M

mlwynn

Well Known Member
Hi All,

My RV 8 has a James Cowl and a forward facing AFP injection system. With the James cowl came a fiberglass induction system into which you are supposed to place a KN filter. The alternate air arrangement goes on the side. The problem is, the alternate air is forward of the filter. Hence, if a pigeon flies into the air intake and plugs it, then you hit alternate air and everything is fine. If your filter ices or gets clogged or occluded with a piece of plastic, the alternate air is of no use what ever.

That did not make any sense to me at all. For that reason, I bought a Rod Bower Ram Air unit that fits on the front of the AFP and connects to the front scoop. that is a seemingly elegant solution to the issue from a mechanical point of view. With the Bower unit, you take off with the ram closed, using filtered air from the inside of the cowl. On some level, this is like taking off with the carb heat on. I know that our planes are somewhat overpowered and this probably won't really matter, but it still seems somewhat sub-optimal.

Has anyone come up with a better solution for getting filtered air to the engine with a functional alternate air? I am thinking about trying to fabricate something out fiberglass that will move the filter forward and place the alternate air behind the filter. The area is cramped, only 9 1/4 inches from the back of the scoop to the AFP throat. Also not a lot of room side to side. Could be an exercise in futility. Thoughts?

Regards,

Michael Wynn
RV 8 Finishing
San Ramon, CA
 
Alternate air

My James inlet that I purchased last year has three pieces , one fits between the filter and the fuel servo , it allows alternate air to bypass the filter . Can email you some photos .
Tom
 
Alternate air

I would love to see a photo. They must have come up with a new design--or else I'm too dense to figure this out.

Thanks,

Michael Wynn
RV 8 Finishing
 
Definitely a Design Chnage

I went on the James site. Under instructions, there are pictures of the airflow conduit. Definitely NOT what I got from them. I bought mind about six years ago (very slow build). The previous design was fairly funky. This looks much more functional. I will give them a call and see what I can do about getting the new design/

Thanks for the info. Would still like to see the photos.

Regards,

Michael Wynn
RV 8 Finishing
San Ramon,CA
 
The alternate air on my sam james system is behind the filter and is opened and closed with a cable from the instrument panel. I had a number of calls with Will James and he did an excellent job of going through the design with me. I suggest you call Will (his number is on their site). If you do not have enough pictures, I can take some middle of next week.
In the end, the system is straight forward. (I am still building)
 
Airbox Alternative

I had looked at Dan's custom intake and was planning to sort out my own when the folks here clued me into the new Mark III James design. It makes better mechanical sense than their original design in that it places the alternate air where it belongs, post filter. The space for induction system is relatively restricted by the cowl design, so there will be some limitations on what I can stuff in there.

I had not thought about the potential restrictive aspects of the filter design. Has anyone done flow testing? Is there a way to sort out how much MP drop I will see with the round filter?

Perhaps I will start with their design for the alternate air and induction and build a variation that uses a less restrictive flat pleated air filter as Dan suggested.
 
Flow Testing an Induction System

Hi Michael,

The following procedure will give you some relative data on the efficiency of an induction system (filter, airbox, inlet, etc).

Turn on your master and, before you start the engine, note the mp indication. This will give you the ambient pressure in the engine. Do a normal run up etc and then, just at lift off speed note the mp. Subtract the noted lift off mp from the ambient number. This will give you a rough estimation of induction loss. You can then test various induction system components using the same procedure and comparing against this baseline. Back in 2006-2007 I was dealing with an induction restriction and used this procedure to test a number of components in my 0360 James induction system. I was loosing 1.8 inches of mp from ambient while, with a Vans standard FAB system the loss was 0.8 inches. The restriction was found to be the carb box (which Will James redesigned in 2007)---which I changed to a home grown design. Now the loss at lift off is 0.6 inches. I recently changed my engine to FI and the loss is still 0.6.

BTW, I have the E-0995 filter--it flows far more cfm than is required by a 360 ci Lyc at 2700 rpm. Do other filters flow more---sure, but can your engine use the excess flow capacity -- or maybe excess flow capacity can be converted into RAM pressure--don't know--maybe others can address this!

Hope this helps.

Cheers,

db
 
Last edited:
You must log in or register to reply here.