Matt21
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| posted on 13/2/14 at 07:24 AM |
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Air filter - cbr900 carbs
After watching that inspirational video in the car chat section, i noticed that the guy/car featured had circles of foam glued over the end of the
trumpets on the air intakes.
has anyone done this on here and had any issues?
I know someone who has a mk1 golf with thorttle bodies and he has used some tea straining mesh things as filters on his!
obviously you would need some strong glue, but does the foam offer enough filtration to prevent excessive wear to the engine?
obviusly the main thing is to stop stones etc dropping in.
atm i have a pipercross sausage filter fitted, but i read that these can be worse for performance than standard air boxes?
whats the ideal type of filter for the carbs? (apart from the standard box)
any oppinions? 
[Edited on 13/2/14 by Matt21]
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MikeRJ
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| posted on 13/2/14 at 09:44 AM |
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quote:
Originally posted by Matt21
atm i have a pipercross sausage filter fitted, but i read that these can be worse for performance than standard air boxes?
whats the ideal type of filter for the carbs? (apart from the standard box)
This isn't due to any kind of restriction (the Pipercross sausage filters can flow a huge amount of air), but rather the fact that the standard
airbox may be slightly pressurised at speed in it's original application, and it stabilises the air around the intake trumpets. If you
don't want to run the sausage filter, there is an airbox/filter assembly that fits in place of the filter using the
They aren't cheap though!.
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Matt21
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| posted on 13/2/14 at 11:05 AM |
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no, not cheap at all!
So basically to get the best i would need stable air in my engine bay, thats also cold... i think i will stick to the sausage 
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mcerd1
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| posted on 13/2/14 at 12:21 PM |
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the only things worse than a sausage filter are no filters at all or or ones stuck on the trumpets !
any filter thats fixed to the end of the trumpet upsets the airflow - the pre-made version of what you want to make is called a 'filter
sock' and they are known to kill the power 
you need a volume of filtered air around the trumpets to get the best results
the tea strainers are only for keeping out big objects, not the dust and finer particles that make a lovely grinding paste when inside your engine....
a good filter will prevent this and won't limit your power either
they probably got the idea by looking at old F1 engines etc - like these on a cossie DFV: (and that tech is at least 40 years out of date now!)
but those engines get a full rebuild after every single race - and notice its actually setup the same as your sausage filter
(you can't buy tea strainers that shape though  )
as above the best option is an airbox - it doesn't upset the airflow into the trumpets, it reduces induction noise (helps with the limits on
some track days) and can actually give you a little power boost or help smooth out the power curve by tuning its size (normally you adjust the length
of a large dia. pipe between the filter and the airbox)
feed the right size airbox with cold air and your on a winner
pre-made airboxes like the pipercross ones aren't cheap - but they aren't all that complex either - how are your fiberglass / alloy
welding skills ?
but saying all that sausage filters are a good second best to the airbox
[Edited on 13/2/2014 by mcerd1]
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Matt21
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| posted on 13/2/14 at 01:11 PM |
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I've had a bit of experience with fibre glassing, making the mould would be the trickiest part, also would there not be 'ideal
dimensions' that would work best?
I think i'll just stick with my sausage for the time being
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mcerd1
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| posted on 13/2/14 at 01:33 PM |
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quote:
Originally posted by Matt21
would there not be 'ideal dimensions' that would work best?
if you google for airbox or plenum design you'll get lots of theory - this old thread will give you something to think about:
http://www.locostbuilders.co.uk/viewthread.php?tid=122399
the old david vizard pinto book is also well worth a read
but the only way to make one exactly right for your engine it to build a trial one
then stick it on the engine dyno and play around with its dimensions until it gives the best results - remembering that one size might give you the
best peak power, but another will give you low down torque and so on...
also your manifold and trumpet lengths have just as much impact as does your primary exhaust pipe lengths - it all comes down to what you can actually
fit in the car and how much time you want to put into it...
so I'd say have a go if you fancy it - but don't spend much and you can always go back to the sausage filter if you don't like the
results
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Matt21
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| posted on 13/2/14 at 02:09 PM |
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but for materials, dyno runs,a filer for it etc.... I might aswell spend £190 on the pipercross one
I'm all for making things myself etc, but for the costs and the hassle it seems to be a bad idea especially if i make one and then it turns
out that i need my carbs rejetting, exhaust changing etc etc
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mcerd1
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| posted on 13/2/14 at 02:23 PM |
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quote:
Originally posted by Matt21
but for materials, dyno runs,a filer for it etc.... I might aswell spend £190 on the pipercross one
you'd be very lucky if the pipercross one was perfect for your engine
at best they are a 'once size almost fits all' design - you could easy make your own to match the performance of one of them, just make
it to a similar size and shape and your done
the time and effort on the dyno is only required if you want to squeeze the last few hp out of your engine...
