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FM-150 snorkel fit adjustment

Nova RV

Well Known Member
The snorkel does not sit perfectly square on the FM-150 since the servo sits out further than the stock Bendix style servo. This is how "I" modified my snorkel to fit, there may be an easier / better way but since I was asked how mine was installed here goes and a level of comfort doing simple fiberglass layups helps: When you bolt the snorkel to the FM-150 it will cause the snorkel to be approximately 7/16 too far forward when you get to the air filter assembly and the snorkel will not slide inside per plans. To start I made an initial trim to length of the snorkel. (this pic shows the snorkel square and was taken before I tightened the snorkel to the FM-150)
otz.jpg


Next is to slit the corners of the snorkel so that you have 4 sides that you can move easily. These slits shown are preliminary, the final ones were several inches long - follow the contour of the snorkel.
otI.jpg


Trim the tabs on the filter frame approximately in half, they are angled and won't allow the snorkel to fit with the adjusted snorkel sides. There is still plenty of flange to secure the snorkel
otM.jpg


With the snorkel bolted to the FM-150 you can now screw the filter flange to the baffle and then push and hold each side of the snorkel against the filter flange and drill/cleco just like in the plans. Remove everything and epoxy the individual sides to the filter frame. Your snorkel now should fit without any tension but look like a mess because you have long cuts in each side. Scuff the outside only and apply epoxy and fiberglass over each cut then apply larger pieces to cover the entire upper snorkel. Several layers of 7.5oz cloth should do it. Don't add any cloth inside the snorkel.
otR.jpg


Fill each slit gap from the inside with epoxy and flox and sand to maintain a smooth inside contour. (this pic shows inside prior to filling the slits with epoxy/flox)
otl.jpg


Bolt all back on and you are finished.
otY.jpg

yes, I know the plastic comes off of the filter before use :)

The final snorkel has the same intake area below the filter and nearly the same airflow pattern so I can't imagine there is any measurable difference in airflow from the filter to the fuel servo.
 
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Nice work. Some of us had problems aligning the filter lip with the lower cowl inlet ramp (see the thread "Cowl fitting and the inlet ramp" on this page) You may be able to correct the alignment with the cowl ramp (if needed) using this technique and save yourself some grief later if you can check the cowl alignment now
 
I'm glad this writeup is here. I got the Thunderbolt engine and didn't understand that when I got the FM-150 I was also due for a special adapter kit for the cables, and extra days refitting the snorkel.

Did you fit up the throttle end of the snorkel at the time of the rough cut even with the filter box? Seems like that end would need to be very fixed to make the rest work.

What is the best way to make sure the snorkel is lined up right on the throttle body to make the hole concentric with the intake?
 
I'm glad this writeup is here. I got the Thunderbolt engine and didn't understand that when I got the FM-150 I was also due for a special adapter kit for the cables, and extra days refitting the snorkel.

Did you fit up the throttle end of the snorkel at the time of the rough cut even with the filter box? Seems like that end would need to be very fixed to make the rest work.

What is the best way to make sure the snorkel is lined up right on the throttle body to make the hole concentric with the intake?
The snorkel fitting shouldn?t take long at all and due to variation in snorkel different people have had more or less modification needed.

I have the same engine as you, thunderbolt.

I was going to adjust the snorkel to the airbox as it is done here but it would take more of a cut and butchering of my snorkel. So I cut the snorkel at the neck where it attaches to the throttle body. I had the flange attacked to the throttle body and the snorkel nicely attacked to the airbox. Then floxed the flange back to the snorkel. With a bit of cleaning, It came out perfect fitting and very clean.
 
I did the same as Bavafa, but used a piece of florist foam to hold the alignment between the throttle and the throttle end of the snorkel. It worked out fine, but was my first attempt at this kind of "major" Fiberglas surgery, so I was worried the entire time. :eek:
 
I considered cutting at the flange side but figured my skills were better with a filter side cut. So now the snorkel is sliced up but fits well and clecos in place. Tomorrow I plan to wrap the assembly with a couple of layers of glass then lay flox on the inside to smooth it out. Is there a minimum number of layers for the wrap? Anything special to watch for?
 
I considered cutting at the flange side but figured my skills were better with a filter side cut. So now the snorkel is sliced up but fits well and clecos in place. Tomorrow I plan to wrap the assembly with a couple of layers of glass then lay flox on the inside to smooth it out. Is there a minimum number of layers for the wrap? Anything special to watch for?

I think I used about 3-4 layers of 7.5oz cloth covering the areas that were slit and a large piece wrapped over the whole area and it was more than enough to match the rigidity of the original part. I did also add flox mixture inside to smooth it back out.
 
My snorkel layup is done and I think acceptable. It changes where the alternate air inlet should be placed because it is too far aft if I follow the dimensnsions on page 47-19.

