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Discussion Starter #1
Things that keep you awake at night. The nagging question, internal airbox pressure vs. external and the effects on fuel mapping?:eek:
Most of the Ducatis with fairings have some sort of ducting to the airbox. This leads me to believe that Ducati makes an attempt at pressurizing the airbox at SPEED. Anybody ever run a pressure/vacuum guage to the downstream side of the airbox in real time, speeds 80-180 mph? The barometric pressure sensor is usually inside the fairing[dead air space] maybe even negative at speed, anybody ever check this value?:think:
Dyno testing is static, fans blowing on the engine and/or radiator, what is the airbox pressure under those conditions?:confused:
Should our pressure sensor hose be hooked into the internal side of the airbox, for real time fuel mapping accuracy? Airbox internal pressure should directly relate to Horsepower.:D
You realize any changes you make to the physical presence[look/angle/shape] of the motorcycle can directly effect the internal airbox pressure at speed? Due to air flow changes around the motorcycle?:(
Any body ever do any checking on these phenomenon?How wil this relate to Dyno figures and results?:sleep:
 

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This is something I have been thinking over for some time. My impression is that in spite of a better (static) dyno with the all open configuration (open airbox + DP exhaust + mapped PC, roughly 120 hp), when ridden hard with fast gear changes the response is more immediate with the standard airbox (+ DP exhaust + mapped PC). It seems as if the bike leaps forward much better at any gear change in standard configuration.

Then again the midrange advantage offers faster acceleration holding the same gear up to 9.000 rpm. It's in the gear changes that something is lost. Maybe it's all about CONSTANT airflow, resulting in higher air pressure rather than just sucking in as much air as possible?

Anyway, maybe a dynamic dyno would give some surprise?

Chris
 

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I always thought it was strange on the ST that Ducati did 90% of the work to duct the air to the air-box, but these flex rubber tubes were NEVER CONNECTED !

I agree that if they were connected, you'd be "adding pressure at-speed", and that the baro. sensor should be placed inside this pressure-sensitive cavity.
 

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Intake Air Pressure

At an altitude of 6,000 feet the air density is about 15% less than the density at sea level, so because you're getting 15% less air on each intake stroke the engine management computer will reduce the fuel map injector duration values 15% at all engine speeds. Consequently you'll always make less horsepower as you climb higher.

The computer doesn't get air density readings directly, it uses a sensor to get a barometric pressure reading that has a direct relationship to air density under standard conditions of temperature and relative humidity.

This means that if you rev the engine at a stop in neutral the fuel delivery at all rpms will be higher at sea level than at altitude in direct proportion to the air density.

If you try moving the air pressure sensor to the inside of the airbox then when you rev the engine the pistons will pull air on the intake stroke and the pressure inside the airbox will drop causing the computer to reduce fuel flow. Clearly, this is incorrect.

Ducati's open-loop engine managerment system doesn't know or care about how fast the bike is moving - it only knows engine rpm, throttle position, air pressure and temperature, and coolant temperature.

Closed-loop systems constantly monitor an engine's exhaust gases and feed this information back to the computer for a real-time adjustment to fueling.

So what effect does the increased air flow to the air runners at higher bike speeds have on the air-fuel mixture? Obviously, a higher bike speed will pressurize the intake air and cause the engine to run leaner than the same engine speed but at a lower bike speed.

Even if we know this intake pressure vs. bike speed relationship from aerodynamic testing, there's still no way to tell the computer when to adjust our dyno run fuel map for this effect without the computer knowing the bike speed.
 

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Shazaam!
 

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Discussion Starter #6
At an altitude of 6,000 feet the air density is about 15% less than the density at sea level, so because you're getting 15% less air on each intake stroke the engine management computer will reduce the fuel map injector duration values 15% at all engine speeds. Consequently you'll always make less horsepower as you climb higher.

The computer doesn't get air density readings directly, it uses a sensor to get a barometric pressure reading that has a direct relationship to air density under standard conditions of temperature and relative humidity.

This means that if you rev the engine at a stop in neutral the fuel delivery at all rpms will be higher at sea level than at altitude in direct proportion to the air density.

If you try moving the air pressure sensor to the inside of the airbox then when you rev the engine the pistons will pull air on the intake stroke and the pressure inside the airbox will drop causing the computer to reduce fuel flow. Clearly, this is incorrect.

Ducati's open-loop engine managerment system doesn't know or care about how fast the bike is moving - it only knows engine rpm, throttle position, air pressure and temperature, and coolant temperature.

Closed-loop systems constantly monitor an engine's exhaust gases and feed this information back to the computer for a real-time adjustment to fueling.

So what effect does the increased air flow to the air runners at higher bike speeds have on the air-fuel mixture? Obviously, a higher bike speed will pressurize the intake air and cause the engine to run leaner than the same engine speed but at a lower bike speed.

Even if we know this intake pressure vs. bike speed relationship from aerodynamic testing, there's still no way to tell the computer when to adjust our dyno run fuel map for this effect without the computer knowing the bike speed.
Well, I have been over 12,000' with this bike this year and it still runs better than any carburated bike[not rejetted] up there. It may have less power, but so does every other NA bike and car out there. I can't believe how well it did run.
Your point about the low speed or stopped, throttle application is a great one. Hadn't thought of that.
At the same time, my whole point was air box pressure on the open loop system at speed. The computer could correct without speed sensors, if it was getting real time airbox information[I think, it seems]. Guess thats why they don't do it, the low speed wo throttle situation etc.
Now I have to lay awake at night figuring how to overcome that without closed loop. Da:think:
 
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