in reality you can easily make changes to the total volume by adding / removing a few inches from the intake the pipe between the filter and airbox -
that way you can try a few sizes quickly while the car is on the rollers
[Edited on 13/2/2014 by mcerd1]
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Dangerstevie
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| posted on 14/2/14 at 08:24 AM |
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Assuming this is on a fireblade engine the CV carbs on the blade are VERY sensitive to airflow. I have had problems with carburation on my
streetfighter fireblade because of turbulent airflow to the standard airbox, its also recognised that a ram air type system with the blade carbs is
not good and upsets things massively. Personally i would be trying to use as much of the standard airbox as possible and feed that with a cold still
air zone, try to replicate the setup the blade had with an air delfector under the airbox intakes and a full fairing and frame blocking off turbulent
air so there is a nice still air zone around the intakes.
If you want to alleviate any issues save the pennies (ie. dont buy the pipercross airbox) and get a set of Kehin or Mikuni flatslide carbs, you can
pick them up second hand from the early GSXR1100's & 750's for about 200 and they work a treat with whatever you stick over them
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Matt21
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| posted on 14/2/14 at 08:41 AM |
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how about....
I put the standard air box on with no filter in it, and a cone filter on the inlet too it?
would that provide more air flow but give the air somewhere to settle down before getting to the carbs?
are the gsxr carbs a direct fit? will they need rejetting to suit?
with standard blade carbs on my car runs like a bag of poo and no power at all, it even struggles to stay running. once the new jets are in its fine,
so do the gsxr ones need them too?
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woodstock
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| posted on 14/2/14 at 09:12 AM |
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I've been looking into this recently too for a 919 fireblade (RRV). I currently have the standard pipercross panel filter but it's so
noisy i'm worried about db limits on trackdays.
I found this modwhich is interesting from a bike point of view:
Fireblade Viking Mod
I started having similar ideas to you about using a standard airbox as a basis and modifying it. I ordered a box of ebay for £20 and planned to gut
it, cut the intake side off and mate it longways to some 100mm tubing which would be blanked off at the far end and the near end would be connected to
this filter which in turn would be ducted to my bonet for intake.
Pipercross Venom
Then I rang Andy Bates at AB performance and it seems that there is a lot more to it than i had thought. He started to explain the differences between
air pressure and velocity and the difference that this can make, his understanding exceeded what I could take in over the phone so I won't try
and relay it here and get it wrong. I'm aware that pressure, velocity and in turn air volume are directly linked but air flow between duct,
filter, airbox, stacks etc is a little more complicated it seems with air flow potentially stalling in places. The AB box has been developed in
motorsport where tenths are important and budgets stretch to significant R+D so i guess that is what you pay for, the materials are the cheap part.
Very different to the locost fettling way i guess.
I've also been reading about the way that the difference in air pressure over the carb is what draws the fuel in and so changing the effective
'atmospheric' pressure on the external (now airbox) side also alters this. I haven't confirmed at the moment if this affects all
carbs in the same way.
Ultimately I've been debating the tried and tested AB airbox and posted on here looking for a pre-loved one. This may be more expensive than the
others but also comes with AB backup (invaluable end of the phone support) and a set of known dynojet settings.
I've also been looking into options for monitoring and tuning carbs if i do anything other than the AB box and decided that any ram-air effect
cannot be reproduced accurately on a rolling road so the best thing for me would be to fit a AFR/Wideband Lambda sensor and monitor it on track
against throttle position, revs and speed. This gives me another issue in logging this and i'm currently investigating analog inputs that i
might be able to hook up to my digidash (need to confirm this). I'm under no illusion that this is going to be a very tricky thing to do and is
going to take considerable time.
I'm certainly no expert so please take all this as my novice opinion only, I wanted to share my views in a constructive way in the hope that we
could maybe help each other. Personally my lack of engineering experience and it background mean i'm swayed towards stats, facts and figures so
take a very scientific approach to this which is why i'm swayed towards the AFR.
Chris
[Edited on 14/2/14 by woodstock]
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Dangerstevie
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| posted on 14/2/14 at 12:58 PM |
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The gsxr carbs are not a straight fit and require tapered runners to the blade head to account for the few mm difference in spacing and the difference
in port diameter (Blade ones are bigger).
My blade before i re-jetted it and played with the airbox would get up to 60ish ok and then buck violently after that as the airflow made the mixture
lean out.
This is my airbox currently, it worked well with a few large holes in the top of it where the airflow was relatively still under the fuel tank, the
same will apply for the locost bonnet i would think as a first pass assessment.
[img]http://www.customfighters.com/forums/attachment.php?attachmentid=41753&stc=1&thumb=1&d=1392382587[/img]
[img]http://www.customfighters.com/forums/attachment.php?attachmentid=41761&stc=1&thumb=1&d=1392382587[/img]
[img]http://www.customfighters.com/forums/attachment.php?attachmentid=41769&stc=1&thumb=1&d=1392382587[/img]
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