 901 question |
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| rcarpen22 |
 Oct 25 2005, 05:33 AM
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#1
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Member  Group: Members Posts: 52 Joined: 16-September 05 From: DC Member No.: 4,805 Region Association: MidAtlantic Region  |
I just bought a '71 3.2 conversion with a 901 transaxle. The gauges are from a 911 of some vintage and the speedometer isn't accurate. With the stock final drive and gear ratios of the 901, what is the gear limited top speed? That info would help me find a correction factor for my speedometer.
Thanks, Rob |
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Replies(1 - 10)
| Joe Ricard |
Oct 25 2005, 05:37 AM
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#2
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CUMONIWANNARACEU Group: Members Posts: 6,811 Joined: 5-January 03 From: Gautier, MS Member No.: 92 |
Not sure what it is you want but my engine pushes my car to 110 in 4th gear (at the moment I forget the 4th gear ratio but it is currently stock for a 914) when it hit the rev limiter 5800 rpm.
195/60-15 rear tire. |
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| ArtechnikA |
Oct 25 2005, 06:00 AM
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#3
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rich herzog Group: Members Posts: 7,390 Joined: 4-April 03 From: Salted Roads, PA Member No.: 513 Region Association: None |
spend < $100 on a GPS. or find a friend who has done this. go drive at some speed. consult the GPS for your actual roadspeed; consult the speedometer to find out how fast it think you're going. ta da. you don't have to worry about tire sizes or gear ratios... |
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| Joe Ricard |
Oct 25 2005, 06:45 AM
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#4
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CUMONIWANNARACEU Group: Members Posts: 6,811 Joined: 5-January 03 From: Gautier, MS Member No.: 92 |
But that's too easy. However I agree.
You could play on the dangerous side.... Just last month the wife and I were heading out of town on the way to an Autocross. Got 4 tires in the rear trunk scooting down the road at 5 am. minding my own damn business.. I know I was doing 70 MPH as indicated on the Speedo. Wouldn't you know the cop told me the very same thing? SO my speedo is there fore pretty damn accurate. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif) |
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| larryp |
Oct 25 2005, 06:46 AM
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#5
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Member Group: Members Posts: 311 Joined: 9-May 03 From: Greenwich CT Member No.: 675 |
Mine was geared to 135. But that depends on your tire circumference also. (205/50 A032s)
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| rcarpen22 |
Oct 25 2005, 08:04 AM
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#6
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Member Group: Members Posts: 52 Joined: 16-September 05 From: DC Member No.: 4,805 Region Association: MidAtlantic Region |
I'm running 205/50 series tires as well and at redline in 5th gear the speedo indicates 145 mph. I know this is way high. I'm thinking it's closer to 125 or maybe 130 but I'm not sure. There should be a theoretical gear limited top speed for stock tire size and gear ratios that I could use to plot a curve and fit an equation that would give me my actual speed vs indicated speed. Does anyone know the stock gear ratios and ring and pinion for a '71 901?
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| Cap'n Krusty |
Oct 25 2005, 08:19 AM
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#7
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Cap'n Krusty Group: Members Posts: 10,794 Joined: 24-June 04 From: Santa Maria, CA Member No.: 2,246 Region Association: Central California |
There WAS NO 71 901. 911's had a 911 trans, 914s had a 914 trans. As I recall, the final drive ratios are all the same for the stockers. You could send the speedo to one of the better speedo shops, No Ho Speedo or Palo Alto speedo, giving them your specifics, and they'll calibrate it for the conditions you describe. Gear ratios, BTW, have no bearing on the speedo. BTDT, The Cap'n |
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| ArtechnikA |
Oct 25 2005, 08:20 AM
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#8
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rich herzog Group: Members Posts: 7,390 Joined: 4-April 03 From: Salted Roads, PA Member No.: 513 Region Association: None |
the ratios have been documented here many times but here is a listing of all the ratios and all the designations.
enjoy. Attached thumbnail(s) 
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| rcarpen22 |
Oct 25 2005, 11:43 AM
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#9
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Member Group: Members Posts: 52 Joined: 16-September 05 From: DC Member No.: 4,805 Region Association: MidAtlantic Region |
Artechnika, thanks, that's exactly what I needed. Krusty, I realize that the gears have nothing to do with the speedo. I'm trying to figure out my actual top speed at redline in 5th. I can take that, along with my indicated speed at the same point and plot them. The error in my indicated speed increases linearly as speed increases. I can plot a curve and fit an equation that will tell me how fast I'm really going at any indicated speed. It's a cheap way to tell my speed until I get around to having the speedo calibrated. Thanks for the replies.
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| ArtechnikA |
Oct 25 2005, 11:47 AM
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#10
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rich herzog Group: Members Posts: 7,390 Joined: 4-April 03 From: Salted Roads, PA Member No.: 513 Region Association: None |
you're welcome.
that chart comes from Bruce Anderson's "911 Performance Handbook" which - if you have a 6 - you really should have... |
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| rcarpen22 |
Oct 25 2005, 12:48 PM
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#11
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Member Group: Members Posts: 52 Joined: 16-September 05 From: DC Member No.: 4,805 Region Association: MidAtlantic Region |
I will look into that. I'm completely new to the air-cooled world. I have always wanted a 914-6 but never could afford one until I got out of school and put a few years behind me. I've gotten pretty good at 944 turbos but I have alot to learn about the ac sixes. Thanks again |
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