| Author | Message | ||
     Ratsmc |
Well, I just de-noided the CR. While in there, I left the airbox cover off just as an experiment. Sounds good that way but that isn't really my concern. I have done quite a bit of reading through topics on the airbox and what it does and does not do. All of my bikes have had some sort of ram air intake and all of them were designed to reach a positive airbox pressure at about 35 MPH which is a reasonable speed and makes the airbox valuable in nearly all riding conditions. From what I have read here, everyone repeats the same point: the 1125 airbox only reaches positive pressure at about 80 MPH. This seems like a really odd design. While airbox tuning has elements of art to it, it is still pretty solid science. Why on Earth would an engineering group that spend so much time thinking through creative solutions to old problems build a system that can only reach initial efficiency at speed that are illegal in every state in this country? So, what I would like to know is: where did this 80 MPH idea come from? Is this number actually based on any published info or actual testing? | ||
| Ron_luning |
The 80mph figure you have heard is probably a number someone pulled out of their ass. However it is probably not far off. I recall in Sport Rider magazine maybe 8 or so years ago they did a ram air test by measuring pressure at various speeds and throttle openings. Kawasaki performed head and shoulders above the other makes tested. If you look at the airbox pressure of a motorcycle without any ram air design, the pressure will basically always be negative. Since the engine is sucking quite a bit of air to run, especially at larger throttle openings, it takes quite a strong wind to overcome the intake's thirst. So...you need to be going pretty fast to get ram air to work. It is that way on any car/bike/plane. The location of the intake could probably be improved to make the most of the available wind blowing over the bike. Take a look at some of the foreign bikes with the intake located at the very front/center of the fairing. That being said, on the 1125R making a straight shot from the airbox to the front of the fairing is made difficult by the fuel-in-frame design (i.e. not feasible to route an air tube through the frame as on other bikes). (Message edited by ron_luning on December 20, 2009) | ||
| Froggy |
Ron, the XBRR had the intake in the dead center of the front fairing, and piped it up over the speedometer area into the airbox.  | ||
| Ron_luning |
That bike has a lot of function over form! Of course any engineer at Buell or any other manufacturer of sportbikes could tell you that the most effective place to put the intake is front/center, but there are a lot of things to balance including looks, cost, and performance. I could picture someone (maybe a particular individual in Australia)pitching an absolute fit about those "pointless" air intakes blocking the rider's view, and why didn't Buell just design it some other way. | ||
| Strongbad |
The 80mph number is very close to the break-even point, and a .5 psi positive pressure is seen above about 140. The reason these numbers are so high is that the stock airbox volume is far too low and the intake snorkel cross-section is very restrictive. The intake is in a very high pressure area, but has a lot of deficiencies to make up for with the rest of the airbox design. Want to see the easiest HP gain on the dyno? Just take the functional airbox lid off. | ||
| Ohsoslow |
weather it works at 80 or 10 mph im leaving mine off.....after 200 miles with it on i took it off and it looked like a gravel pit in there from all the shit sucked up into the intake, and no i have never taken it down a dirt road. | ||
| Milleniumx1 |
Anyone else remember turning the factory air cleaner lid over on the old GM Quadrajet carb? Step on it ... WAAAAAAAAAAH I know it never made it faster, but it sounded faster. Mike | ||
| Hdwrenchtx |
taking the lid off makes it sound better and there is no loss in performance? or if there is it would be 80+ mph? might try it | ||
| Sknight |
I'm all about airflow, and I did notice the factory scoop was a little weak looking. I'm thinking of opening it up and putting a bigger scoop on there to make it more effective. | ||
| Gearhead571 |
OEM's also have big brother to deal with on the sound requirements. Can't forget about that little bit holding em back on the functionality of the design. | ||
| Froggy |
Yep, and thats why we have the 'Noid. It gave the engineers a little more freedom with the airbox.  | ||
| Marcodesade |
