OX
|
| posted on 15/6/03 at 09:56 PM |
|
|
Air box for bike engines
been having a browse around the forum's and have noticed alot of guys using motor bike engines have not been using the air box,this is not the
best way to get the best out of your engine.even race bikes still use some sort of air box just with a bigger air capacity,blade engines using the
standerd air box but with K&N air filter,a dynojet kit and a race can will turn your boring blade it to a mind blowing scud,any motor bike engine
not running fuel injection will benefit from a dynojet kit,it just smoothes out the power and gives it more mid range and faster eccelaration,or a
cheaper way is to use weeker slide springs and drill a little hole in the slider ,there may be 2 there all ready just make them bigger,if any guys are
using fuel injection they might well invest in a power commander unit ,takes abit of setting up and realy needs to to be settup on a rolling road but
lordy lordy does it make a difference
|
|
|
|
|
Jasper
|
| posted on 16/6/03 at 07:23 PM |
|
|
Try getting a zx9 airbox under the bonnet - then you'll find out why we don't use them.
|
|
|
OX
|
| posted on 16/6/03 at 09:33 PM |
|
|
any air box is better than nothing,im sure with a man of your capabilities can figure out something,just seems a shame to flatten the performance of
the engine.where there's a will there's a way bro,do you know any one that can plastic weld,as long as you get the same plastic soldering
sticks as what the air box is made of there shouldnt be a problem .
maybe a stupid question but have you tried the air box facing the other way and yes i am aware of the shape of the airbox
only tryingto help m8 
[Edited on 16/6/03 by OX]
|
|
|
Stu16v
|
| posted on 16/6/03 at 10:36 PM |
|
|
As Jasper says, room is almost always the deciding factor. Most modern bike engines have semi downdraft/downdraft carbs or throttle bodies on, and
putting an airbox on top just isnt gonna happen without a huge bulge sticking out of the bonnet. Some airboxes may be able to be modified to fit, but
if the clearance between carb mouth and back of airbox is reduced, performance will be affected, usually for the worse.
A well designed airbox will also drastically reduce intake noise, something to bear in mind with tightening noise regs at track days etc. But on a lot
of engines it is physically impossible.....
Dont just build it.....make it!
|
|
|
ChrisGamlin
|
| posted on 17/6/03 at 12:09 PM |
|
|
I think you are over stating the gains / losses here a bit OX, if a bike airbox is so great, how come when going to a sausage foam filter, you have to
enlarge the main jets from about 114 to 126 to cope with the extra air going through? Part of the reason a bike uses an airbox is for noise reduction
and also packaging under the tank, its not really for performance purposes.
Ive had my blade engine rolling roaded which gave me 112bhp at the wheels, which equated to nearly 140 at the crank and a very linear torque/power
curve, so its not doing too badly with a foam filter considering its about 5bhp up on what it should be in the bike 
Chris
|
|
|
OX
|
| posted on 17/6/03 at 06:26 PM |
|
|
the reason a bike uses an air box is becouse it needs a plenum chamber(a chamber of still air)
and thats a mighty big jump in main jet size m8 and probable the reason for you needing to use such big jets is that with your air filter its getting
so much air from all directions it cant cope so it needs the bigger jets to run the damn thing lol
the blade engine as you are well aware does not use the ram air system unlike the zx9r engine.if you ride a bike thats has these big scoops and then
block it off and then u tell me if im over stating the gains ,that big scoop on a F1 car is not just there to stick the camare on m8 also go to any
race bike meeting and take alook down the pit lane ,they spend thousands of pounds making carbon fiber air boxes to produce more power if they could
gain a measley 5 bhp by sticking a foam air filter on dont you think they would
|
|
|
Macca
|
| posted on 17/6/03 at 06:46 PM |
|
|
if you ride a bike thats has these big scoops and then block it off and then u tell me if im over stating the gains
Thought we were talking about airboxes and not the merits of ramair systems?
the reason a bike uses an air box is becouse it needs a plenum chamber(a chamber of still air)
How does that work with a rammed system?
Col
|
|
|
OX
|
| posted on 17/6/03 at 07:23 PM |
|
|
hmmm well the ram air system still needs still air at low speeds but the need for 2 smaller inlet tubes to balance out the pressure on top of the
throttle slide's to cope with the amount of air pressure being developed inside the air box when traveling at high speeds,not used on all ram
air systems some systems use solinoid's and tps's and a little help from the brain(little black box or dci) to open and close vents in the
airbox which all help the bike engine maintain smooth power also cool air makes more power
|
|
|
ChrisGamlin
|
| posted on 17/6/03 at 10:03 PM |
|
|
Errm we werent talking about ram-air systems as far as I was aware and F1 isnt really relevent if we arent talking ram air. Even with ram air, they
only gain at higher speeds due to the increase in air pressure, and under 100mph you arent going to see any significant gain.
This is a quote from the Yahoo BEC list that was posted today funnily enough, when commenting on Ram air and the gains a Caterham Blackbird found on
the rolling road by ditching the air box and putting on a foam filter:
According to the laws of Physics (in particular Newton's Second Law as
applied by Bernoulli) the pressure rise due to ram-air is equal to the
"stall pressure" of an airstream moving at the same speed as the airbox
intake.
