The following thread and advice by Twinfan, plus the additional input from Gob-ny-geay, set the ball rolling
as to where to proceed next in improving the stock airbox, but without actually removing it.
So, a few clicks on the PC brought two sets of these to the door........
Mikuni RS velocity stacks which can connect directly to the 55mm O/D of the stock CVK carb inlets.
I bought the 70mm and 50mm length stacks so a little “playing around” can be done.
Now we all know what the original airbox/carb rubbers look like, with their internal step and alterations
in shape............
After removing the side of the airbox, (which can be done fairly easy by just removing the battery and the 4
small securing bolts in the battery box, plus the two mudguard torx screws (adjacent to the igniter) to loosen
the box enough to get at the difficult screws) and pulling out the original rubbers, the 50mm stacks slotted in
like this....
You can see I had to grind off a portion of the circumference of the bellmouth to allow it to sit next to the
central bulkhead of the airbox.
A little Dremmeling of the oval opening was required and a section of the supplied sealing rubber was cut
and siliconed into place...............
The airbox was then all reassembled and the double-entry Unifilter replaced.
Outwardly the airbox looks no different from original, other than the connection to the carbs are now shiny aluminium!!
I decided for now to just fit these as a direct replacement to the rubbers, without playing with the plenum
length by adding to or removing the rubber spacers (Insulators, as Triumph call them) at the cylinder head
entry. I can save that for another day!!
I decided to test run the bike first, without altering jetting, to see what difference the stacks made to A/F ratio.
Testing showed I was now getting an amazingly lean reading of over 16:1 at everything over 3000 revs!!
In other words I’d dramatically increased the airflow to the engine, by the biggest marginal increment of all the different freeing-up mods so far!!
I have now had to step up to 145 jets to regain A/F parity of 13:1, which equates to the same size needed when I ran the bike, while experimenting, with no airbox and NO filters!
The assumption is that an ARK’d Scrambler would require 140 jets. And I’ve now surpassed that!!
(maybe some ARK'd Scrambler owners could confirm?)
I’ll leave you all to draw your conclusions on that, and invite the comments which will follow.
Next step is obviously the dyno to compare the results and get some comparisons.
Testing the bike by SOTP would certainly indicate performance gains across the board.
Also I'll try to play around with differing plenum and stack lengths.
On that I’ll keep you posted!
A big up to Twinfan for his guidance and suggestions. Those guys in Germany are so knowledgable in the stealth-mode modifying of the engine (due to official restrictions imposed on them). It would be great if they could impart some of their vast knowledge on us here.
Cheers also to Gob-ny-geay for the very detailed and informative description of his version of the above.
Wow, 145s - who'd a thought?? I guess taking out that S curve in the intake rubbers had something to do with it, too. I wonder if running with the stacks and without the box would make any difference? I'm guessing not. Well done.
Now I think your on to something here. I have a b.c. ark kit running 140 mains runs great . Micken- dude claims the small k&n pods don't flow that well. He likes uni says they flow better -he's right only I' don't like them less protection. I've seized a few dirtbikes from foam filters mind you dirt bikes . In the dirt you need to run two foam filters for better protection. So back to the point I'm glad I saved my airbox double opened sides, a large k&n air filter (more airflow than small pods),velocity stacks to straighten out the flow. Just think I'll only be out $300.00 bucks for the ark kit. With my luck & Ventura's smarts this will be the hot setup. I hope it is my right side cover didn't mount that well & the my fuse box mounting job is mickey mouse - (on the scrambler). Can't wait for the dyno results.
Very interesting ,how much did the stacks cost? I would bet the stacks with no air box would flow better then just the carbs withno air box.I think you are on to something for guys who live where you must have the air box to be legal.I wonder if it would flow enough to keep up with better flowing carbs it seams to work with stock carbs.
Varna the unis are fine for a street bike they are under the side covers so unless you run the bike under water they will work just fine.
