so my question is does my car have 3.45's or does it have lower gears in the rear end
at 60mph i am reving about 2100 rpm in 5th
my buddy (vett guy) says that it reving to high to have 3.45's
car is coded to be 88 formula 305 tpi, t5, 9 bolt with 3.45's
maybe somebody changed out gear in the past
i have found other sleeper modification before
just wondering

 

Sounds about right to me. Driving the car at 70 mph in 4th gear (manual) or 3rd gear (auto), the RPM's will tell you your axle ratio.

 

"If you tach is accurate"
"If you have a .73 5th"
"If your speedo is accurate"
"If you have 25.7" tires"
You probably have 3.7 gears. 64 miles an hour would be 3.4.

 

^^^ This ^^^

Since they usually fail by reading high, they make all kinds of people think they have gears other than what they actually do. (higher ratio # than reality)

If what gear you have actually matters to you in some way, LOOK AT IT. All of those "calculations", "spin the {fill in the blank} and count", and all that, is nothing but a bunch of GUESSES, which are hardly ever right. I would go so far as to say NEVER, but it's possible that ONCE, sometime somewhere someone somehow accidentally got the right # from some one of them somehow, although I don't think I've ever seen it happen, personally.

Changed your rear end fluid lately? I thought not. Go do that. While you're catching up on the "deferred maintenance" (politically correct term that means "neglect"), make a point of ACTUALLY LOOKING at the gears. Count the teeth. There is NO WAY for there to be any uncertainty in that. And since your next post is likely to be something about "posi", make a point of looking at that too; once again, all the "spin this and look at that" crap usually is WRONG, most usually in the direction of falsely identifying an open as a posi. Don't fall for it, go straight to the source, and avoid all the guessing.

 

Start with that !! If the Tach reading is accurate,...... Your T5 tranny has a 1:1 4th gear. Get the car to 70MPH in 4th gear and note the RPM. RMP @ 70MPH in (T5) 4th = Rear End ratio.

 

I don't think that is very accurate with stockish height tires.
My car spins under 3500 rpm with 3.73 gears in 4th.

 

It is;

With an ACCURATE TACH,....... If the car is an AUTO then put it into 3rd (1:1) & run it up to 70 MPH and note the Tach. RMP @ 70MPH (700R4) in 3rd = Rear End ratio.

 

Eh. Sorry. I was comparing my t5 in 4th. Must be a fair amount of slip in the auto?

 

Engine RPM calculator - http://www.csgnetwork.com/multirpmcalc.html

Says 3.45 gears at 60MPH in a 5-Speed trans puts it at 2,174 RPMs with an .80 5th gear

Here's the chart that shows the gears of the T5 - http://www.moderndriveline.com/Techn.../tremec_t5.htm