I'm under propped. What should I move up to?

[Chotu]

Originally Posted by MicHughV

"horse power" is not to be confused with " torque"
"torque" is the actual work being done..."horse power" is the effort to keep it going

...torque can be measured on a dyno....horse power is basically a mathematical equation.

like riding a bicycle...your legs ( torque ) provide the pedal power, but your lungs ( horse power) provide the effort to keep your legs going...

The horse power wars is basically all marketing as few people understand the intricacies of the two together...

Researching the max torque available for a 30hp 2 stroke and a 30hp diesel, I see

30hp Diesel: 70 N•m
30hp 2 stroke gasoline: 60 N•m

So these are a little more torquey than the 4 strokes.

[a64pilot]

Originally Posted by MicHughV

"horse power" is not to be confused with " torque"
"torque" is the actual work being done..."horse power" is the effort to keep it going

...torque can be measured on a dyno....horse power is basically a mathematical equation.

like riding a bicycle...your legs ( torque ) provide the pedal power, but your lungs ( horse power) provide the effort to keep your legs going...

The horse power wars is basically all marketing as few people understand the intricacies of the two together...

Horsepower and torque are inseparable, torque is a force applied, horsepower is torque x RPM / 5252, so work done.
People think they have low HP but high torque engines, there is no such thing, they have low RPM engines is all so the torque is made at low RPM, but since HP is torque times RPM, they are low HP.

Every dyno chart will always have HP and torque cross at exactly 5252 RPM, if the engine won’t turn that fast, extrapolate the curves.

You can’t change it, it’s simple math. You can “play” with a dyno to show different numbers as many will correct existing conditions sea level standard day, the Harley shop in Savannah Ga did that to make it look like their bikes were making more power when they weren’t, but that’s easily caught if you know what your looking at.

The number of idiots lined up with their wallets open to have their Harley’s “raced tuned” was amazing.

[MicHughV]

true.....there is a difference between a planing hull and displacement hull, but when my fishing boat is not on plane, and just laboring along, the 100 rpm difference is still noticeable...maybe more...

I can get my fishing boat on plane with just a single engine, but it takes some doing and the engine is not happy about it. The fuel burn with both engines running at the same speed is about 13 gal/hr at cruise..but with just a single engine doing the same thing, I need more rpm and considerably more fuel, about double.

and yes, engine manufacturers play games with the general public....their 9.9 engines being identical to their 15 hp counterparts but for an additional 500 rpm.

the whole 9.9 hp engine came about as some inland lakes had a max 10 hp requirement. Manufacturer's simple re-jetted the 15 hp to have less rpm and thus produce less " horse power"....

anyway, just giving my take on it and not trying to pass an exam here....

[MicHughV]

yes, I've owned several HD's and their hp/torque charts always cross at the 5252 rpm, but not always the case.

attached is the hp/torque curve for a 2019 Corvette...I can show you others too, no crossing at the 5252 mark.

[a64pilot]

Originally Posted by MicHughV

yes, I've owned several HD's and their hp/torque charts always cross at the 5252 rpm, but not always the case.

attached is the hp/torque curve for a 2019 Corvette...I can show you others too, no crossing at the 5252 mark.

Not crossing at 5252 screams that the dyno chart has been spoofed. A Dyno chart HAS to cross at 5252 the HP formula requires it, as long as your using industry standard ft/lbs and RPM

On edit, I have not watched the video but know what it’s going to say
https://www.motorauthority.com/news/...ss-at-5252-rpm

[MicHughV]

a64 pilot, it's an interesting topic.......you get a room full of 10 gear heads, you are going to get 10 different viewpoints and opinions...

the new 2020 Corvette is claimed to make just under 500 hp...yet independent dyno shops peg the engine at 600 hp plus...but I acknowledge, that running the car in different gears, with monster cooling fans, etc, can slew the output.

some time back, I drove a 4 liter V-8 BMW M3, claimed to have 414 hp. I did not really notice much difference between this and the early M3, which had a 6 cylinder, 3.2 litre and around 330 hp, until I had that V-8 singing at it's redline around 8,400 rpm.

I've also had to pleasure of driving some Italian exotics, likewise, the "power" of those cars does not really come on until those engines are spooling at 8,000 plus rpm.

I'm not an automotive guy...so can't really provide input here..

My HD was a beast, kick it back into 3rd gear and wind the throttle and you'll know what torque is all about...and those are basically very slow revving engines.
I've also had several Japanese imports....750,900 cc, that had probably twice the HP, but half the torque. Faster top end, but not near the power. My HD could climb the side of a building if so prompted.

What does this have to do with sailboat engines....nothing...but...but trying to muddle thru' manufacture hype, testing, etc is swimming thru' muddy waters.

[a64pilot]

This is how to lie with a dyno meter, play with the “correction” factors.
https://www.dynomitedynamometer.com/...horsepower.htm

Low RPM motors are often preferable in marine applications, I cruise my high RPM Yanmar at 1800 RPM, because I can’t stand the noise at higher RPM. I even overpropped some to help with that.

Your Harley was perceived power, it wasn’t really there, just felt like it to you, just as very often putting loud pipes actually may hurt power output, but it’s sounds louder so you think its faster, but it’s not.