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Darthane
| | Posted on Sunday, September 07, 2003 - 05:04 pm: | 
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Gonen60, I'll send you the same e-mail I did Ckj. If that's not enough I'll do some digging and pull up the old posts I put up on the subject. This was a hot topic back in late May.
Bryan |
Kevyn
| | Posted on Monday, September 08, 2003 - 06:09 pm: |
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Henrik, et al; searched around over on the Duc board for more info about snorkels and such as the Duc SS air box has two nicely shaped snorkels protruding from the air box under the gas tank(where's V2Win when you need some relief?) that most users remove with the entire air box cover shortly after purchase.
From what I could gather from some dyno charts on modified SS motors, the covered/snorkled airbox restricts about 2HP from max. Torque? No word.
The main reason to alter the airbox was to improve the overall engine breathing in conjunction with exhaust mods...all in the name of performance and to improve the symphonic eminations--that famous desmo 'wonk' that follows generous throttle application and which is followed by a skyward lofting front end!
I recall the air box modifications on the tube frame Buells all too well... |
Kevyn
| | Posted on Monday, September 08, 2003 - 06:19 pm: |
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Not Buell, but applicable somehow
http://speedzilla.zeroforum.com/zerothread?id=16921 |
Glitch
| | Posted on Tuesday, September 09, 2003 - 08:51 am: |
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Great post Kevyn!
you should have at least 130% of engine capacity in available air volume between the throttle butterflies and the air
filter element.
This explains the "breadbox" the Tube Framed Buells have...
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Darthane
| | Posted on Tuesday, September 09, 2003 - 09:13 am: |
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In between, not outside. The filters in the breadboxes were pretty tiny. Still more than a filled pair of cylinders, I'm sure... |
Ckj
| | Posted on Thursday, September 11, 2003 - 11:14 am: |
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Bryan
Finished the airbox and looks, sounds and runs great. Thanks for the pictures and instructions |
Darthane
| | Posted on Thursday, September 11, 2003 - 12:44 pm: |
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You're very welcome.
Anybody else?  |
Mookie
| | Posted on Thursday, September 11, 2003 - 12:51 pm: |
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I wanna take a look
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Darthane
| | Posted on Thursday, September 11, 2003 - 01:43 pm: |
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We can handle that tonight, then, Mookie. I've even got an extra plexiglass plate in my garage.
Bryan |
Puffysleeves
| | Posted on Thursday, September 11, 2003 - 03:08 pm: |
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You are correct in saying that more air equals more power but are not correct when you assert that opening up the airbox will provide more air. The airbox on any modern sportsbike should be able to provide enough air to the motor at top speed or the engineers who designed it seriously screwed up.
When the motor is running, it opens up the intake valve and sucks air in from the airbox. This gives the air momentum. When the intake valve closes, the air moving toward it slams into the valve and creates a pressure wave that is reflected back up the intake and into the airbox where it bounces around for a while. The pressure wave will eventually find its way back down into the intake. If the intake valve is open when this pressure wave arrives then it will ram even more air into the combustion chamber and produce more power.
The downside of this is that there is also a negative pressure wave bouncing around the airbox at the same time. Imagine a box that contained still air; there is equal air pressure all over. If you move some of the air from one side to the other then you'll have more pressure than normal on that side and less pressure from the side that you stole the air from. That is basically what the pressure wave in the airbox is doing; creating pockets of high pressure and pockets of low pressure that move around.
If the negative pressure wave arrives in the intake when the valve opens then it will inhibit air from getting into the combustion chamber and will reduce power.
The manufacturers use this knowledge and a lot of complicated math to build airboxes that help smooth their power delivery. If you have excess power at one RPM and a hole at another then you can modify the airbox to rob some air from the former to help fill in that "hole". This ultimately improves the driveability of the bike which has more to do with how fast it can go than a few extra horsepower.
So by hacking up the stock airbox, you may be gaining a few HP but are likely creating annoying dips in the powerband. Henrik mentioned that the SV650 racers saw this exact effect.
You can get some big benefits by doing this on old-technology bikes that don't have advanced airbox designs. The Ducati SuperSport series definately falls into this category, as well as the old Honda Hawk GT.
Drew
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Mikej
| | Posted on Thursday, September 11, 2003 - 03:20 pm: |
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Drew,
Does the XB airbox design take advantage of this? And do the race bikes with the Ramhorn air intake ducting modifications take advantage of this by manipulating it towards the top end?
