Airbox mod



johncal

Registered
After reading about a lot of guys removing the flapper valve, I thought I'd add my 2 cents.

What the flapper valve does is restrict the opening of the air intake below 3000-4000 R.P.M. The reason this is done is for better torque.

It works like this. When the engine is turning slowly it takes in less air. If the air intake opening were big, the engine lazily sucks the air into the cyliders. By restricting the opening size in the airbox, at low R.P.M.s it forces the air to move more quickly to get into the cylinders. This increased air velocity will actually act to pack more air into the cylinders.

When the R.P.M.'s climb, the valve opens to allow a greater amount of air through to keep the velocity and air packing going.

By removing the flapper, you actually allow for less air to get into the cylinders at low R.P.M. and you actually loose power.

It may actually feel faster, but that's because the power is reduced at the low R.P.M.'s so when the speed increases so does the power curve more drastically. Removing the valve actually makes the power curve steeper and hurts drivability and response.

Also, removing the flapper valve will change the airflow to the motor so the stock fuel map, or any maps from Yoshi or PC will not work correctly.

If you remove the valve, you actually need to get an ECM just so you can go spend a lot of money on a Dyno tune to get most of the performance back.

Hope I didn't rain on anyone's parade.

BTW, if you did see a horsepower increase on the Dyno, it's because of the tune-up, not the airbox mod.

I will make the following statement however, if you are going to use your Busa for RACE ONLY purposes and only care about peak horsepower, then rip the whole damn airbox out and set it up properly for racing. then you'll get that increase you're looking for. just remember, you're throwing out low end performance for more on top. Not my first choice for street use.

Johncal
 

drewwerd13

Registered
So are you recommending not cutting anything at all? Or just leaving the flap but cutting the rest of the stuff around the opening? Doesn't the flap move around a bit more without all that plastic around the opening?
 

drewwerd13

Registered
I'm trying not to sound totally ignorant, but I'll ask anyway... What exactly happens just from cutting away some of that plastic around the airbox opening? Could it help that much?
 

johncal

Registered
I'm recommending you don't do anything at all......not at least until you call the dealer and find out how much all the parts will cost to replace that you just chewed up.

Johncal
 

SLEEPERBUSA

Registered
The box is an excellent design , for a bone stock bike.
There is NO doubt that the velocity IS needed!
If you increase the workings of the engine, it will need more fuel AND air!
MY bike went faster with a small box mod.
I "may" have lost a VERY small amount of real lowend torque, but more than made up for it in mid and topend HP.
 

Busashot

Registered
I did the small(Medium) box mod. Whatever you want to call it. Even though I have not put in the BMC Race filter in, I noticed a slight increase at top and very little loss down low. The problem I didn't like was that the lean surge at part(cruise) throttle. I felt it slightly when stock, but now it appears even a little more. With the BMC I imagine it will be even worse.

So now I will be adding some sort of PC box or ECU mod to correct the issue. No big deal actually.

Most of the guys I've seen doing this mod with BMC RACE have seen between 5-7HP without any tuning. I think that is awesome since it costs only the price of the BMC.

Steve
 

btreaves

Registered
Joncal is 100% right. I recently changed the spark plugs on my 2000 Hayabusa and noticed that the vacuum hose for the flapper valve hadn't be connected and it hadn't been connected in quite some time, because I believe that I neglected to hook it back up the last time I did some maintenance.

Anyway, I thought that my bike was running a tad bit soft on top end. While it would still pull all the way up to 200mph+ (indicated), it seemed to be sluggish getting there and the distance needed was far more than usual, but I guess I had gotten use to it and I couldn't exactly quantify it. Plus I was punishing damn near everyone around here in drag racing and roll-on racing.

Well anyway, I reconnected the hose last night and took her out for a quick "shake down" run. The bike still runs like it use to down low, but now on top it runs like a fuggin "stripped ape". It pulls so quickly and effortlessly to 200mph in a much shorter distance than before. I actually had to reaquaint myself with shifting because it goes through the revs much quicker. I banged the rev limiter in damn near every shift...Something that I rarely did before.

After reviewing the service manual I think you'd be an absolute fool to remove the flapper in the air box on a Hayabusa that's not a full on race bike. The flapper valve is there to give you excellent low end response and as the engine speed increases the ECM tells the valve to open to allow huge volumes of air to flow into the motor for better performance on top end.

That's my two cents. If you're in the Washington, DC metro area and you want a demonstration of a "bone stock" BUSA's awsome power...drop me a line on this site and I'll be more than happy to come out and demonstrate it for you.

BT Express
evil.gif
 

Johnnycheese

Registered
Joncal is 100% right.  I recently changed the spark plugs on my 2000 Hayabusa and noticed that the vacuum hose for the flapper valve hadn't be connected and it hadn't been connected in quite some time, because I believe that I neglected to hook it back up the last time I did some maintenance.

