Engine intake pressure?

[Blaylock1988]

Does anyone know the cylinder intake pressure for a stock XB9sx? I am doing an analysis on my bike for my Internal Combustion Power-plants class to help review for my next test. If no one knows I will probably just assume it is slightly lower than atmospheric (maybe 14.5psi).

This might be a long shot but if you also know the air mass flow rates for the factory air filter and a K&N filter I could calculate the performance change at stoichiometric and lean/rich full ratios (as if it were tuned or untuned)

Thanks!

 

[user_deleted]

K&N publishes the CFM flow rate of all their filtes on their website. the perfect or stoichiometric fuel to air ratio is always 14.7 to 1. their is no constant intake pressure per se in any internal combustion motor including diesels and rotaries. the intake track air constantly changes from vacuum to static to pressure. depends on many factors including piston position in cylinder, cam specs, valve specs and timing, on and on. your instructor should explain that if he's holding a class on IC engines.

 

[Blaylock1988]

Cool I didn't know K&N had that info I will go check it out. The stoichiometric ratio ideally is 14.7 with no humidity at sea level, but on a day with 100% humidity (like here in NC) with Isooctaine the stoichiometric A/F is 15.54:1.
There is a constant pressure on the intake stroke and exhaust stroke. Usually the intake pressure is lower than the exhaust pressure (usually just about atmospheric) which causes reversion (unless it is a super finely tuned engine, or boosted, where intake is more then exhaust. I am looking for that pressure on the intake. Megalog viewer doesn't display this information, usually it is calculated by checking the pressure in the manifold upon intake. I am hoping someone else already knows it.

Oh, and this is assuming it is running at max horsepower at 7500 RPM.

 

[Mike Van V]

the perfect or stoichiometric fuel to air ratio is always 14.7 to 1.

This comment is incorrect for anything other than "perfect", no load conditions.

If one uses this ratio for acceleration, 1. it'll accelerate like crap and or 2. it'll detonate so bad, you'll loose the pistons to big holes....

While 14.7 may be close for cruise applications...what road is perfectly flat.

Also as Blaylock, states, ambient temp., humidity, and altitude also plays a part in the ratio for the location.

Depending on what year your bike is (has or hasn't got the air inlet in the left side scoop with no other holes in the box cover) whether, when and how much pressure or vacuum is in the airbox.

Blaylock -

You might try an undampened vacuum/pressure gauge tapped into the airbox somewhere to get the answer you need. Check McMaster Carr or someplace like that for a gauge.

Mike

 

[anrkizm95]

the perfect or stoichiometric fuel to air ratio is always 14.7 to 1.

This comment is incorrect

[up]

 

[user_deleted]

mike: what i was trying to say is that the air to fuel ratio of 14.7:1 has always been and always will be considered the "ideal" ratio for an internal combustion gasoline engine. perfect? no. what is perfect in this world? my wife. just ask her.

 

[anrkizm95]

(14.7:1) that is the ideal ratio for lowest emissions, but this isn't the best ratio for power

 

[Blaylock1988]

Yeah, it isn't best for power because there is always residual fuel that doesn't burnt and is wasted out the exhaust.

My bike is a 2007 model. I don't have it with me at school and can't measure the pressure myself, I was hoping someone here might happen to know offhand from their own experimenting/testing (or even a close estimate?).

 

[user_deleted]

14.7:1) that is the ideal ratio for lowest emissions, but this isn't the best ratio for power

wrong. 15.2:1 AFR is considered the perfect ratio for lowest emissions in a gasoline engine running a cat and closed-loop injection system.

