Ram Air on a GS ?????

[werase643]

back to my first response.....why?
....1- 1.5 HP MAX!!!!!

Racing.  Riding ability can carry you only so much.  When your talking about a bike with lets say 40 Hp, thats 2.5-3.75 % increase in power.   That is a pretty good jump.

and another great racing furmula.... 1 HP = 7 lbs
you can push a lighter bike just as fast with less power

get off your butt and start running
or
even better stated by a friend.... "i'll take a dump before i hit the track and gain a HP"

[werase643]

Im pushing 53 HP as I sit right now. Ive race 2 seasons on this motor and it has no signs of letting go yet.

2 mil over high comp pistons, cams, shaved head, timing, K&N pod filter, V&H oval, ...

so a built GS is still down on a stock EX500....55HP

and i have seen a fat man on a FAST EX600+ pumping 96 hp
he replaced the cases every 2-3 races...wear item!!!!!!

named Stromann, ya might have heard of him
they changed the rules in WERA because of him

[Blueknyt]

hope you dont have to race with a 10 mph tail wind.

[GeeP]

Do you have a reference for your figures?

Not that I don't believe you, but yours are a bit... pessimistic than those I've seen.

No problem.  I'm glad to share.

First off, I provide this link to pitot-static airspeed measurement.

To estimate the dynamic pressure "ram effect" we use a simplification of Bernoulli's theorem.  (At least, that's how I like to remember it.)  This will work to roughly 220 MPH.  Above this speed, compressibility needs to be considered.

q = (1/2) (rho) (V squared).

Where:

q:  Dynamic pressure, Water Column (WC)
rho:  Density of air at standard atmosphere, .002377 slugs/cu.ft.
V:  Velocity, feet per second.

So...  At 100 MPH (146.67 FPS) the dynamic pressure is equal to .5(.002377)(146.67 squared) or .17PSI

To determine the zero loss power gain is straightforward.  The ISO standard atmosphere is 14.696 PSI absolute.  Air density is directly related to pressure, volume, and temperature.  If we assume volume and temperature are constant, the amount of combustible air available is directly proportional to the delivery pressure.

A GS 500 with no ram air has a maximum possible induction pressure of 14.696 PSI.  A GS 500 with zero loss ram air at 100 MPH will have a maximum induction pressure of 14.696 + .17 = 14.866PSI.  That's an increase of 1.15% of available combustible air in the cylinders.  Therefore, if the fuel scheduling is increased accordingly the engine should put out 1.15% more power not accounting for mechanical losses.

This simple computation works because it's relative.  We know how much power the GS puts out under a standard atmosphere.  Therefore we can, within reasonable limits, "scale" the effect of air density.  

Errors:  I assume in my calculation that the speed of the airflow through the intake is 0.  Obviously, this is not the case.  I do this because the cross-sectional area is unknown.  The larger the cross-sectional area of the intake duct, the lower the speed through the duct, and therefore the more ram air recovery.  To get a closer figure you need to subtract the speed of the air through the intake duct from the forward velocity of the motorcycle.

It can be argued that the change in relative density affects the viscosity of the working fluid and results in a slight error due to fluidic drag.  This is true.  The error is negligable.

[werase643]

i was searching on ram air...but couldn't find it

KEWL
thanks for posting source!!

i was also looking for the info on air box resonance design / theory....
quick ugly.....  http://www.chrysler300club.com/uniq/allaboutrams/ramtheory.htm

there is more to it than duct taping on some drier hose.

[GeeP]

No problem.

Couple other things that came to mind...

To recover as much ram air as possible you need to have total stagnation around the inlet to the duct when the duct through velocity is zero.  An efficient ram air recovery system might be a tube up to several inches ahead of the stagnation point on the front of the fairing and aligned with the "direction of flight" like a pitot tube.

An inefficient design might be an inlet flush with the fairing and aligned with the "direction of flight".  It's less efficient because the air never stagnates in front of the inlet when the through velocity is zero.  That's because the fairing has "deflected" it to some angle less than 90 degrees before it passes the inlet.  The velocity of the potential inlet air is no longer in-line with the "direction of flight".

The NACA technical server could be of interest.  http://naca.larc.nasa.gov/  NACA technical notes are notes and reports on actual testing of all kinds of things aircraft-related.

