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
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
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.
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.
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
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.
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
I'm saying 3:08's as my Chief ran the same RPM at the same speed with my BBC 4 speed. That's where my maximum torque curve was @ 480 ft/lbs. Pulled so hard!!!!
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