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Author Topic: Peerless 820 Transaxle: Torque vs Gearset Upgrade Computation  (Read 529 times)
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RoMow
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« on: April 13, 2014, 12:29:16 PM »

Heymowers,

   I have been asked about whether changing to one of my Final-Drive Gearset Upgrades will increase or decrease torque with an 820 transaxle.  Well, let's see...  For purposes of computation, this Post will use a 20hp engine driving the transaxle with a 1:1 pulley setup (the engine pulley and transaxle input pulley are the same size) at the engine’s top governed no-load speed of 3600 RPM.  For simplicity, we will also use the 1:1 (25T:25T) gear-selector ratio, which is normally 3rd or 4th gear in most 5- and 6-speed 820s.

   The stock input ratio is 2.54:1.  The stock final-drive ratio is 8.02:1.  With the 1:1 gear-selector ratio, this gives a 20.37:1 reduction ratio, meaning that at 3600 Input RPM, the axles are turning 20.37 times slower, or 177 RPM.
   Gearset Upgrade 1 changes the 8.02:1 stock final-drive ratio to 5.61:1, meaning that the axles are turning at 253 RPM.
   Gearset Upgrade 2 changes the 8.02:1 stock final-drive ratio to 3.44:1, meaning that the axles are turning at 412 RPM.

   To convert these RPM figures to Torque, we will need to use the standard scientific formula Torque = (HP x 5252) ÷ RPM.

   With the stock final drive, this gives us 20 x 5252, or 105040, ÷ 177, which equals 593 units of axle torque.
   With Gearset Upgrade 1, we have 105040 (the same 20hp and 5252 formula constant, multiplied) ÷ 253.  This gives us 415 units of axle torque, a 30% decrease, or 70% of stock axle torque. 
   With Gearset Upgrade 2, 105040 ÷ 412 gives us 255 units of axle torque, a 57% decrease, or 43% of the stock axle torque.

   So, even though the Gearset Upgrades give us increased axle speeds, we have less torque available.

   If you know your engine horsepower and RPM, you can use your pulley sizes and the above formula to compute torque for any of your gear ratios.

   And, for those fortunate enough to be running the "017 Kit" with a 2.31:1 Final Drive Ratio, your axle is turning at 613 RPM, with a corresponding torque value of 171 units, 29% of stock torque (a 71% decrease).

   I hope this helps.

Respectfully; Rodney Rom; Rom's Reworks; Butler, MO
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berthyd
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« Reply #1 on: April 13, 2014, 05:09:36 PM »

Rodney, you better check your math. There is not a 71% loss of torque. There maybe a 20% parasitic loss if you are not over driving the spur gears. And that is the key to a good 820, 700 350 etc.

What you are saying is that my 55hp+, 60 foot pounds is coming out the rear at 16hp and 17.4 pounds of torque. Ahhh, I don't think so. That won't get you 73mph on a fifth mile track.

Garbage in, garbage out, as they say.

Bert
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« Reply #2 on: April 13, 2014, 05:52:36 PM »

Bert,

   I was only trying to answer a question using the standard accepted scientific formula for computing Torque using known Horsepower and RPM.  I questioned the results, as well, but thought I'd go ahead and offer them as mathematical calculations.
   Suggestions?  Is this formula not acceptable for our needs?

   What about your RPM?

Rodney
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heymow.com - Lawn Mower Racing Forum
« Reply #2 on: April 13, 2014, 05:52:36 PM »

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« Reply #3 on: April 14, 2014, 06:46:45 PM »

Rodney, yes I have RPM. Now, onto other things..

Each HP lost in the transaxle for whatever reason would create 42.4 BTU/minute. Now, figuring an average feature race in Wisconsin lasts a little under 4 minutes (we don't have yellow flags, kids) and I am losing 40 HP through the transaxle, I am putting 6800 BTU into my trans axle. If those numbers are right, I'd be melting a transaxle housing pretty much every race.

Bert
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RoMow
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« Reply #4 on: April 15, 2014, 09:51:19 AM »

Bert,

   You have to have RPM or you wouldn't have any torque.  I was wondering at what RPM you are developing your 55+hp and 60 foot-pounds.

   And...this formula is calculating torque and, for the different RPMs, torque loss.  It is not calculating horsepower loss, so your 6800 BTU heat creation is probably not accurate.  Your 55+hp is likely what's giving you your 73mph.

   Any physics professors out there who can tell us why these results aren't making sense?

Rodney 
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« Reply #5 on: April 15, 2014, 11:17:42 AM »

As the driver of the aforementioned machine, I can verify that there is RPM present at the time of said thermal event.

The BTU calculation was sourced from the 1996 edition of the Fluid Power Handbook, Womack Publishing, Dallas Tx.

According to my finely tuned posterior dynamometer (and, yes it is fine. Thanks for asking) The horsepower and torque levels are good during the presence of RPM.

And, for the record, I only stayed at a Holiday Inn Express once.
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