rielcrazy

I have what appears to be a stock rear-end casing on my 98 transam M6. I bought the car with 100,000 miles on it and I'm not sure if the rear has been regeared. I have 275/40/17 tires. My rpm at 80 in 6th is 2000 on the nose. You guys think I have the stock gears?

I have searched the threads and have found a couple people who say their rpm at 80 with 4.10's is 2100 or so which has led me to wonder if the car has 373's or something.

Appreciate the input.

moge11

3.42. should be 1350rpm at 60mph

soundengineer

iTrader: (16)

by doing the math...
you have a 3.90 rear gear..

VandykeT/A

74,75 should be right at 2k with 4.10s. According to a Fbody gear calculating site I found with 373s you should be at 82 and with 390s 78. Since 373s would be a little more common to run across I would be thats what you have. When I had 373s in my 02 I was right around 80 at 2k. Someone had the speedo corrected , did your car come with a programmer by any chance? If it did you could see what it was set at. If not someone had a shop do it through tuning so no way to tell that way.

rielcrazy

sounds like it's probably 3.73's then because the needle is resting on the bottom of the 2k mark, not below but on top of the start of the mark probably 1950. I'm surprised, I thought it would have to be 3.47 with the way it takes off. It was pretty slow when i got it (bone stock). I've cammed it and done the ls6 intake and texas rumbler catback. Had it tuned by frost. It's definately faster but not as fast as I want it to be.

I was up against a new SS the other day and he pulled his rear bumper to my front bumper on the start but couldn't gain anything else on me though I never could catch up. I'm figuring it was my reaction time. I really need to time the car to see where it is.

You guys think i'd notice a difference with 4.10's or 4.30's? I have a truck I daily drive, this is more of a good weather or run around in car.

bww3588

iTrader: (49)

Going off the factory tach won't tell you **** when your splitting hairs between 100 rpms. I would just open the cover and look at them. The car has100k miles on it, a look inside to check for damage, wear etc won't hurt as well as a lube change.

VandykeT/A

You'll notice some difference. It'll get you through the gears quicker. What cam is in the car?. A cammed LS1 shouldn't have any trouble taking a stock 5th gen.

soundengineer

iTrader: (16)

Just because 3.73 is more common, does not mean its a 3.73
and a 3.90 is a common gear that you can get for a 10 bolt from Motive...who make gears for the stock 10 bolt.

Just like when you order a 9" from moser, the gears go in whole #'s with a 0.25 step between them...so you get a 3.75 or a 4.0 or a 4.25

only true way to know what you really have, is to count teeth...

actual gear ratio can be fudged in the tune...especially if somebody does the tire calculation wrong.

rielcrazy

I have a TR224/224 .563/.563 114 LSA. I also put on the ls6 intake texas rumbler catback and had it mail tuned by frost. Perhaps I need to take it in to frosts shop (he's about 80-90 miles from my house but I had a newborn when i finished doing my engine and had to budget) and have him do a full dyno tune. Maybe he can tell me where i'm going wrong.

Maybe with the duration of my cam I need longtubes.... I'm sure they would help but I just don't think they are what's holding the car back. I was sure it was gears.

I think popping the cover off and doing a lube change is probably a good idea. give me a chance to see what shape they are in and count the teeth. How many teeth on ring gear for the different sizes anyone know?

soundengineer

iTrader: (16)

number of teeth on ring gear divided by number of teeth on pinion gear

ring/pinion=gear ratio.