Gutted/modded airbox on

[mik_str]

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....

[mik_str]

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

[sirch345]

Cheers for the update Micky Going by what you have achieved so far it's sounds to be pretty close. It'll be interesting to see what the dyno results are like.

Chris.

[mik_str]

Indeed Chris. The only downside is that as I have performed quite a few mods since last time it was strapped to a dyno (HRC ignition, airbox mods, Krankvent sump breather - applies a partial vacuum to the sump to reduce pumping loss) so I will be unable to say exactly what mod does/did/contributed what in the grand scheme of things. I can state, however,that every step has seemingly felt like a positive evolution (ie. everything seems to have produced an improvement of some sort, based on my riding impressions anyhow).

The final dyno numbers should be interesting though.....

[seb421]

Indeed Chris. The only downside is that as I have performed quite a few mods since last time it was strapped to a dyno (HRC ignition, airbox mods, Krankvent sump breather - applies a partial vacuum to the sump to reduce pumping loss) so I will be unable to say exactly what mod does/did/contributed what in the grand scheme of things. I can state, however,that every step has seemingly felt like a positive evolution (ie. everything seems to have produced an improvement of some sort, based on my riding impressions anyhow).

The final dyno numbers should be interesting though.....

look forward to the dyno results hope it's got as many horses as you hope, what you think it might be putting out now since the last run?

[mik_str]

Let's just say I will be truly disappointed if it's below 130 hp and 80 lb-ft at the rear wheel. Anything over that would be a bonus....

I should add that I have ceramic wheel bearings going in just before the next dyno run, yet another "event" to blur the results....

[tony.mon]

Hi, Micky.
"Inspiration" lol- I'll have to add that to my CV....

Good that you got the fuelling set; it's pretty much what I found, although I haven't yet made up spacer gaskets yet. Did you find that they fitted ok and the tank still sat where it should?

The other thing I was wondering was whether those spacers might have a different effect is fitted ABOVE the filter, to increase volume in the lid area, which looks very small and I've often wondered how the air flows properly through that section.
Although it effectively tapers downwards toward the rear of the lid, the airflow will be disturbed a great deal by the front pot grabbing huge lungfuls of air every intake stroke, so I'd imagine that there's a lot of turbulence.

Which of course is why Honda fitted the little airflow blade in the lid, to try to persuade enough undisturbed air to get to the rear stack area.

So fitting the spacers so that the upper volume is increased might just have a bigger overall benefit than fitting them below; or perhaps you could try one either side, of course.
Shouldn't affect fuelling much, if at all.

Just sharing a few thoughts; but as you have a similar airbox set-up to mine I wondered if you'd have a play as well to compare notes?

[mik_str]

Hi Tony,

I have tried in the past to fit the spacer on top of the filter but those expeiments were short-lived so I can`t really comment. Were it not for the fact that in the absence of the spacers the stacks contact the filter, I would likely have put them over the filter. The main purpose of the spacers, however, is to raise the filter away from the stacks so that the air can flow with less disturbence (the gain in volume is a bonus). Weere I to use shorter stacks, I would definitely mount the spacers above the filter, however.

With a single spacer, you can get away with only lifting the front of the tank slightly but with both on, you need to raise both ends. As I am using a shim on my shock, I was already borderline on available threads on the shock mount bolt (which doubles as the anchor bolt for the tank bracket) so I had to get creative (used a titanium nut with one slightly tapered surface and machined a countersink (using a dremel) into the tank bracket, thus allowing the nut to recess into the tank mount). Another matter to contend with is the steel collars at the front. With the angle of the tank changing slightly, you will either have to discard the said collars or mod them to allow the bolts to line up with the holes. I discarded them and made some with some 6mm aluminum tubing I had laying around (sandwiched between two flat washers). Now all is well

Hope this helps.

[masterdave]

So have any improvements been seen from using an spacer either above or below the filter? i have a spare filter and lid sitting in my garage and am tempted to have a play