Hmm.. i have 3.55's, and when shifting at around 5500 into 2nd, and about 5200 into 3rd, I always cross the line at the very top of 3rd. I have never hit 4th gear in the 1320. Is this possible with 3.55s? Do I not even have 3.55s? The guy I bought the car from a year and a half ago told me it has 3.55s, but I haven't actually jacked the car up to mark the driveshaft and check it out.
Mulch - if you're running up around 90-100 at the top of third, you don't have 3.55's. The link provided above will do all the calcs to help you zero in on it - but the easiest is to simply count shaft revs per 1 tire rev. My guess is 2.73's or 3.08's.
When crossing the line, i'm usually around 93 mph at 2700 ft. elevation, which calculates to 96 mph at sea level. My tires are 255/60/15s, and i'm not exactly sure about the RPMs when I cross the line, but i think its around 5000-5500 in 3rd.
The tag on my door has a 'Z' under AX, so I think that means my car came stock with 3.08s. I would be the happiest man in the world if I found out I actually have 3.08s, then i'll be able to get me a set of 3.73s, which I plan on doing anyway.