A few months ago, I added short velocity stacks to my 5th gen & after much research it would appear that a larger airbox would be an advantage. So without the room to make one I decided to modify the existing one in a way that I think will improve the effect of the short stacks. The main issue I have with the standard one is the filter is in the middle & it obstructs the airflow to the velocity stacks.
So with a leap of faith I removed the K&N & started work, below is the result.
Take one K&N & cut it up, to keep the airbox seal & give me a filter element to relocate.
Airbox bottom half with my short stacks & no rim seal.
As above with the K&N rim seal.
Take a top half that normally looks like this.
Then make it look like this.
Add the filter element to the new hole.
Then add some sealant around the rim & rivet or bolt down.
View of the inside, if you bolt down, then use nylock nuts to ensure they don't come loose.
Just needs reoiled before use. I have a ramair intake under the headstock, so need to redo the seal to the bottom of the tank & get a dyno run to see if it works. Will let you know the result when I do.
Shortening the stacks I think will have a very significant effect on the spread of power, as their length is usually tuned to prevent major holes in the powerband. If I remember correctly the MV Agusta F4 had a variable intake system so that the trumpet length changed with revs, a bit like a the old YPVS system on the Yamaha two-strokes, and that was done so that the trumpets could be optimised at all revs. Other bikes (I think maybe the Kawasaki Z1000) have different length on the outer and inner inlets. I will watch your progress with interest!
Well another idea I have kicking around my head is variable intakes & now I have the space in the airbox for it !!! :)
That said I did a 2600 mile euro tour with the short stacks & the bike ran a treat, does not appear to have lost any power anywhere & pulls harder up top. Had a power wheelie in 4th at 100mph off a tiny rise just before the trip ! Never did that before.
The whole point was to try to move torque higher up the revs to make more power, only a dyno run will tell if I was successful, but it feels good.
Man... you are brave! Great idea... brave execution!
I would've locktighted, superglued, and then safety wired the nuts on the inside of the airbox lid... there nothing between them and your intake tract. My Dad cracked a piston once accidentally dropping a small nut down his carb throat...
Well I'm working on the principle that I have used nyloc for many years & never had one come loose. I was going to rivet them on then discovered the long rivets I had were too short. I may rivet in future once proven to be good.
The bolts are under compression load from the rubber of the filter surround so combined with the fact that the airbox is plastic the nyloc nuts it will be fine. The ones holding the velocity stacks are over length & soft thread locked in place, been in there for over 3500 miles & never moved.
It reminds me of the K&N clamp on filters, except its a rivet over filter. You had better turn in a patent on that today in case it works. We may be seeing "cover-filters" as K&N's 2015 new line of high performance filters.
I didn't do a stock run as there are loads on the net showing 94-96 HP. The 98 is with a K&N, airbox top opened up, Motad headers, same Delkevic can as now but on a low mount & a new PC3 fitted with a downloaded map. 101 is with custom map. 102 is as before but with my new cams old map, 107 is custom map for the new cams.
The vtec has 2 long & 2 short velocity stacks & best I can tell the short ones are about 10mm shorter than the other two, but the vtec has peak torque approx 250rpm higher than the 5th gen (8750-v-8500). So my plan with the short velocity stacks is that the bike will prodiuce peak torque around 9500-10,000rpm. If that works, then peak power should be about 113rwhp. I know its breathing more air as my fuel consumption has gone down & general running temp has gone up.
If this works, its a simple mod. The extra space above the stacks with the latest airbox mod should encourage good breathing with a larger slug of air directly over the stack. If I lose too much bottom end then I might do a set of adjustable length stacks ! But that's another project :)
I've just bought a TBR full high mount system & looking at other peoples dyno traces, they add about 5hp on stock bikes, so I'm hoping it will work better with my other mods & if I can add another 5+hp, I'll be well chuffed. My original plan was to reach 200Kg wet & 120rwhp. Not quite made the weight, but it is approx 30Kg lighter than stock at 214Kg wet. So if I can get close to the 120hp, I'll be well impressed :)
OK got a dyno run done today. The only mods since the last custom map in July 2012 are the short velocity stacks & big airbox mod as pictured in this thread, plus the custom high mount link pipe I had made.
So without further ado;-
So as you can see my estimate of peak torque rpm has been realised, even if it has lost approx 3ft/lb. Likewise the power numbers are approximately where I estimated. The fuelling is a little lean in a few places, but 112rwhp is good for now :)
Well it feels noticeable this was how I rode it all round Europe back in July, apart from the filter mod to top of airbox. Revs hard, goes great, love it.
Wow... got to love it when the math works out! You were right on track with your HP estimates.
I'm surprised it started to get leaner after 9k rpm... dial in that top end fueling and add the TBR exhaust and I think you may accomplished your goal!!!
Good power figures Mohawk!...I have fitted the short stacks to my Vtech and the difference is really noticeable..It pulled 150 mph with the long and short stacks..with the short stacks pulls 163mph,clocked by a mate on a K1200s...not on a public road obviously...I'm getting 110bhp on the dyno with motad headers and FMF cans..I've got a spare airbox and you've got me thinking..smoked a tuono and z1000 top end also!
Have you had any grit getting past the air box lid?..
would these trumpet filters work for the big air box mod, so you dont have to mod the airbox- except for removing the filter? Just slip them over the stacks?
Don't think there would be enough height to get these within the airbox.
I've done a similar mod with the K&N filter as what Mohawk outlines in this post.
There is a small difference between the Gen5 and Gen6 airboxes but it is completely doable.
I used to use sock type filters like these on MX bikes modified for Grass Track back in the day.
You need to be able to use the entire sock area to pass enough air.
One thing I did do as I was making up the airbox top with the cut up K&N was to measure the pressure drop across a standard Honda paper filter and the K&N at the same RPM level using an electronic manometer capable of measuring down to 0.1mbar. Stuck a 4mm nylon elbow in to the side of both of my airbox bottoms, below where the filter would normally fit.
What I found what that at 5000 RPM the paper element showed -0.2 mbar pressure drop across the filter.
The K&N, at the same RPM showed -0.1 mbar drop. This was a brand new K&N filter straight out of the box and plastic bag.
So they do pass more air as they say they do.
Just thought it worthwhile proving once and for all.
