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

[IanDMacDonald]

Ian so the bottom is gone on the air box, really want it to look stock.
Ever thought of putting just the bottom sides on ?

Nope! Looks good to me!

[crazy steve]

There's another method for installing carbs that works well too. Install the carbs to the motor first, then work one side or the other of the airbox onto the carb inlets. Once you get the airbox started on one side, loosely install the mounting bolt on that side (the airbox will be 'cocked'). This will prevent that side from popping out, and you can now 'lever' the other side on.

[James England]

Nope! Looks good to me!

nice gear linkage!

[donebysunday]

Ian, you have near matching XS750/850 and XS1100, both look good the way you've done them. Both have the filter mod ?

[Dan Hodges]

Drilling For Air

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

You can use the stock snorkel and a K&N replacement filter and drill holes in the tray beneath the stock filter for more square inches of filter area than you are getting with your combination.

I wound up with 4 one inch holes in my tray when I was beating mine on the dyno. I had room for a couple more 1/4 inch holes however I failed to get anymore power with more holes than with my original 4 holes. I first used 2 1 inch holes then four and so forth.

I eventually went to K&N pod filters attached to 4 inch long rubber boots(velocity stacks) that I bought from the hardware store.
The stock velocity stacks in the stock airbox are 4 1/4 inches long as I recall however a 4 inch stack is as long as you can use with the pods because any longer and the outbbard filters hit the frame.

If you use the K&N pods without the velocity stacks you will lose low and mid range power and some of the cheap pod filters are restrictive.
I vented the crankcase via a hose to a small K&N filter mounted on a fabricated bracket behind the center two filters in front of the battery and out of sight.

I used a Dynojet stage II jet kit in my carbs with the pods and it made about 5% more power than it did with my modded air box.....after I got it jetted right which was a pain with the pods.

If you ride in a heavy rain with pods you will need what is called a rain sock for the filters and with a modded air box like you have described you will suck in all the water in your town and if you try to pass an 18 wheeler on the Interstate in a heavy rain sucking water through your trick airbox, OMG..........tis the reason the little guys put the stock snorkle under the seat.

Good luck with your Eleven.

Dan

[skids]

Steve, did you notice changes in performance indicating the need for jetting changes?

[crazy steve]

....If you use the K&N pods without the velocity stacks you will lose low and mid range power and some of the cheap pod filters are restrictive.

This confirms my reasoning for modding the OEM box; to retain the stock velocity stacks...

If you ride in a heavy rain...

Not if I can help it.....

Skids, this bike isn't together yet so I can't say what if any jet changes may be needed. I'm hoping for a performance increase...

[LoHo]

Geez, Steve...I was perfectly content with my stock air box and now you have to go and come up with a great idea that retains the look and tuning of a stock bike with a more available and larger area filter? Now I'll think how great the mod would be every time I look at her. If I follow my usual pattern, I'll buy the new filter tomorrow and keep it in on a shelf for two years, or do the mod next time I bend some valves..whichever comes first.

Curse you, Steve...I was so content, but now....

[crazy steve]

Yeah, I know what you mean... I was ready to start reassembling the '78 'modder' bike when Phil posted his FJ fork conversion, which I decided I just had to have. One thing led to another, and the bike still isn't together...