To qualify engines, they take a couple sample engines out of the box
(just like they would on the assembly line), put it on the dyno, fire it
up, adjust the dyno to the max load it will handle for a 6 hour (full
load) break in period. Then they run a full torque vs rpm curve for the
engine. Simple math gets you the max hp.

The dyno guys tell me that the B&S Intek 10 HP engine we brought in ran
out at 9.4 hp on a "10 HP engine", one of the best that they had seen.
My students were fairly shocked that it was that low. The dyno guys said
they had seen similar tests running at something like 55%.

Any of the standard things would improve the numbers: bigger jets is
probably the first thing on the list since these engines are designed
for minimum fuel consumption. The engines we were playing with had
fixed jets, no replacement jets available from the mfg. Pretty lean.
These engines were used for class racing, no mods allowed. We figured
that balancing, slippery oil, and larger jets would have pushed it to an
easy 11 hp. Tuned exhaust rather than stock muffler would add another
couple ponys.

We didn't try any of the 84 to 85 octane gas we get in Colorado, we
figure that might have gained a solid 10% right there. The lower octane
has slightly more fuel value per pound plus it doesn't have any alcohol
to lower the fuel value.

Jim Wilkins wrote:
On Apr 4, 10:02 pm, RoyJ wrote:
...
Not really, we have run these small engines on a legitimate dyno at one
of the major lawnmower mfg facilities. (They paint their stuff red) The
engines tend to put out less than the engine mfg lists: something like
95% of the nameplate number down to not much over 50%
...

Do you know why? Compression, carburation, ignition?