Anyway, I thought that my bike was running a tad bit soft on top end.  While it would still pull all the way up to 200mph+ (indicated), it seemed to be sluggish getting there and the distance needed was far more than usual, but I guess I had gotten use to it and I couldn't exactly quantify it.  Plus I was punishing damn near everyone around here in drag racing and roll-on racing.

Well anyway, I reconnected the hose last night and took her out for a quick "shake down" run.  The bike still runs like it use to down low, but now on top it runs like a fuggin "stripped ape".  It pulls so quickly and effortlessly to 200mph in a much shorter distance than before.  I actually had to reaquaint myself with shifting because it goes through the revs much quicker.  I banged the rev limiter in damn near every shift...Something that I rarely did before.

After reviewing the service manual I think you'd be an absolute fool to remove the flapper in the air box on a Hayabusa that's not a full on race bike.  The flapper valve is there to give you excellent low end response and as the engine speed increases the ECM tells the valve to open to allow huge volumes of air to flow into the motor for better performance on top end.

That's my two cents.  If you're in the Washington, DC metro area and you want a demonstration of a "bone stock" BUSA's awsome power...drop me a line on this site and I'll be more than happy to come out and demonstrate it for you.

BT Express
evil.gif
Hahahahahaha the flapper stays open when the hose is disconnected so your seat of the pants dyno is WRONG
iamwithstupid.gif
 

SierraFlyer

Registered
The flapper is gone from mine, along with the surrounding plastic. Even for a street bike it is just fine. The reality is that the low end "driveability" is not affected by removing the flap much at all. I am not even sure I can feel the loss (if any). It might be measureable on a dyno? Remember that this is just off idle throttle settings for that power level. You can't tell where the actual throttle position is while riding. So a little more throttle twist easily makes up for the loss of power down low. I have a TRE and have had no problems with surging any more anyway. The top end is definately stronger with the better breathing.

A couple of HP loss in the part throttle area is not a factor for a bike this powerful. If you need all the power this engine can give, just click down a gear or two and bump the RPM up into the high end of the range and enjoy the even greater HP the mod creates. To get the most out of it, remap is needed.

A vaccuum leak like you had is what was robbing your power, the flap has almost nothing to do with that RPM.
 

btreaves

Registered
Whether the flapper stays open or closed when the hose is disconnected is neither here nor there...The bottom line is the bike runs better with the flapper working that without it working... If what you say about the flapper is true then what I had is the "poor mans" airbox mod with the flapper always stuck in the full open position.

Now that I've reconnected the vacuum line I'm telling you that the bike runs much stronger.

I guess I just don't understand why Suzuki would spend all the time and effort engineering such a sophisticated air box when a few shade tree mechanics could do a much better job.
 

johncal

Registered
Johnnycheese - Glad you looked in the manual. It's easy to see how much better it works when you really examine things scientifically.

A lot of these guys are telling you how much faster it feels with the flapper removed but where is the DYNO proof.

I know how much SLOWER my bike felt as I got used to it. Did the bike actually get slower, no. I'm sure what most guys feel as "faster top end" is the fact that the bottom end has been diminished by removing the flapper and loosing the torque that is generated by the flapper design.

If someone can show me dyno charts to back up the airbox mods, I would be way more than happy to retract my position. I'm always eager to learn something new.

Johncal
 

johncal

Registered
The flapper is gone from mine, along with the surrounding plastic. Even for a street bike it is just fine. The reality is that the low end "driveability" is not affected by removing the flap much at all. I am not even sure I can feel the loss (if any). It might be measureable on a dyno? Remember that this is just off idle throttle settings for that power level. You can't tell where the actual throttle position is while riding. So a little more throttle twist easily makes up for the loss of power down low. I have a TRE and have had no problems with surging any more anyway. The top end is definately stronger with the better breathing.

A couple of HP loss in the part throttle area is not a factor for a bike this powerful. If you need all the power this engine can give, just click down a gear or two and bump the RPM up into the high end of the range and enjoy the even greater HP the mod creates. To get the most out of it, remap is needed.

A vaccuum leak like you had is what was robbing your power, the flap has almost nothing to do with that RPM.
Just so you know, the flapper valve operates based on R.P.M. NOT directly on Throttle position. It starts to open after 3000-4000 R.P.M. based on sensor readings and ECM calculations. Besides after installing the TRE, you've changed the advance curves so much that it would be impossible to compare the original low R.P.M. engine response to the original. With the TRE installed, you now run the 5th gear advance curve regardless of what gear you're in. Personally, I would not install any of the exsisting TRE's available since the ignition curve SHOULD be different for the different gears. The load at the lower gears is much different than the higher gears, requiring different advance for proper operation.

