The guy I bought my 96z from was trying to BS me about alot of stuff that he "did" to the car. Well one thing he said , was the installation of 3.73 in the rear. My car is around 1650 rpm in 6th at 60mph. My buddy has an 05 GTO and I was with him lastnight , and noticed at 60mph he is spinning around 1450!!! He has a 3.46 too, and my stock is 3.42.....so he should be higher in rpms right? Does it sound like I really have 3.73's in my car? I just bought no2 and wasnt sure if 3.73 or 4.10's would be better ( when I thought the car had 3.42 I bought a set of 4.10's already.....but can use them in my 67 if you guys dont recommend them with a juiced car ), THANKS---

 

unless it's a track only car I would say you would be better off sticking with the 3.73's if you are going to be using N20.

 

With 3.73s...

1400 RPM's = 47mph
1500 RPM's = 51mph

Sounds like you're on the money.


The guy I bought the car from lied about pretty much everything...

He told me it had a WS6 suspension...on a Camaro, ok. Figured maybe 1LE but I checked everything and it was all stock.
Magnaflow cat-back? Nope, just stock piping with a Magnaflow muffler.
160 thermostat and a "chip"....nope, stock tune, stock t-stat.

 

So it looks like 3.73's huh?! For now this is my DD. LOL...the funniest thing he told me was the car had an lt4 CORVETTE computer with all the programming ( madz28 told me they are the SAME THING, lol )---

 

You may want to check your speeds again. If you are really reving 1600 RPM's in 6th @ 60 MPH then you have 4.11's...

With stock wheels/tires going 60MPH you will be at:
1350 RPM's with 3.42's
1480 RPM's with 3.73's
1620 RPM's with 4.11's

If you have different wheels and tires use the calc in my sig to get a more accurate number...

 

The stock speedometer and tach are not the most accurate gauges and you're also assuming that he had the computer reprogrammed after the gear change.

 

Very true...

 

See how many turns of the driveshaft it takes to get the wheels to spin once if you really want to know.

 

Yeah its the stock tune, lol and I have 315/35/17's in the rear.....I am sorry for not listing that first :doh:!!! I guess it would be hard to tell now????---

DAMN!!! Using that gear calculator it says my speedo is about 8 mph off!!! Thats why the cop said I was doing 81 in a 55 and I thought I was between 70-73 I need to get that FIXED!!!---

 

To tell for sure what gears you have, do like Matt said above since you are running with the speedo uncalibrated...

• jack up the rear, keeping tires free to spin (use jack stands for safety if you have them)
• put the tranny in neutral
• get under and mark the d-shaft where it would be easy to reference
• mark the tire for reference
• slowly rotate the tire and watch the d-shaft
• count the number of rotations the d-shaft makes for one rotation of the tire

It will probably be at least 3 full rotations then a little more...
If about:
3+ 1/4 turns you have 3.23's
3+ 1/2 turns you have 3.42's
3+ 3/4 turns you have 3.73's

And obviously if it is a little past 4 turns you have 4.11's, and so on...

 

You really should physically check what ratio you have, 'cause possibly the car has 3.73's but maybe the guy never calibrated the speedo to compensate for them from the original 3.42's??

 

I appreciate the help guys, I will jack her up this weekend and check ---