best ramair system

[Guest]

I just had to put in my 2 cents. First I am a Suzuki fan, they are late in the ram air, and Kawasaki had it for a long time and they do it right. The air intake on all Kawasaki bikes is in the center of the fairing for maximum pressure. Suzuki placing their ram air to the side, results in a lesser pressure. The air movement causes this, like the wing on an aircraft, the pressure actually drops on the sides of the fairing, and at high speeds the wind effect of the straight on coming air mixing with the side stream causes the higher pressure for Suzuki 140 mph +. The formula for calculating pressure of air from speed is (mph * mph)/57600 = psi, so (180*180)/57600= 0.5625 psi. The above post about turbo charging a 6-psi equaling ram air is not true. BUT a turbo is only about 75% efficient if it sized properly. That means that it generates heat compressing the air and the 5-6 psi is equal to about 4 psi of ambient temp air. While superchargers are only 35%, (much more heat induced). A Busa on a 6-psi boost from a turbo would have a horsepower in the range of 250. With efficiency between 70 and 75 percent the intake temp would be around 150F with 60-degree ambient air. It would take about a 500mph-intake speed to equal that.
Airflow of the motor is dependent on efficiency, valve size, valve lift, intake and exhaust tracks, air temp, etc. The formula is ((cubic inches * 1/2 stroke* RPM)/1728) * volumetric efficiency. A busa at 90% efficiency at 11000 rpm would use about 217 CFM of air for all four cylinders or about 54 CFM per cylinder. This is with no ram air. Ram air changes the efficiency of the motor.
Turbo Rick you are correct in assuming the restriction. Cut the damper valve out, under the air filter all the way to the lip.
David G.

 

[Guest]

I looked at the graphs in the Oct of Sport Rider magazine a little closer. The lower than ambient pressure occurs until about 140 mph. It's a good article. It made me go out and buy a copy. I'll undoubtedly buy next months too. But I have to wonder about the lower than ambient pressure up to 140. Does anyone know the authur Kent Kunitsugu ? Does he have email? I have a bunch of questions for him.

 

[OB_Turbo Rick]

An interesting thing to note is if you compare the graph of the Busa and the cbrxx
you will see when they close the throtle both pressures go up to 35mb.
That leads me to beleve that there is a restriction in the airbox of the Busa.
maybe the small flapper valve assm. It would be interesting to see what the pressure would be with the area inside of the airfilter cut out.
I'll talk to kent about that
you can email him at srmail@petersenpub.com

 

[Guest]

Bob, is correct on it is air mass that makes the horsepower. The more air and fuel the more power. But combustion chamber efficiency also effects how much power you can get out of a given displacement, Piston and cylinder shape, compression ratio etc.
On the question off how much can I gain, we can ball park the number. Most dyno s are correct to 60F 0% relative humidity and 29.92 inches of mercury, this is considered 100% Air density, a base line or standard. Temp changes this 1% air density for every 5 degrees but the effect on the motor is about 70 % of that, in other words you would not have 99% at 65f but 99.3% motor effect in horse power. Relative humidity is about 1 to 1 so for every 1% change in air density you get 1% change in horse power. At 60F 50% RH is equal to about 1% change, so at 29.92hg, 60F and 50% RH you would have 99% of your power. Humidity is not linear the same 50% at 90F is over 2% in air density, not including the drop in power from the temp. So 29.92 at 90F and 50%RH would be about 93.8% of the dynoed horsepower.
Now to get to pressure, the atmosphere at sea level is about 14.68 psi or 29.92 inches of mercury, at 100 mph the increase in pressure would be about 0.1736psi. So 14.68 + .1736 would be 14.85psi absolute pressure, or 0.1736 gauge pressure. This would mean that the reading in inches of mercury would have changed from 29.92 to about 30.27. For every 0.3 would be a 1% change in air density and the ratio is about 1.2 to 1 so that means if you had a 0.3 hg barometer increase you would have 101% air density and about 101.2% engine performance.
Now if your bike dynoed 155hp and you where traveling at 92 mph, that would be about a 1% air density increase and about a 1.2% motor increase. 155 X 101.2% = 156.86 horsepower. At 180 mph the increase would be about the same as 31.06Hg or 3.8 Air Density or 4.6% motor increase ….= 155 X 104.6% = 162 hp. Now the gains in efficiency are not linear for many reasons, dynamic compression along with increased volume with increased inlet pressure are a couple. The restricted area of the bike can cause a lower increase in pressure at the intake, making the air opening twice as big, increase the area 4 times. The pressure change at the valve opening is increased greater than 4.6%.
Lets Take a bike with the ram air mod and slip-ons that dyno 162.5 hp, the same bike at 180 mph would make about 170 hp if it where linear. The actual gain should be a little more.
The same bike at 162.5 hp at 60F 29.92Hg 0% RH with a turbo operating at 70% efficiency would have an increase of about 138.6% increase or 225 hp without an inner cooler.
Ram air increases the air mass not only by pressure, but also by supplying the intake with cooler air.
Lets say it is 40 degrees 10% Rh and 30.20Hg, your bike dynoed 160 hp, you would now have a little over 166 hp with no ram air. With ram air the power would increase to around 181hp. Dyno's are great because they calculate every thing to a standard, the down side can be the person running it entering the data or the instruments used to get the air condition data. I believe that I have used two years of posting by Bob's measuring system.
David G

 

[Guest]

God I love this technical talk.

