[Arizoni]

More on the adventure of the air filter:

As I was looking at the inside of my plastic air filter plenum I noticed the hole thru the back wall where the air comes into the inside of the filter seemed rather small for a filter with a 3 inch inside diameter.
It turns out that the hole is only 2 1/2 inches in diameter and the metal piece that runs down the center is almost 5/8 inches wide.  That leaves an open area of about 3.4 square inches, the equivalent of a thru hole that is 2.08 inches in diameter.

I realize the paper filter material is a substantial blockage but the area of the inside of the paper filter is at least 16 square inches in area.

With this in mind I set to work with my Dremel tool to see if I could enlarge the inlet hole, at least to about a 1 1/2 inch radius.
Because of the metal strap down the center of the hole and the two wiring harnesses that are immediately behind it I had to leave the central area alone but I did manage to enlarge much of the hole towards the front and rear of the motorcycle.

On today's ride up the local freeway I was quite amazed.
The bike accelerated effortlessly to over 80 mph and was still accelerating when I had to back off for the slower car ahead of me.  Remember, this is climbing a moderate grade.
I also noticed that from a stop light, the engine seemed to rev up much faster and it didn't seem to be losing power at the higher revs.
My buttometer and earometer seemed to think the bike was accelerating faster at WOT in all gears.

Maybe it was due to the cool air temperature (56 degrees F)?  Maybe it was due to the humid air (60 percent)?  Maybe it was due to the enlarged air inlet?

Below is a drawing that shows the added inlet areas.  You may not be able to enlarge your inlet as much as the drawing shows.  I know because of the wiring behind the plenum and some frame tubes I couldn't.  I also "hit metal" when I was removing the plastic the inlet is made from so I stopped when that happened.

If you try this on your bike, be sure to get all of the filings/grindings out of the inlet plenum before buttoning it back up.  It's a direct path into the engine for anything that is left behind.

I am hoping that someone on the forum will try this on their RE's inlet and let us know if it makes a difference.  It may have been a fluke but if it's not, it might be the best thing since sliced bread.

[Ducati Scotty]

I'll check my C5 when I get home.  I think in addition to the small opening, on the C5 there is a shroud to prevent any water/crud getting in since the opening faces the center of the bike near the fender.  I think that opening may be even smaller.

When I had the pod filter mounted right on the throttle body, there was certainly a bit more power everywhere and a beautiful intake howl.  But the drop in MPG indicated it was a less than perfect solution.  That said, I think you may be on to something, spotting the inlet as a restriction.

Scott

[Arizoni]

As you may know, my bike is a G5 and I have no idea what the C or B bikes plenum looks like.
There did seem to be some baffling behind my air box to keep out water but I didn't fool with it.

[1 Thump]

Prof Stack tested his C5 on a dyno and noted that just opening the airbox (with a KnN) resulted in a 5% HP gain at the rear wheel when compared to closed airbox (With a KnN).

http://www.enfieldmotorcycles.com/forum/index.php/topic,10706.msg125425.html#msg125425

[singhg5]

Arizoni:

That sounds a good idea to open up the hole a bit. On my G5 also the electric wires run right behind the air hole across the middle, so widening the hole has to be done very cautiously.

Ducati:

How does your C5 look compared to G5 whose pictures I have attached below ?

[deepaksuttatti]

i did increase the inlet hole to dia.80mm(3.15") just as arizona did. Yes the bike feels smoother at all rpm's. It does easily accelerate to 110+ Kmph (70mph). An exercise worth doing on the C5.