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New alternater tach Question??rpm??

Old Oct 9, 2006 | 07:56 PM
  #1  
pred's Avatar
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From: Philly PA
New alternater tach Question??rpm??

I think that i have the new tach dialed in just right, or nearly just right, I just want to double check.
Someone here with a 5 sp getrag, with a 3;55 rear and still running 235-85-16 tires,
What is your rpm at 70 mph in 5 th
And 40 mph in 4 th
I havent been to 70 yet, but at 40 mph, i am at 2k rpm in 4th
does all this sound right????
I looked at the gear caculators, and i must be some kind of ???????????
Mabey i was doing something wrong, But i couldn't get it to make sense to me, Yet it took me 45 min to do the tach mount and install,
Some things i am good at,, well others, not so good
Thank you all for your help and referance!
Peter.
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Old Oct 9, 2006 | 08:38 PM
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From: Charlotte
what did you use for tire size...assuming you had to convert to inches (which is what most of the calculators I found use)...


I have the figures for mine...but I have 215/85R16...

Greg
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Old Oct 9, 2006 | 08:42 PM
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From: Charlotte
this one was kind of neat:

http://www.car-videos.net/tools/spee...B1=Recalculate

Greg
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Old Oct 9, 2006 | 08:47 PM
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From: Charlotte
Originally Posted by pred
I think that i have the new tach dialed in just right, or nearly just right, I just want to double check.
Someone here with a 5 sp getrag, with a 3;55 rear and still running 235-85-16 tires,
What is your rpm at 70 mph in 5 th
And 40 mph in 4 th
I havent been to 70 yet, but at 40 mph, i am at 2k rpm in 4th
does all this sound right????
I looked at the gear caculators, and i must be some kind of ???????????
Mabey i was doing something wrong, But i couldn't get it to make sense to me, Yet it took me 45 min to do the tach mount and install,
Some things i am good at,, well others, not so good
Thank you all for your help and referance!
Peter.

best I can calculate...you should be ~1500RPM in 4th @ 40MPH...

the best way to do it is set the tach at the highest speed you can...and as you drop back down it'll be more accurate...

I set mine at 70MPH in 5th...

Greg
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Old Oct 9, 2006 | 09:23 PM
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From: Charlotte
I'm going to bed...but figured I'd post these up for you...

using 235x85R16...your tire height should be 31.7...

chart will be your RPMs:

MPH = ...20.......30.......40.......50.......60.......70
3rd.......1204...1806....2408....3010............. ......
4th.......752.....1129...1505....1881.....2257.... 2634
5th..................869....1159....1448....1738.. ..2028


Hope that helps...

Greg
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Old Oct 10, 2006 | 05:31 AM
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From: Philly PA
Great ! ! ! !!
Thank you,,, I use 32" as a 235-85-16
Thank you for your time!
Peter
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Old Oct 10, 2006 | 07:04 AM
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From: Charlotte
Originally Posted by pred
Great ! ! ! !!
Thank you,,, I use 32" as a 235-85-16
Thank you for your time!
Peter

it works out to 31.7"...and it's actually probably smaller if you measure it...

either way, you must've done some calculating wrong somewhere...because it wouldn't have been off from 2000RPM to 1500RPM due to that small amount...

I'd use the 70MPH in 5th or 60MPH in 4th numbers to set it...then as you slow back down, check to see how accurate the lower speeds/gears are...I had really good success doing it that way on mine...

good luck!!
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