[AT] Horsepower Question

[Will Powell]

RPM is a main factor.. 

I recall Allis Chalmers increased their hp from 18 to 20 with the same engine by increasing the RPM by 10%. 

Also I believe that HP on the tractors is measured at the PTO and at the tow bar. Of course the PTO hp is usually the higher value. I believe the mowers measure HP right at the crankshaft, so the playing field is not always equal... 

A calculation I found on the net: HP = Torque x Engine Speed) / 5252 

So, lets say a one Cylinder engine the Torque is constant at 71.5 then running at 1500 rpm 

HP = 71.5 x1500/5252 
HP = 20hp (rounded) 

Now, double the speed to 3000 rpm 

HP = 71.5x3000/5252 
HP = 40hp (rounded) 

Double your speed, double your HP. 

Two Equal Cylinders running twice as fast as Four cylinders should be equal... 

I'm sure someone has a more scientific answer, but I think I'm close. 

Regards, 

Will 


I recall that measurement of the mower 
----- Original Message ----- 
From: "Ben Wagner" <supera1948 at gmail.com> 
To: "At" <at at lists.antique-tractor.com> 
Sent: Wednesday, October 6, 2010 9:00:13 AM 
Subject: [AT] Horsepower Question 

Here is a puzzler that maybe someone with a better knowledge of 
engines can answer. I was asked this question, and had to announce 
that I needed to look it up. What better place than the AT Mailing? 

I have a Super A with four cylinders, producing c. 20 HP. 

I have a lawnmower, with an engine that says it is also 20 HP, with only 
two cylinders. 

What is going on? Is this two different measures of HP? Or has 
technology improved that much? What makes a little two cylinder "small 
engine" have the same HP as four cylinder "tractor" engine. 

Thanks, 
Ben Wagner 


_______________________________________________ 
AT mailing list 
http://www.antique-tractor.com/mailman/listinfo/at