EVO 36 NVA Conversion

I found a quick and dirty way to eliminate the rear NVA from the EVO 36.
Details here:
http://hangarflying.proboards18.com/index.cgi?action=display&board=wire&thread=2536&page=1
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And your point is?
Have you even run it with the remote NVA?

p.s.- Your NVA outlet needs to be at the max - mid-point of the venturi, not dumping fuel against the other side.

I put 4 bench runs on it as supplied. It ran fine, as long as you used muffler pressure. Without it, it wouldn't run at all.

>I put 4 bench runs on it as supplied. It ran fine, as long as
>you used muffler pressure. Without it, it wouldn't run at all.
>

Which venturi did you use? Perhaps it was a large one? With the spigot you will need a lot smaller venturi than with a wider needle running all the way through. Perhaps your spigot is choking down the venturi more.

Oh, and why not simply copy and past what you posted elsewhere on this board, too? I don't like references to other boards because I don't know how long they are going to be up, or even if they might change. Our data base has been here since the beginning of the board dating back to the year 2000. I will keep it there as long as I am able to do so, but if someone goes back in the archives and sees a post that refers elsewhere to a post that is no longer there, it destroys the whole purpose. Thus if you could post here what information you want to share, it will stay in the archives as long as this board continues on the Internet.

OK, here it is:
Advertising picture:
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Stock venturi as delivered, largest one.
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My "quick and dirty conversion", smallest venturi with OS R/C NVA installed:
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The outlet needs to be cut to end up at the middle of the venturi, I didn't want to take the time to do that at the time. It has a fair amount of fuel draw the way it is.

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You'll only need to shorten the NVA spigot if the motor has problems due to fuel flow. The offset opening MAY be more likely to cause problems on a profile. I've seen some very strange setups work fine and other motors get very fussy with what look like straight forward, through-the-venturi setups.

This type of needle valve has lots of holes in it, and may be troublesome to seal, speaking from experience. And it is twice the weight of the OS 1a remote or a through the stack standard needle valve. The Evo looks to be 1/2-1 oz. heavier than a Magnum 36 depending on the needle valve, but still not bad at 260 gr.(less muffler). Both the standard NVA and the OS are a problem on a profile, sticking well above the fuse to get broken if the plane happens to flip over on landing.

The rear NVA can be rotated 90° on the backplate for profile installations. A through NVA can be installed with needle facing down, though this does making adjustments less convenient, but a lot less prone to being damaged.

don Burke
Menifee, CA
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways - body thoroughly used up, totally worn out and screaming, WOO HOO, What a Ride!

When you move the needle valve parallel to the cylinder the fuel feed ends up against the motor mount, or the needle is rubbing against the exhaust stack. If you are using the motor on a profile the simplest set up is to use a standard OS needle valve across the venturi and take the spring extension off. Slightly more complicated is to mount the OS 1a needle valve on a cut-off control horn from the upper left backplate bolt and feed in to the Evo fuel spigot.

Unless you have leaks in the system, the only problem I've had with remote needles on profile planes is getting the fuel up and over the engine during starting. fixing that requires either an oversize prime, which may start the motor backwards, or keeping a thumb ready to lightly choke the motor as it fires.

Good point about the fuel feed position. On some of the remotes setups I've seen the fuel feed can be reversed, don't know if that's possible with the Evolution setup.

I've found that before attaching the battery choking and flipping a couple of times so that fuel is up to the needle helps.


don Burke
Menifee, CA
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways - body thoroughly used up, totally worn out and screaming, WOO HOO, What a Ride!

>You'll only need to shorten the NVA spigot if the motor has
>problems due to fuel flow.

I have had the best results with the a spigot that goes approximately 1/3 of the way across. Shorter is OK until it gets to about .015, then it works like it had a sprinkler. 1/2 way works but seems to have less draw for a given choke area than 1/3. I think the spigot will make it much less prone to funny asymmetries (like the 45 degree angle), since if you get it the right length the spray will be centered in the venturi.

I am saddened but not surprised that people are already modifying them without even having run the engine. There were some pretty sharp people behind this development and I think we owe them the courtesy of running it the way it was intended before just dismissing it out of hand. If there's an identified problem that's a different matter, but this is just as silly as tossing the 20FP muffler because we all know it's "too heavy" - when in fact that's a key factor in making the engine work properly! But I suppose some of us are still willing to argue about that, too, so, why not this?

Brett

So, it apears the threads on the OS and EVO spigots are the same...

That's a great thing to know. I expect the spigot depth can also be adjusted simply with spacer washers outside the insert OD?

Another thing I noticed on the remote spraybar mount arrangement: the "other 2" Phillips head screws are the same thread as the fuel nipple for the line from the tank, and feed into the same 'plenum' or reservoir chamber metered by the needle assembly in stock-as-boxed position. That doesn't help fore and aft space on a crowded profile, but if the fuel delivery to the remote NVA works in-line, instead of looping up behind the cylinder, and the NVA mounting can be rotated parallel to the cylinder, it might reduce crash damage breakage...

We're visiting away from home this week so no chance to prove/disprove any of this. As a fallback, tho, the common thread size w/ the OS piece is a great bit of info.

Speaking of mufflers, the EVO muffler is the most restrictive I have seen yet. I suppose there is a reason for that too? It certainly doesn't seem to affect the power level. Somehow that doesn't seem possible.

I tried running mine on the bench with no muffler. Aside from being hard to start, it ran fine. I also tried a Tower 40 muffler then the EVO tongue muffler. It started easily with both, but the power was down with the tongue.

>Speaking of mufflers, the EVO muffler is the most restrictive
>I have seen yet. I suppose there is a reason for that too? It
>certainly doesn't seem to affect the power level. Somehow that
>doesn't seem possible.

Well....
It shows that there is more to exhaust emissions than just "holes".
Complicated situation, exhaust gas pressures and thermodynamics.
The results can often be well worth a little extra weight.


Randy C

I went ahead and modified the fuel outlet of the R/C NVA to center the jet in the venturi. Here are the before and after shots.


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