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#1




85 MPH at 3500 rpm?
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1984 MB 300D Turbo Diesel W123 Sedan 132K 1987 MB 300D Turbo W124 Sedan 295K 1983 Porsche 944 104K 1989 Audi 80 Quattro 180K 2002 Audi A6 3.0 Quattro Avant 49K (Wife's car with warranty ) 
#2




Me again, but this time, my info may not apply.
My M103 motor does 70mph at 3400rpm, but my 126 weighs alot more than the 124. It's possible that at the same rpm, a 124 car would have greater ground speed? Perhaps one of the 124 members will provide a better answer than mine. 
#3




If you want it Exact, take the ratio # of the differential and do the math [ using rolling circumference...]
RC is easily found by checking for proper air pressure and then mark the tire with the ground and push car one wheel revolution,  Measure ground distance covered.. This eliminates guessing on tire circumference and is accurate for each individual car/tire set up.. More accurate , of course, for stand trans [ no OD] vs auto/torque conv. 
#4




260E axle ratio = 3.27:1 (300E is 3.07:1)
195/65R15 tires = 837 revs per mile Speed at 60 (1:1 top gear assuming no torque converter slippage): 3.27 x 837 = 2737 Any other revs at speed can be determined by linear proportioning, e.g. at 85 MPH: 2737(85/60) = 3877 Speed per thousand RPM = 60/2.737 = 21.92 The speed/rev relationship is established by speedometer gearing and speedo head calibration and is independent of actual installed tire revs per mile or installed axle ratio. An axle ratio change or installation of tires with different revs per mile will affect speedometer accuracy, but not the speed/rev relationship. Duke 
#5




The speed/rev relationship doesn't change.. the Actual ground speed does..
So, if one were check speed accuracy , tach rpm can be used . Knowing ratio and tire size tells one what RPM will produce Actual speed.. I drive 2 of my Vintage cars and monitor speed via tack [ per 1000 rpm] as one has had diff. gear change and the other is Km only...just by habit.. 
#6




IZELJIC, the simplest way to check the accuracy of your speedometer (which I take to be at least part of your basic question) involves a stopwatch (cheap at Radio Shack) and a freeway with mile markers at a lowtraffic time. Ideally, pick a stretch that's fairly straight and flat. Time yourself over two or three miles at a steady speed and do the math. Arithmetically convenient speeds are 60, 72 and 75 but any speed you can maintain consistently will do. For the most precise results, do several runs at different spots and take the average.
As a point of reference, my 560SL turns 2110RPM at 60 mph, according to the Road & Track test of the model in 1989. My speedo incidentally is spoton at 80, both by stopwatch and GPS; most of my other cars have indicated anything from 77 to 81 at a true 75. Useful to know when maximizing time efficiency while minimizing ticket risk.
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Craig Bethune '97 SL500, 40th anniversary edition '04 Olds Bravada (SWMBO's) '06 Lexus ES330 '89 560SL (sold) SLAnything else is just a Mercedes. (Kudos to whoever said it first) 
#7




my Euro 500 Se is only turning 1800 at 60 , lets see 120 at 3600 , speedo is right on the button so if it would pull 5400 in fourth that would be 180 ,something is wrong here? it has correct size tires,tach seems to function well? Tach must be off.....
William Rogers........ 
#8




Quote:
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Craig Bethune '97 SL500, 40th anniversary edition '04 Olds Bravada (SWMBO's) '06 Lexus ES330 '89 560SL (sold) SLAnything else is just a Mercedes. (Kudos to whoever said it first) 
#9




My 94 E320 is at 90 mph at 3500 RPM. You may be able to use speed displays found at the side of the road to make motorists aware of their speed, or you can have a friend follow and compare the speeds.
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Zafar 94 E320 58000 Miles 
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