Dont take this the wrong way but if you dont have to run the air box what do you gain over no air box ? If it flowed more air or made the bike more rideable I could understand it .Looks like to me just neatly cutting the air box out of the way and putting on pod filters is easy and allso makes it easyer to pull the carbs.
.......... but if you dont have to run the air box what do you gain over no air box ?
If it flowed more air or made the bike more rideable I could understand it .
Looks like to me just neatly cutting the air box out of the way and putting on pod filters is easy and allso makes it easyer to pull the carbs.
By my reckoning Ive reached at least the point of equating to an ARK'd bike, or maybe I've surpassed it?
And the airbox is still in place!
The dyno will tell all.
But cost-wise I havent had to shell out for an ARK and pods, and all I've spent is my time and the stacks, plus a few jets along the way!!
And during the whole process I've taken great enjoyment and satisfaction from it all!
Yeh Pokeyjoe, I still have the 790 cams in there.
When I fitted them it didnt make a lot of difference to the jetting, altho it certainly did to performance!!
I think I went for 132 to 135 when they went in.
I'd hoped to dyno the bike with the 865's in there but would need a stock Gill igniter to make sense of a comparison.
Unfortunately I cant get hold of one as mines been Pieman'd!!
Well done Ventura. This goes to show that continual experimentation, and ignoring the "virtual degradation" stuff pays off big time.
Did you open up the opposite filter side?
I see by your pics that you also still have some of the ribbing and mounting shelfs for the inner airbox components. A few minutes with a hacksaw and dremel will trim these out, as you know. You can see in the photos where the "Restrictor" mounting channel sits right in front of the stack opening.
My SOTP Dyno clearly detected the obvious gains, as your air/fuel set-up confirms. I would expect to see some low end torque gains on your dyno chart, from the improved air flow / cylinder filling at high velocity via the stacks.
The $300 saved can now maybe be put towards a five angle valve seat cut, and raising the compression ratio a point or so. You can clean up and bead blast the intake manifolds and rubbers for free, as well as the intake ports, valve bowls and combustion chambers. The exhaust valve bowls and ports you can also clean up and mirror polish vs blast for free. Additional proven gains here once again for a little time in the workshop well spent, a steady hand and a few dollars.
So, basically the stock air cleaner or aftermarket one (K&N) has more surface area than UNI or K&N pods. The problem is the restrictive airbox . With both sides opened up, the box gutted and the addition of velocity stacks it might be the best setup. Simply because this might be less restrictive than 2 small open air pods. The velocity stacks I think are the key. Now chew on that. Course I might have to if ventura gets a negative dyno run.
I have modified my bike's inlet with knowledge gained from your previous posts.
Sweetened it up nicely!
This latest project of yours is definitely on my to do list over our upcoming southern winter.
Do you think that the mods you have just done, would benefit from the ignition module modifications that Pieman does, and would a better cam be a timely addition when doing this work.
In asking this, I am seeking your thoughts on the air intake modifications as a stand alone tune up.
Slightly off topic, I did about 1800 k's last week on the Bonnie, down to and back from Phillip Island to watch the World Superbikes, apart from the seat, this bike rocks!
I've modded my '06 Scrambler to the extent above minus the addition of velocity stacks. It certainly is fufilling work for such a small amount of $$. Plus I just love beating my airbox into submission to get to everything. Everytime I manage to get it back together and relatively sealed, another tweak comes up that I must attempt.
So far I've been very pleased with all my airbox butchering, and I'm far shy of $300+ that I'd be out for a box elimination kit.
Ventura-
Are you using the foam (or what looks like foam) to seal the area between box opening and vel. stack? If so, what is it, and where would it be found?
Also, what do you mean by "supplied sealing rubber"? Is it someting that comes with the stacks to be used for mating them to the carb inlet?
As an aside, I just picked up a set (comes in set of 4) of Mikuni RS 50mm velocity stacks like those used/referenced in Ventura's op. If anyone's interested, I'll make them a good deal on a pair as I obviously only need the two. Just shoot me a PM.
