Seems like false advertising then. I wonder how they "got to" 18 horsepower with their tests.
From what i can tell is that took the peak torque rating that typically happens at 21-2500 rpm, and then multiplied it by the peak rpm the engine produces (3600-3800 rpm). The problem is that peak torque doesn't happen at peak rpm.
Duromax is a small enough company (not like honda/briggs/tecumseh) to where they can get away with it right now.
They will have a class action lawsuit against them in the future for false HP ratings if they keep this up.
You can get legitimate horsepower ratings through the SAE test methods. The same SAE organization that has test methods for the oil you put in your car has test methods for rating horsepower and torque in small engines.
I spoke with a SAE representative that performs oversight to honda/briggs/etc and he said that engines must be held under static conditions in order for them to be SAE certified.
some of the static conditions include:
temperature
rpm
load
The dynamometer must be capable of being certified via a known laboratory standard to a very precise tolerance.
So what happens is that you run an engine that must be held at a the same load, rpm, and temperature (intake shroud and head) for minutes and minutes until ALL variables are static. The head must come up to temp, the intake shroud must come up to temp, load must be stable, rpm must be stable, THEN a measurement is taken at that specific RPM. This is often done in steps, liek 1500 rpm, 2000 rpm, 2500 rpm, with the peak hp and peak tq steps being taken wherever they occur.
So in other words, a load bearing dyno is the only dynamometer that can produce SAE horsepower numbers.
From what I am aware of, BRIGGS, KOHLER, and HONDA all follow these methods because they ADVERTIZE or list in their footnotes for their torque curves the test methods that they used. Briggs is a little sneaky about it and will report GROSS HP instead of NET HP. Briggs will remove the intake and the exhaust and report gross hp, whereas the NET hp is with the intake(air filter)/ and exhaust (muffler) attached.
