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RPM question

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tomgt6

Jedi Warrior
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I have a 63 spitfire and would like to know what the RPMs you guys average at 60. I run about 4300. Is this normal?
 
What makes you think that your tach is accurate(they rarely are).I would get it verified,then get worried.Doubtless at the end of the day ,you'll need a 5 speed conversion.....
MD(mad dog)
 
Not sure it would be the same, but my Mk 3 Spit owner's manual gives 635 rpm @ 10 mph without OD; which would only about about 3800 rpm @ 60 mph. That's with stock (for a Mk 3) 4.11 gears. I'm sure Andy will be along shortly with more info on gear ratios.

But as MD says, having a tach that reads 500 rpm high is not unusual at all. You could also check your diff ratio and tire size.
 
Hi; sorry I'm late. (Had a "gig" tonight, as I'm part of a double quartet a capella men's group.) Another way of looking at Randall's figures is that a 1963 Spitfire, with 4.11:1 diff and 5.20 x 13 (stock OE size) tires gives 15.7 mph per 1000 rpm in top gear. That translates to a wee bit over 3800 rpm @ a true 60 mph. Obviously other tire sizes could affect this. More likely though, with a 46-year-old car, is a somewhat inaccurate speedo and/or tach. (Even when new, Triumph speedometers often read a good 5-7 mph faster than true speed @ around 60 mph!)

With no other changes beyond a 3.89:1 ratio, the figure is 16.7 mph per 1000 rpm in top gear -- or about 3600 rpm @ 60.
 
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