If the airbox was 100% efficient this would equate to about a 1% increase in
power at 100mph, which translates to something like a 0.3% increase in speed in an ideal world.
This goes up to nearly 4% at 180mph, so worth having then, but at BEC
speeds?
I am not claiming the above to be gospel but Im sure I could back it up by digging though some old engineering notes, but it was boring when I studied
it so aint gonna start reading through it now! 
Basically though, its saying that anything below 100mph, you are going to see less than a 1% power increase even if the ram-air airbox is 100%
efficient, and a BEC rarely goes above 100-120mph so is it really worthwhile?
Anyway, even if ram-air is relevent in a BEC, fundamentally it is trying to achieve the same thing as a free flowing filter, as it allows the engine
to suck in more air, and as we all know, more air + more fuel = more power.
So, if my blade engine (and others) needs bigger jets, surely its cos its also gettinng more air into the cylinder, and bigger jets are needed to keep
a stoichiometric fuel/air mix, which means more power?
I know what you're saying about an airbox and still air being better as you want laminar flow around the trumpets to get the most air in, but as
long as the air isnt actively turbulent around the filter, In my opinion it makes very little difference, and the restriction you get from most stock
airboxes (which are also designed with emmsions / noise in mind) will be far worse than any loss you might see from slightly turbulent air around a
foam filter.
cheers
Chris
|
|
|
OX
|
| posted on 17/6/03 at 10:49 PM |
|
|
i see your point my friend and no its not worth the effort if the BEC doesnt exceed more than 120+
how ever i still argue the fact that an air box is better ,just need to find some proof 
|
|
|
ChrisGamlin
|
| posted on 17/6/03 at 11:39 PM |
|
|
I think you're right in that a perfect airbox probably would be marginally better, especially if the airflow around the carbs is
turbulent without it, but I dont think that many, if any, standard bike airboxes are anywhere near perfect, and you're more likely to get good
repeatable results by not having an airbox at all than by trying to design your own without proper modelling software etc.
As a demonstration, try running a standard blade on standard jets with and without the airbox. When run without an airbox, or with a foam filter, the
engine wont even hit the limiter on wide open throttle! This is because there is less restriction on the inlet side so the engine can
"breath" more air, and so as the revs rise, the mixture leans out and it wont rev cleanly cos the jets cant supply enough fuel. Therefore
I can't see how the standard airbox can possibly be a good thing cos fundamentally its restricting the amount of fuel you can burn in the
cylinder.
However, if the airbox was totally unrestrictive and correctly designed then I agree that there maybe a small gain by having an airbox, but
that's not the case, at least with the blade airbox, and judging by other BECs Ive seen, its similar with other engines (ZX9, R1, Blackbird
etc).
cheers
Chris
[Edited on 18/6/03 by ChrisGamlin]
|
|
|
Macca
|
| posted on 18/6/03 at 07:51 AM |
|
|
Would there be any advantage in turning the complete engine bay in to one large airbox.If you could duct away the airflow from the radiator and
"sealed" up the bay, to restrict air flow, would you have in affect an engine sitting in an airbox?
Also should the zx9 users be trying to copy the ramair system but on a larger scale to gain the benefits at lower speeds?
Col
|
|
|
ChrisGamlin
|
| posted on 18/6/03 at 09:17 AM |
|
|
Hi Col
If you sealed up the entire engine bay you'd have very hot air going into the engine (so less power), and / or you'd have major engine
cooling issues due to all the hot air around in the engine bay.
Regarding Ram Air, regardless of how big a ram air airbox you have, you will still only get significant pressure inside it when you are into 3 figure
speeds, these things are limited by the amount of air pressure you can generate inside them, which only comes from ramming the air in at higher speed,
and is not related to the size of it I'm afraid
cheers
Chris
|
|
|
Wadders
|
| posted on 18/6/03 at 01:55 PM |
|
|
Another problem with ram air, as anyone with a ZXR will confirm, is that the air filter quickly blocks up with debris and dead flys e.t.c.
i]Originally posted by ChrisGamlin
Hi Col
If you sealed up the entire engine bay you'd have very hot air going into the engine (so less power), and / or you'd have major engine
cooling issues due to all the hot air around in the engine bay.
Regarding Ram Air, regardless of how big a ram air airbox you have, you will still only get significant pressure inside it when you are into 3 figure
speeds, these things are limited by the amount of air pressure you can generate inside them, which only comes from ramming the air in at higher speed,
and is not related to the size of it I'm afraid
cheers
Chris
|
|
|
OX
|
| posted on 18/6/03 at 05:43 PM |
|
|
the engine will hit the red line with no airbox on if you rev it up slowly but by just snatching the throttle back it would struggle to get past
4-5000 rpm due to the amount of air that is being sucked in (or forced in due to atmospheric pressure)but!! i was stating that with an air box you
would get better performance over all,from tick over to flat out,may i remind you that the main jet only really works form 3quarter throttle and
more,bottom end running and mid range is mainly depends on the pilot jet and needle jet on the throttle slide but if its speed you want then maybe
you guys are right to use just a filter but if you want better out of corner speed and ecceleration then airbox and a good brand of air filter is what
you need .The help of dyno kit is a must
|
|
|
benedict
|
| posted on 19/6/03 at 08:38 AM |
|
|
Has anybody got or seen a dyno plot for a ZX9 BEC with an airbox, preferably from TTS's RR? It would be interesting to compare with the the
(strongly correlating) plots that myself and others have achieved with the foam filter.