What are the critical issues in hole location for the alt air? I’m thinking to keep the same vertical dimension and just move it forward 3/4 inch to fit better.

I also notice that in the drawing on page 47-19 and the next page with the flange flat and the neck of the va-192a sticking into the hole that the flange holes are mirrored from what the pic shows. Nutplate holes are correct.
 
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Diameter?

When I was helping a guy with his snorkel and FM-150, the first thing that jumped out at me was the small diameter of the snorkel outlet at the servo end. The FM-150 has a larger diameter inlet than the Bendix unit. We built it up around the narrow "neck" and then hogged it out to match the servo. This was after dealing with the fit at both ends.

Ed Holyoke
 
I was pretty excited to find that after snorkel fitting my lower cowl lands about even with the right air inlet ramp. Didn?t do it on purpose it just worked out that way.
 
I was pretty excited to find that after snorkel fitting my lower cowl lands about even with the right air inlet ramp. Didn?t do it on purpose it just worked out that way.
It would be nicer if it is a it higher so the seal can be on top of the baffle without a whole lot of bend/stress but that should be close enough to manage it right.
congrats
 
I think modifying the snorkel intake side is way easier and less critical. Just cut down the square corners, get a fit, trim the excess, and glass in to fill. I spent 20 hours thinking about 3 hours of work.... maybe 5
 
ok--another dumb question:

I assume that the CB-00035 snorkel drill template is not used with the FM-150 and I should just make my own for the drilling the holes in the snorkel flange where it connects to the FM-150.

Basically you want the hole in the snorkel to be concentric with the hole in the FM-150.

thanks
 
I can't remember but at the end of the day that flange has to mate to the FM-150. But I think the pattern matches if you line it up on the FM-150..... And it ends up concentric done that way.... trust but verify!
 
I wonder what company makes the snorkel for Van's. It would be nice to be able to contact that company and have them make a snorkel specifically for the FM-150. It just has to shift forward about 1/2".

It doesn't help me, but I bet others would love to not have to do this Arts and Crafts project.
 
When I was helping a guy with his snorkel and FM-150, the first thing that jumped out at me was the small diameter of the snorkel outlet at the servo end. The FM-150 has a larger diameter inlet than the Bendix unit. We built it up around the narrow "neck" and then hogged it out to match the servo. This was after dealing with the fit at both ends.

Ed Holyoke

This is fairly important and it doesn't seem like a lot of the builders here are doing anything about it. I am not intimately familiar with this set-up, so forgive me if I am talking out of school. But the snorkle fit to the servo should be such that there is a smooth transition of the interior walls of the snorkel tube to the internal bore of the servo.

If there is a step because the diameter of the snorkel is smaller, there will be some pressure loss and turbulence feeding into the servo. I don't think it is a good idea to make a transition that extends into the throat of the servo--that could affect its calibration. If it is just a small diameter difference, then building up the exterior and then grinding out the interior until the diameters match would be one approach, as described by Ed here. It may be hard to tell whether you have a good smooth flow transition between the parts that way.

I would be inclined to machine a flange with a stubby tube that fits the servo perfectly and then glass that onto the end of the snorkel - again with a smooth transition.
 
well, I emailed Airflow Performance to see what their thoughts are on this topic.

My question to them (more or less):

The ID of the snorkel is 61-63 mm (not round).

The ID of the FM-150 is about 66 mm, but the lip where the FM-150 transitions from the tube to the flange is rounded. The ID of the lip where it becomes aligned with the flange is about 77mm.

So what ID should the snorkel be: 66 mm or 77 mm.
 
The FM-150 came with a gasket to go between the snorkel and the FM-150.

I have read that this gasket is not necessary.

Any thoughts?
 
I have no objection to using, but others indicate it is not necessary. I just want to have it in place when I attach the air filter flange to the body of the snorkel. I know the gasket is thin, but I might as well have it in place.
 
well, I emailed Airflow Performance to see what their thoughts are on this topic.

My question to them (more or less):

The ID of the snorkel is 61-63 mm (not round).

The ID of the FM-150 is about 66 mm, but the lip where the FM-150 transitions from the tube to the flange is rounded. The ID of the lip where it becomes aligned with the flange is about 77mm.

So what ID should the snorkel be: 66 mm or 77 mm.

Any response on that?
 
Airflow Performance suggested opening up hole to 3" for optimal performance. It was pretty easy to open up hole. I put down a tick layer of epoxy with flocked cotton. Then peel ply. Removed the next day then put down 4-5 layers of prepreg glass. Most of it is in videos on my FB page.

someone contacted me in a PM and they will be sending the stock snorkel to AP for testing. Hopefully we will hear something in the next week or two.

cheers
 
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