IML: Formulas for calculating top speed

["Rob McCall" <Rob_Mopar@xxxxxxxxxxx>]

Boy, I lay low for a while and all the sudden the IML is discussing 200 MPH
runs in a '57.  I was happy a couple weeks ago driving my '67 up the street
at about 35 MPH so I could put it away for the winter.

Here's how to calculate top speed:
- Take the Miles Per Hour (MPH) and convert it to Miles Per Minute
- Take the MPM and convert it to Inches Per Minute (IPM)
- Take your Tire Diameter and multiply it by Pi, then divide it by IPM to
get you Tire RPM
- Take your Tire RPM and multiply it by your rear gear ratio to get your
engine RPM.

Now this method will give you a theoretical number.  It does not take into
consideration torque converter slip.  For a stock converter add about 10-15%
slip to get you a closer estimate.  To calculate that multiply the RPM
calculated above by 1.1 or 1.15.

Note this formula can be used to calculate normal street speed/RPM
combinations too.  (That last statement was reaching for Imperial content
but I know I'm pushing it).  You could also calculate the RPM per gear by
adding a step to multiply 1st & 2nd gear ratios then the rear gear ratio.

So a 30" tall tire with a 2.76 rear gear ratio would require 6800+ RPM to
hit 200 MPH.  I don't know what RPM limit Remco has targeted for his 6-71
blown 392, but if it's around 7200 he'll have the RPM's.  The aerodynamics
will be the hardest obstacle to overcome.  And tires rated to handle both
the weight and speed (possibly Ram SRT 10 or Ford Lightening truck tires?).
I don't have the formulas or data here to estimate the horsepower needed to
push a '57 to those speeds.  Or a way to calculate the rate of acceleration
to determine how much distance he'll need to get the car to reach 200.

This year I took up land speed racing so I have been playing around with
various gear ratios and tire diameters.  No, I did not run in the Imperial,
but the thought did cross my mind.  All of our vintage iron was not in any
state to race so I put my Intrepid (at least it begins with an I right?) up
to the task.  I ran at the East Coast timing Association in October and the
car reached 121 MPH within one mile from a standing start.  

Next year I plan to attend again with a car setup to race.  Again, no it
won't be the Imperial unless I get a great deal on an SRT 10 Ram quad cab
drivetrain (the quad cab comes with the automatic).  And my '67 weighs less
than one of those Viper engined 4-door trucks.

I now turn you back to your regular IML subject matter.

Rob McCall
'67 LeBaron (at least it saw the road this year)
'72 Duster race car (aiming for 200 MPH on a closed course)
'00 Intrepid R/T
And many other Mopars






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