I hope this thread progresses as the previous chapters have, that is, with lot's of usable info including results/findings. That thoroughness is what got my box mods to the point they're at!
as ventura said he was informed by me with a lot of pictures, infos and even where he can get them
one thing i can tell you for sure is: those stacks even work with CR, FCR, dellort PHM 40...i know some guys here in germany with these configurations and it works well on all carbs with stock airbox...
the biggest problem is the step in the original rubberpart...that causes interferences and turbulences
evenmore i know guys increasing airboxvolume by using LifePo4 RC-car batteries instead stock battery to gain 2l more airboxvolume...others close the stock hole on left airboxside and put an airfilter on top of the box where normally the battery is
and so it gets better and better...but i think just this little improvement with perfect buck to bang ratio is great
@ ventura and all other airboxusers
go to your local VW-dealer and ask for tapping screws with an allen wrench head...they have the right ones with washer fitted in the correct length...but in silver...not black
so when you have fit the velocity stacks put in those 4 screws for the battery box so that the box is fitted in place...now you can put in all the screws and at the places where you normally don´t get to (behind the frametubes) you can use a long nose pliers so that the screws fall in the hole and from the backside you can tighten the allen screws with an open-jaw wrench
now you don´t need to dismount the airbox anymore
@ gob-ny-geay
you will gain better results when using those steps ventura bought...those sit directly on the carb and flow is better...your version is fine...but still turbulences and interferences
@all
motors with (doesn´t matter if 360 or 270) 790 cams better use those 50mm stacks to get better results in hp...the 70mm version is especially for the 865 scrammotor to gain more torque at lower revs...you have to throw out the plastic distanceplate between cylinderhead and inlet manifolds to get the right length and best performance (right length is important for best results...just try out with/without distanceplate and/or maybe 50 or 70mm version)
but at least you can try out which version you like more...it ain´t that much money you spend
at least i want to say that all these informations and improvements about the velocity stacks in combination with stock aribox base on the testings from our godfather of twintuning here in germany who´s called andreas...he´s the one who should be with our best thanks
Many thanks to all for the positive comments.
I must reiterate that Twinfan should take a lot of the credit here.
Our PM's have been quite technically involved!!
Great info Ventura!
Do you think that the mods you have just done, would benefit from the ignition module modifications that Pieman does, and would a better cam be a timely addition when doing this work.
In asking this, I am seeking your thoughts on the air intake modifications as a stand alone tune up.
Pete, thanks for the info on your road trip to Phillip Island!!. The best I could do was watch the highlights of the racing on TV with the heating on full blast and the bike securely tucked-up in the garage!!
Your a lucky boy!!
I would recommend to anyone the changing of the cams and Piemans magic-making to the igniter.
Cam swapping is a very straight forward undertaking and the results are quite dramatic.
Regardless, the airbox/stack mod on its own will undoubtedly lead to very positive increases in performance.
The A/F results themself clearly show that.
Ventura-
Are you using the foam (or what looks like foam) to seal the area between box opening and vel. stack? If so, what is it, and where would it be found?
Also, what do you mean by "supplied sealing rubber"? Is it someting that comes with the stacks to be used for mating them to the carb inlet?
The stacks come in a kit, are specifically for fitting to our bikes and include instructions, clips, sealing rubber and stacks.
The rubber is for sealing between the stack and the opening in the airbox thro which it is poking.
twinfan what have the guys running the fcr carbs done to there heads are they stock heads? What kind of hp are they getting? A good big valve flowed head will out flow fcr carbs a stock head wont flow as much as a fcr carb will.In other words I dont know if the air box mod will work with a 80+hp motor.It should work fine till you get to the point where the head/carb set up needs more air then it can flow.I would have to bet money it wont flow enough to keep up with the 42mm carbs on my bike.
twinfan what have the guys running the fcr carbs done to there heads are they stock heads? What kind of hp are they getting? A good big valve flowed head will out flow fcr carbs a stock head wont flow as much as a fcr carb will.In other words I dont know if the air box mod will work with a 80+hp motor.It should work fine till you get to the point where the head/carb set up needs more air then it can flow.I would have to bet money it wont flow enough to keep up with the 42mm carbs on my bike.