In my own humble opinion, the engineers that spent YEARS developing this and other Suzukis have a much better handle on what's best.

When I make modifications such as Exhaust system changes, I added a PC3r to actually keep the engineered performance specs as close to the O.E.M. design as possible. In other words, that change was dyno tested by professionals to keep the air / fuel ratio as close as possible to the theoretic limit. The new map preserves as closely as possible the intent of the original designers.

Besides, if I roasted my valves by modifying my air box, I'd hate to have the dealer say that they were voiding my warranty because of the way I screwed up the motor by cobbing it.

There is a huge amount of engineering and millions of dollars spent to make your bike work as good as it does. I'm all for changing things if done properly.

Just my humble opinion,
johncal
 

Johnnycheese

Registered
Besides, if I roasted my valves by modifying my air box, I'd hate to have the dealer say that they were voiding my warranty because of the way I screwed up the motor by cobbing it.


If you did it was not caused by modding the air box it was something else.
I have had no Airfilter from day one and a big box mod with no filter from 4K onward.
I have built many bikes with big airbox mods and small ones all without airfilters and not ONE has roasted a valve.
I think you should provide more info on this.

Also yes the Suzuki engineers do one fine job but have you ever seen the A/F on a BUSA or better yet on a Honda VTX1800
crazy.gif

the VTX 1800 is at 10:1 A/F with a Hypercharger and straight pipes so what is it with the stock stuff???
Ask the customers getting 22 MPG on them
baaa.gif
 

johncal

Registered
It is more than possible to roast a valve due to not using an air filter. Any solid debris such as sand that can easily get kicked up into the air intakes can get into the engine. If it happens to lodge against a valve the valve can easily fry since 95% of the valve cooling is done by it's seating against the head. (The rest is through the stem). It is not only important that valves seat properly for sealing but for heat disipation as well.

Also, that same sand or whatever can get into the piston rings and really scuff up the cylinder walls causing compression or oil usage problems.

Further, the air filters do a good job of stopping backfires through the throttle bodies.

If it were not necessary to use air filters, the engineers would not design them into engine design. Why would they, unless they all have air filter company stock.

Unless you are racing and don't care about engine damage, I would use a high performance air filter. All of the major race teams that win nationals DO use air filters. just check on the net for their endorsements.The slight increase in performance possible by not using a filter at least to me is not worth risking my engine.

Just my opinion.

Johncal
 

monsterspeedfreak

Donating Member
Registered
Johncal.......not dissin ya at all here.... but JC has very good credentials.......tell us a bit about yerself please, so we know if yer in the know.
super.gif
 

johncal

Registered
Early in my career I worked in the automotive field where I spent a lot of time working on the top half of motors almost exclusively 4 cylinder japanese cars. I've done many re-builds of heads and seen a lot of damage caused by improperly set up motors....and BTW I've screwed up my own plenty of times doing most of the things I'm saying NOT to do.

Anyways, before I left the automotive field, I designed and built custom auto exhausts for people that had "different" types of situations, like the hod rod vegas with 350's in them, etc. did that for about 3 years. Also had 2 previous bikes I did all of my own work on.

At this point in my career, I am a mechanical engineer that has run a research and development department for the last 23 years. Our specialty is electro-mechanical coin operated amusement games. Heavily in the mechanical end.

I design large electro-mechanical games that interface electronics with, pnumatics, hydraulics, ac and dc motors, etc. etc. I work with on a daily basis almost every type of mechanical device known to man. (Just kidding, it just seems that way).

In fact, the first game I ever Designed / invented was the SUPER CHEXX hockey game. The big arcade hockey game with the bubble on it. I'm sure a lot of you guys have seen it and played it. (Also, I'd be happy to challenge any of you to a game of Chexx and ....). I've personally designed over 45 coin operated amusment games for the Bars and Arcades. I've also developed a few toy products as well.

As to my credentials, I'm sure there's a lot better out there, but since my career depends on good, sound engineering practice, I like to look before I leap. If you're interested,you can see a lot of the products I've designed at www.icegame.com. About 1/2 of the games there are my design.

Sorry if off topic, just answering a request.

Johncal
 

Johnnycheese

Registered
Just wondering how an Aifilter can stop a backfire through the Throttle bodies???
The air fiter is on top of them last time I checked.
 

johncal

Registered
Just wondering how an Aifilter can stop a backfire through the Throttle bodies???
The air fiter is on top of them last time I checked.
Backfire comes up intake valves, through throttle bodies, meets air filter. Stops there. Air filters do a good job of arresting a backfire. Of course, Mr. airfilter might not look as good as he used to.

Johncal
 


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