did horsepower ratings change?

I have an old Allis-Chalmers b10 garden tractor with a 9hp briggs & stratton cast iron engine. I was looking at replacing it with a new briggs vanguard engine...maybe 16hp or so. When I compare the engine specs, my old one has a 3.5 inch bore and a 3.2inch stroke, where the new 16 hp has a 3 inch bore and 2.6inch stroke.
I know that is it overhead cam/valve and all, but will this deliver the same kind of power that I am used to? That old briggs has been a workhorse, and I don't want to downgrade power/torque..etc. Did something change in horsepower ratings?
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Looks like the old one was heavier-better built, isnt that the trend in most everything. I wonder how the new motor compares to hp ratings on build size alone to your old b&s, likely 8 hp. So they shove in more fuel and up hp.
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On 27 Dec 2005 06:27:46 -0800, snipped-for-privacy@yahoo.com wrote:

I think they just lie about these things. They invented some "new" ways to define "peak" HP or some such nonsense. Smokey Yanuck (race car mechanic) used to say the only way to beat inches is with inches. A smaller engine, producing the same HP as a larger one is working harder, is going to fail sooner and is probably not really producing all that usable HP anyway. Look at the RPM rating necessary to get the HP they claim.
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Smokey said "you can't beat cubic inches", and the reply was "and cubic inches can't beat cubic bucks".
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unless they did something to significantly change compression, I think you can assume the new one will have less torque. Their marketing trick on this may be that some newer equipment that uses the new engine is configured to operate at much higher rpm's, thereby having a higher hp rating.
bill

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On 27 Dec 2005 06:27:46 -0800, snipped-for-privacy@yahoo.com wrote:

The Vanguard is a commercial duty engine. It's the Top of the Line for Briggs & Stratton. It is a V-Twin, which means TWO cyclinders to your old engine's one.
Commodore Joe Redcloud
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wrote:

Well, that's completely different. Nevermind.
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Smokey also said "torque wins races - hp sells cars", check the specs, the newer motor likely developes more torque and maybe they spin it faster. Hp is a function of torque delivered over time - what you are looking for is equal or more torque in the rpm band you most often operate the machine in

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While engine size has some influence on HP there are many other factors. Just look at car engines you can find 350cuin chevys with 230HP and you can find them with 300HP. Your new engine is prob fuel injected, with electric ignition, better designed heads, etc. Is the 9HP single cyl? The new one is prob 2 cyl.
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If you're asking whether or not the work equivalent of 1 HP has changed, then: No. HP is still HP and is still equal to 550 ft-lb/second.
More HP doesn't necessarily equal more torque though. Mass-produced engines today have better materials, better designs, and are manufactured to tighter tolerances, allowing higher rpms. This, coupled with lower friction losses, lighter components, and improved combustion chamber design can result in a higher horsepower from a smaller displacement engine, though torque might be lower in your new engine due to it's smaller bore and shorter stroke. If you're already thinking of modifying the tractor to accept the new engine, you might consider the operating RPM difference (if there is any) between the engines and change the gearing accordingly.
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Flatheads in general have much lower compression-ratio than ohv/ohc engines are capable of. This translates to lower volumetric efficiency and lower mechanical efficiency, besides torque curve biased toward the bottom end.
Boiled down: oldie bigger, heavier, thirstier for given power output rating. One place where cast-iron is beneficial: cylinder bore, for lube retention. Some aluminum engines have cast-iron cylinder-liner(s).
And ... you really don't want to approach rated power anyhow.
J
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snipped-for-privacy@yahoo.com wrote:

No possibility of rebuilding the b10? New ones are not built like that. While rebuilding you can improve it somewhat as well. Tony
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