need help speedometer vs rpm
08-04-2006, 10:06 PM
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need help speedometer vs rpm
Hi , i'm new to 911's and i have a special problem , i bought a 1970 911 on ebay (2.2 liter 2 carbs) and i must drive it back home a long long way and the speedometer is dead , it has a 5 speed tranny , what i need to know , because i can't have it fixed before the trip , approximately what is the rpm on which gear for 35mph , 50mph and 60mph .
I know it sounds a bit silly but i'm short on time to go get it and it's the only way i figured out to bring it back without hearing a siren or having me honked .
Thank's for anyhelp
I know it sounds a bit silly but i'm short on time to go get it and it's the only way i figured out to bring it back without hearing a siren or having me honked .
Thank's for anyhelp
08-04-2006, 10:14 PM
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08-05-2006, 07:53 AM
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The following data applies to a 1970 911 5-Speed. I tried to paste in the plot, but was unable to do it.
RPM MPH
1st 2nd 3rd 4th 5th
1000 5.5 9.5 13 18 21.5
6500 35 61.5 90 118 139
Just draw straight lines on the RPM Vs. Speed plot.
Al
The following data applies to a 1970 911 5-Speed. I tried to paste in the plot, but was unable to do it.
RPM MPH
1st 2nd 3rd 4th 5th
1000 5.5 9.5 13 18 21.5
6500 35 61.5 90 118 139
Just draw straight lines on the RPM Vs. Speed plot.
Al
08-05-2006, 04:44 PM
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Thank you guys but you are too precise for me , or i did'nt get it ....
To be sure you understand what i need to know , by the way i don't have the gear ratio , if you're in 2nd gear and you go 35mph what is the rpm ? and in 3rd at 50mph ? and in 4th at 60mph ? and in 5th at 60mph ?
Thank's again , i desperately need these infos , i take a flight tomorrow morning to bring back that car.
To be sure you understand what i need to know , by the way i don't have the gear ratio , if you're in 2nd gear and you go 35mph what is the rpm ? and in 3rd at 50mph ? and in 4th at 60mph ? and in 5th at 60mph ?
Thank's again , i desperately need these infos , i take a flight tomorrow morning to bring back that car.
08-05-2006, 05:10 PM
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I don't have the data on the '70 model, however, as a rough guide, take the rpm in 100s in 5th gear & double it to get an approx. of speed. ie: 3000 rpm yields 30 x 2 = 60mph. to get an idea just how close, drive at a steady rpm (in 5th) that yields 60 sec per mi on a flat interstate (use the nifty mile markers & avg over 10 miles). that will give you a precise rpm / speed equivalent. another rough approach... staying between 3&4K rpm, 2nd gear in residential areas, 3rd in city on four lanes w/ traffic signals, 4th on divided 4 lanes, & 5th on limited access highways should keep you out of trouble.
you can do similar calculations in your head for 3rd & 4th as you drive the interstates - it will keep you awake & mentally occupied for quite some time as you start the trip. enjoy!
you can do similar calculations in your head for 3rd & 4th as you drive the interstates - it will keep you awake & mentally occupied for quite some time as you start the trip. enjoy!
08-05-2006, 05:24 PM
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I plugged in what figures I could find on gear ratios for 1970 (could be wrong though. And I didn't know your tire size so I stuck in 60-16. Here's what that charts says:
