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RPM in Relation to Gear (5spd) and Road Speed

Discussion in 'Discussion Forum' started by lookforjoe, Jun 10, 2018.

  1. lookforjoe

    lookforjoe True Classic

    Trying to determine if my Tach is reasonably accurate - I'm using a non-standard setup to feed it.

    To help gauge accuracy I'm trying to find out what the normal rpm relationship to speed in any given gear is for the 5 speed trans.

    For reference, if anyone can provide the speed readings at 3,500 and 4,500 rpm for each gear?

    I can't find it.
     
    Last edited: Jun 10, 2018
  2. Dan Sarandrea (Phila)

    Dan Sarandrea (Phila) Waitin' On Parts...

    Location:
    Philadelphia, PA
    Didn't Road and Track used to pub those numbers?
     
  3. Dan Sarandrea (Phila)

    Dan Sarandrea (Phila) Waitin' On Parts...

    Location:
    Philadelphia, PA
  4. lookforjoe

    lookforjoe True Classic

    I found the original R&T review, but that was for the 4spd

    "Speeds in gears are
    50 kph (31.1 mph) in first, 80 kph (49.7 mph) in second, 120 kph (74.6 mph) in third and over 170 kph (105.6 mph) in top."

    Assuming at 6,6K rpm, since that is redline
     
  5. lookforjoe

    lookforjoe True Classic

    Thanks Dan!

    So: First 4.090 Second 2.235 Third 1.469 Fourth 1.043 Fifth 0.863

    Tire height: 22.9 (225/45x15)

    3500/1st: 14.31____4500: 18.39_____6K: 24.52
    3500/2nd: 26.18____4500: 33.66_____6K: 44.88
    3500/3rd: 39.83____4500: 51.21_____6K: 68.28
    3500/4th: 56.1_____4500: 72.12_____6K: 96.17
    3500/5th: 67.8_____4500: 87.17_____6K: 116.22

    now I'll have to see what I actually have.
     
    Waterbury likes this.
  6. Dan Sarandrea (Phila)

    Dan Sarandrea (Phila) Waitin' On Parts...

    Location:
    Philadelphia, PA
    You can also download a GPS-based speedo app onto your phone for a second opinion.
     
  7. Rod Midkiff

    Rod Midkiff True Classic

    Location:
    Eugene, OR
    You could also get a timing light with an RPM function as well. That is how I calibrated my tak.
     
    mkmini likes this.
  8. carl

    carl True Classic

    Location:
    Virginia
    Using the Fiat speedo and the Fiat tach to draw any conclusions is a waste of time as both tend to be not very accurate. I would use GPS for speed readings. Why not use an after market tach to verify rpm as it would probably be a better method for doing this.

    My Bertone uses a speedo app on my phone as my speedo and an Autogauge tach. If the weather permits, I'll try to get the speed/rpm info you want.
     
  9. carl

    carl True Classic

    Location:
    Virginia
    Here is the data I came up with using a Speedometer app on my phone and an Autogauge "monster" tach. Data logger was bionic (my daughter writing down the info as I yelled at her). Tires are 158/60/13 on iron cross wheels and the trans is from an 80 X.

    3,500rpm 4,500rpm

    2nd 22mph 28
    3rd 35 44
    4th 50 60
    5th 59 75
     
    lookforjoe likes this.
  10. Yves

    Yves True Classic

    Hi Hussein,
    we have similar setup ... I will came back with my numbers.
     
  11. lookforjoe

    lookforjoe True Classic

    Thanks guys.

    so far I have (add the rest as I remember to record them)

    EDIT 6/14 : tach is way off. 2.4k is actually 3K, 3.3K is actually 4K

    2nd --- 27/28 @ 3500 ?? @ 4500
    3rd --- 45 @ 3500 60 @ 4500
    4th---- 65 @ 3500 ?? @ 4500
    5th----- 68 @ 3500 ??? @ 4500

    What speedo app are you using? I tried one called "Speedometer" simple - with black face/large numbers, no workie.

    I'm confident the (electronic, Punto) speedo is accurate with Yves's settings. Using mile markers and those solar speed warning displays it has been on the money.
     
    Last edited: Jun 14, 2018
  12. Yves

    Yves True Classic

    Ok there is my numbers... with wheels base 195/45R15

    1 --- 14 @ 3500 18 @ 4500
    2nd --- 26 @ 3500 34 @ 4500
    3rd --- 40 @ 3500 50 @ 4500
    4th---- 55 @ 3500 70 @ 4500
    5th----- 67 @ 3500 85 @ 4500
     
  13. lookforjoe

    lookforjoe True Classic

    Ok, so my tach is way off.
    Compared it to Volvo tach hooked up at same connections. Free revving the motor.

    Volvo tach 1,1k = 800 Fiat
    Volvo tach 3k = 2.4k Fiat
    Volvo tach 4K = 3.3k Fiat.

    Need to hook up the tach with long leads so I can drive with it, and check high end under load. Fiat tach hangs at 4K sometimes also.

    After that, I’ll remove the cluster face & tweak the needle at rest to see if I can get it in the ballpark.

    Ultimately the current cluster will go away when I do the dash a la Clark
     
  14. Rod Midkiff

    Rod Midkiff True Classic

    Location:
    Eugene, OR
    Their is an adjusting Pot inside the cluster (on the tach)
     
  15. carl

    carl True Classic

    Location:
    Virginia
    I had an X with the tach reading low by 1,000 rpm near redline. Nothing like spinning the poor dear to 8K when you think you are trying to hit 7K.
    I suppose you could just get an after market shift light and just go by that and leave the stock tach for setting idle speed.
     
  16. lookforjoe

    lookforjoe True Classic

    Where do people's needle rest when off? I can use that as a guide. Mine currently sits at 500, I think it was higher before I fiddled with the cluster mod and switched needles.

    Rod, do you have more info on the calibration pot?
     
  17. lookforjoe

    lookforjoe True Classic

    LH2.4 has a built in upshift indicator. I disabled it as it appeared to be engaging way to early :D I'll have to revisit the settings for it. I do still want to get the tach in the ballpark though.
     
  18. lookforjoe

    lookforjoe True Classic

    Hooked up my Volvo tach and the Spider tach to function check

    [​IMG]

    [​IMG]
    [​IMG]

    [​IMG]
     
    mkmini likes this.
  19. lookforjoe

    lookforjoe True Classic

    Since I know the Fiat tach reads OK, I put it on the dash. Tomorrow I'll pull the cluster apart & see if I can get the original tach fixed.

    [​IMG]

    [​IMG]

    [​IMG]
     
  20. Rod Midkiff

    Rod Midkiff True Classic

    Location:
    Eugene, OR
    you have to pull all the gut's out of the cluster (remove, pull the face off, remove the tac from the plasic.) I drilled a hole in my housing so I can adjust the pot without dissambling the entire cluster (still have to pull it though)
     
    AKimball92 likes this.

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