Airbox Options for Raven Cold Air Intake with RSA-10 Servo

[coosbo]

I’m trying to sort out how to package a Raven Aircraft cold air intake with one of the larger, older RSA-10 style fuel servos inside a cowling, while also housing a filter, ideally providing a MAP boost, and incorporating some form of alternate air if feasible. The main challenge with this setup is that the front of the servo sits very far forward and the entire assembly hangs down quite a bit.

After brainstorming with another builder, the leading idea at the moment is to modify a Vans RV inlet (similar to Nev’s approach), make an additional slight modification to the bottom of the nose bowl so the two fiberglass pieces mate more cleanly, build a custom airbox inside the chin of the scoop, and then connect that airbox to the fuel servo using an elbow or 4” SCEET.

My reservations with this approach are the ~90° turn just ahead of the fuel servo, the lack of a defined filter solution, and the amount of custom fabrication it would require. Those skills aren't my strong suit, so I'm concerned about both the time required and the quality of the end result.

If anyone has advice, ideas, inspiration, off the shelf pieces I should consider utilizing, or lessons learned from a similar setup, I’d really appreciate any direction you’re willing to share.

Colby

[Nev]

Colby, I can add a couple of considerations now after 600 hours of operation. The Vans RV inlet works well. I've never removed it by itself, I just remove the whole cowl which is a quick exercise. Making it permanently attached would be a good solution. Fiberglassing certainly wasn't my strong point at that stage either but you learn as you go.

Do you need an alternate air ? I'll throw this grenade from a safe distance then stand on the sidelines and watch the debate with interest :) Having an alternate air mitigates one risk (though on a VFR machine it can arguably be a relatively low risk), but it can introduce another. There are several cases on the Vans forums where parts of the alternate air mechanism have broken, been ingested, and caused an engine failure. Just a consideration.

[FFTravism]

I have a Raven Cold Air Intake also for mine but haven't started working on that part of the plane. Watching to see what you come up with.

[dramsey]

Wow, that cold air induction presents a huge challenge! I would likely attach an elbow to the RSA-10 and point it up. i would then build an airbox similar to the RV -10 filter air box but make it for a thicker filter to help offset the pressure loss of the elbow. i would use all the space available to maximize the volume and slow intake air to maximize RAM. Taper the airbox inlet much like RV does and bring the inlet (which i would suggest around 4 inch diameter) out to close (maybe 1in gap) but not touching the cowl to allow engine movement. Cut a hole in the nose bowl where the filter box inlet wants to line up, ideally not to close to the spinner to allow the prop to help pump air in. Build a 4 inch external nozzle and attach through hole to filter housing inlet with a 4inch hose. You can bond it in place or attach it with a flange. your choice to make maintenance and removal of the filter housing easier. If you want alt air you can use the RV design but Nev is right they do fail.


Option B is just build a cowl that fits. Thats what I did when Vetterman would not build my exhaust unless i built a cowl with at least 2 inches of curvature. Happy to share photos of that process. Its not difficult, just time consuming.

[N204jh]

Question for folks that have decided to use the Raven Cold Air Intake for a IO-540/580 engine: why? I'm struggling to understand the physics between the principle of CAI. There's a big debate about how CAI increases horsepower - is it the ram air (like a supercharger) and / or is it the cooler air (the name is cold air intake), but then warm air can hold more fuel and that's why the Lycoming air intake is routed through the oil sump.

This is from an email from Rhonda Barrett on their CAI:
"This biggest advantage to running cold air is that you run a larger throttle body, which results in somewhere between 3-3.5" of extra MAP. You cannot do that with the stock 540 updraft sump. The Lycoming angle head sump from a -K series or AE2A sump runs the larger throttle body, but I don't believe any of those sumps accommodate intake pipes for a parallel head engine.

The cold air system is particularly beneficial if you have a high base elevation, encounter high DA regularly or need extra power for short field takeoff situations. It would also be beneficial in aircraft on floats or running air conditioning."

That implies that needing the Raven to actually bypass the oil sump so the air is colder won't help that much. And Colby and others have commented, the sheer amount of work to the lower cowl is extensive and I'm trying to weigh the benefits.

I'd love to hear from folks that have Barrett CAI as well as anyone using the Raven in the field? What results have you experienced? In the end, was the extensive FF work worth the investment?

Thank you!

[coosbo]

Nev, thanks for confirming the Vans RV inlet works well and I'll potentially be taking your alt air input as permission to save myself some work.

Dramsey, I appreciate your thoughts. They've pushed me to look more seriously at an airbox in the nosebowl kind of like a C-182T. I tracked down some pictures of your cowling. Wow! Looks really great, but I'm not sure I have the time and skills to go that route for my first cowl.

John, I’d put little to no weight on my thought process on this one, but here’s what I was thinking at the time I bought the Raven system back in 2022. There really weren’t any forward‑facing induction K series adaptor options proven on the Model Five yet. I’d heard about the adapter Bob was working on, but it wasn’t available then, and I was having a hard time getting excited about the idea of running ram air straight into a wall and then turning it 180 into the warm stock sump on a K‑series. I seem to remember the Barrett option being more expensive, but can't quite recall why I didn't go that route.

The Raven setup at least had been proven on K‑series engines on other aircraft, and I liked that it gave me cooler air. My understanding is that any benefits of warming the intake only apply to carbureted engines. For a FI Lycoming it’s mostly downsides, mostly since warmer air is less dense and carries less oxygen.

There were also a few things in this old Kitplanes article that nudged me that direction. One point I hadn’t heard before was that longer runners (which the Raven system creates) can actually be beneficial for FI Lycomings.

I’ll have to report back down the road on whether I’m ultimately glad I went this way. I still think it’s one of the better options for converting a K‑series to a forward‑facing induction system, but if the adapter that many Model Fives are flying with today had been available then, with good examples to follow that also fit under the stock cowl, I’m pretty confident I would’ve gone that route instead.

And maybe as a note for future readers researching this topic. Many of the angle‑valve IO‑540 variants come with a rear‑facing induction that places the fuel servo right where the BH Five engine mount lives. Salvage and run‑out engines with this configuration are extremely common and often priced attractively because supply outweighs demand. Most of these models begin with a “K” prefix, though there are a several less common exceptions. In my case, changing to a forward‑facing induction wasn’t a performance mod, it was what I thought was the most practical way to use a more affordable engine that otherwise wouldn’t fit the Five’s mount geometry.