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Post Info TOPIC: 60 MPH 2800 RPM


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60 MPH 2800 RPM
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i took  my  Beaumont   for  a ride  this  weekend  ( i drove barely   100 miles  since  last spring )  i tried  it  on the  highway  after  installing my  tach  and  my  rpm  was  2800  a 60  mph   could any one  give me  a clue  what gear  i would  have   in my  diff   ( 67 Beau  283   )



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1967  Beaumont 2 door post  3 options 283     V 8  P G   AM radio

1965  Chev Bel Air 4 door  230  3 on the  tree,  very basic

 



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Could be 3:08, mine is.

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1965 Biscayne: 350, PG, 12-Bolt. PS, PB.

1970 Chevelle Malibu: 53 on 753.

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Tire size ?



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205 70 14

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1967  Beaumont 2 door post  3 options 283     V 8  P G   AM radio

1965  Chev Bel Air 4 door  230  3 on the  tree,  very basic

 



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Your tire diameter is 25.30"

Stole this formula from another forum

Here are simplified formulae for calculating RPM vs road speed (the "336" is a factor that allows the use of the tire diameter rather than its circumference):

MPH = (RPM x Tire height) ÷ (Final drive ratio x 336)

RPM = (MPH x Final drive ratio x 336) ÷ Tire height



-- Edited by wauto on Sunday 1st of November 2015 09:54:24 PM

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If my math is right, your running 3.55 gears



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Correct

Dan

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Ok smart people. 25" tall tire 3000-3200 rpm @70mph. Let's see if the formula works. I know what my gears were and the speedo was dead on as I got speeding ticket for going 70 in a 60 and my friend's car was all stock and the speed matched driving beside each other. And anther one...255/60x15 tire 80 mph 4200 rpm.I'm guessing at the speed here as speedo not working but that strectch of highway everyone averages about 80mph. 40 mph is 2000-2200 as checked by friend driving beside me with a working correct speedo.

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First one is 3.23, second one should be 4.10 or close to that. I used an online calculator versus the formula. I used to have an excel spreadsheet formula that calculated it, but I can't find it now.

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I came up with 3.31 and 4.10

Dan

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Dan wins!The 3.31s are in my avatar and 4.10s are what is in my chevelle. Here's one more...I can get the diff from the guy he says it's 4.56 or 4.88 . He is not willing to open it up at the moment. Car is sitting on the ground with no wheels and the the drums are seized. If I want it he will pull it out. He said it revved at 3800 @ 50mph with 27" tall tires. He can't remember which gears are in it but he said they are not 4.10. 



-- Edited by bigbowtielover on Tuesday 3rd of November 2015 10:13:01 PM

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Need more info than that......at best this is a coin toss at this point.

Are you saying that the rear end is a factory 4.56 or factory 4.88? If so, get the code off the rear end....that will tell you. Plus it's just good to know the code regardless.....just incase it is something really valuable

Dan

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WAS a 4.10 when he got it but he changed the gears. Originally a 3.31 posi '69 chevelle. I want the 4.56 if that's what is in it. I already have a set of 4.88s. He said when he last drove it over 25 years ago it would turn 3800-4000 @ 50-55 with L60x15 tires.27" tall. 3500 stall converter also made driving around on the street a bit tricky but lots of fun.

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Either his memory is foggy or he has much deeper than 4.88s in it. 4.56 with 27" tire is 3205 RPM at 55. 4.88 is 3430. That is auto trans but does not allow for a real loose converter. Best thing to do is pull the rear cover. I used this calculator to calculate it: www.ringpinion.com/Calculators/Calc_RPM.aspx

Here's another one that's easy to use: http://www.summitracing.com/expertadviceandnews/calcsandtools/gear-ratio-calculator



-- Edited by Pat Dilling on Wednesday 4th of November 2015 10:32:59 AM

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He had a B&M 10" super holeshot 3500 stall converter in it behind an LS7 454.

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