OT. Figuring Horsepower of an engine.

Anonymous-0 · Aug 16, 2010

I have an old Briggs-Stratton engine. It has a bore of 2.25" and a stroke of 2.25", Is there a formula that you can get the HP with these numbers. I would guess it would work for any engine, except you would have to multiply by the number of cylinders.

RN · Aug 16, 2010

Old Brigges- as in flathead turning 1800 rpm for power ? or 2400 rpm? or 3200, 3600? type code would be handy as 1st couple digit is dispacement. So about a 8 or 9 cubic inch engine- newest would be maybe a 5hp engine, slightly earlier with 3000 rpm governor a 4 horse, earlier 2000 rpm a 2, 2.5, horsepower. Old SAE taxable formula give a horsepower based only on bore and number of cylinders- at about 800/1200 rpm it is close

Dean · Aug 16, 2010

One does not "figure" the HP of an engine but rather measures it.

That said, I would expect that your engine was rated at somewhere around 2 1/2 - 3 HP at around 3200 RPM.

Dean

Old Roy · Aug 16, 2010

do you have the engine shroud and the numbers off it I may be to give you that info

Anonymous-0 · Aug 16, 2010

This engine was made in March 1938. It's a Model H, The type # 60648 and the serial #21535. I got the year it was made from data from Briggs but the other data from the type or the serial number don't seem to work out.I have just got the engine running today and was wandering what HP it is.

JDemaris · Aug 16, 2010

Sounds like you've got an old cast-iron Model 9 or something close? Newer Briggs tend to have big bore and short stroke to allow higher RPMs. Your engine is "square" with equal bore and stroke and made to run slower.

Briggs model 9 is 2.25" bore by 2.25" stroke and has 8.95 cubic inch displacement. Runs a max of 3200 RPM. It was rated around 2.6 horsepower because it ran slow. Made a max torque of 5.3 pound-feet at 2700 RPM. Has a compression ratio of 5.3 to 1. An engine's horsepower output is pretty much determined by how many explosions it can make, i.e. RPM. Also how high a compression-ratio it can run. Double the RPMs and you can double the horsepower (up to a point).

A later Briggs engine, like the model 92500 is also 9 cubic inches but rated 3.5 horsepower at 3600 RPM. Has 2 9/16" bore by a short 1 3/4" stroke. Has the higher RPM, shorter stroke, and higher compression ratio of 6 to 1. Max torque is only 5.2 pound feet though . . . lower then the lower horsepower model 9.

Anonymous-0 · Aug 16, 2010

I got the model number off the tag on this engine and it's a Model H. Thanks for the comeback guys.

JDemaris · Aug 16, 2010

Model H is the predecessor of the model 9 and runs slower. Thus it's rated less horsepower. Model H is governed to a max of 2100 RPM. The later model 9 was governed to a max of 3200 RPM.

KEB1 · Aug 16, 2010

The model H was rated at 1/2 horse. See more info at the Antique Small Engine Collectors Club website

Keith
poke here

OT. Figuring Horsepower of an engine.

Anonymous-0

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RN

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Dean

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Old Roy

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Anonymous-0

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JDemaris

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Anonymous-0

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