My '89 Formula 350 has an Aussie 9-bolt, and therefore I assume 3.27 gears. is it possible that my car has a different factory gear ratio? did they make that, or were they all 3.27's?

the reason I ask is because sometimes when i'm driving down the road I look at my speedometer and think "there's no way i'm doing 70 right now." and to clarify, it feels like i'm going slower than the speedo indicates. wouldnt that be indicative of a numerically higher gear [than a stock 3.27?]

the car has a performance build with heads, cam, ect. and a Fast Chip by Ed Wright. i had the chip burned under the assumption that it had 3.27's. i suppose if it has 3.08's or something and a chip that thinks it has 3.27's, that could throw my speedo off a bit.

thanks for any new knowledge on this matter.

 

Theres 2.77, 3.27, 3.45 and others that I am forgetting.

What is your tire size? Do a simple driveshaft check to see what it is if you don't want to pull the cover.

 

Does your 89 have a cable drivin Speedo? If so I don't think a chip will make a difference

 

245/50/16.

i did do a driveshaft check when i first bought the car - 3.27 seemed to check out. i'll go ahead and do it again. if i find out i'm rockin' 2.77's i have 345's in there in a week.

btw, what the heck is the mechanical difference between a 230 HP 2.77:1 model and a 240 HP 3.27 model?

 

good point. it probably does [have a cable driven speedo].

but then, in the absense of any mechanical changes between the gears and the speedometer, could it all be chalked up to my own insanity, the fact that it 65 feels like 50?

 

Where are you getting 3.45s? As far as I know all the aftermarket gears for these are 3.70's, and although there are factory 3.45 gears, they're not super easy to find.

As far as the second part - I have no idea what you're talking about and I'd be surprised if someone else did either. You're going to need to clarify where you're getting that information and the context of it.

 

A 1989 Firebird won't have a cable driven speedo. They switched to electronic in 85 unlike Camaros that didn't switch until 1990.

 

https://www.thirdgen.org/1989-pontiac-firebird

on the chart, check the third-to-last and second-to-last rows.

 

I am pretty sure the difference is the dual cat system.

 

The upgrade option that got 240hp also got the better gears at the same time.

 

If I remember correctly, all 9 bolts should have a tag on one of the cover bolts with the gear ratio.

 

Some were 3.08's. The one I have in my IROC is a 3.08. We counted the teeth on the gears when we pulled the cover and inspected it prior to putting it in my car.

We got it from a junkyard 85 or 86 Trans Am.

 

well, mine was a dual-cat model. it's sounding more and more like i should have my head examined. or see if i can have a State Trooper clock me.

 

thanks. unfortunately, the diff cover and bolts have been replaced with a TA Performance unit.

 

Ive seen a few 3.45 9 bolt rears in the junkyard.AFAIK they only came on 5 speed cars.There is one on a junkyard 87 GTA not too far from me.I ran the memcal code and its for a 3.45 rear

 

the ratio is also stamped on the ring gear.