how fast have you been in your sc???

  • Thread starter kamikaze racing sc
  • Start date
Re: I thought the calculation was...

acros323 said:
Doesn't the top speed calculation go like this:

MPH = (RPM * TireDiameter)/[(TransRatio * AxleRatio) * 336]

For Instance
MPH = (4600RPM * 255)/[(3.27 * 8.8) * 336]
MPH = 1173000/(28.776 * 336)
MPH = 1173000/9668.736
MPH = 121.318

????

Not trying to pick on your calculation Ed (or that you didn't reach 150MPH) but you had all the available information to calculate. Is this calculation accurate or am I missing something? Just curious :)

You have the right formula, but you're plugging in the wrong numbers !! :)

255, or whatever the first number of your tire sizing is, is the section width of the tire in millimetres, not the diameter. You need to calculate the diameter using this formula :

section width X aspect ratio (the 2nd number in the tire sizing) X 2 / 25.4 (converts millimetres to inches) + rim diameter.

So for my example ... ( 255 x .45 x 2 / 25.4 ) + 18 = 27.035" , which is very close to the spec listed in the Goodyear catalogue for my tires, 27.05".

Then, for trans. ratio in 5th gear, that's 0.75, not 3.27. Axle ratio in my case is 3.27, not 8.8, that's the ring gear diameter in inches, which doesn't matter for this calculation.

So if you plug in 4600 x 27.05 / 3.27 x 0.75 x 336 , you will get the 150 mph figure I came up with.


cheers
Ed N.
 
Ed,

Seeing as how it's too late for me to bother with the math...

...just tell me what 6000rpm in MPH would be....so that I know.:D

(as you know, 3.27, 255/45R17, 5spd etc)
 
Re: 150 in a 5 Speed

imbonked said:
The 5 Speed has a 2.73 rather than a 3.27. I am using the calculation from Dr. Fred.

I have 225 60 16s on my car so I used 27.57 for the tire size.

3750 RPM * .002975 (Conversion) *27.57 (Tire Size) / (2.73) Manual Tranny * .75 (Axle Ratio) = 150.22

If this is wrong let me know. I'll be happy to recalc mine. Don't want to be blowing smoke on the board.

Happy Trails

Tim

Tim, 5 speeds are 2.73 ratio stock, I've changed mine to 3.27 for some more oomph up top. Your tire diameter is off a bit, should be 26.63 for 225-60-16 ... SO ... it now comes out to 145.15 mph, which is about what my car would pull when it was pretty much stock with the 2.73 gears.

cheers
Ed N.
 
Bill McNeil said:
Ed,

Seeing as how it's too late for me to bother with the math...

...just tell me what 6000rpm in MPH would be....so that I know.:D

(as you know, 3.27, 255/45R17, 5spd etc)


Bill, if you can pull 6000 in 5th, that would be ...

189.569 mph !!! :eek:
 
Methinks your tach is a bit optimistic Bill. I know your car is making some serious HP, but think about this comparison ... it took the NASCAR guys with slippier versions of the T-Bird bodies a lot more power to go 190 to 200 mph ... like another 200 hp or more ! On my old 5.0 Mustang, the tach read about 600 rpm to high at 6200 rpm ... indicated about 6700 !!

Guess you'll have to find a cop to verify the speed on a radar gun for you while making the run :D


cheers
Ed N.
 
speedo.jpg


Sorry it's so blurry, but you get the idea
Notice it's still pulling 10lbs of boost....I still had my foot in it when I snapped that
 
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