Modded/gutted airbox on...
 

First, my inspiration: www.vtr1000.org • View topic - Airbox modding

Now, I have been toying with the idea of doing something to bump up the airbox volume to help the big twin breathe better and seeing what Tony did (see link above) inspired me. So, project overview:

Objectives:
i) maximize aibox volume
ii) remove all impediments to airflow in and around velocity stacks

work
o removed all internal piping and vent-related mouldings
o blocked off all entry holes
o cut all unnecessary mouldings

estimated net volume gains*
o internal mods: @ 0.5L
o 9mm spacer under filter: 0.9 L (added benefit of lifting filter off top of stacks for reduced turbulence and improved airflow)
o total @ 1.4 L add’l (9 to 10.4L, or about 16% bigger)

Installation:
o placed small cone filters over carb vent intakes
o sump/valve cover vents routed info Krankvent and fed into airbox

I made slight changes to the jetting but have to take it out for a test ride to see how it works (raining today, have to babysit my daughter....). I can say, however, that adding the two (4.5mm) "shims" under the filter gave positive results. In addition to raising the volume, it helped lift the filter off the stacks (was touching before).

Will keep you posted on how it works but the added volume should help performance....

Are you gonna make those mongo air snorkels? This seems interesting. I would like to see what amount of jetting is required to exploit a ram air intake/ huge airbox. Honda was already doing ram air in 98 so there must be answers somewhere.

no, no ram air. First of all, I don't have the fabrication skills to undertake such a job. Second, it is of very little use on the street, the benefits only truly beginning at speeds well above legal, the kind that get your driver's licence pulled.

My airbox is a modded stock unit, not a custom carbon unit like that used by Moriwaki on the BSB bikes

I had similar thoughts a couple years ago. What I did was removed and seal everything. Crankcase breathers each have a cone filter that vent to atmosphere. For the slide diaphragm ports I ran tubing from each and joined them together with a 'T" fitting, with a single cone filter on the 'T' so that both slides get the same air pressure. I did not do anything to raise the airbox internal height and am using stock velocity stacks.

So the weather was a bit more cooperative this morning so I got to go out and try my new set-up.

FWIW, while fitting the "new" box, I adjusted the jetting in anticipation of increased airflow: I eased off the fuel screws by @ 1/4 turn and I raised the needles 0.0155" using some Yamaha plastic shims. Figuring those changes would be pretty darn spot on, I backed off the F-C adjustment screw to 3/4 turns out (had been running at about 1/3 turn out before the mod). I thought that this should get me close, but likely on the lean side (which I prefer as a starting point as I find it's easier to tune the F-C (indeed, any carb tuning) when starting a bit lean and adding a bit more fuel in small increments until all hiccups and hesitations are gone).

So bike ran ok at low speed and didn't sputter when I rolled off the throttle, telling me the fuel screw was pretty darn close. I found it was surging lightly at highways speeds so I evnetually got back to the 1/3 out on the F-C screw (which richened the mixture) and was good. Impressions: bike seems to have a smoother response when rolling on the gas at any speed up to legal speeds; same pull, just a bit less frantic with the initial hit. As for higher up the rpm scale, I tried rolling on it in 4th at about 5500 rpm and it seemed to come on harder than I remembered, charging remarkably hard to redline.

I will have to get it dynoed to see (butt dyno is not the most accurate measuring device) but so far, no bad vibes from this experiment or the others I have tried this year (which includes adding the two 4.5mm shims under the filter, and cutting a hole at the front of the plastic shelf under the airbox - greatly increases the influx of air to the box).

From the rider's seat, the bike now runs smoothly at all speeds, with no flat spots or hesitation anywhere, response is "right now", and it seems to run slightly smoother (in terms of vibration) too.

cheers

Have you kept the snorkel?

Snorkel is still there, albeit heavily modded too. The internal divider is gone, I removed as much material as I could with the dremel, and finally, I removed the internal foam and smoothed over the step with silicone.

Induction noise louder than the exhaust now? :))

nope. It`s all good.

Seems like the FC screw is in pretty far; I keep mine at 2-4 turns out. Turned in more than that and it goes wildly rich.

It all depends on where your baseline is. As I live at sea level, once it`s jetted for the coldest temperatures (fall and spring riding), I have no need to go richer, ever. On the other hand, should I wish to go riding somewhere at higher altitudes (Mount Washington,....) then I will surely need to go leaner. With the F-c set at 1/2 turn out (at this time of year), I will at most have to go 1/4 richer for early and late season riding, while retaining a fair amount of flexibility on the lean side should the thin mountain air come calling......

For argument`s sake, what additional benefit would I get from jetting up only to be able to turn the screw leaner? Reply: None at all....... In light of my explanation above, it would actually rob me of the flexibility I may need at some point. Besides, the bike runs absolutely great now, and that is all that matters.....

You are correct that the bike running absolutely great is all that matters.

The benefit from jetting up and then turning the screw leaner is that you get more of the airflow synchronizing benefits of the FC that way. With the screw nearly closed it is not doing much of that at all.

Good point. I may have to look at that at some point in the future.

Thanks for the insight.

cheers

More feedback for this series of mods.
 

There are now several people trying this mod/series of mods out in the UK; with good results. the link that Mik posted at the start of this thread is to my original work and trials, but the thread's opened up to include other people's experiences. Hopefully there will be dyno figures to show exactly what benefit or losses there are.
My own bike now feels much stronger; bottom end and midrange has improved but fuelling needs attention. Due to work shortage at present I'm not able to dyno it, but might be able to get a fuelling run or two past the wife....

Tony.mon

Hi Tony,

I have since removed my fully modded box (although the Krankvent and 9mm spacer under the filter remain). I ran into some problems and, in the process of diagnosing it, decided to go back to a known setting that worked. That being said, the fully modded box is still sitting in the garage and will surely find its way back onto the bike at some point in the future.

FWIW, it seems the problem I was having was traceable to the hole I had cut in the plastic shelf located below the airbox. The bike was prone to surging, a problem which has since disappeared (with the blocking of the hole).

I am leaving for a a short bike vacation at the end of the this week and would rather head out on the road with a bike that I know works well (and not to deal with roadside tuning). However, it`s open mod season when I return......

i have just done this mod to mine and it works very well .
i will be getting it on the dyno next month to see whats its fuelling like.
but seat of the pants feels stronger with no lean serge's and pulls harder to the red line