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Tight Cowl / Airbox on older RV - 4

M

Mark Bolton

Active Member
From Van's Parts Catalogue

Filtered Airbox - Vertical Draft
Standard FAB (Filtered Air Box) System Filters Air to Engine

Offers all the advantages of a ram air induction system but with an efficient filter. Excellent manifold pressure recovery for maximum power and economy. Provision for alternate air may be adapted to carb heat. Requires cowl modification when retro-fit to older RV-3/4. Order the system that fits your aircraft, engine and induction device.
Click to expand...

The kit I have was manufactured in the late 80's and I am presently looking at the proximity of the carby to the inlet bump in the cowl. I cant see any way I can fit a FAB in there since there is a cuppla inches only clearance there.

From the above it seems possible that the cowls for the "OLDER RV3/3" are too tight. Has anyone been down this path before? I am not that happy with the cowls that I have since they have a few cracks and the firewall fit is a bit scrappy. Maybe it would be easier to buy a fresh set of cowls?

THX in anticipation.

Mark
 
New scoop

Mark,
I put a FAB on my mid '90s RV-4 and I had to cut the old scoop off and install a larger one. Van's knows what you need and it wasn't really that hard of a job. I think the scoop was about $60. The new scoop is much bigger than the old one. Hope this helps.
 
Tight Squeeze...

You can't fit a FAB on the older cowls as the original builders manual called for a "home made" airbox. Part of the purchase when the FAB came out was a cowl scoop you had to glass on to make the FAB fit. I built and ran Ram air on my RV4 for 12 years and never bought a FAB. The 1989 RV4 builders manual showed nice drawings and I modified them slightly to incorporate a K&N filter mounted on top via a 2" flange. I installed a flapper valve like the FAB has except mine was closed for ground ops (filter) and open for ram air inflight. I always could get 2"increase of MP open. My Rocket has the exact same setup and the IO-540 really growls when you get that ram air door open!
When the FAB was first introduced back in the early 90's Van did testing on one of the company RV's and posted the results in the RV8R newsletter. He found very little MP drop although the old "Ram Air box" still reigned supreme. In 1500 hours in my RV4 and Rocket I have never found dirt or signs of any contamination due to dust, the ground filter works well.
The old vinylester cowls are primitive compared to the pre-preg cowls currently produced. My old cowl had hairline cracks in the gellcoat over time despite all my efforts to the contrary.
Overall, I recommend coughing up the money, buying a nice, new pre-preg cowl and be happy. You'll be glad you did...If you want to go with the old cowl, I have a scoop I'll send you free of charge...

Rob Ray
F16,RV4ormerly
HR2 currently
 
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pictures?

You wouldn't happen to have any pictures of your installation would you Smokey? I am right at that point in construction. I bought an older RV4 kit (1988) and just mounted the engine last night. Am ready to install the cowl and would kind of like to use the polyester one since it actually seems to fit fairly well. I bought the FAB a while back without thinking about the fit, but after this discusion, it does look like it would never fit without the scoop mod.

Dave Mader
RV-6 flying
RV-4 90% :)
 
Fresh Air...

Dave/Mark,

Here's a picture of my "Smokey FAB" with K&N filter, flapper valve on inside. Good Luck!

RR





If you still want to use the FAB, I can get you "the scoop"...see ya!
 
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filtered air

Smokey,
Thanks, just what I was looking for. A couple other questions. What length prop extension did you use with that set-up? Can it be done with the shorter 2.25? Also, just got off the phone with Larry Vetterman, and he said the exhuast is really tight in those older cowls and you hardly have room for any heat shrouds. I don't see any on your plane. Wouldn't fit??
Thanks
 
Tight Squeeze...

Dave/Mark,
4" extension, the 2.25 should work fine. I lined the inside of my cowl with thermo tech race car insulation where the pipes came close (my Rocket as well). I do have one heat shroud near my gascolator. Also, as you can see, I like firesleeve, it saved my butt once in a Scout, I highly recommend it. I also have a small heat muff visible in the far left of the forward view photo (using 1" scat). My friend Arvil welded it from a SS tube.
Larry's 4 pipe exhaust is absolutely a home run. I do recommend putting fiberglass insulation under your floorboards and behind the firewall, alot of heat comes through there. I broke Larry's rule and had my pipes ceramic coated, awesome! The one newer (uncoated)pipe is when I went to a wide deck 0-320 (they're different!)
Let me know if you need "the scoop"...

Smokey

http://www.thermotec.com/
 
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Thank you gentlemen for your help. I would sooner replace the cowls than cut / rebuild them since

Overall, I recommend coughing up the money, buying a nice, new pre-preg cowl and be happy. You'll be glad you did...If you want to go with the old cowl, I have a scoop I'll send you free of charge...
Click to expand...

makes good sence and many thanks for the offer of the scoop but I dont think I will go that route.

If one were to persist with the existing cowl I reckon smokey's ram air system is terrific and definitely the fix I would be implementing.

I am still puzzled however since I dont know if there would be room for even that amount of hardware under the carb. Like I say it is way tight.

I am still assessing the situation as I havent sourced the exaust system and if that is a squeeze too then the new prepreg cowl will look even more atractive.

Kind regards to all !!

Mark
 
I have a question regarding the intake with alternate filtered source for Ground ops.
Isn't there still a slight chance that you get debris into the first part of the intake, which will get sucked into the engine when changing to unfiltered RAM air once you are airborne.
I am asking this because I am in the same situation with the old cowling and an unfiltered intake. When running on ground you change to carb heat which takes air through a screen below the exhaust pipes.
 
scoop

Smokey, I have an older RV-4 and my scoop is in questionable shape...I am interested in your scoop if still available and no one else needs it...happy to pay you something for it or will donate to the forums!!!
Charles
 
"I lined the inside of my cowl with thermo tech... "

Checked thier website and they have different products available...may I ask which you used and how you applied/secured? I have vettermans straight on IO 360, one side of cowl modified for pipe...no issues so far but worried pipes a little close to cowl and would like to add some protection...thought about encasing some aluminum foil in a layer of epoxy, maybe at least prevent heat from hurting core or paint on outside...opinions?
Charles
 
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UPDATE

I wound up doing pretty much exactly as :

Charlie "T.Bear" Guarino
Springtown, TX
RV-4 Flying

suggested a few posts back.

It was pretty easy to chop out the old scoop and replace it with the new one using the standard technique of feathering the mating surfaces over about an inch of overlap and bonding them with epoxy.

Regards

Mark Bolton

http://rv-4builder.blogspot.com.au
 
Smoky
Thanks for your reply,on the stock RV4 induction system do you still have the old unit that filters on the ground and is ram in flight?
 
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