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rpm and speed calculator

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Woodie

Woodie

Jedi Warrior
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Here is the calculator we all need
https://www.fisc-racing.com/misc/ratios.html
Given not quite accurate readings I figure I have a 3.55 rear end in my midget
All values are approx but fit in the range of +/-5% accuarate for a 3.55
My readings while driving alone(eyes on road not dash)
60 mph = apprx 3000
70 mph = apprx 3500
75 mph = approx 3750

and with a 3.55 rear
60 mph = 3145
70 mph = 3669
75 mph = 3971
 
Cool page. Are you using the stock speedo for your road speed calculation? They can be wildly inaccurate.
 
yes stock speedo, but validated the 60 mph with wife driving behind in jeep, while on cell phone with me.
 
Probably pretty close then, though the Jeep may be off as well (my last 3 bikes have all been almost 10% high, though the last 2 cars seem to be pretty close). I can't remember which diffs when with which year cars. No memory for that sort of detail.

It's certainly a taller diff than my Bugeye. At 3500, I'm doing about 55ish (have the stock 4.2 rear end I assume).
 
Woodie, have you checked the accuracy of your tach? Mine is starting to loose accuracy, esp at high rpms. If you have a 3.5 rearend, you are lucky because those are not cheap.
 
all I have is the tach in the car, I will need to get a digital unit from somewhere to validate
 
is there any visual marking on the backend to tell what it is?
 
Yep, is stamped on the housing, hard to tell you where.

Top, front, side where there are some wings on the casting.
 
...but the gears inside might have been changed. You might have to jack up one wheel and count revolutions of the tire and drive shaft (with car in neutral) then divide the larger number by the smaller. Do several revolutions of the tire to increase accuracy (it is hard to estimate a partial revolution of the drive shaft).
 
Thanks for the link. Since I lack a spedometer in the race car I was wondering what I was hitting the other day. Apparently I was getting up to 90mph on the straights and about 50 in the turns in the parking lot where I was flying around. /ubbthreads/images/graemlins/thumbsup.gif /ubbthreads/images/graemlins/devilgrin.gif
 
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