BluePrint Engines

Visit our community sponsor

Thanks Thanks:  0
Likes Likes:  2
Results 1 to 8 of 8

Thread: Rear gear ratio question

  1. #1
    Senior Member
    Join Date
    Jun 2018
    Posts
    205
    Post Thanks / Like

    Rear gear ratio question

    Hi guys is there any way to know what the rear gear ratio is? I'm running a T5, with a 347 stroker, at 70mph Im turning 2,000rpm

  2. #2
    Senior Member Gordon Levy's Avatar
    Join Date
    Feb 2011
    Location
    Maricopa AZ
    Posts
    1,273
    Post Thanks / Like
    I am assuming you are in 5th at the time. I would say ether a 3:27 or 3:31
    99/2000 NASA PSO Champion-2005 west coast FFR challenge series Champions
    Sponsor Tony B's 2007 ST2 National Championship
    2009 NASA TTC runner up-2010 NASA TTB runner up

  3. #3
    Senior Member
    Join Date
    Jun 2018
    Posts
    205
    Post Thanks / Like
    Quote Originally Posted by Gordon Levy View Post
    I am assuming you are in 5th at the time. I would say ether a 3:27 or 3:31

    yes thanks very much

  4. #4
    Senior Member
    Join Date
    Feb 2011
    Location
    Woodstock ,Illinois
    Posts
    749
    Post Thanks / Like
    I’d say Gordon is right on... with a 308 year you’d be going about 77-78 mph at 2k
    FFR 5136 Started as a donor...donor guages, engine, trans,etc. Now...TFS street intake,stage 1 cam, GT40p's,24# injectors and 80mm MAF,70mm TB,Z-spec t-5, and PSE Halibrand wrapped with Nitto 555 G2’s. My ever evolving dream car!!

  5. #5
    Not a waxer Jeff Kleiner's Avatar
    Join Date
    Feb 2011
    Location
    Bloomington, Indiana
    Posts
    8,000
    Post Thanks / Like
    Since there may be some speedometer error try this---jack the rear of the car up, mark the tire and the driveshaft and count how many revolutions the driveshaft makes for one revolution of the tire. 2 3/4 turns=2.73, a little more than 3=3.08, 3 1/4turns=3.27 or 3.31, a touch more than 3 1/2 turns=3.55 and about 3 3/4 turns= 3.73.

    Jeff

  6. Likes mburger liked this post
  7. #6
    Senior Member
    Join Date
    Jun 2018
    Posts
    205
    Post Thanks / Like
    Quote Originally Posted by Jeff Kleiner View Post
    Since there may be some speedometer error try this---jack the rear of the car up, mark the tire and the driveshaft and count how many revolutions the driveshaft makes for one revolution of the tire. 2 3/4 turns=2.73, a little more than 3=3.08, 3 1/4turns=3.27 or 3.31, a touch more than 3 1/2 turns=3.55 and about 3 3/4 turns= 3.73.

    Jeff
    Interesting you mention this, I checked the speedo when I first bought the car it is the GPS unit, versus a handheld gps that I had and it was spot on

  8. #7
    Senior Member
    Join Date
    Oct 2012
    Location
    Tybee Island, GA
    Posts
    505
    Post Thanks / Like
    For reference, as Gordon states, my stock 302,T-5 with 3.08 does turn 2,000rpm at 78mph.
    Dave
    Mk 3.1 - #6882 - 5.0L 302 - FiTech EFI - 3-Link - 3.08 Ratio - 15" Wheels
    Greenhorn and doing the best I can
    My photos are at: My Flickr acct
    Videos are at: YouTube Videos

  9. #8
    bobl's Avatar
    Join Date
    Aug 2014
    Location
    Spicewood, Texas
    Posts
    491
    Post Thanks / Like
    Your GPS speed will be accurate. If you get the RPM in 4th gear (which is 1:1 ratio) at 70 mph you can plug those numbers into this calculator to figure your gear ratio.

    http://www.wallaceracing.com/calc-gear-tire-rpm-mph.php

    You'll also need to measure your tire diameter to assure accurate results.
    Mk IV Roadster, 347/516 HP, 8 stack injection, Holley HP ECU, Astro Performance T5, 3-Link 4.10 gears, A/C, PS, PB Purchased 08/2015, Graduated 02/2017

  10. Likes mburger liked this post

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Martin's Dent and Collision Shop

Visit our community sponsor