cooperess wrote:
Is there a formula?
of course there is!!
distance (mm) times distance per minute (km) over distance per revolution (mm) times diff ratio times gear ratio = engine revolutions per minute
(1000000*60/60)/(((145*80/100)*2 + (10*25.4)) * pi)*(59/19*1) = 2033.81rpm
What's more interesting though is that I put a 3.1 diff under my new motor, and my standard mk2 S speedo is as near to perfectly accurate as you could hope for. I did 100km or so on Saturday afternoon doing my ignition timing and the GPS on my phone was spot on with what the speedo indicated. Dad has a 3.1 under his MK1 S, and it's the same, absolutely accurate, no fiddling with speedo drive ratios (6/17) or modifying speedo gearing/springs/whatever
Previously I had a 3.44 under mine, which was a fair way off - the speedo said I was doing 100mph, but the GPS speed it was only about 90 - any other speed had similar % errors
I reckon the 1312 TPM on the MK2 speedo face is wrong - I think it's meant to be 1280 like a MK1
_________________
did I tell you that I won a
trophy?