more on the magical air box

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bikeazoid
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more on the magical air box

Postby bikeazoid » Thu Sep 12, 2002 1:09 am

i was bored, so i did the airbox drilling, and pulled the smog on my bike. i know ive covered this allready, but this is going somewhere. <br><br>the bike runs tons better, and think now the bike runs rich from the factory in the middle. anyway, looking at the air box i was thinking, is this thing really good??? it pulls from such a small inlet, and its from behind the engine, nowhere near the air tubes kicking in cool air from the front. my 90 with individuals and a jet kit, felt soooo much stronger. <br><br>my question is, is it better to keep the airbox, and just do the stage one approach, or is the individuals, and stage three the far better approach????<br><br>in other news, i rode a pristene 87 gsxr1100 tonight 7k miles, and have this to say, i feel more midrange, less up top, horid handeling (18 inch hoops), and a much larger feeling bike. ive never ridden the 87/88 fzr1000, but cant imagine it fellt like this. for the record, i loved riding it, but it dosent compare to the allmighty exup.<br><br>zoid <p></p><i></i>

flyingcircus68
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Re: more on the magical air box

Postby flyingcircus68 » Thu Sep 12, 2002 11:03 am

bikeazoid,<br><br>The airbox does offer some restriction under high flow conditions so you lose a little on top with the stock airbox. I have an 87 with the airbox. I have also ridden a couple without one and I can attest that there is a little more top end oomph without one. Under 8000 rpm, its a different story entirely. the airbox has an advantage in this range. heavy throttle at 6000 rpm and below without an airbox leads to horrendous noise and little more. when the power comes in, it is gangbusters immediate and can fool you into thinking that it pulls much harder. Dyno numbers and quarter times don't lie, your but does. You also have to consider that peak horsepower values by themselves are not an accurate indicator of how quick the bike will accelerate. Say for example you had a dynochart with two power curves overlayed onto the same graph. Say the curve with your modifications has a higher peak for the last 500 rpm, but the stock curve leads everywhere from that rpm value and below. the stock bike will be quicker, since it makes a higher average output. In other words, the motor will spend a very brief amount of time in that last bit of the graph where the modified curve has the advantage. Its the "area under the curve" that rules. If your looking for quicker acceleration during full throttle runs through the gears, you have to concern yourself with the upper part of the curve starting from the rpm the motor is at after shifting to a higher gear to peak rpm. If you increase power over this whole range, your going to go quicker. If you robbed some power from the lower rpm and added some to the peak, you might not be faster. In the extreme case, you might be slower. Lastly, consider that the airbox has a specific rpm where it resonates in sync with the intake pulses. if you alter it, or remove it. the stock jetting will run rich at this particular rpm. When the airbox resonates, its pressure is higher than ambiant. Carbs spray fuel through pressure differential. In other words, the higher pressure in the bowl forces fuel up the passageways into the throat which has a lower pressure due to the velocity of the air. When the airbox resonates, it lessens the pressure differntial, forcing less fuel into the carb throat. jetting is very tedious, so think it over before acting. <p></p><i></i>

bikeazoid
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Re: more on the magical air box

Postby bikeazoid » Fri Sep 13, 2002 12:49 am

thank you, that is deffinetley food for thought, do you have a drop in filter??? <br><br>zoid <p></p><i></i>

flyingcircus68
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Re: more on the magical air box

Postby flyingcircus68 » Fri Sep 13, 2002 10:29 am

Yes, but its not the stock one. I posted the details of my mods earlier. I just finally settled on jetting that seems to be a good compromise for temp and barometrics pressure variations. A quick way to a performance gain is to make a thermal barrier that keeps the hot air from the intake. You could use the aluminum/foam insulationg for air ducting. you woud have to take to sheets and stick them together so that the aluminum foil is clad on both sides. Just cut it to shape and put holes in it to allow the intake ducts to go through and form it so that it covers all gaps up to your frame. <p></p><i></i>

bikeazoid
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Re: more on the magical air box

Postby bikeazoid » Sat Sep 14, 2002 2:29 am

what thread was that that you chatted about it, what air filter do you use with your trick air box??? if i just made a decision between the stock air box, and individual filters, is the same info true, or does it lean twards the individuals more than??? i really dont want to loose that great mid range.<br><br>zoid <p></p><i></i>

flyingcircus68
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Re: more on the magical air box

Postby flyingcircus68 » Mon Sep 16, 2002 10:54 am

The thread is from 4/12/02. The info is tailored to the 87 model. The first year model had a smallish intake snorkel and round filter element. I took the yzf750 parts which had greater cross sectional area and an oval filter element and adapted them to my bike. If you have a newer model, The snokel has already been increased from the 87. Since your in the mood to hack, you could chop the top of the snorkel off and space it up to increase the area. You could tape it together temporarily for experimentation. You need to duplicate the resonant frequency. You can do this with a manometer and a restrictor to average the pressure pulses. The airbox is typically tuned to fill in the void at about 5500 rpm caused by the exhaust system. You could then increase the are by modifying the snorkel as mentioned above and adjust the length of the snorkel to bring the resonant frequency back down to the original rpm. At this point you can adjust your jetting for the increased flow. Actually jetting for more air is a misconception. when you remove a restriction upstream of the carb ( such as airbox ), you have removed an element which adds to the pressure drop seen in the carb throat. Total press. drop in throat = press. drop due to velocity (bernouli) + press drop due to restriction. So with that in mind, if you plug up the carb inlet with your hand, the pressure drop is due to your hands restriction. If you run the carb open to atmosphere, the pressure drop is from the velocity in the carb throat. Having an airbox gets you somewhere in between. <p></p><i></i>


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