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

Try getting a zx9 airbox under the bonnet - then you'll find out why we don't use them.

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]

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.....

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

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

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

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

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

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

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]

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

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

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

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

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

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

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.

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

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

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

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

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

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!

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

The second part of your Avatar says it all OX

To be honest, your arguments have been all over the place all along with things such as "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 " which kinda backs up my argument all along does it not? With stuff like this, is it any wonder that people like myself are questioning your wisdom?

I think its time to put up or shut up OX, you've yet to show any proof of your claims (either showing the pro's of an airbox or your bike tuning credentials), and there is a fair wave of evidence on the other side of the fence to say that foam filters work very well thank-you very much. Like I said before, Im not saying the perfect airbox wouldnt show a very slight improvement (in mid range if anywhere), but what you dont seem to be able to grasp is that STANDARD AIRBOXES ARE RESTRICTIVE, and Im sure we can all agree that more air + more fuel = more power, so if everyone gets more air into their engine using a foam filter rather than a STANDARD airbox (which is proved by the need for bigger jets) then thats pretty damning proof I would say.

Chris

quote:

---

Originally posted by OX
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

---

The label in my hat says MEDIUM.

The label in my hat says MEDIUM. ???

So Rorty, who will add the next reply then??


Col

to quote from david vizzard
'to make extra power it is necessary to increase the airflow of the engine in question'

now unless the principles of the internal combustion engine have changed regarding bikes ? this means that more air = more fuel = bigger jets = more power

so even vizzard would dissagree with ox and perhaps ox would like to tell him he got his theory on engine tuning all wrong.

As for the trend for personal attacks on people Don't . its not big and its not clever and it shows people for what they are.

Hmm... maybe we should write to the likes of K&N and Pipercross and tell them that their fancy graphs and sales claims are are load of old horlicks. Performance air filters indeed!

<inserts large cat into flock of fat pigeons>

lol,i am up for a laugh and to take the wee as much as any one ,my avatar was ment to be humoures but obvisouly it wasnt ,the opinion of the airbox is not just my own but it is on this forum,i dont see the standard air box as being much of a restriction on a none tuned engine but the air filter is thats why people use k&n filters and dyno kits,if your engine is tuned then yes the standard air box is restrictive and a bigger one is needed,but then is the need for a bigger carbs.its the way the air flows that matters and sausage filters can affect this,,,,,,,,,may be i should just take chris's wise words and shut up,didnt mean to wee any body off

Apology accepted Captain Needa.

Woohoo, 200 post

Sorry.

(201 now )

as a total missing the point reply.
on my old carb blade engine the standard blade airbox can be fitted upside down in the car(only requres a small bonnet bulge)but to run it i had to go back to standard jets.a big drop in power.
but was under 100 db @10k static
but it was so flat that im now back on foam sock filters and only go to noisy tracks
cant get under 100 db @ 7k now

After reading the above heated yet enjoyable debate, I asked a friend for his advice on the subject. He is a well repected race bike engine tuner, and I trust what he says.

I was told that the airbox was a MUST.
If I could fit one, it would lead to all sorts of problems. The reasons for this were all fully explained, but were all a bit too technical.

The advice is a s follows:
Fit the standard airbox, dynojet and filter kit.

If it you can't, cut it down a little.

If you can't fit a box at all, fit a foam sausage thingy fit bigass jets and try your best to tune around the problems that your about to encounter.

If you don't agree with the above, please do not shoot the messanger and slag me off. I am only trying to pass on the advice of a well respected bike tuner.

I too know some top bike tuners/factory race tuners, and they all swear by the air box.
It's quite simple to understand. The airbox in a bike, has its air fed from vents in the front of the fairing/frame. Few alternatives will return the same values in a bike, due to the inaccessability of the air tracts of the carbs/injector bodies, beneath the "fuel tank".
Take the same engine, and stuff it in a much more spacious chassis, with no restrictive tank shell/fairing etc, and all of a sudden, there's a whole lot more air available. Add a much better breathing filter arangement, re-jet (and you don't have to "try your best to tune around the problems that your about to encounter." There are after market kits for this very purpose), and you have a healthier, more powerful engine.
Do the maths, look up how much a standard bike filter flows, then compare with the flow of a sausage or bucket filter for the same model.
Yes, I am shooting the messenger, 'cause I'm fed up with unsubstianted "my best mate's" theories, when they're totally inappropriate.
Quite a few of us here have experience with after market/home made filters and alternative jetting, and the results aren't a figment of our imaginations, some of us have dyno results exalting the improvementsI have had quite a few bikes in my time too, and I always (bar one) retained the basic airbox.

Building friendship across the world are you? Choose wiser words.

I don't think that there is the need to be so aggaresive.

This is suppossed to be a forum (debate and that sort of thing). And I believe everyone is entitled to their opinion.

My comments were my view, and I dont think I deserve a personal attack for stating them.