Sknight: I'm pretty un-knowledgeable about ram-air (even though I removed my airbox nearly a year ago). So I looked it up on wikipedia. As it turns out, the ram-air effect is caused by SLOWING the air --- and thereby increasing its pressure --- as it moves from a narrow cross-section (the snorkel) to a wider one (presumably the airbox). So I'm guessing (but am not sure) that increasing the snorkel cross-section would be counterproductive. However, what I'm not clear about is why removing the airbox would decrease the effect, even if it only begins to happen at high speeds. Because removing the inner airbox INCREASES the area, thereby apparently increasing the ratio of the cross-sections. Is it due to the lack of a seal between the upper airbox cover and the bottom? If so, would devising some sort of a gasket help? | ||
| Cme2c |
Haha Mike, always flipped the lid on my 350 Nova (only had a 2 bbl) sure sounded fine. But had to flip it back over before I got home cause it pi**ed off the old man, God rest his soul. | ||
| Littlebutquick |
i have backed to backed it down the drag strip on same day minutes after each run always been slower buy about a 10th if that helps . but sounded faster  | ||
| Sknight |
Marco: What I was looking at was the size of the TBs and the size of the air scoop. They're roughly (As in I've glanced, not really looked yet.) the same cross sectional size. I'm going to do a little winter research and see what I come up with. | ||
| Ratsmc |
Littlebutquick, What was your top speed on those runs? | ||
| 1_mike |
I'll be looking into a divider wall between the two velocity stacks. On any V-8 engine that has two cylinders firing right after the other, it's been proven (depending on the cam) that the first cylinder will rob air from the second cylinder. This is why most cam manufacturers have switched the firing order of #5 and #7. I'd be willing to bet that if monitored correctly, the air intake in the 1125 should show some of the same intake problems that the V-8's do. Since the 1125 can't be altered, maybe a wall of some sort in the airbox may help even out the second cylinders air intake. I'll be looking into a divider over the holidays. Mike | ||
| Oldog |
Note look close at the air box cover of the XBRR there are 2 ducts running forward | ||
| Ratsmc |
1_mike, It seems (admittedly, without any analysis) that the two cylinders would be firing opposite each other so the intake strokes shouldn't interfere. | ||
| Avalaugh |
Wouldn't the engine be sucking in more hot air though with the air box lid removed ? these things get hot enough to boil the fuel in the frame, so with the lid removed that hot air would rise up and get sucked in, especially in normal street use ? | ||
| Vtwinbuell |
the engine is a 72 degree v-twin with the rods connected to a single pin. So the cylinders fire 432 degrees and 288 degrees apart. This explains why if you look at the fuel maps, one cylinder gets less fuel than the other. I have already separated the intakes because of this. | ||
| Xl1200r |
The 1125 does not use a single crank pin design. The TBs will be pulling in air at equal intervals. | ||
| D_adams |
Xl1200r - Check your service manual, it's a single crank pin. | ||
| Vtwinbuell |
It doesn't use a fork and knife rod design, but it is a single crank pin. | ||
| T_man |
140mph approx top speed without inner cover - 160pmh approx top speed with inner. Personal observations. | ||
| Redscuell |
"140mph approx top speed without inner cover - 160pmh approx top speed with inner. Personal observations." Now THAT'S useful information; seriously. | ||
| Strongbad |
That increase in speed would require a 30% increase in power. So if your bike makes say 130hp on a dyno without a pressurized airbox, it would be making nearly 170 with the possible .5psi increase in air pressure. Not going to happen. More like a 3-4% increase in power or 2-3mph could be expected. | ||
| Slaughter |
People keep thinking of these as "ram air" intakes... they're NOT. They are COOL AIR intakes. Keeping the air/fuel charge as cool as possible does much more than a false sense of "turbocharging." (and I've got NO data to back up ANY of my opinions on this) | ||
| T_man |
Your right guys - I made a mistake when converting km/h to mph. Its closer to a 10mph gap - This however is EXACTLY what I did observe; Inner air box cover off indicated top speed: 237kmh or 147mph. Inner air box cover on indicated top speed: 261kmh or 162mph. Thats honestly what I observed fellas, take it for what its worth - I now run with my inner cover on all the time, even though it 'felt' stronger with the cover off. | ||
| Xelerator |
It feels stronger when it sounds stronger |