Pipe flow is a very complicated subject, even for something as simple as a round tube.  Changing area compound curve ducts are impossible to calculate without software.  Even then, I hear it's hit-and-miss.  However, all you need to develop a duct empirically is a calibrated air source and 20 ft of plastic tubing.  (Water manometer.)

[GeeP]

i was also looking for the info on air box resonance design / theory....
quick ugly.....  http://www.chrysler300club.com/uniq/allaboutrams/ramtheory.htm

there is more to it than duct taping on some drier hose.

Most certainly!

I can recommend:  http://www.bentleypublishers.com/product.htm?code=g309

[falcon0321]

and another great racing furmula.... 1 HP = 7 lbs

I completely agree.  I heard it was around 10lbs though.  I like your number better.    

I have already made the bike as light as I can and I am pretty thin myself ( there is always room for improvements).  As it currently sits, I have the bike fully faired and I am even debating if the extra weight is worth the better aerodynamics.   I could feel that it hurt my braking so I added a 2nd rotor to fix that.  

We predominately race at BIR where the front straight, turn 1, and turn 2 can be taken at full throttle.  It is about 1.5 miles and aerodynamics do play a facter.   This, all out part of the track, is mainly why I am debating RA.   1.5 mi at 120+ mph is definately worth looking into RA.

[Blueknyt]

guess you could set it up anyway, if nothing else, it will add cool air in the low to mid range and alittle bump up top where the GS peters out.  why not give it a shot anyway

[makenzie71]

The 636 sees a 9rwhp max gain with ram air.

The biggest problem with ram-air on a carbed bike is keeping the pressures equal throughout the carb.  High pressure in the vortex + and low pressure in the bowls = no fuel.

[Blueknyt]

one would need to put a vent tube with a check valve into the tank so the takn can be presureized, OR use an electric fuel pump with a regulator to maintain a constant pressure.

[makenzie71]

one would need to put a vent tube with a check valve into the tank so the takn can be presureized, OR use an electric fuel pump with a regulator to maintain a constant pressure.

That wouldn't work, and you'd need more.

Ideally, you would need to pressurize the float bowls...they'd actually be best fed off their own seperate ram-air tube.  You don't want a pressurized fuel system.  What you want is equalibrium between the vortex and the bowls.

On top of that you would need stronger floats.

Kawasaki had the BEST ram-air systems on any carbureted bike.  You should look into that.

[V8Pinto]

Sure is nice to see someone present a fact-based conclusion vs. emotion based he/she/my uncle said.

[JamesG]

The simple way is to enclose the carbs within the pressurized air box.

You usually don't have to worry about the pressure differental from the tank. Gravity overcomes it.

[GeeP]

To make things simple, yes, the fuel system probably needs to be pressurized.

The carburetor on the GS as built is not designed to work with an induction pressure higher than the surrounding air.  The best solution is to pressurize the float bowls and fuel tank.  Alternatively, a carburetor change could work too.

It's not possible to just pressurize the carburetor float chamber.  That may solve the metering problem but it won't solve the fuel supply to the carburetor.  With 1" of gas in the tank the GS has about 6" of head.  If we assume the density of fuel is 6.14 lbs per gallon, a 6" head of gasoline will be about .16PSI.  This is a rough estimate of the head a GS will have with 1" of fuel in the tank.  

So, at a pressure of .17PSI in the float bowl fuel is going to flow back into the tank.  Not good.  This is why the tank needs to be in equilibrium with the float bowls and the induction pressure.

[Blueknyt]

figure it wouldnt be much differnt then the turbo bikes, the carbs are sealed in a way that the bowls see the same atmosphere the Plenum box see's and the fuel is pumped via electric pump, regulator and return line.


if the tank and floatbowls are pressurezed to the same psi even if its low, then the gravity flow fuel system will still work like normal. IF your just pressurizing the bowls and not the tank, then the fuel flow will slow down as airpressure is trying to make its way from the bowls past the float needles and up the line into the tank.    Putting a pump inplace with a regulator would be more then enough to over come the built up in pressure.

[falcon0321]

These are all really good ideas.  Thanks for the help.  

One thing that has not been discussed is the slides.  They also operate on the vaccum that is created.  With the forced air creating a "lower" vacume force,  do you think it would be sufficient changing the air/fuel mix or should that be looked futher into as well.

From the sounds of it. It might be easiest to get some carbs that are from a ram air bike and set up tubing just like the factory's...or look into FI...