one guy with PHM 40, overworked head (still with stock valves) and 10 or 10.5 compression (don´t know 100%) , 790 bonniecams, camshaft retiming, 2-1 zard, aftermarket igniter, stock airbox with no snorkle/restrictor, 800gr. lighter flywheel, shark 2-2 exhaust, velocity stacks...he´s got 77bwhp...still with stock pistons
he´s now making bigger valves through a machinist and will put 904 any time
the next one...he´s got 904, fcr carbs, stock airbox with no snorkle/restrictor and all the other stuff...he´s got sth about 90hp...so it works even with the airbox
those stacks mean so much to the airflow...whether on CVK, CR, FCR...with CR, FCR, PHM next problem will be the small valves...but you know that
just try some of these stacks...they must be sth. about 50 bucks in US...go for the 50mm version with bonniecams
As you know, I've been an extremely strong proponent of the "Airbox" mod for many years, and you've seen my mod's. The only difference is in the how the velocity stack / rubber mount arrangement is fixed, and I'll need to think awhile on that.
My feelings have been that the "Airbox" was never really an effective "Airbox" in it's original design from Triumph, but moreso an intake noise restricter, and a simple air filter housing. That said, with all of the interior restrictions removed, and the velocity stacks installed, we may now have a few things we didn't have before:
1.) Free air space. The formula for an effective airbox design calls for many things, including a minimum volume of 1.6 times the cubic capacity of the cylinder(s), 0r 1384 cc. The gutted airbox has this easily. Further to this, the carburetors like to see filtered, non-turbulant air at their entrance. This is easily and amply supplied with the gutted, but sealed airbox.
Note on your next dyno run how placing your moving hand in areas around the carb entrance immediately effects the results. Airflow into the carbs is best left still, and undisturbed. Turbulance and air/fuel mixing occur AFTER the carb inlet, via the Bernoulli (sic) effect and intake plenum / valve inlet / squish band design.
When is an airbox not an airbox? When you put a hole, or opening in it other than the filter openings, and break the seal effect. For those who may argue that there can be only one entrance - see Hyabusa for example, and V-Max.
2.) Maximum airflow is maximum airflow, and without either supercharging, or pulse tuning, you cannot get more than the cylinder(s) will accept. That said, if we are now achieving more than straight, open carbs, pulse tuning must be taking place, and we have achieved much greater Volumetric Efficiency. Having the velocity stacks on creates the plenum length required, and helps to allow for the pulse intake phenomina. Previously, with the rubber intakes, this "pulse" was difficult. Try playing a rubber saxiphone!
Two very small concerns / questions I have are:
A.) The total elimination of the "rubber" connector between the carb and airbox. Although our great Bonnies are much less vibration prone, we are still advocating connecting the carbs / stacks, and airbox somewhat rigidly. Yes, their seems to be a foam piece, but is this a true seal? Back to #1 and #2 above. This led me to retaining the rubbers. Please advise of how you feel about this seal. At roughly US$37.00 each, the "twinfan" versions are no problem, and a bargain at that for the performance returns - just need to be convinced of the longterm sealing quality.
B.) Twinfan - you noted earlier an idea about cutting out the battery box, and adding another filter. Isn't this again against the Airbox design principles?
I concur and fully appreciate the fantastic and obvious great results of these airbox / velocity stack mod's seen thus far on my bike, and without any doubt whatsoever can claim better performance, so you definitely have my vote and full support on this. Let's see Ventura's dyno results, which should be interesting.