And do the older Buell breadbox's take advantage of this? And are the carbon fiber Buell/Harley/Sportster hamcan air filter assemblies designed to take advantage of this?
Where would one learn more about this design aspect from a hobbyist/novice/tinkerer point of view?
Okay, that's five questions, I'm done for a bit.
Thanks for any feedback you'd care to give.
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Darthane
| | Posted on Thursday, September 11, 2003 - 03:43 pm: |
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Obviously we're oversimplifying things by saying that more air = more power - there are plenty of dynamics involved. However, at constant throttle, more air does indeed = more power.
As you noted, creating a completely open airbox, such as Joey and I have, does indeed shift around the 'dips' at WOT. I've noticed that mine is now at 5K instead of 3800. Not really a dip, just a flat spot. It does, however, increase peak HP. I'm actually going to put my stock airbox cover back on and begin really playing around with it (meaning I'll probably go through two or three of them busily boring holes in it), as well as getting my hands on a stock velocity stack again. It should be an interesting experiment to see what kind of combination produces the best SOTP kick.
Bryan |
Puffysleeves
| | Posted on Thursday, September 11, 2003 - 04:12 pm: |
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More air does equal more power, but opening up the airbox won't necessarily give you more air. It will likely increase power at some RPMs and decrease it at others and will almost certainly give you a bit more kick in the seat. The problem is that a kick isn't fast; for speed, you want a nice smooth power delivery that you can rely on so that you are comfortable getting on the gas early in the corners. Comfort = fast. Smooth = fast.
If you want kick, try an 80cc dirtbike. You whack the throttle and get nothing until it hits the powerband and throws you off the back. All power, no rideability. Great for training kids in the dirt, sucky for old people like me on the road. I don't bounce, I plow.
Please don't think that I'm trying to stop you; it would be _very_ interesting if you could get dyno runs of your changes. I'd love to see how the torque curve changes as the airbox is opened up and the velocity stack height is modified. This kind of tinkering is, if nothing else, a lot of fun. I just don't want everybody to start hacking their airboxes thinking that they'll get more power until after I buy stock in the airbox lid manufacturer. 
Mikej, I currently do not own an Buell and am here doing research on such a purchase so I can't answer your questions definitively. But in general, I would say that the new XBs definately use a tuned airbox simply because it's one of the easiest ways to smooth out the power deliver of the motor. Why put so much effort into making the heads better and then ignore such a powerful tool? Buell doesn't have the advantage of having a special-purpose built motor and therefore needs to use every trick in the book to be competive.
The best (and by far the most complicated) book I've read so far is Gordon P. Blair's "Design and Simluation of Four-Stroke Engines" but there are definately less technical books out there. A. Graham Bell's "Four-stroke performance tuning" is a pretty good place to start.
Drew |
Bud
| | Posted on Thursday, September 11, 2003 - 04:17 pm: |
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i have read the book,
good stuff
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Mikej
| | Posted on Thursday, September 11, 2003 - 04:34 pm: |
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Thanks for the followup, I've got a background project I'm starting to work on and this should help. |
Gonen60
| | Posted on Thursday, September 11, 2003 - 08:35 pm: |
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Just had a friend come over, who has cut the panels out of his inner air box on his "firebolt"
He runs the stock pipe, and his His engine noise is louder than his exhaust noise... |
Darthane
| | Posted on Thursday, September 11, 2003 - 09:49 pm: |
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Yes, with an opened airbox the valvetrain clatter is much, MUCH more noticeable.
Puffy, I'd love to be able to dyno it before and after every little change, but I'm not rolling in dough and I'm not a professional tuner, therefore I'll just tinker until whatever I've done 'feels' the best to me. And who knows, the most comfortable configuration, as you noted, may very well be one that makes less HP than another.
Without a completely different pipe, the XBs will never make really 'smooth' power such as I've felt riding a friend's M2. They tend to light up between 4500-5000 RPMs, and if you're on the gas you know it. Not like it's going to toss you, but definitely a kick in the pants. The M2 just pulled from 2000 and had a nice bell to the torque curve. If you've seen a XB's, you know they are very distinctive (using a stock or Race muffler, anyways).
When I get around to doing this monkeying, I'll definitely post impressions, but I don't know how many dyno charts I'll get out of it, since I'm not willing to spend more than a half hour on it (the dyno, that is) and I don't know how many different configs I can swap on and off in that time.
Bryan |
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