Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

I have a 15 year old Ariens . ST 924. It came with a 8 hp Techumseh. I'm planning to retiring the engine .  Which is better  a Subaru Robin sx30  with 9.5 hp 4000 rpm max , a Honda GX 390. or a 305 Briggs?  The Subaru does not give me as much  HP as the Honda, but I get more rpm. If i put Clarences kit on my unit then is will be even better. The Briggs is the cheapest , but I do not really know its power output They only tell me 305 cc and 13.5 lbs of torque. My Techunseh is a 318 cc so I guess the 305 Briggs is close to 8 HP. I prefer 12 volt electric start. The biggest Briggs is there 342 16.5 I was considering that one too.

I believe that the Briggs engines are an excellent choice.  The 305 with 14.5 torque  for blowers up to 27 inches.

and the 342 with 16.5 torque  for blowers over 27 inches.     I am referring to the engines built in the USA  and they are stamped  as built in the USA.

But it seems that the 305 and  342  engines (and other sizes) labelled "Polar Force engines By Briggs "  are  manufactured in China.

If anyone has other information on these Polar Force  engines., please reply.   Thankyou

Well, there's the formula most of us know about:

Horsepower = torque (in ft-lbs.) x rpm (typically 3600)
                                                5252

Thus, if you have a 305cc engine with a 14.50 torque figure, it comes out:         HP = 14.5 x 3600   =   9.94
                                                                                                                                             5252

The 5252 is a real figure, not just something made up to make us happy:       http://www.epi-eng.com/piston_engine_technology/power_and_torque.htm

See the end section of the article entitled "Derivation of the Power Equation (for anyone interested)".  It explains how the number 5252 is arrived at.  Very interesting.


Rearranging the formula gives us :

Torque = Horsepower x 5252
                rpm (typically 3600)

So, if you have an engine like the 10HP Tecumseh 358cc on my El Toro! 1028LXE, it looks like this:     Torque = 10.0 x 5252   =   14.58
                                                                                                                                                                                          3600

Do these figures seem good, realistic?  I think so.   The only thing I'm not sure about is that I've read that torque is supposedly measured at 3060rpm instead of 3600rpm.  Assuming that's the case, then how could we plug in a torque figure based on 3060rpm into a formula assuming 3600rpm, and expect a decent result?  That would change the above horsepower formula to a higher final result, assuming the torque keeps climbing all the way to 3600rpm.  Doesn't it peak out before that on these engines?   The torque formula is based on 3600 since we didn't start with a torque figure to begin with, so my result of 14.58 ft-lbs for my Tecumseh engine is based on the horsepower figure and 3600rpm.  And we assume horsepower is calculated on 3600rpm, anyway, so that 14.58 torque number seems to be right.  Also, assuming that a 358cc L-Head is equal in torque/horsepower to a 305cc OHV, that 14.58 is mighty close to the 14.50 figure we get from today's Briggs 305cc engines.  After all, the Briggs 305cc replaced the Tecumseh 358cc on the Toro 1028 (LXE going to OXE).  I hope I'm not losing anyone on this.  I find it interesting.

Here is an 11 HP Honda GX 340
Peak HP at 3600 RPM, Peak Torque at ~2400 RPM.
Most engines have similar torque curves.

coasteray wrote:
Careful.  HP is a function of RPM and torque at that RPM.  And peak torque and peak HP rarely, if ever occur at the same RPM.  Many times the peak torque occurs well below 3600 RPM.  See the example chart above.  I don't know what constraints manufacturers are under when reporting torque.  Probably, they can report peak torque at whatever RPM it occurs.

So, as you essentially state, it is key that you know at what RPM your torque value occurs.  Then you can calculate the HP at that RPM, but not necessarily peak HP.  If you know that your 14.5 torque is at 3060, then your HP is 8.44 at 3060.  Peak HP may be higher at 3600 RPM.  You appear to come to the same conclusion.

Honda Engines come with sediment cupsfuel shutoff, a throttle (most new machines no longer have a throttle the way your 15 year old machine did, and the B&S engine is probably made in China by coolies.

manjestic wrote:
That just does not seem right. torque with out HP behind it is useless . My 1" 1800 ft lb impact wrench has more torque than my wifes 2.3 engine in her car. If torque was the only factor then i could power my wifes car with my torque wrench. I DON'T THINK SO

bus708 wrote:
Measure your impact wrench's RPM under load.  Then we'll talk. 

I get 20 rpm full load   1800 x 20/ 5252= 6.8 hp    at 1 rpm stall speed i get  .34  hp which is nothing

bus708 wrote: You say your wrench is rated at 1800 ft. lbs. -- but at what RPM? You have to know the rated torque at RPM to determine HP. I suspect that 1800 is stall speed torque.
HP doesn't drive torque, it's the other way around.

BTW, 1/3 HP isn't nothing, look at the rating of the motor in your drill press. Nothing compared to an auto engine, yes.

http://en.wikipedia.org/wiki/Horsepower#Relationship_with_torque

  Referring to cars, Dan Gurney  said :  "   If 200 horsepower was good and 300 horsepower was too much, then 400 horsepower would be about right. "

My   Chrysler  300c  SRT8 is rated at 425  horsepower and it is about right.