Airbox modding

[seb421]

that bottom one looks pretty good, i'm not sure but aren't storm carbs 48mm, if only it was that easy

sweet those ITG ones you can get in 48mm diameter and 40 or 70mm tall



http://www.demon-tweeks.co.uk/motorspor ... n-ram-pipe

[tony.mon]

Seb: Yes, normally the inlet tracts have a rougher finish than exhaust, mainly because it encourages fuel droplets that hit the walls of the inlet tract to vapourise faster.

But as the stacks are before the point at which fuel is introduced, the stack surface makes no difference, polished or rough, except for the shear surface/linear flow effect, or as you say, golf balls..
As regards linear flow, I believe that the differences are minimal anyway, around 1%. To me, this means that there's no point spending ages mirror polishing ports, when a rougher die grinder finish will be fine.
Although there is still an advantage in a mirror polish right at the point where the divider between ports extends into the cylinder, that few mm at the knife edge needs to be polished for maximum effect,. Can't remember where I read this, but is seems to make sense. Probably no measurable advantage, of course.

BSM: Yes, for the average owner it's easier to just buy an off the shelf item, but where's the fun in that?
I'll never ride into a meet bike park and find someone with the same bike, that's for sure
And it's not as if mine will out-perform billet stacks. (Although they might). I'm not trying to teach HRC a trick or two (unless I can beat the grabby clutch problem once and for all), more using what I have to hand to try a few ideas out for minimal cost.
If the parts were visible, aesthetics might come into it, but as they can't be seen once installed, I have the luxury of not bothering about the looks of the thing, as long as it works.

Lastly, with an off the shelf product, you never know if they've got it as good as it could be. Stacks, for example- did they try a pair 1mm longer, flared a degree more or less, and run back-to-back dyno tests, to see what's best?
And if so, is it best for track use, drag strip, street? I'm building something that I think will work with my own riding needs, it might not suit another application. That's why I went for a long and a short, but both slightly longer than stock. I wanted low and middle rpm torque improvements, but I'm not too concerned if it doesn't improve peak bhp at 9500. More is always nice, but you can't have everything.


Seb: Re the filter socks- yes, these should work, and so should the K&N conical filters, but they've been tried in the past- have a read up in Superhawk about this- and removing the airbox gives a whole new set of problems. As far as I'm concerned I'm sticking with an airbox, but I've increased the actual and effective volumes as tbh I don't think the airbox is big enough for a 1 litre vee twin.
Evidence is when the engine's cams are timed 180 out, the bike won't run past 5K, because the airbox can't recharge itself fast enough when the second cylinder is trying to suck air in only 90 degrees of rotation past the first one.

I'm probably never going to try it, but my enlarged and more efficient airbox will have moved that air starvation point higher; in theory if you have a large enough airbox (or two separate ones) you can set the cam timing 180 out and it'll run fine. A big bang engine......

All of the above are just my own theories, thoughts, bodges, drunk ideas and inspirations, backed up by a bit of analysis and cross-checking with other sources, trawling through t'interweb, previous posts on this and other forums; it ain't necessarily so, just because I've done it this way. It would be great if I've encouraged others to have a play- if you have a spare airbox and a few hours, you can recreate what I've done here; that's the whole point of posting detailed info and photos.
If you think it might be better with your own modifications or variations, go right ahead, this isn't the Holy Grail

If it works better than mine, I'll "borrow" the ideas next time. But importantly, all of this airbox work is reversible; you can just take it off and put the standard airbox back on; you won't have changed anything beyond changing it back if you don't like it, unlike things like head porting, etc. In fact I'd suggest that you don't chop up your original airbox; buy a spare or two first and set your original aside, just as a failsafe option. You can always sell it afterwards if you decide to keep it that way, or include it with the sale when you get to selling it, like standard cans.

Come on, you lazy buggers, someone else have a play with this idea, I'm keen to see what difference it makes to a standard-ish one.

[AMCQ46]

bloody good work there mr Mon, you are putting your enforced free time to some good use

I never thought to check how close the Billet inlets were to the base of the filter, and having seen Marty's fueling curve, I know I should go and heve mine checked now I am running the new inlets as they do seem to make other bikes a bit lean.

[VTRDark]

and having seen Marty's fueling curve, I know I should go and heve mine checked now

Don't forget his carbs are not set up right mate.

I like the Scottish accent in you text

go and heve mine

(:-})

[lloydie]

bloody good work there mr Mon, you are putting your enforced free time to some good use

I never thought to check how close the Billet inlets were to the base of the filter, and having seen Marty's fueling curve, I know I should go and heve mine checked now I am running the new inlets as they do seem to make other bikes a bit lean.

al the billet stacks are
23mm front
12mm rear
Below the k&n air filter

[tony.mon]

bloody good work there mr Mon, you are putting your enforced free time to some good use

I never thought to check how close the Billet inlets were to the base of the filter, and having seen Marty's fueling curve, I know I should go and heve mine checked now I am running the new inlets as they do seem to make other bikes a bit lean.

al the billet stacks are
23mm front
12mm rear
Below the k&n air filter

If the nearest section of the stack is under the filter part of the filter plate the gap doesn't matter as much; if the highest point is under a plastic part it will affect air flow into the stack, though.
I would have thought 10mm is enough clearance, bearing in mind that the stack is angled.

