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Author Topic: What will happen?  (Read 1566 times)

Online Perry Rose

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What will happen?
« on: March 08, 2019, 06:30:13 AM »
The Evo .60 c/l engine has a short venturi. What will happen if I make it taller? I've seen 2 stroke engines running with a fog coming out of the intake stack (go cart in the early 60's).
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Online Perry Rose

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Re: What will happen?
« Reply #1 on: March 08, 2019, 11:37:59 AM »
Ty, that is what I was getting at. I remember Hilborn injected drag cars with the tall stacks. I believe the length of the stacks were used to tune the intake system for whatever rpm the engine was turning. If that is so can we use the same principle (not principal) on stunt engines?
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Offline Steve Helmick

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Re: What will happen?
« Reply #2 on: March 08, 2019, 01:52:33 PM »
For our purposes, I'd expect the longer venturi would react more consistently to maneuvering. Try adding an extension tube to the existing venturi, like the "stuff tube" that is popular in combat events. When the model crashes (i.e., is "stuffed") the tube pinches closed and keeps most of the dirt and grass out of the engine.   y1 Steve
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Online Perry Rose

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Re: What will happen?
« Reply #3 on: March 09, 2019, 08:10:47 AM »
I used the protective top from a one ounce c.a. bottle and cut the plug end at an angle and jammed it over the venturi. With 5 ounces of my fuel and with the engine running at 88 to 8900 at launch it ran through the pattern on 63 foot lines and kept on running. I timed the total run and got 8 minutes 40 seconds. I know this engine and fuel and prop usually uses 4.5 ounces for the pattern in less than 8 minutes. I hadn't flown the full pattern with this plane so I put in enough fuel.
 The venturi extension sticks up .465 above the venturi at the front and .900 at the back. Before the venturi was below the lip of the cowl. More testing later.
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Offline Brad LaPointe

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Re: What will happen?
« Reply #4 on: March 09, 2019, 08:20:03 AM »
Bladder tubing, a piece of silicone tubing or the housing of a intake filter works ( with or without the filter) . I also find it helps fuel economy a small amount. Sometimes this makes choking the engine more difficult. Your mileage may vary .

Brad
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Offline Brett Buck

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Re: What will happen?
« Reply #5 on: March 09, 2019, 10:22:28 AM »
Quote from: Perry Rose on March 08, 2019, 06:30:13 AM
The Evo .60 c/l engine has a short venturi. What will happen if I make it taller? I've seen 2 stroke engines running with a fog coming out of the intake stack (go cart in the early 60's).

     Hard to say, but I would make it as long as practical to act as a flow straightener, and then use a diffuser (air filter or panty hose) over the end. The goal is to minimize the effects of the air direction changing as you maneuver the airplane.

    Brett
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Offline RandySmith

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Re: What will happen?
« Reply #6 on: March 12, 2019, 12:06:52 PM »
Quote from: Perry Rose on March 08, 2019, 06:30:13 AM
The Evo .60 c/l engine has a short venturi. What will happen if I make it taller? I've seen 2 stroke engines running with a fog coming out of the intake stack (go cart in the early 60's).

Depends on how tall you make it , and how  short it is not, making it larger also makes it act like a smaller venturi, It also helps if the one you have now is  TOO short, in keeping the fuel, inside the venturi,  I have found that  the ratio should be no smaller than 2 to 1, or no larger than 3 to one, That is just the measure of the venturi at the point it  meets the engine or O-Ring.
I most  applications it will not matter much, but if you are right on the edge of being too small with a short stack venturi, You may want to make the tall one 3 to 5 thou larger inside diameter .

FYI the engines with a lot of duration on the crankshaft opening, and retarded the most  will  blow the most fuel out of the top of the venturi.  and  as  Brett  mentioned  putting a filter or layer of panty hose over, either the small or tall venturis  will help greatly with keeping the fuel inside the venturi
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Offline FLOYD CARTER

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Re: What will happen?
« Reply #7 on: March 12, 2019, 05:51:27 PM »
The good old Fox 35 has been around for a long time.  Its venturi is about as short as possible, and still be called a venturi.

If there was an advantage to a long intake tube, the Fox would have been fitted with one long ago.
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Offline Brett Buck

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Re: What will happen?
« Reply #8 on: March 12, 2019, 08:54:08 PM »
Quote from: FLOYD CARTER on March 12, 2019, 05:51:27 PM
The good old Fox 35 has been around for a long time.  Its venturi is about as short as possible, and still be called a venturi.

If there was an advantage to a long intake tube, the Fox would have been fitted with one long ago.

  Good one!

     Brett
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Offline RandySmith

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Re: What will happen?
« Reply #9 on: March 12, 2019, 10:35:33 PM »
Quote from: FLOYD CARTER on March 12, 2019, 05:51:27 PM
The good old Fox 35 has been around for a long time.  Its venturi is about as short as possible, and still be called a venturi.

If there was an advantage to a long intake tube, the Fox would have been fitted with one long ago.

I have seen  Many, and  I actually have  2  that have  long extension tubes grafted onto the FOX 35 Intake
Maybe someone  knows  something we don't  LOL :-)
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