Venturi question

[Tim Thompson]

Question about nylon standoff/spacer as venturi. I've read to use them and don't use them. Which is correct ? I  need a venturi to replace an RC carb.I have a nylon spacer that is the perfect size that I need.
I'm thinking that the automotive industry uses nylon without problems so it should work for a model aircraft engine.
What I'm asking for is first hand experience please. Not something that someone said or you read

[Perry Rose]

What size engine and what i.d. of the spacer? I've used them without a problem.

[Dave_Trible]

Many (most) competition Stunt engines used today have nylon Venturi.  The material isn't the problem.  Getting the opening size and design shape correct is far more important.  Lee' s Machine Shop and others can furnish a proper Venturi for whatever engine you have at very reasonable prices.

Dave

[Brett Buck]

Question about nylon standoff/spacer as venturi. I've read to use them and don't use them. Which is correct ? I  need a venturi to replace an RC carb.I have a nylon spacer that is the perfect size that I need.
I'm thinking that the automotive industry uses nylon without problems so it should work for a model aircraft engine.
What I'm asking for is first hand experience please. Not something that someone said or you read

   Nylon or delrin is fine for a venturi, as far as materials go. The size and the shape are what matters.

    Brett

[George]

...What I'm asking for is first hand experience please. Not something that someone said or you read 

I made a venturi for a VECO .19 glow from a nylon electrical spacer from Lowe's. I found the nylon hard to work with using hand tools and a drill press. I also made a venturi for a MVVS 2.5 diesel using aluminum tubing filled with epoxy, then shaped. Both work but probably not as good as a professionally made one.

My suggestion would be to get one made for you. They know the best size and shape.

George

[Randy Cuberly]

I made a venturi for a VECO .19 glow from a nylon electrical spacer from Lowe's. I found the nylon hard to work with using hand tools and a drill press. I also made a venturi for a MVVS 2.5 diesel using aluminum tubing filled with epoxy, then shaped. Both work but probably not as good as a professionally made one.

My suggestion would be to get one made for you. They know the best size and shape.

George

I would definitely recommend NOT using this (epoxy) method.  While it might work fine for a while, it risks particles of epoxy breaking out from vibration and being digested by the engine.  Very bad things would happen to the piston/cylinder, not to mention the bearings!

Nylon (6/6 because it machines cleaner), Delrin, or Aluminum (6061 also because it machines cleaner) are certainly the preferred materials.

Randy Cuberly

[Air Ministry .]

The Thunder Tigre 25 , Magnum 25/ GP  40 , and super Tigre 35 C ( plain bearing ) venturies are compatable with the D7 MVVS , & V c V .

[Tim Thompson]

Thanks guys.

[George]

I would definitely recommend NOT using this (epoxy) method.  While it might work fine for a while, it risks particles of epoxy breaking out from vibration and being digested by the engine.  Very bad things would happen to the piston/cylinder, not to mention the bearings!

Randy Cuberly

 

Good thought, Randy. Since I have not run this engine for a few years, guess it's time to get a real venturi.  


George

[Fredvon4]

There is a LOT of very different ways to skin a cat on this forum and a thousand opinions...

BUT between Randy Smith and Lee's machine shop----- I have been able to tell those 2 gent exactly what engine I had and what airplane and initial prop I planned to trim/tune with

Each provided me with a relatively low cost solution and further advice...like best muffler or number and size of holes in the tongue muffler

In each case ----now, for 6 different engines, the sale and advice fell in line with the recommendations of venturi size and NVA ( IE total choke area) of Tim, Brett, Mark, and others that pay attention to these details and how they relate to a stunt run on some particular engine

So rather than Roll your own...I highly recommend asking Randy Smith and Lee machine shop and between the two put together a near perfect first time NVA Venturi combo that should work well without too much trial and error

Do NOT forget the great advice to try panty hose/O-ring holder as a restriction--- and keep the intake air clean ----while maybe choking down a too larger venturi------seeing as how the recommend intake filters are no longer for sale anywhere