I don't see how more air going in to the engine can be a disadvantage as long as you're not running lean at any stage. People spend
thousands modifying/designing bits to do just this.
Cheers,
Ben
|
|
|
ChrisGamlin
|
| posted on 19/6/03 at 08:49 AM |
|
|
Mine wouldnt hit the red line at all without the airbox in neutral and feathering the throttle. let alone in any gear and pulling, it would just fluff
and stutter as soon as it hit around 8krpm. Not quite sure how atmospheric air is forcing itself into the engine with the airbox off, with a good
airbox you should have the same atmospheric pressure inside, and if you havent, its cos the airbox is restricting the airflow into the engine.
You're right on the main jets only working with large throttle applications tho, but even at lower revs, to get max acceleration, you need to
use large amounts of throttle, so the mains will always determine peak torque and power above about 3-4krpm, and in a BEC thats so low geared, you are
rarely below 4krpm unless pootling in traffic, in which case you don't really need any power
cheers
Chris
|
|
|
Ninja
|
| posted on 19/6/03 at 10:27 AM |
|
|
I ran my ZX9r with just a foam filter and no re-jetting for a few weeks without major problems, and yes it did hit the rev limiter easily under
load.
Having said that there was hugh benefit in having it re-jetted by STS, particularly mid range and driveability. I do believe that one of the main
reasons they use the airbox is for noise (drive by) reduction.
My Dyno results are in the picture archive, with 119BHP at the wheels I don't think I'm losing too much.
|
|
|
ChrisGamlin
|
| posted on 19/6/03 at 10:44 AM |
|
|
Yeh its quite possible that the ZX9 airbox is less restrictive, therefore when you take it off, there is less of a difference in airflow into the
engine when compared to a blade, so it is possible that it will run to the red line OK, albeit a bit leaner than it should be.
Anyway, I dont wanna make this a constant game of tennis with OX, I think the main point I was trying to make all along that there isnt any
disadvantage to going to an open foam filter setup, and any gains that might be seen with an airbox, would only be seen if the airbox is 100%
efficient, which most production ones arent by a fair margin.
cheers
Chris
|
|
|
jimgiblett
|
| posted on 19/6/03 at 11:39 AM |
|
|
When you come fit the R1 you will notice how tall it is compared to alot of the other bike engines. The rubber bellmouths are nearly at the bonnet
level on my Phoenix. The Yam airbox will add nearly 10".
My R1 is smooth all through the mid and high range 4k to 11k. 127rwhp on dyno foam filter, dynojet and tuned 4-2-1 manifold and low restriction
can.
Just to add my 2p worth.
Jim
|
|
|
OX
|
| posted on 19/6/03 at 06:19 PM |
|
|
well its been good to read every ones opinion and i know you guys know you stuff but im going to try my damned best to fit the air box.Engines on its
way so i had better get the drawing board out
|
|
|
loafersmate
|
| posted on 20/6/03 at 12:00 PM |
|
|
I hacked the top off my blade airbox and made a aluminium top to seal it up again....it revs its nuts off! I recon the airbox volume has only been
reduced by 5-10%
Cheers
Ben
|
|
|
ChrisGamlin
|
| posted on 23/6/03 at 12:33 PM |
|
|
It will do cos a modded airbox will give the same amount of air restriction as a standard airbox as long as you havent chopped it too much, which by
the sounds of it you havent, its only when you remove that restriction that you need to think about changing to bigger jets.
Chris
|
|
|
Rorty
|
| posted on 24/6/03 at 07:52 AM |
|
|
I don't want to appear a know-all, but I've been racing bike engines in off-road cars for years, and have seen all types of air boxes in
attempts to improve tuning/keeping the 5hit out.
It always comes back to foam filters and huge increases in main jet sizes. This all points to only one thing. At realistic speeds, the air boxes are
too restrictive, and there are real power gains, across the whole range, to be had from foam filters and properly jetted carbs.
Incidental clue: OX's signature! 
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
|
|
|
OX
|
| posted on 24/6/03 at 10:42 AM |
|
|
hehe haha arnt you the funny one ,listen you big headed twat if i can get 180bhp+out of a 750 engine and still use an airbox tell me why i should use
a foam filter,if you want more air buy a bigger set of carbs you should get a good set for a couple of grand,iv been working with bikes for 14 years
on and off the race track and am telling you they run better with some type of airbox
|
|
|
fastavatar.jpg){kind=avatar}