 

[user_deleted]

i can see this thread continuing until christmas at the present rate of AFR techno jibberish. LOL

 

[anrkizm95]

the stoichiometric air-fuel ratio (14.7:1) that is the ideal ratio for lowest emissions, but this isn't the best ratio for power. It used to be that 12.5:1 was considered the best power ratio, but with improved combustion chambers and hotter ignition systems, the ideal now is around 12.8:1 to 13.2:1. This is roughly 13 parts of air to one part fuel. It's what combustion engineers call an excess fuel ratio and is intended to ensure that all the air is used to support the combustion process. This is because air is the oxidizer in combustion. Too many enthusiasts think that adding additional fuel beyond the ideal to create a richer mixture will make more power. This doesn't work because you can only burn the fuel when you have enough air to support combustion. That's why engines make more power when you add a supercharger or nitrous--you're shoving more air in the cylinder so that you can burn more fuel. Regardless of the amount of air in the cylinder, it still requires a given ratio of fuel to burn. Add too much extra fuel, and power will decrease.


These simple graphs illustrate... read full caption
These simple graphs illustrate why the narrow-band oxygen sensor (A) is only accurate around 14.7:1 air-fuel ratio. Note its near vertical line at that air-fuel ratio. Graph B illustrates the more linear wide-band sensor that offers more accuracy across a much wider range from around 9:1 to roughly 19:1.When it comes to fuel mileage and increased fuel efficiency, this ratio changes again. All new cars run at 14.7:1 air-fuel ratio at part throttle because this is the lowest emission point. But depending upon the engine, it's possible to run an engine at leaner mixtures like 16:1 or more at part throttle to gain mileage. The difficulty with this is that driveability and throttle response suffers at these ratios. Engine response is lazy and stumbles are commonplace.



Read more: http://www.carcraft.com/techarticles/116_0402_innovate_air_fuel_ratio_meter/index.html#ixzz1chPPSilb

 

[user_deleted]

this tech has the answer. everybody else on here is wrong including myself.

http://www.youtube.com/watch?v=MXW0bx_Ooq4

 

[anrkizm95]

lmao thats awesome[up]

 

[user_deleted]

steve...ya like those "marzel vanes" and gimbel rods? LOL LOL WTF?

 

[Blaylock1988]

It also has a Geiger scale as well...for those radioactive leaks.

 

[Blaylock1988]

So, would anyone happen to know the Coefficient of drag for an XB9sx and the drag cross sectional area as well? Then I could calculate the theoretical terminal velocity.

 

[user_deleted]

yes sir, i happen to have vast aerodynamic coefficient of drag knowledge as well. the generally accepted cd.# for a XB9 cityX with factory installed handguards, mirrors, stock air cooling scoops is .382
the cross sectional area as it relates to relative drag measures approx. 214.6 square inches. if you remove the turbo encapsulator, gimbel rods, transthermal thyristor and marzel spanners it drops to .029 removal of these items voids factory warranty and is NOT RECOMMENDED by myself, erik buell, or ralph nader.

 

[Kid1620]

or ralph nader.

Lmao

 

[Blaylock1988]

yes sir, i happen to have vast aerodynamic coefficient of drag knowledge as well. the generally accepted cd.# for a XB9 cityX with factory installed handguards, mirrors, stock air cooling scoops is .382
the cross sectional area as it relates to relative drag measures approx. 214.6 square inches. if you remove the turbo encapsulator, gimbel rods, transthermal thyristor and marzel spanners it drops to .029    removal of these items voids factory warranty and is NOT RECOMMENDED by myself, erik buell, or ralph nader.

Awesome, in the mean time I tried backing out the Cd number assuming a max speed of 120 (as advertised) and a generic cross sectional area of 5sqft, and was getting stupid high Cd numbers like 1.6. I am going to talk to my professor tomorrow and see what I am doing wrong. I was also getting a strangely large mass flow rate of fuel (190 lbm/hr assuming 90% volumetric efficiency) which is like 30 gallons an hour. Even running the bike at 7500 RPM for a solid hour I might use up a tank or 2, so I think I messed up somewhere there too.

 

[Blaylock1988]

I understand my Cd calculation error. I was assuming that the force of drag at 120mph was what caused the max speed, but it is in fact a limitation from the transmission.

So according to my calculation, aerodynamically, our bikes could theoretically go up to 295mph on a 100% relative humidity day, with 80hp before the drag force is greater than the bike's force on the ground, IF there were enough gears to get that high, lol.

80hp max is what I got from the ASB shootout with the stock exhaust.