Even scarier, you guys make sense.

All this to say that we need to work on our air boxes. Would taking the little screens out of the intakes help much? Perhaps, increase flow with out materially changing the look of the bike.

[This message has been edited by Lyle (edited 14 August 1999).]

 

[Guest]

Ok David G, you've done your homework, so what sort of horsepower does the stock ramair add at say 100mph...

For instance, if the bike dynos at 155rwhp, what rwhp would we see at 100mph?

Just for an idea, if we increase the size of the ram-air intakes 50%, with the same airbox/duct restrictions, what would be the gain in hp over the STOCK system at 100mph???
Who wants to know this besides me? Does anyone like the idea of modifying plastic scoops to gain hp??

 

[Guest]

Yes, removing the screen would increase the flow, but at the risk of rocks or debris that may get in you air box. The gain is not worth it.
David G.

 

[OB_Bob]

David hit a key point on the head. Its all about volumetric efficiency (V.E.).
I don't know the V.E. of the Busa as delivered, and as I stated before, I am much more familiar with Autos, which generally are in the 90% region if mild performance built.
RAMAIR improves on the volumetric efficiency, which is how well the engine breathes. The better the breathing ability the higher the V.E. V.E. is really the wrong term but its been used for so long it will not be stated as what it is--"Mass efficiency" V.E. is the ratio of of actual mass (weight) of air taken into the engine-compared to the mass which the engine displacement would theoretically take in, IF THERE WERE NO LOSSES.
Cold air is heavier and thats why your bike should be quicker on a cold low humidity day.
Altitude has the same effect--A bike up in elevation in Colorado will never make as much power as an identical bike at sea level.

The ratio is expressed as a percentage (%). It is quite low at idle or low speeds because the "pump" or engine is being throttled.

V.E.=Actual mass of air taken in / Theoretical mass of air which could be taken in
V.E. reaches a maximum at a speed close to that where maximum torque at wide open throttle occurs, then falls off as engine speed is increased to peak rpm. V.E. curve follows closely to the torque curve.
I any of you are still reading this one of the points I am trying to make is that there is a loss in the ramair system we have versus the others, which affects V.E. The loss is in the runners and airbox.
David G--posted some calculations.
I calculate required CFM for carburetor sizing roughly by using --

Engine Size (Cubic inches) X Max. RPM / 3456
@ 100% Volumetric efficiency.
For our Busa's --1300 cc's = 78.8 CI
78.8 X 11000 / 3456 = 250 CFM, but we probably do not achieve 100% V.E. and if we use 90% like David G did you get 250 X .90 = 225 cfm. Interesting considering TOJ on another post flow benched his heads and they came in at 225 cfm at 28" H2O 10mm lift.
By the way this formula illustrates why "there is no substitute for cubic inches" in regards to power. Yes it may weigh more.

The article explains the theory of pressure build-up well.
Pressure build-up from ramair is according to the Pitot-static tube theory--this same device was used for years to measure wind speed for aircraft.
the follwoing is from the article--
P = 1/2 x p x v(squared)
P is force divided by area (lb-force/in sq'd)
which translates to psi.
p=density is mass divided by the volume (lb-mass)/in-cubed.
v=air speed ft/sec
This is all fairly useles to most of us, but IF TLR makes a change that can improve on the loss of the ramair system its possible to improve V.E., in theory. Whats it worth--tough to say. My opinion is probably not alot without more sophisticated testing/design, but who knows I have seen some posts about air box mods that say 5+ hp.
My problem with this type info. is that there is no ramair on the dyno so what will it do on the road?
The article also states that the losses of a good ram air system can be as much as 70%. The losses are getting the air to the carb.
Also max. theoretical pressure at 150 mph would be approx. 0.4 psi or 27mb.
I think I used up my posting space for the year--time to ride
Bob

 

[OB_Bob]

TOJ made an interesting post on dyno runs after air box mods. If you have not seen it go to it.
I sealed up my ramair runners to ensure no leaks. Don't know how much it will help but it is a quick mod.
I have not decided to make the other changes yet to the box.
Bob