[AMCQ46]

[quote="cybercarl"I like the Scottish accent in you text

go and heve mine

(:-})[/quote]

lol, sorry Carl, you are reading too much into my dyslexic typing

[lloydie]

bloody good work there mr Mon, you are putting your enforced free time to some good use

I never thought to check how close the Billet inlets were to the base of the filter, and having seen Marty's fueling curve, I know I should go and heve mine checked now I am running the new inlets as they do seem to make other bikes a bit lean.

al the billet stacks are
23mm front
12mm rear
Below the k&n air filter

If the nearest section of the stack is under the filter part of the filter plate the gap doesn't matter as much; if the highest point is under a plastic part it will affect air flow into the stack, though.
I would have thought 10mm is enough clearance, bearing in mind that the stack is angled.

yep the nearest part is under the filter plate not the filter :-(
So I'm half way through the air box mod just need to get one more air box so I can cut the lip off .

[VTRDark]

So I'm half way through the air box mod just need to get one more air box so I can cut the lip off .

So which mod are you doing. IIRC you already have the billet stacks, so are you gutting the airbox and raising it to make more space? I would like to see a thread on gutting the airbox and re-routing breathers etc, as I would like to give that a go.

(:-})

[tony.mon]

So I'm half way through the air box mod just need to get one more air box so I can cut the lip off .

So which mod are you doing. IIRC you already have the billet stacks, so are you gutting the airbox and raising it to make more space? I would like to see a thread on gutting the airbox and re-routing breathers etc, as I would like to give that a go.

(:-})

Erm, try the start of this thread.....
Regarding breather routing, once you've cut the corners out of the airbox you just need to fit some hose from the breather outlets on top of the cam boxes into a catch tank somewhere.
I didn't detail that bit as there are a lot of choices and it's easy to work out.
I found that the little white catch tank that normally lives inside the airbox base will just about fit alongside the rear cylinder between it and nestling in the frame spar.
Then I fitted a little scooter conical air filter onto that to keep the weather out.

[lloydie]

what did you do with the carb breathers tony?

what im doing to the air box is very much the same as tony but with billet stacks .

i did the snorkel l mod a few months and tried it but it ran like sh1t with hi level exhaust and 45s pilot jets .
so now i have fitted the 48s pilots and the 2-1 exhaust i thought i would try it .
so i fitted it and took it out in the rain and i must say works good on its own
.
it has more punch when you crack the throttle open .
it nearly caught me out as i gave it full throttle from 3rd gear and the rear spun up .

so i have to finish the air box bottom , ive gutted it and removed all the bit that tony had done .
and when i get some more plastex i will finish it .

i hope to have it done for the open dyno day on the 11th aug at projex
so i can do back to back testing with the standard box and the modified box

[tony.mon]

Hey, Lloydie.
The carb breathers ? I just wrapped the ends in some oiled foam filter material, and put a little jubilee clip on the end of each one.
I wondered if they'd need to equalise air pressure with that in the airbox, but apparently not.
All they do is allow air in behind the slide diaphragm, if they were to be sealed the air behind the slide would pressurise and it wouldn't rise properly.
I know some people have said that they are routed into the airbox to equalise pressure both sides of the slide, and if you were to run a pressurised airbox that would possibly be necessary, but with a normal unpressurised airbox it doesn't cause an issue.
Re back to back testing; you might need to change jetting between boxes.
I tried the same thing when I first gutted the airbox, and found that the gutted box lost .5 bhp....
But since then I've opened up the snorkel, and now added the stack conversion as well, so all is very much well once more.

How did you make the patches to cover the corners after you'd cut them off?

[lloydie]

thats good then i will get some rc car carb filter and use them on the carb breathers .
http://www.ebay.co.uk/itm/51708K-1-8-Sc ... 2654wt_826

How did you make the patches to cover the corners after you'd cut them off?

when i cut the sections out i used gaffer tape on the out side of the air box to the get the shape i wanted (like a mould).

As the gaffer tape is sticky the power from the plastex sticks to it very well .
then add the liquid then more powered .
so you build up the layers till its nice and thick .

when it sets over night it will be as strong as before if not stronger .
i need to get more as i ran out lol.
when its done i will sand it down so its nice and smooth inside and out .

i will take and post the pics when im done and put then in this thread if it ok with you tony ?

[tony.mon]

i will take and post the pics when im done and put then in this thread if it ok with you tony ?

Yes, fine by me, the more the merrier.
I asked because although it worked, my method was quite laborious and messy-looking. But next time I would not only follow the outside contours of the box but enlarge it- there are some areas you could extend into easily- front left corner and rearwards over the rear carb seem easy enough.
The box won't be very regular in shape, but it's volume you need, more than anything else.

[lloydie]

i did remove the corners out to gain a little extra
i tried to follow the shape of the box but i got a little carried away at the same time keeping it simple .

i made the lower spacer from an old standard air filter .
i want to try a little lift both sides of the k&n instead of just above or below .
but that can wait till i finish to bottom of the airbox .
because i will need to get hold of a standard box lid so i can cut the mounting lip of.
i want to try to keep a working standard box i case i fook it up lol