Gear ratio Vs. 55 MPH w/3.50 gears.

[1967 eight barrel]

What are most of you turning on the highway with 3.50 gears? I know my tire height is about 25" tall. I don't know what the original tire height was on 1967 Shelbys.
                                                                                                -Keith

[Greg]

Automatic or Manual trans?

[shlby66]

I know my tire height is about 25" tall. I don't know what the original tire height was on 1967 Shelbys.                                                                                                -Keith

          The Speedway 350's, were approximately, 26.75" in diameter.

           Doug
         

[1967 eight barrel]

Manual... Would be 1:1 in 3rd Auto  4th Manual.

255-40-17.  25.02 tire height
                                                  -Keith

[Greg]

My guess is 3000RPM but someone that is running with the set up you have will need to report what they see.

[1967 eight barrel]

I was curious too. An FE turning 3K at 55MPH gets on your nerves quick.

                                                                                               -Keith

[kjspeed]

Here's a simple calculation tool if you know the gear ratio, tire height, trans high gear ratio and MPH: http://www.csgnetwork.com/multirpmcalc.html

[deathsled]

About 3800 rpm at 70 mph. 3:50 rear. I love the sound! Only fear in back of my mind is that the engine might blow up but it hasn't yet. And I recall zray saying that the revs are fine and no fears. I'm going with that line of thinking and if the engine blows so be it. Will then put a four bolt main svo block in her.
At 55 I believe the revs are around 2800 maybe a tad more.

[Greg]

I was curious too. An FE turning 3K at 55MPH gets on your nerves quick.

                                                                                               -Keith

The 427 in my Fairlane has 3:89 gears with a 4 speed and runs 4K at 70 which scares me to death so I stopped doing that 

[2112]

I wish that Hone overdrive company would actually make and sell overdrives.

http://hone-o-drive.com/hone-o-drive/

Anyone live near Branson able to peek in?

[1967 eight barrel]

I came up with 3K too, but it seems to be a bit over that. I am considering  3.25 or even a bit numerically lower.

[texas swede]

Keith,
Bowling & Grippo program gives 2586 rpm at 55 MPH with tire diameter 25.02 "
Texas Swede

[1967 eight barrel]

Thank you!  Some ask the final transmission output, which with any four speed I know of is 1:1.  The calculator I used showed about 3000 rpm.  It seems I am turning more than that.  The tach was rebuilt and calibrated, so I don't think that's the issue. 

                                                                                                                         -Keith

[kjspeed]

Tire diameter is somewhat vague, circumference is what really counts. More or less air pressure could affect the circumference, which in turn determines RPM. Also, if you're not 100% sure of the gear ratio jack it up and turn the driveshaft so that the tires make one complete revolution (turning the tire and counting driveshaft rotation could be affected by the diff).

Thank you!  Some ask the final transmission output, which with any four speed I know of is 1:1.  The calculator I used showed about 3000 rpm.  It seems I am turning more than that.  The tach was rebuilt and calibrated, so I don't think that's the issue. 

                                                                                                                         -Keith

[1967 eight barrel]

Unless they installed the wrong gears, they are 3.50s. I went by the tire manufacturer's information on diameter. I used the calculator to confirm the speedometer driven gear. It just seems a bit steep for 3.50's.   I appreciate the input.

                                                                                                        -Keith