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Predator 80cc Four Stroke

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Old 08-29-2017, 03:06 PM
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av8tor1977
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Default Predator 80cc Four Stroke

So I was wandering through Harbor Freight yesterday, ogling tools and making a mental "wish list". (So easy to do there!) Anyway, I spotted this really cute Predator 80cc four stroke gas engine for only $110 bucks. I was kind of fascinated by it, and of course started mulling the "Conversion" possibilities. I finally had to reach up and grab myself by the collar, and DRAG myself away because I already have TOO MANY PROJECTS!! (I still went back to it 3 times; it really was cute!)

It wouldn't be any good for aerobatics due to the weight and the wet sump configuration, but it would be an easy conversion and awesome for something like a large glider tow rig

https://www.harborfreight.com/3-hp-79cc-ohv-horizontal-shaft-gas-engine-epa-69733.html

Then the other thought I had was "Here is something with a lot of complex machining and precision moving parts that they can apparently make a profit selling for 100 bucks, yet we have to pay several hundred dollars for a simple airplane engine with only THREE moving parts!!"

Yeah, I know, I'm an old crudgemugeon about prices these days....

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Old 08-30-2017, 03:03 AM
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I know,I know. Banggood is selling a conversion kit for a bicycle to make a motorbike. The complete kit with motor, handlebar control, fuel tank, mounting brackets, and an engine is $90.00. Go figure.
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Old 08-30-2017, 09:37 AM
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Not surprising at all.

That's the way it's always been - anything that is labeled hobby immediately gets a highly inflated price compared to what it would otherwise be.

Let's go back a few years when people got fed up with the high costs of engines. Well, along came the low cost Quadra industrial engine and large scale models. All the components resulted in a larger model than the current popular sizes for less cash.

So what happened? The usual. Engine conversions were labeled as being specifically modified for hobby use. Now there was a great excuse to increase the price. And then they were allegedly designed exclusively for model use. Jack up the price some more. And then came the horsepower race, an equivalent to the mine is bigger than yours boast. Another good reason to charge more.

And so it goes.
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Old 08-30-2017, 12:58 PM
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Why would an engine that big only put out 3 HP? My MDS .61 had 3 HP.
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Old 08-30-2017, 01:15 PM
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Banggood! Oh man, I love that place!! It is funny you mention that bicycle kit, as just yesterday I watched the installation video of that. There's a lot of people riding those around my neighborhood. I looked it up, and here in Arizona you don't have to have a motorcycle drivers license to ride them, and they don't issue a title for them. But get this; you DO have to register them, and you DO have to buy vehicular liability insurance for them!! They will get in your wallet no matter what you do won't they??

I dabble in electronics projects, and that Banggood site has fantastic prices on various modules and electronic goodies. I bought a Bluetooth receiver from them for 5 bucks with free shipping, and later saw the exact same one in Walmart for 20$. So far I have been quite happy with everything I bought from them, and it's all free shipping. It takes about 3 weeks to receive things however. My "Wish List" with them is over 50 items!!!

Re-the pricing of things for modeling, it is the very same thing/problem for full size boating, Ultralight Aircraft, and of course, times 1000 for full size aircraft.

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Old 08-30-2017, 01:20 PM
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Ah yes, but horsepower is never the whole story. TORQUE! Larger diameter props turning slowly are far more efficient. That engine makes 3 horsepower, but at only around 3000 rpms, so it has a ton of torque and would turn a huge prop.

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Last edited by av8tor1977; 08-30-2017 at 01:25 PM.
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Old 08-31-2017, 08:35 AM
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Quote:
Originally Posted by av8tor1977 View Post
Ah yes, but horsepower is never the whole story. TORQUE! Larger diameter props turning slowly are far more efficient. That engine makes 3 horsepower, but at only around 3000 rpms, so it has a ton of torque and would turn a huge prop.

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Agreed.

Horsepower is really a sort of useless number which is good only for impressing those who don't know.

It's an arithmetic calculation. Horsepower = torque x RPM

So go stick that 3 hp MDS .61 on your bicycle and see how fast it grinds to a halt. No torque.

It's good for high revving, free revving racing engine applications where a high torque low revving engine would be slow to rev up and down. One giant, single cylinder going really slowly with high torque would not get you accelerating very fast. Perfect application for that is the engine in a steamship.
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Old 08-31-2017, 01:31 PM
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Default Horsepower

It's all about "Work", and "Time". Horsepower is a measure of just that, and as you say, is Torque x How many Times that torque is being applied in a given time span. So you can obtain a given horsepower by applying a Large torque fewer times, or a Smaller torque many times. The case of a hot .61 glow engine would be a great example of an engine making horsepower by applying a relatively quite small torque many times rapidly.

One horsepower will move 33,000 lbs. one foot in one minute. And the key is you can juggle the force, time, or distance around any way you want, and as long as it equals that equation; that total amount of work in a given time, you will have one horsepower.

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Last edited by av8tor1977; 08-31-2017 at 02:10 PM.
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