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canna change law physics
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Why jonny can't speed.
I just replaced my 1971 speedo (which wasn't working) with a 150 mph version (not that I care, this 1.7 will only do 150 if pushed off a cliff slightly more than 750 high, in a vacuum...)
It is reading high by about 3%. Probably due to my tire choice (205-60). Is there anyway to calibrate this speedo ? |
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11-15-2000, 07:15 AM
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Registered
Join Date: Jan 2000
Location: Atlanta, GA
Posts: 105
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Not exactly what you need, but this web site has a nifty wheel/tire ? speedo error calculator on it. Anybody remember what the stock tire size was for our 914s when they first came out?
http://www.paspeedo.com/ It also looks like they sell a triple guage cluster for 914s. It doesn't look like a kit like Pelicans'. i wonder how much? |
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11-15-2000, 08:08 AM
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Registered
Join Date: Jan 2000
Location: Atlanta, GA
Posts: 105
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Not exactly what you need, but this web site has a nifty wheel/tire ? speedo error calculator on it. Anybody remember what the stock tire size was for our 914s when they first came out?
http://www.paspeedo.com/ It also looks like they sell a triple guage cluster for 914s. It doesn't look like a kit like Pelicans'. i wonder how much? |
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11-15-2000, 08:10 AM
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Registered
Join Date: Aug 2000
Location: Centre, AL, USA
Posts: 205
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The original tire size for the 914 was 165-80/15, which would have a height of 25.39". The 205-60/15 has a height of 24.69". Speedwise, if the original was registering 60MPH, the other would be 61.72MPH or about 3% difference.
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11-15-2000, 09:57 AM
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canna change law physics
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It seems that a 205-65/15 would be a better fit, using the speedo calculator.
Oh well, when these wear out... |
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11-15-2000, 10:03 AM
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Registered
Join Date: Dec 1969
Location: chula vista ca usa
Posts: 5,697
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Get the GEARS.EXE program I wrote from the PP site here. It will figure the speed/RPM for each gear exact. The best way to figure tires is by circumference by making a mark and rolling the car for one rev of the tire and measure the distance in inches. It will change slightly at 60 MPH but not enough to worry about. For the gear ratios and final drive check the owners manual. Good luck.
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11-15-2000, 10:33 AM
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Administrator
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To re-calibrate the speedometer and odometer, you may be able to find a gizmo that rallyers used to use. It's a small gearbox that has the speedo cable plug in one side, and another cable coming out the other side going to the speedo. The gears inside the box change the speed of rotation of the outgoing cable.
No idea where you'd find one... --DD |
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11-15-2000, 08:42 PM
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Registered
Join Date: Dec 1969
Location: Dade County, FL.
Posts: 1,145
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I have 195/50/15's on mine and decieded to go with a VDO electronic speedo. It is user adjustable either by feeding in the ratio or by clicking off mile markers. The sender is the unaversal GM one, it threads onto the 901. I can't remember if it threads right on the output thigy or the angle drive thingy, but I did have to make a female adaptor out of brake tube to mate the two square male ends, one from the trans and one from the sender. I'm sure there is a better way, VDO is really good about responding to e-mail, ask them if they make an adaptor.
The gauge was $115+/- and the sender was maybe $40. Brake tubing was free 
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11-16-2000, 09:00 PM
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canna change law physics
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For $155, I could buy 2 rear tires, which are the right size!
Anyway, Everyone, thanks for the help! I will contact VDO and see if they have something. I do know the "new" 914 I picked up this weekend has tires which are _way_ off. Of course, it needs a hydraulic line to the right rear brake, but that's another story... James |
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11-17-2000, 04:39 AM
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1970/1982 Porsche 914-6/911SC 2.7 RS
74 Porsche 914 2.0 
