What Gear ratio Rear end?

[Jim]

Hi there. i have looked for stampings etc where it says to look for
stampings from different web pages and i can't seeem to locate any info on
what type of rear end I have in my 1977 Vette. I have a regular chevy 350
motor and a 4 speed standard transmission and am turning P225/70SR15
Michelin Radials. If I told this group that in 4th gear at 3000 RPM I am
travelling at a speed of 65 MPH is there a way to figure out my gear ratio?
Thanks for any responses... Jim

[Robotron Tom]

Jim started a controversy when he said... :

> Hi there. i have looked for stampings etc where it says to look
> for
> stampings from different web pages and i can't seeem to locate any
> info on what type of rear end I have in my 1977 Vette. I have a
> regular chevy 350 motor and a 4 speed standard transmission and am
> turning P225/70SR15 Michelin Radials. If I told this group that in 4th
> gear at 3000 RPM I am travelling at a speed of 65 MPH is there a way
> to figure out my gear ratio? Thanks for any responses... Jim
>
>
>

There were 4 axle options on the 1977: 3.08:1, 3.36:1, 3.55:1 and 3.70:1

Easy way to check is to jack up the rearend to get the wheels off the
floor, put the car in neutral, slide under the car. Mark a line on one of
the tires so that you can see it, then mark a line on the driveshaft. Now
rotate the driveshaft until the tire makes a complete rotation. You will
get about 3.??. That will be your approximate ratio. The ratio is number
of driveshaft rotations to 1 wheel rotation. So if the shaft rotates
right at 3 times it would be a 3.06 and if it rotates about 3 and a
quarter times it would be a 3.36 and so on.

Hope this helps,
--
Robotron Tom *remove nospam to email*
See the Flashback Arcade at: http:// www.arcadeguy.net

Standing for right when it is unpopular is a true test of moral
character.
-M. Smith

[kage]

You probably have 3.70's.

Karl


"Jim" <jim> wrote in message ...
> Hi there. i have looked for stampings etc where it says to look for
> stampings from different web pages and i can't seeem to locate any info on
> what type of rear end I have in my 1977 Vette. I have a regular chevy 350
> motor and a 4 speed standard transmission and am turning P225/70SR15
> Michelin Radials. If I told this group that in 4th gear at 3000 RPM I am
> travelling at a speed of 65 MPH is there a way to figure out my gear
ratio?
> Thanks for any responses... Jim
>
>

[MES]

If im not mistaken 3:55 was standard from the factory
"Jim" <jim> wrote in message ...
> Hi there. i have looked for stampings etc where it says to look for
> stampings from different web pages and i can't seeem to locate any info on
> what type of rear end I have in my 1977 Vette. I have a regular chevy 350
> motor and a 4 speed standard transmission and am turning P225/70SR15
> Michelin Radials. If I told this group that in 4th gear at 3000 RPM I am
> travelling at a speed of 65 MPH is there a way to figure out my gear
ratio?
> Thanks for any responses... Jim
>
>




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[helter skelter]

I have a program that I downloaded recently that is an RPM predictor given
certain factors. Enter in tire size, gear ratio, axle ratio, and speed and
it'll
give you RPM at a given speed for every gear in your box if you enter it in.

If you want to reply to me I can e-mail it to you (sorry, forgot where I got
it
but it is shareware).

Other than that you can do it the old fashioned way....

Standard equation is
(engine rpm)(tire diameter in inches)(.00297)/Final Drive Ratio =MPH

..00297 is the sliding K factor in this case. An exact figure can be figured
for every vehicle pretty easily that will make this equation as good as
it gets. But, the standard equation should give you a close enough Idea.

Since you know your speed already, you can use algebra to isolate
your differential. Since 4th gear is 1:1, Final Drive Ratio is just your
differenial ratio. So the equation looks like this.....

(engine rpm)(tire diameter in inches)(.00297)/MPH=Final Drive Ratio
Since there is a sliding factor (.00297) we're looking for a number close
to a ratio that was offered for this car. The number calculates to ratio
3.756
so I'd say 3.70 for sure. With a gps or a stopwatch you can determine
your cars K factor and be exact here but it sure looks like the 3.70

z

65 R/R Air 2 Top


"Jim" <jim> wrote in message ...
> Hi there. i have looked for stampings etc where it says to look for
> stampings from different web pages and i can't seeem to locate any info on
> what type of rear end I have in my 1977 Vette. I have a regular chevy 350
> motor and a 4 speed standard transmission and am turning P225/70SR15
> Michelin Radials. If I told this group that in 4th gear at 3000 RPM I am
> travelling at a speed of 65 MPH is there a way to figure out my gear
ratio?
> Thanks for any responses... Jim
>
>

[Tom in Missouri]

Try this one.
http://www.angelfire.com/fl/procrastination/rear.html

Plug in your numbers.

In your case, guess on a rear. Then check the available rears below to see
if any match.

Based on your 3000 RPM, guessing a 27 inch rolling diameter tire, guessing a
3.55 rear, I got 67.88 mph. but checking the 3.70 rear box, I see 65.12
mph so you could have a 3.70.

To get rolling diameter, chalk where your tire hits the ground and the
ground. Roll the car forward until the chalk on the tire hits the ground
again. Mark the ground. Measure between the two marks and divide by 3.1416.
Close enough for government work.



"Jim" <jim> wrote in message ...
> Hi there. i have looked for stampings etc where it says to look for
> stampings from different web pages and i can't seeem to locate any info on
> what type of rear end I have in my 1977 Vette. I have a regular chevy 350
> motor and a 4 speed standard transmission and am turning P225/70SR15
> Michelin Radials. If I told this group that in 4th gear at 3000 RPM I am
> travelling at a speed of 65 MPH is there a way to figure out my gear
ratio?
> Thanks for any responses... Jim
>
>