[keypilot]

first ride tonight and i am trying to figure out my speed and gear ratio.

at 45 mph showing i am turning about 2750 rpms feels like i am going faster than 45 though. the rear tires are about 26 inches tall.
i have a 350 auto trans.

is this enough info to answer my question?

i tried to look up the rear end codes but i cant find any on the car. it is a 10 bolt though.

 

[JimM]

nope, not enough info. The "it feels like it's going faster" part kinda screws me up.

Take her out on the highway. Note the odometer reading when you pass a mile marker. Run for a while (when I want to be real accurate, I do 10 miles, once I did a hundred, you could get by with just one mile) Note the odometer reading at your end mile marker.

From there, it is easy to figure how much if any your odometer (and therefore your speedometer) are off.

To calculate gear ratio, we need accurate speed and rpm.

 

[keypilot]

ok thanks. tomorrow i will take the GPS with me and know the speed for sure.

 

[davidpozzi]

You will have to jack it up and turn the driveshaft and count the turns, or remove the cover to count teeth to get the axle ratio.
Once you do that, go here:
http://www.car-videos.com/tools/speedrpm.asp

 

[keypilot]

ok jim, i was right about feeling faster. it is 4 mph slower on the speedo than the gps.
at 50mph it was turning excatly 3000 rpms
can you get a gear ratio with that with the above info?

 

[Andrew69]

Sounds like a 4.11 or 4.56 to me.

 

[keypilot]

x33d80, i did the math forward and backwards (the formula in the tech refrence pages) I come up with 4.56's
can anyone confirm this?

thanks

 

[Andrew69]

I have 4.56's and 3 thousand at 50 MPH looks really familiar.

 

[keypilot]

thanks, i think you are right

 

[Lost in the 60's]

Holy deep gears Batman....what the heck was the PO doing with 4:56's in there ??? She outta be snappy off the line !!:thumbsup:

 

[Andrew69]

Anyone ordering a 4.56 from the factory must have planned to do some kind of racing. I bought the rolling body with the 4.56 rear from the Los Angeles, CA area and have always wondered how this car spent the first 35 years.
Yes it is snappy off he line. I am glad that I found the high revving 302 to put in, it has many opportunities to rev.
This car begs for one of the new O/D transmission kits.

 

[Lost in the 60's]

Keypilot's car was originaly a 6, so I kinda doubt it has the original gears in it. The PO musta been doin' some street racin'....:thumbsup:

 

[keypilot]

i think you are right mitch. i dont mind them, although i will be looking for 200r in the future.

 

[burgdob]

Put mine in a spreadsheet. To get [email protected] you got a 4.73

45 mph
4.73 ratio 26 Radius 582 revs/min at wheel
2752 revs/min axle

2.25 1st gear 6192 revs/min at engine
1.52 2nd gear 4183 revs/min at engine
1 3rd gear 2752 revs/min at engine

Sure the tire diameter is correct, since you probably got a 4.56.

 

[mstehle]

I get 4.56. Here is a link where you can input data and figure out any number of things. http://www.f-body.org/gears/ I used it to figure out what tranny and r4ear end I wanted. I put the tire dia. and transmission gear ratios in and came up with 4.56. Here is also a link to the specs for most tranny's. http://www.ridgecrest.ca.us/~biesiade/Specs.htm Hope this helps

Mark

 

[keypilot]

mark thats very helpful. i can see if i keep this rear end and go to a 200r, i will be turning 2000 rpms in OD.

that might save a little fuel. lol