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Fullpower
| | Posted on Thursday, January 20, 2005 - 08:18 pm: | 
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unless you drop one out of an airplane, the XB does not have a high enough top speed to use "ram air" |
Spatten1
| | Posted on Thursday, January 20, 2005 - 10:01 pm: |
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Truth hurts. |
Craigster
| | Posted on Thursday, January 20, 2005 - 10:03 pm: |
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Never said the Buells used a 'real' ram air system, but........ if you've ever done any research involving ram air, you would be surprised at what it takes to buffer out the intake surge and keep positive pressure. That's where it benefits to allow the engine as much air as it can gulp in a single breath. I had a hard time getting an air box big enough when designing a set up for a v-twin drag bike. The air box under the 'tank' had to extend into the scoops and down the back of the bodywork above the transmission.
For what it's worth ram air systems can work at lower velocities. For example, at 45 mp a zx11 gains a mid range boost in power while at 90 and above the bike loses some midrange and gains top end. The other Jap manufacturer's have had a decade to come up with better ram air systems but most still require a fair amount of speed to make any appreciable increase in power. Kawasaki still rules in this regard. |
Trenchtractor
| | Posted on Friday, January 21, 2005 - 02:00 am: |
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When my bike was playing up (pinging) with the Pro Series kit, we tried every combination of stock and Pro Series parts...
Not only will I say that the K&N makes a big difference over the OEM filter, but it is the cheapest part of the pro series kit, and also provides the biggest gain when used in isolation.
That's right, I'm saying out of all the parts of the pro series kit, the K&N has the biggest noticeable gain as an individual part... |
Glitch
| | Posted on Friday, January 21, 2005 - 07:58 am: |
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There's no need to even mention ram air when talking about an XB. Unless you're wondering why the Buell web site says the XB has ram air. It ain't there.
That being said, I agree, with why we have such a big air box. But, it's not got positive air pressure, it's got no air pressure at best, then you start the engine. |
Opto
| | Posted on Friday, January 21, 2005 - 10:42 am: |
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And if an XB12 starts pinging, it'll ping harder with a K&N, ask me how I know  |
Blake
| | Posted on Friday, January 21, 2005 - 01:11 pm: |
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Ram air is not magic. A perfectly efficient ram air intake can provide no more pressure boost above ambient atmospheric pressure than...
DP=V2/56300
Where:
DP is the delta increase in intake tract air pressure above ambient in PSI (LB/IN2.
V is velocity in MPH.
So at 45 mph, the pressure increase above ambient atmospheric pressure for a 100% efficient ram air intake would be a whopping 0.036 psi which represents approximately a 0.25% increase over ambient. In reality, nothing.
At 100 mph a 100% ram air intake would add 0.18 psi which amounts to around 1.2% increase over ambient. Starting to become significant.
At 150 mph we find a 2.7% increase.
At 200 mph we find almost 5%.
But that is just ram air.
More important is to optimize airbox resonant tuning characteristics, the way that positive and negative intake tract pressure pulses behave and are timed with respect to intake valve opening will have far greater effect than ram air for a street bike.
Just like how a well designed exhaust tract will significantly aid scavenging and cylinder fill, so too will a well tuned intake, albeit to a much lesser degree.
It would be the optimum resonant design of the ZX11 intake that benefits performance in the mid-range at 45 mph. Optimum intake resonant configuration will provide the same benefit at mid-range at any speed/gear as the resonant tuning is only engine speed dependent for WOT scenarios.
Very interesting stuff.
In the end, for overall performance across the rev range, it is awfully dificult to beat an open supply of ambient air. |
Blake
| | Posted on Friday, January 21, 2005 - 01:22 pm: |
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I should add, that the one challenge of optimizing resonant design of an intake, just like that of the exhaust tract is that what is optimum at one engine speed will not be optimum and may in fact be horribly detrimental at other engine speeds.
Thus we now have valves and bearings in our mufflers.
Have you lubricated your muffler bearings lately? 
I keep waiting for a sliding trombone style exhaust to show up on some bike somewhere, where tailpipe length would change according to engine speed, always maintaining absolute optimum resonant performance. We're just talking about an infinitely variable exhaust tract rather than a two configuration (valve open versus valve closed) exhaust.
I may have to do that one of these days. Seems like it might could even be an analog system.
Fun to imagine anyway. For off road applications only of course. |
Craigster
| | Posted on Friday, January 21, 2005 - 05:16 pm: |
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The exhausts exist. We used to run what we called 'slippy pipes' on the formula cars I worked on. |
Craigster
| | Posted on Friday, January 21, 2005 - 05:27 pm: |
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Blake,
You sound like you'd like chatting with Kevin Cameron. He had all the math worked out and proved that a ZX11 could never make more than a 2-3% power increase at speed.
Unfortuanately the ZX defied logic by posting only 128 hp with no air forced in and jumped to (I think) 135 with a 120 mph blast.
His next theory was the intake air was working in concert with the harmonic resonance of the air box. I don't know if he ever came up with an explanation on why that is. What I learned from that was: Do the math - build the air box(or what ever your project is) based on the math and then and test, test, test. With plenty of modifications during the test.
There's always something to be learned from testing, that may not show up on paper.
Sportrider had a great article on modern ram air and airboxes a few years ago. Showed that each of the Kawasakis produced more power with lower air speed than each of its class rivals. |
Charlieboy6649
| | Posted on Saturday, January 22, 2005 - 11:52 am: |
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After reading the cleaning instructions at my 10,000 mi servicing I found something very interesting. They recommend you avoid over cleaning the K&N. The instructions claim the filter actually works better the dirtier it gets without hampering flow, unlike a paper filter where flow degrades with use. They'd rather you re-oil than clean too often. Mine was pretty dirty on the intake side but clean on the right side, I cleaned it anyway... |
Kowpow225
| | Posted on Sunday, January 23, 2005 - 10:52 am: |
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I've read that somewhere too, charlieboy. I don't know if I'm buying it though. A dirty filter flows as well as a clean filter...doubt it. |
Reepicheep
| | Posted on Monday, January 24, 2005 - 08:57 am: |
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Hopefully we can lure Aaron in here (hint hint...)
Blake, I was thinking the same thing. The control system for a trombone exhaust would be pretty straightforward. Basically a "RPM versus Length" thing. I don't understand why it has not been done, perhaps the solution is nonlinear, and difficult to map, or just doesn't give much more then a simple butterfly valve on a two length system can do.
As for the ram air benefit... I will quote Donald Knuth, a famous algorithim theoritician, who had just completed a mathematically rigorous proof of a particular algorithim, and went on to state:
quote:Beware of using the following code, I have only proved it correct, not actually compiled and run it.
As a software developer, let me say that truer words have never been spoken. |
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