Piston pounding

Scooter

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Joined
Oct 30, 2003
Messages
61
Location
Cabot, Arkansas
I would like to commend everyone for making this an enjoyable forum. And I hope we keep it that way.

Back in the propeller section, I asked why certain props weren't approved for direct drives. I still don't have an answer I can accept. Ken said, (Ken please don't take this as an attack, I don't mean it that way), that, to paraphrase, piston pounding causes excessive stress on the prop.

Well I thunk about this for a long time and reached the following conclusions. If you use a normally aspirated engine (carbureted) with some sort of a standard ignition setup, then your logic considering the above, I can understand. Dumping relatively uncontrolled volumes of raw fuel on top of pistons with timing which is just a calculated guess depending on jets and other outside influences, can indeed cause erratic pounding of pistons.

However, today's automotive engines have long evolved from that archaic technologic stance. I can't understand why some companies like Jabiru only produce carbureted engines. I even called them and ask them just that question. Their answer was that people in remote areas aren't trained to work on fuel injection engines. Piss poor excuse as far as I am concerned. The right answer is they don't have the technology and/or know how or the market isn't there. Which is the probably correct answer, they are dealing with people who just don't know better. It is totally beyond my logic why someone would pay many thousands of dollars for a 40/60 year old technology engine, when they can get a modern converted automotive engine for a faction of the cost.

One final thought about piston pounding, if the fuel and ignition is controlled as in a modern fuel injection engine, whereas the fuel input is adjusted and the timing is adjusted on the fly via sensors/ecu then there is no piston pounding. That's not even considering the increased engine longevity (at least double), reliability, fuel economy, and increased horse power you get with fuel infection.

I know a FI engine cost more, but the payoff is worth it.
 

Scooter

Member
Joined
Oct 30, 2003
Messages
61
Location
Cabot, Arkansas
Re:piston pounding


You are correct, except I would think it is minuscule with a finely tuned engine versus an out of tune engine. Which most carburetor engines are out of tune to some degree. Which in layman's terms causes erratic application of energy from one piston to the next because they are not getting the same mixture air and fuel.

Oh well, like someone else says, "just my two cents worth". Larry
 

rehler

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Oct 30, 2003
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New Braunfels, Texas
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Re:piston pounding

Larry,

I suggest you call (telephone not e-mail) the man who owns PowerFin (I can't remember his name). I have talked to him several times about props (not about direct drive applications) and believe he is VERY qualified to know and give you the straight answer about his or other props on direct drive engines.

You can also talk to the Ivo Prop and Warp Drive folks. They also can answer your questions. Ivo Prop makes a special prop for direct drive applications.

It will be worth the phone calls.
 

Scooter

Member
Joined
Oct 30, 2003
Messages
61
Location
Cabot, Arkansas
Re:piston pounding

Thanks, just needed other opinions. I will follow it up some more and let you know what I find.
At least you have put enough doubt in my mind that I won't buy one unless the manufacturer certifies it for direct drive. I have no desire to come down faster than I want to.
 
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