| Author | Message | ||
     Angushendrick |
I know this is a well worn subject, and there's a strong consensus that either gutting the airbox or installing a forcewinder is the best way to provide more ventilation to the engine (coupled with an aftermarket can and the Race ECM), but... I found the following when I was surfing: http://www.thebikezone.co.za/latest_launches/buell/04-02-2002.htm A special camshaft increases lift and duration of valve opening. Induction is by means of the Saab-developed fuel-injection system that serves so well on the 88-cubic inch ’Glides, with an interesting tweak: the huge air box uses resonance within the intakes gases to pressurise the inlet port just as the valve is opening, forcing extra mixture into the cylinder. It’s called the Helmholtz principle and it works like a two-stroke expansion box - only in reverse. From the little bit I know about resonance this seems wrong. A classic example of a Helmholtz resonator is a beer bottle that you blow over the top of. The sound is (of course) time-varying pressure. The basic idea makes sense--there are pressure peaks that could be exploited. The problem is synchronizing the pressure peaks from the resonance with the air-valve opening cycle. Changing the natural frequency of a Helmholtz resonator requires changing the volume of the resonance chamber. You can observe this (and annoy your friends) by repeatedly blowing over the top of your beer bottle as you drink it down. The Buell's airbox has a fixed air volume (except for the air displaced by puking oil) and so has a fixed natural frequency that will only match a particular engine RPM. I can't see how this could provide benefit for all RPM's. That said, I'm hesitant to conclude the quoted statement is just Buell marketing because (my understanding is that) the Buell race kit does not gut the airbox. Is there some feedback phenomenon, perhaps because the flow into the airbox is not steady but only occurs when the valves are open, that makes this thing work as advertised? Anyone got an explanation? On a related note, I've seen some taller venturi rings available. What do these do? My understanding is that a venturi converts flow energy (AKA pressure) to kinetic energy (AKA velocity). The characteristic feature of a venturi that determines how much flow energy is converted into kinetic energy is the change in flow area (i.e., reduction in diameter). As I understand it, both of these venturis have the same flow area change, one is just longer than the other, so the reason for improvement is not obvious to me. Can someone explain how the longer venturi throat improves performance? Thanks, Angus | ||
| Ara |
Angus, most of what you said is technically over my head. But I do remember that Tat's (American Sport Bike) longer venturi ring produced more midrange torque at the (moderate) expense of high end horsepower. Why, I don't know. | ||
| Djkaplan |
Unless plenum volume or runner length is changed, you are correct in your statement that the natural frequency is fixed. I'm sure this phenomena is used cover up dips in the power band and not for maximum power at all rpm. As for the venturi ring, I don't think the ring itself creates a venturi effect - it smoothes the air entry into the carburetor inlet. | ||
| Bomber |
the stock Samsonite Airbox did a couple a things -- it produced decent power outa the engine (more accurate to say, I imagine, is that it didn't kill an inordinate amount of power), and greatly quieted the intake noise (leaving more margin for other engine noises -- one of the things h2o cooled motors got going for em is reduced noise) it also made it tough for 6-foot plus riders to be comfy on the thing for long ;-} the race kit did't gut the airbox, it replaced it altogether | ||
| Panic |
Does anyone know the interior volume of the plenum chamber? | ||
| Deltacruiser |
In response to the factory race kit not gutting the airbox, that is not accurate, at least for the X1's. I'm not sure about other models. I installed the factory race kit on my 99 X1 and the instructions that come with the kit do call for gutting the airbox. The snorkel is removed completely. Really all there is left is a box with a K&N filter at one end in place of the stock filter and then open space between there and the intake venturi. } | ||
| Angushendrick |
I just got my service manual and realized the previous owner had "gutted" the airbox--the snorkel is gone. However, some of the interior features remain, specifically the plastic "wall" surrounding the filter. A number of the "how to gut an airbox" discussions mention removing this structure, so I thought I had the stock box. I don't. I'm a little puzzled now about what the Helmholtz resonator even is in the stock set up. Normally people talk about a large trapped volume of air as the "spring" and the air which oscillates in a smaller neck as the "mass." In the stock setup, its just one long tube of constant diameter. I talked to a physicist at the office today who suggested how the the longer venturi might work. The longer venturi creates a longer tube of resonating air. More air in the tube, means more "mass," which means a lower natural frequency than the shorter stock venturi which would resonate at lower RPM. | ||
| Wardan123 |
One of the racing shops I called (Tilly's I think)when researching an alternative to the stock air box said that they had great results gutting it [the stock air box] and following the race air filter instructions for venturi and breathers - and removing via dremmel any extraneous plastic that may impede air flow. They then plugged the existing opening and cut a new one on the front of the stock airbox and fitted a high flow filter there. The gentleman on the phone said it had a ram-air effect on the track and really boosted HP. I didn't try it but it sounded interesting. I went with the Buell race cleaner and fitted the temp sensor inside and plumbed a Jaz catch can. | ||
| Djkaplan |
"In the stock setup, its just one long tube of constant diameter." That's not all there is to it, though. The long tube has two round ports at the elbow. These ports open to the plenum area created by the large airbox. This fixed volume is part of the intake system. Think of the two ports in the tube as the top of your beer bottle when you blow across the top. | ||
| Angushendrick |
Ahh... that makes sense. | ||
| Bomber |
Delta -- oops, I was forgettin X1s -- you are likely correct (sorry) -- other tubers used the CF hamcan in lieu of the airbox | ||
| Deltacruiser |
Bomber, Not a problem. It's easy to forget the stock X1 airboxes. They are just flat ugly. I'll be switching mine to the CF hamcan style or a forcewinder once I save the required funds for the aircleaner, tank accents, and either a catch can or XB rocker cover conversion. |
