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Adding an air filter on an rv4

S

sslayden

Member
I've purchased an older rv4 (1989) and it does not have an air filter. Ram air from the scoop on the cowl goes through a mesh screen directly into the carb. What does it take to get an air filter on it? Does the FAB Vans sells retrofit easily or will the current scoop need to be cut out and rebuilt?

Also, there is not any real carb heat. On top of the fiberglass conduit from the scoop to the carb is another mesh screen that takes air from inside the cowl area. The carb heat knob switches air intake from the cowl scoop to the mesh screen on the inside of the cowl.
 
You'll need to buy the airbox from Vans along with the appropriate lower cowl 'snorkel' (they make one for the O-320 and one for the O-360). Then you'll have to fab and fit the airbox per the plans. Your lower cowl will no longer fit.....so....as you stated....you'll have to cut off the existing air intake and put the lower cowl back on the plane with the new airbox sticking out of the bottom. You can then fit the 'new' snorkel in place...cutting and trimming as necessary. Once fitted and taped in place you'll be able to drill some holes and cleco the snorkel on.....then remove the cowl/snorkel and begin the process of fiberglassing it on permanantly. Not difficult at all....just be sure to finish sand real good to prep for paint when you're done.
Also, you can buy Vans little carb heat muff.....this will be installed as you fab your new airbox.....just follow the plans.
Good luck.
Rick Gray in Ohio at the Buffalo Farm - RV6, 4 RV4's, RV8, RV10 & F1 Rocket in progress. Ohio Valley RVators
 
I have this conversion kit. I was going to put it on my RV-3, same system though. I'll sell it for the price of shipping.

-Bruce
 
My Dad just did this on his -4, I did not get in on the job but it only took him a couple of afternoons, I think it was very easy, easer then he thought it would be, He did note that he thought he lost a little power / rpm after the mod. Is a small performance penalty normal???
 
sslayden said:
I've purchased an older rv4 (1989) and it does not have an air filter. Ram air from the scoop on the cowl goes through a mesh screen directly into the carb. What does it take to get an air filter on it? Does the FAB Vans sells retrofit easily or will the current scoop need to be cut out and rebuilt?

Also, there is not any real carb heat. On top of the fiberglass conduit from the scoop to the carb is another mesh screen that takes air from inside the cowl area. The carb heat knob switches air intake from the cowl scoop to the mesh screen on the inside of the cowl.
Click to expand...
As an other alternative, you could leave it the way it is or I have seen one retrofitted with a filter without having to cut the cowl. The fiberglass body that goes from the scoop to the carburater was extended to the rear and a hinged aluminum door put on it like for a carb heat. The rear extension went to a foam air filter. You pull on a cable in the cockpit to use air thru the filter for on ground operations then switch back to ram air once airborne. Paul Besing's rv-4 used to have this setup. Maybe he can be talked into taking some pics of it and posting here?
Regards,
Tom Velvick
N53KT RV-4
 
Before you cut...

I have an old RV4 as well, I started it in 89, pre FAB airbox which I don't like anyway.The builders manual has drawings for an airbox with filter, here is a picture of my setup with the builders manual version as a guide. I drew it up on a knapkin in our chow tent during a deployment to Iraq and my friend Arvil built it out of .040 using a TIG welder.
It has over 1400 hours in all weathers, rough strips, rain and dust. Works great and was easy to build. The Ram air as you know is good for 2" MP inflight above the FAB (Van's own testing). I didn't want to lose the performance so I designed the Tunnel Ram where I could close off the outside air in lieu of warm filtered air on the ground, ram-air inflight. I fitted a flapper inside that I can close from the cockpit. Since the K&N filter sits right under the sump between the vetterman 4-pipe, it gets plenty of warm air. I had symptoms of carb ice once in AK in 40 degree air and visible moisture and the alt air capability cured it.
My setup requires no cowl cutting, messy glasswork or large modifications to your exisiting setup. You may be able to modify your current AB...
Let me know if you need drawings...(non-knapkin...:)

Rob Ray
97' RV4
97" HR2
F-16 (2 weekends a month)

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Takeoff ?

Rob,
Do you take off with ram air or the alternate ? I would think ram air but curious if you ever tried it with the alternate and does it lose a lot of power...

thanks

John
 
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