Need help....

[MKIII_Joey]

Hello folks....
i am new here and an Austin-Healey driver from germany. Perhaps someone can help me. I have an overhauled rev. counter from speedograph...very good work:joyous: Now my question: What is the right rpm at 50-60 mph in top gear? My OD doesnt work, an i can drive only with max speed at 60-70mph in the top gear and i have forgotten what the rev. counter must show....
Thanks fot your answer---
...and sorry for my small english...:friendly_wink:


Happy Healeying....

 

[Bob_Spidell]

Lot's of 'calculators' on the Net. Just google 'axle gear ratio calculator' or similar. I like this one: https://www.angelfire.com/fl/procrastination/rear.html

 

[HealeyDave]

For 60 mph. Some 'back of the envelope' calculations:

If your transmission is in hi gear, no overdrive, then the ratio is 1:1
15 inch wheel diameter (38.1 cm)
4.5 inch tyre wall height (11.43 cm) This is an assumption. If your tyre has a different rolling radius, then the engine rpm will be slightly different.

Then, for the various Healey axle ratios (I think these are correct): I don't know which axle you have.

With a 3.545 axle - at 60 mph the engine rpm is 2975 rpm
With a 3.667 axle - at 60 mph the engine rpm is 3082 rpm
With a 3.909 axle - at 60 mph the engine rpm is 3285 rpm
With a 4.10 axle - at 60 mph the engine rpm is 3445 rpm

Check this v the calculator and see how close (or far off) I am.

 

[DerekJ]

Don't forget that your speedometer is probably not accurate due to the car having modern tyres. Unless a previous owner re-calibrated it, which is probably unlikely.

 

[MKIII_Joey]

Hello again....
thanks for your answers they have helped me a lot

Happy Healeying.....