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Easy engine RPM calculator

M

marine_enlisted

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Location
Stafford, VA
I found this while surfing. I'm sure many of you have seen it, but some may find it very useful...I did. Plug in your tire size, gear ratio, tranny type and MPH, and it tells you your engine RPM. /forums/images/graemlins/thumb.gif
 
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I found this while surfing. I'm sure many of you have seen it, but some may find it very useful...I did. Plug in your tire size, gear ratio, tranny type and MPH, and it tells you your engine RPM. /forums/images/graemlins/thumb.gif

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You forgot the link...or was this the psychic calculator? /forums/images/graemlins/grin.gif

Rene
 
That calculator tells me that with my 33's and 4.10's and 55mph I'm running 2357 rpm's and I know that is WAY off, its more like 2900rpm's
 
55 mph, 4.10's and 33's with a non lock-up automatic would be 2425 rpm at 55 mph. Time to get a better tach...

mph x final drive ratio x 355 (for non lock-auto) / tire diameter.

55 x 4.10 x 355 / 33= 2425 rpm

with a lock-up tranny or a manual tranny you'd use 336 instead of 355.

Rene
 
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I agree with muddytazz it is off oh well ...Jason

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It's right on the money...at least for a manual tranny without OD.

Rene
 
Come down and drive my burb, with the TH350 and fulltime 203 its running HIGH rpm's....you can tell its higher than 2500 rpm's
 
Are you claiming your ear is more accurate than math or a proper tach? /forums/images/graemlins/thinking.gif

Rene
 
I'm not arguing with ya Rene, but with a damn near brand new tach that at 55mph, it definitely sounds like it needs to shift again because of the high sounding rpm's.
 
I'm sure there are gonna be a few variables that this thing won't compensate for. As you know tire hieghts vary greatly due to wheel width, wear, and manufacturers rounding to the nearest larger size. Also, the final drive ratio is not going to be the same for every vehicle.
 
I check my tach using the math, not the other way around. I drove for 4 years with only a tach and no speedo. Using the math I could tell you with 3-4 mph of my true speed. I went through quite a few speed traps without ever getting nailed. In Oregon of all places I've seen the un-manned radar trailers and my speed versus rpm was always very very close to the math. The math works...unless your tranny is slipping badly.

For true tire diameter measure the circumference and divide by pi.

At 2500 rpm or so it should sound like it needs to shift again.

Rene
 
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Here is the best one I have ever seen:

Florida 4x4

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/forums/images/graemlins/waytogo.gif /forums/images/graemlins/peace.gif
 
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Here is the best one I have ever seen:

Florida 4x4

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If that one I right I normaly going about 80 down the high way. /forums/images/graemlins/yikes.gif /forums/images/graemlins/doah.gif /forums/images/graemlins/whistling.gif
 
[ QUOTE ]
I found this while surfing. I'm sure many of you have seen it, but some may find it very useful...I did. Plug in your tire size, gear ratio, tranny type and MPH, and it tells you your engine RPM. /forums/images/graemlins/thumb.gif

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Looks JUST LIKE randy's that is in the links at the top.
http://www.ring-pinion.com/calculators/calculatorsind.html
Wonder who stole from who?
 
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