Ventura - any chance that you could make a dyno run with the Velocity Stacks alone? Then the additional runs with the stacks properly installed inside the box? This would tell us a lot.
thx for your last email with lots of information...great
especially for point 2.)
you write sth. about pulse tuning...and thats the thing on those stacks...with stock rubber parts you don´t have any because of the step...andreas - the guy i mentioned before did all the tests and came to the results of 50mm for 790 bonnie cams and 70mm for scram cams for best pulse timing effects...
for point B.) i can tell you:
he closed the original entrance hole and threw out the stock airfilter...he cutted out the battery box to get more airboxvolume...in additional with the removed stock airfilter you get 2-3l more volume...then he put a PC25 CBR 600 filter on top place...fixing it with silicone to get tight...picture:
u can even use some silicone to fix the foam surrounding the stacks to get fixed and tight to the airbox
at least:
my english is good but not perfect...i miss a lot of tech. words i don´t know in english...like pulse timing...when i was reading i knew what you mean...but i didn´t find the right words on my own...it sometimes is really hard to me to understand all...i even don´t have a mechanic apprenticship or sth. else...i am just interested on bikes and do a lot by my self...so there may be some missunderstanding in making sth. understandable to others in combination of my english-knowledge...thats why i don´t post that much here...
i just hope everybody can achieve sth. from these threads here - like u do, too
Thanks for the great reply. I understand fully now - the battery box was cut out, and a different style filter (Honda) fitted, but the kicker is that the original airbox filter was also removed, and the original airbox end(s) blocked off. Interesting. That would provide much more airbox volume, and get rid of the flat plastic surface plane of the old battery box right in front of the stacks. Great idea.
Twinfan - Don't worry at all about English, writing, getting the right words, and so on. We read you loud and clear, and hope you post very, very often. Your information has been very helpful to many of the folks here, and these are the enjoyable modifications that many of us love to trade information on.
Lastly, I am running two of the carb insulators, stacked up, on each intake manifold to increase plenum length and volume (pulse tuning stuff again). To do this, you need to slot the top two side mounting holes of the airbox by 7mm, then add two spacers (sleeves) to the mounting brackets behind the battery box, also 7mm each. This moves the Airbox rearward the same thickness as the insulators. Rear fender fit is a little tight, but achievable.You also need longer mounting bolts (4) for the intake manifold assemblies, which are the same as the crankcase cover bolts, 6mm X 70mm long.
As mentioned in the original post, the insulators, intake manifolds, and rubber connectors were all assembled, and the interiors smoothed out to remove any irregularities, and to match all the way with the Cylinder Head port I.D. shape. This was relatively easy, maybe one hour of work, but the end results were well worth it in airflow velocity improvement.
Please keep posting. These airbox results are something we've been experimenting with and working on for a long time, and it also sounds like you have many other great ideas to share with us.
twinfan thanks for the info.If I lived over there and had to run the box that looks like a good set up.Here in the USA we dont have to run the box.I have a filter setup that I think is better.I am running bigger carbs with 2mm over valves and bigger cams 989cc stroker from my testing you would never feed that through a air box it takes very high flowing pod air filters to flow what my carbs flow.I found that out the hard way.
To test to see if the stacks /air box flows enough for the bigger carbs you need to do some dyno runs with the 39mm carbs with no filter get the mix right then dyno it with the box and see if the mix changes at high rpm.If it stays the same you got something if it goes rich it wont feed the big carbs as it should.A filter set up that as it should be should flow as much as not haveing it on the bike does.Any less and its hurting hp.
But you dont want to run it with out the box with the stacks on because we all know stacks will flow more wide open on the carbs then with out.But motors dont like eating dirt lol.
when i have some more infos which are new on any modifications i will let you know...at the moment, thats all i can do for you...and as i mentioned...all those ideas are based on testings from andreas our most able guy on twins here in germany
i now put such a welding thing on my downpipes from the zard 2-1 to put a wideband-commander which a friend will lend me any time later
then i can do some testings on stacks, different airfilterpositions and so on and so on...
as i don´t look to get the max. out of the bike i will be happy with sth. about 70bwhp...i don´t know where i am now as i still have to break in the engine...but after that i will do some testings with CR carbs i got for a real good price...plug & play...thats best to me
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