this February I bought a 89 firebird formula 305 tpi.How can I check what kind of differential I have? a friend told me that it was around 3.5 so I believe its the 3.45 rear end, I guess he did it on top of the lift and spun the tires and looked at the driveline, would that be accurate? Also I have heard that there where a couple of sleeper formulas that had the T5 tranny and want to find out if mines is one.

 

1989 Formula 305 TPI/T5 should have a 3.45 9 bolt. However, anything could be in it now. The way to find out for sure is to jack it up and pull the cover. Look on the edge of the ring gear and you'll see a stamped number with either the gear ratio, or the number of teeth which you divide to get the actual gear ratio. Marking the driveshaft and a tire, and turning the tire one full turn while counting driveshaft turns will get you close, but the stamp is as accurate as you can get. There's no time like the present to change the fluid anyway.

 

sleeper? no, you dont have one, and there is no "sleeper" formula.

there are 1le cars, which is the factory performance package, which is pretty much just a sway bar and front brake package. Your RPO list will have the 1le RPO, but again, its very unlikely you have it. 1le birds are few and far between

 

You could also use an online rear end calculator,

Here u go:

http://www.richmondgear.com/101032.html

 

The Formula had the 36mm hollow sway bar... how did the 1LE package upgrade the sway bar?

 

Let's not hijack the thread guys... Once again 1LE hype is getting out of control. The 1LE RPO code (when present) only identifies that the car has the dual piston large front brakes. None of the other features commonly associated with the 1LE option, were truly specific to 1LE cars. Most all of it (except the brakes) were used on other thirdgens.

Ok, now that's out of the way, back to the topic. There's no hidden treasure in these cars. The truly rare cars are well documented and easy to spot. The chance that the car is a 1LE is EXTREMELY limited, to the point it's probably not even worth mentioning. You can check the front brakes, if the calipers are rusty it's not a 1LE.

What's really unique about the Formula is hard to miss. It's the only TPI thirdgen without the ground effects. The focus of the car was more on affordable performance then cosmetics and luxury. That makes the car special. An 89 Formula LB9/5spd has all the same go fast options as a 1LE, it probably just wouldn't stop as fast.

 

thank you all guys for you help Im new at this and its sick!!!

 

You hit the nail on the head, Drew. In effect, all Formulas were "sleepers", especially the Formula 350. Many folks never realized that w/careful optioning these cars could be built about 200 lbs lighter than a comparable T/A.

 

The car is not a "sleeper" because of the "Formula" callouts. You are broadcasting you have at the very least a 305 under the hood. People see "Formula" and they expect you to put up a damn good fight. A sleeper would be undetectable in a group of stock 6 cylinder models.

 

Speaking from experiance, I have owned both an 1982 T/A, and a 1989 Formula 350. The Formula attracted CONSIDERABLY less attention from the law than the T/A did, and that's even w/o removing the side "Formula 350" decals. That would have made it even more a "sleeper". Apparently state police didn't pay much attention to hood buldges. I also think 305 equipped Firebirds probably outnumbered V6 Firebirds, but I could be wrong, so the hood buldge is moot.

 

does the ws6 performance suspension mean anything, at least Im sure that the car came with it?

 

Every forum ever built had the WS6 suspension.

It means it has stiffer springs, 36mm front sway bar, 24mm rear sway bar, and a quick ratio steering box.