Air Box Mod... Lots of Pics.. Part 1

[crazy steve]

Well first, the reason for doing this. Looking at a stock airbox it's obvious that intake air is restricted as there's only a bit over 2 sq-in area in the stock 'snorkel'. Drilling the lower box doesn't seem to have much effect in terms of performance either. Installing pods doesn't offer a meaningful gain from what I can gather from those who have done that (other than making getting the carbs off easier); I think the loss of the OEM velocity stacks with pods may offset any gain because of 'turbulent' air (IMHO).

Looking inside a stock air box, there's sure a lot of 'stuff'. You've got the velocity stacks, but with all the internal brackets/filter/hardware, the air has to dodge around all that to get to the inlets. So I decided to gut the air box, converting it to a open plenum, and use a flat panel filter in the bottom; I picked up a spare air box with this in mind. This is a bit ambitious in terms of time to build, but is still something that can be done with hand tools. So, here it is...

[IMG][/IMG]

This is the filter I choose. Selected on size, it's a YA-1602 K&N that just so happens to fit a '02-09 Yamaha XV1700 Road Star. Actual filter area is 4.375 x 2.75, for a total of 12 sq in. One reason I picked this one is it's not as 'thick' as some of the other choices. And before anybody points out that this is smaller than the factory filter, remember: you're currently sucking air through an opening only slightly larger than 2 sq in. This is nearly a 600% increase...

[IMG][/IMG]

Here's the hole laid out; size is 4.875" x 3.875". Can't go much bigger...

[IMG][/IMG]

Ok, it fits... now to make the attaching hardware. The bottom of the stock box isn't all that flat (plus having part of the original filter recess under the filter), so I need to make a flange for the new filter.

[IMG][/IMG]

I'm making the filter mount out of .100" aluminum. I'm bending flanges on this to prevent flex. Clamp it in the vice and beat it over, the piece is oversize so I can get the bends on all sides....

[IMG][/IMG]

Finished flange and retainer. I designed this so it can be serviced with the airbox in place. The two small holes at the back accept 'pins' I left on the retainer; slip the filter in, engage the pins, then 'lever' the retainer up to seal the filter. I'll use a couple of wingbolts to hold it in place.

[IMG][/IMG]

The filler piece for the snorkel hole and the new top mount (I was missing the stock one). I designed this so it could be removed/installed from outside the box, and moved it back for a more direct support.

.... continued in part 2

[crazy steve]

Part 2

.... here's the rest...

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Finished bottom. The piece in front of the hole is the retainer for the wingbolt nuts. Everything except the snorkel cover is attached with 3/16" aluminum pop rivets, and I also used those to seal unused holes. The pieces sticking up around the edge are to join the two halves. I pulled the chrome trim off to conceal the rivets behind them.

[IMG][/IMG]

Finished top. For the top mount, I just rotated the OEM hardware and drilled new holes.

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I cut away most of the stock crankcase vent; more air flow..

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Finished box, rear view. I gooped the seam heavily with black silicon before assembling, then pushed it into the seams with my finger... messy...

[IMG][/IMG]

Finished box, front. Here you can see the finished filter mount with the wingbolts. I powdercoated all exterior parts before putting it together.

Will this offer a performance boost? I'm hopin'...

This is for my 'modded' bike, and I'm still not ready to assemble that one yet, so you'll have to wait to see how much 'go fast' is here. One side effect is the airbox ends up lighter by a bit (about a lb, or 20%), so less weight is always good.

Anybody want any details, let me know...

[xs11lover]

Alright you've got my attention, how long until we know?

[tom clisham]

creative juices

Thanks Steve,
You come up with more ideas than anyone I know! & always good ones.

Thanks for sharing

[Bellerophon]

All I can say is wow! I like the idea of keeping the stock look while improving performance and making maintenance easier. Way cool Steve!

[Toolmaker Tim]

Nice job Steve! Your mind must be a very, ahem, fertile ground for ideas. It just so happens I have a airbox for a 81H doing nothing at the moment. I'm going to try it. Thanks Steve

[crazy steve]

I'll add a couple of details I should have included....

Probably the worst part of this is fitting the two halves of the airbox together. Being plastic, all the edges don't quite line up and it takes careful fitting getting everything matched. I had three tops and two bottoms and used the two that matched the best. Basically, I got the front edge/corners lined up, then 'pulled' the other sides to fit.

On the front edge by the carbs, there's a 'slot' in the lower half. The top matching edge won't quite fit in the slot as it's too thick as-is; I filed it down until it would go in. This will keep this edge straight.

At the back, the top and bottom are different thicknesses (top is thicker). I shimmed the joining bracket by putting an extra plate behind the main bracket on the lower half. I used .060" aluminum, maybe could have added two pieces for a better fit.

At the front and back, you want as tight a fit as you can get. But not quite so tight on the sides; you need to leave a slight (>1/16") gap so the flanges on the chrome trim can go between the halves. Mine 'snapped' in, so I got it pretty close. There's some give in the plastic, so too tight is better than too loose.

The chrome trim on the finished air box has a better fit (no gap between, front corners lining up) than a OEM box...

[lee_dutcher]

Very impressive steve! big kudos on this mod. might have to show us the mesurments of the pieces u used so we can duplicate

[3Phase]

So that's what you were doing ... it looks great!

The only 'problem' I can see is that without the internal plastic blowby recirc spider the oil mist and vapors from the crankcase breather will go mostly into #2 and #3 carburetors, changing the mixture at medium and high speeds when there's more blow-by, and it's going to be interesting to trying to clean the airbox if the oil puddles on the bottom next to the filter instead of getting dispersed into the carburetors.

But that's just a theoretical problem and it hasn't even been run yet! Nice work, Steve!

[crazy steve]

...might have to show us the measurments of the pieces u used so we can duplicate

I've always felt that too-detailed plans tends to stifle the imagination...

[mharrington]

I salute ones who show creativity and ingenuity! For what its worth on my 1100 I still have the vent tube plugged into my airbox but I snipped off the 4 internal tubes that plumbed into each carburetor velocity stack inlet. So the crankcase still vents into the airbox but not directly intruding into the air intake path of each carb. I eventually will install a small PVC breather/filter instead of routing into the airbox.

[cywelchjr]

I've kept mine the way it was because from what I can see of the design, it will at higher throttle settings actually pull a little on the crankcase vent, helping to keep the crankcase pressure down a little. I figure this is a good thing, since there is not a common vacuum source I can use for a PCV valve system. But anything that helps scavenge the crankcase is going to help the engine last longer.

[skids]

So steve, what is the result? More acceleration at mid or high rpms? Better gas economy overall?

[crazy steve]

So steve, what is the result? More acceleration at mid or high rpms? Better gas economy overall?

The bike this is destined for is still just a collection of pieces... so it'll be a while...

Toolmaker Tim says he's going to try this mod, he may have results to report before me.

[lee_dutcher]

well if all the work u put into it (it looks like u put some decent time into it anyways). i hope u get some notacable improvments in performance and mpg. either way i wish i had your ambition