Engine H/P Ratings Question

[KBEAT]

I have a few Cub Cadets and Wheel Horse garden tractors with Kohler Command engines that vary from 16HP to 22HP. My question is Kohler & Briggs will make an engine that is 624cc's and sell it as a 16, 18 & 20HP. If I look up the parts lists the heads, carbs, valves are all the same. What do they change on the engines to reduce or increase the HP rating with a common displacement ? I was looking at a lawn tractor that has a Vanguard 12.5HP engine with the same displacement as the 16HP version, that's a pretty wide range with no differences I can find.

 

[sld]

I have a few Cub Cadets and Wheel Horse garden tractors with Kohler Command engines that vary from 16HP to 22HP. My question is Kohler & Briggs will make an engine that is 624cc's and sell it as a 16, 18 & 20HP. If I look up the parts lists the heads, carbs, valves are all the same. What do they change on the engines to reduce or increase the HP rating with a common displacement ? I was looking at a lawn tractor that has a Vanguard 12.5HP engine with the same displacement as the 16HP version, that's a pretty wide range with no differences I can find.

Good question. I have wondered the same thing about outboard engines and it usually boils down to fuel delivery.

On the mower engines, maybe carb jet size? Max RPM differences? Exhaust size?

 

[PoorPlowboy]

In my experience the only difference was the carburetor and/or jetting, maybe a little timing with an offset flywheel key. Many years ago my first run-in with this was a 22" push mower with a 3.5 Briggs and a bad carb. The closest I could find was one speced for a 5 HP. It worked like a charm and was stronger than ever. It never bogged in thick weeds again.

 

[KBEAT]

That's what I was thinking, just not sure. I have the service manuals for Briggs and Kohler engines and everything I can find is the same. Rpm's are the same, valves, heads, main jets were common on the ones I looked at. You know there has to be something, just not sure what it is.

 

[V1Rotate]

How about a different camshaft profile or maybe higher compression?

 

[Raw Dodge]

I too find this very aggravating...i think it's a numbers game in most cases where we are being mislead by the numbers...I have several kohler commands ,vanguards and Hondas. I have a 14 and 16 hp vanguard that are both 480cc and everything is the same pn except the carburetor.I have an 18hp command that's the same exact engine as my 22 command,same displacement and compression,the governor gear is different,not sure if that affects the way the governor handles the power in 3200-3700 range because that's where the differences are according to kohlers website.
I find it funny that several manufacturers and retailers have stated that they will be rating engines by displacement and have revamped their system of power ratings they go on to make a big deal about being honest about the Power and displacement... After all that they sell engines that are rated by displacement , the name of the engine has a displacement and it that
Number is incorrect! So they are still lying it's just now it's a blatant out right lie you can see on paper. If you don't believe me grab a northern tool catalog and look at the Honda GXV series, the vtwins. It seems like they really only have one engine that they are using different numbers for it in order to make it look like it covered a broad range of power requirements with it... The Honda GX630/660 and 690 series all are the same exact engine even though they are lying about the displacement look closely at the bore and stroke they're all the same 3.1x2.8". So it's the same game different numbers but now we can pin them down,before it was to hard to prove they weren't giving you the power you paid for..even horsepower is variable due to conditions,and there continuous ,intermittent,and peak ratings...all add confusion to those who don't know how to differentiate them..

 

[OldBuzzard1945]

There was a big class action lawsuit that was settled in 2010 about horsepower ratings.

Basically they have changed the way that they rate Hp.

Now what you see is the CALCULATED THEORETICAL maximum Hp. with everything taken off the engine except for what is absolutely needed for it to run.

During the time covered by the lawsuit, there was one engine that was rated from 3.5 to 8 Hp. The exact same engine but rated for different mowers.

Part of the problem is that it's the engine mfg. that make the 'standards' for how to rate Hp. It's kind of like the fox guarding the henhouse.

Personally I think that engine Hp. should be determined by running them on a dyno with all accessories that the mower comes with as standard equipment.

Even better would be something like the NEBRASKA TEST that is used for farm tractors where actual tractors are used by an independent tester.

 

[DarkBlack]

Different methods, here are 2 real examples:

Mercury/Mariner outboard 15HP and 9.9HP( under 10hp pond restriction). Difference- 9.9 removable restrictor behind carb.
MTD snowblower models with 9 and 11 HP techumsuh engines. Difference: None- 9HP had governor adjusted 400rpm slower.

 

[RandyT]

After the HP lawsuit it is now required to be a change on the engine. Could be different carb jetting, different camshaft, different ignition timing. for the guy that posted the 18,20,22 command. The difference between the 18 and 20 is a throttle limiter screw in the carb, that only allows the throttle to open half way, Dealers like to joke about the $130 screw because that is what the price difference between the engine was when it came out. the different between the 20 and 22 is that spark advance is used on the 22, so different ignition modules.

 

[djdicetn]

I was of the understanding, that with the mandated hp rating changes for small engines , the way to differentiate between the "power" of engines with the same cc displacement was to look at their torque output rating. The higher the torque, the more powerful the engine(and relatively, in a mower more "cutting power"....aka blade tip speed and less resistance to the grass blades causing the engine to bog down). Of course, I believe BTS(rated in fpm or feet per minute) is also associated with rpm, so I'm not certain how that figures into the engine's "power". And further, I have no idea(technology wise) what changes between engines with different torque ratings(or rpm's/BTS achieved) that have the same displacement:0(
Maybe someone with more knowledge of small engine technology can elude to these statistics.