Author Topic: Gear ratio Vs. 55 MPH w/3.50 gears.  (Read 3686 times)

1967 eight barrel

  • Guest
Gear ratio Vs. 55 MPH w/3.50 gears.
« on: August 20, 2018, 02:58:20 AM »
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

  • SAAC Member
  • Hero Member
  • *
    • View Profile
Re: Gear ratio Vs. 55 MPH w/3.50 gears.
« Reply #1 on: August 20, 2018, 08:07:30 AM »
Automatic or Manual trans?
Shelby's and Fords from Day 1

shlby66

  • Full Member
  • ***
    • View Profile
Re: Gear ratio Vs. 55 MPH w/3.50 gears.
« Reply #2 on: August 20, 2018, 09:28:51 AM »
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

  • Guest
Re: Gear ratio Vs. 55 MPH w/3.50 gears.
« Reply #3 on: August 20, 2018, 10:25:26 AM »
Manual... Would be 1:1 in 3rd Auto  4th Manual.

 255-40-17.  25.02 tire height
                                                  -Keith

Greg

  • SAAC Member
  • Hero Member
  • *
    • View Profile
Re: Gear ratio Vs. 55 MPH w/3.50 gears.
« Reply #4 on: August 20, 2018, 10:46:21 AM »
My guess is 3000RPM but someone that is running with the set up you have will need to report what they see.
Shelby's and Fords from Day 1

1967 eight barrel

  • Guest
Re: Gear ratio Vs. 55 MPH w/3.50 gears.
« Reply #5 on: August 20, 2018, 10:47:42 AM »
I was curious too. An FE turning 3K at 55MPH gets on your nerves quick.

                                                                                               -Keith

kjspeed

  • SAAC Member
  • Sr. Member
  • *
    • View Profile
Re: Gear ratio Vs. 55 MPH w/3.50 gears.
« Reply #6 on: August 20, 2018, 12:19:08 PM »
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
1968 Shelby GT350
1968 Mustang GT S-code
2009 Mustang Bullitt

deathsled

  • SAAC Member
  • Hero Member
  • *
    • View Profile
Re: Gear ratio Vs. 55 MPH w/3.50 gears.
« Reply #7 on: August 20, 2018, 02:35:32 PM »
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.
« Last Edit: August 20, 2018, 02:37:34 PM by deathsled »
"Low she sits on five spoke wheels
Small block eight so live she feels
There she's parked beside the curb
Engine revving to disturb
She's the princess from his past
Red paint gold stripes damned she's fast"

Greg

  • SAAC Member
  • Hero Member
  • *
    • View Profile
Re: Gear ratio Vs. 55 MPH w/3.50 gears.
« Reply #8 on: August 20, 2018, 02:52:27 PM »
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  :)
Shelby's and Fords from Day 1

2112

  • SAAC Member
  • Hero Member
  • *
  • Fox Island, WA
    • View Profile
Re: Gear ratio Vs. 55 MPH w/3.50 gears.
« Reply #9 on: August 20, 2018, 05:18:06 PM »
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

  • Guest
Re: Gear ratio Vs. 55 MPH w/3.50 gears.
« Reply #10 on: August 20, 2018, 06:28:32 PM »
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

  • Sr. Member
  • ****
    • View Profile
Re: Gear ratio Vs. 55 MPH w/3.50 gears.
« Reply #11 on: August 20, 2018, 06:34:43 PM »
Keith,
Bowling & Grippo program gives 2586 rpm at 55 MPH with tire diameter 25.02 "
Texas Swede

1967 eight barrel

  • Guest
Re: Gear ratio Vs. 55 MPH w/3.50 gears.
« Reply #12 on: August 20, 2018, 06:56:15 PM »
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

  • SAAC Member
  • Sr. Member
  • *
    • View Profile
Re: Gear ratio Vs. 55 MPH w/3.50 gears.
« Reply #13 on: August 20, 2018, 08:14:59 PM »

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
1968 Shelby GT350
1968 Mustang GT S-code
2009 Mustang Bullitt

1967 eight barrel

  • Guest
Re: Gear ratio Vs. 55 MPH w/3.50 gears.
« Reply #14 on: August 21, 2018, 02:50:51 AM »
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