Do you have a 4 speed with 3.23 gears? Please check something for me.

Back in the dim time (1972) I bought a new 72 Challenger 340 4B with a 4 Speed transmission and a 3.23 rear end.
I sold it to pay for college, and 37 years later managed to scrap together enough money to buy a 72 Challenger with a 440 6B, and a 4 speed transmission.

Back in the day, I remember having trouble starting out on hills because of that 3.23 rear end, but my high end was takeoff speed (I had it up to 134 mph).

The new car feels like I have 4.55 gears in the rear end (or more).   Based on engine whine/noise I'd swear that the car's top speed is about 80mph.  So I took it to my local mopar specialist to replace the gears.   The first thing he did was to check the rear end, by turning the wheel (not posi-traction) and counting the turns of the drive shaft.  Lo and behold the ratio was 3.23.   Next we checked the transmission.  It was 1:1 in 4th gear.
That had us scratching our heads.   Because he agreed that based on engine noise, and the Tach readings, the rear end should be a 4:10 at least.

We found that the tach is reading way high.   When my tach reads 4000 rpm, it's really at 3100 rpms.   But still the engine whine/noise suggests that the rear end is higher than 3.23.

My mechanic feels it's all perception. It's just real loud, and it's fooling me (and everyone else).  (The previous owner mentioned that there was no way that I could drive this car 1000 miles to get it to my house, as the gearing is wrong for highway driving. So he had the same opinion that I do)

So I have a question.   If you have a 4 speed and 3.23 gears, and normal tires, what rpms are you at at 50 mph?  60 mph?   70 mph?   80 mph?  134?

Your help is appreciated.  

It is all very easy to calculate. Only thing needed to solve the equation is the exact diameter of the rear tires. Here is one easy to use calculator: Speed vs RPM or:


(0.00595) * (RPM * r) / (R1 * R2) = vehicle speed in miles/hour

   where:
          RPM = engine speed, in revolutions/minute
          r = loaded tire radius (wheel center to pavement), in inches
          R1 = transmission gear ratio
          R2 = rear axle ratio  

Tach is probably hooked up as a 6 cyl. that would explain for the high rpm reading. Trans may have a bearing going, reason for the excess noise. Or even a pinion bearing also creates a lot of noise.
Doc  

RPM=MPH X gear ratio X 1056 / tire circumferance. so at 60 mph with a 26" tall tire rpm is 2505. 134 mph is 5596 = awesome = right around a stock 340 peak HP rpm . with not traction lock or sure grip rotating the tire and counting the shaft is not accurate - due to slippage - u maybe have more than 3.23