISE-Which Upgrade should I do first?
 

Hello,
I am wanting to upgrade my 1990 mustang gt but am not sure what upgrade I should do next. I already have a good exhaust system, a cold air fender mounted intake and am working on some underdrive pulleys. What should I work on next? These are my choices: Cobra upper and lower intake, 70 mm Throttlebody, New mass air sensor, chip or fuel injector and fuel pump upgrade. I eventually want to put a NOS system on the car but I would like to get some raw engine power first before the bottle. Thanks for everyones advise.

In my opinion, I wouldn't spend any money on that stuff if your going to keep the stock heads. Here's my guess for the amount of horsepower you'll pick up with each mod:

Cobra intake- 5-10 rwhp
70mm tb- maybe 1 rwhp, but it could hurt performance.
mass air- 3-5 rwhp
fuel injectors- most likely hurt performance on a stock engine.
fuel pump- 0 rwhp
chip (off the shelf)- waste of money, break out a timing light instead.
custom chip- maybe 1-3 rwhp, wait until you have a lot of mods.

I'd put a different gear (3.55-4.10 depending on transmission, future mods, and miles driven on the street) in the rear end. I've done the bolt-on route, and the gear made the most noticeable gain when compared to all other simple mods (This includes everything on your list, and then some).

If you go with the nitrous though, you'll need to make some of those fuel upgrades, but I wouldn't at this point in time.

I don't really want to replacing the stock heads is over my head! I want some great performance so I am not the SLOWSTANG in town. I am not the original owner of the car so I am not sure what gears I have. More than likely they are stock. I wish there was a way to tell? I am looking at putting some 3.73 gear in. Is that over kill for a daily driver? I live really close to work and don't do much highway driving but love to take off from a light.

If you want a ballpark figure, you can count the # of rotations of the driveshaft compared to 1 rotation of a rear tire. For example: If the drive shaft turns 3 1/2 times vs 1 rotation of the tire, the gear is roughly a 3.55. A more accurate method would be to count the # of pinion and ring gear teeth, but that would be a lot more work.

A 3.73 is a good street gear. That's what I used for over 2 years (even in the snow), now I wish I had gotten a 4.10.