Forced Air/Ram Air induction

[IanDMacDonald]

I know absolutely nothing about this. What would happen if you designed air scoops or found a way to channel air to the airbox? Run leaner? Any performance increase?

[WMarshy]

Here is some reading materialfor you...

http://grassrootsmotorsports.com/for...k/48999/page1/

Basically, the theory is real but hp gains are small and you have to be doing triple digits for it to even have an effect. I recall reading an article in a sport bike magazine about the ram air systems and it was basically the same as what I said above; need to be breaking laws for it to actually provide any gains.

[IanDMacDonald]

Interesting. Thanks Wade.

[TADracer]

My two cents is that if I were to put the time and effort in setting up something to take advantage of the airflow, I would concentrate on providing a supply of cool, undisturbed air before trying to set up something sticking out into the airflow. Ramming air in does not really give you anything of a real gain because you cannot build up enough natural boost just from sticking a scoop into the air. But cool, straight air does have a true effect.

That's why velocity stacks seem to work because they straighten out the airflow. One reason the stock air box works so well from the factory. It is taking in cool air from under the seat and has velocity stacks to straighten out the airflow into the carb bell.

[D0wn5h1ft]

It is very difficult to provide streamlined, non-turbulent, airflow to create superatmospheric pressure at the intake. Also, as with the case with most forced induction carbureted engines, if you do see psi gains at the intake it can severely impact the performance of basic carb functions (especially on motorcycle carbs!). I'm pretty bad at explaining things so here's a nice excerpt I found that lays it out pretty nicely why trying to cram more air through a carb intake is a poor idea:

"Blow-Through Design: In a blow-through arrangement, the turbo forces pressurized air through the carburetor. This presents two problems. First, a carburetor does not understand pressure. Remember, a carburetor supplies fuel by creating a pressure drop across the venturi. The outcome is an inversely proportional disparity between the air and fuel mixture ratios. For example, if the carburetor sees a 2psi pressure drop across the venturi, only the corresponding level of fuel will be supplied, regardless of the turbo boost pressure. The practical result is the engine running very rich at no/low boost psi, and running very lean at maximum boost psi. The second problem you will encounter is that when you force pressurized air into the carburetor, it will cause the atomized fuel to flow in ways that it is not supposed to. The increased air pressure will try to crush the fuel float, as well as attempt to blow the air/fuel mixture out the throttle shaft, or back into the fuel line."

There is another technique to turbocharging a carbureted engine which is a "Draw-Through" design. Long story short, instead of trying to force feed your engine you can actually increase the natural vacuum on the front side of your carbs to drawn in greater amounts of fuel/air on each stroke. Downside? Special kind of turbo and it takes up a large amount of space (since it sits between your carbs and your carb boots. Upside? Easier to set up (ironically), [relatively] high boost/gains. Side note: the old Mr. Turbo Kit you see out there for our bikes is actually a draw-through set up!

If you take a look at the pictures of the front of my FZR you'll see "ram-scoops" at the front . I laughed when I first saw it because there's no way it does anything with that big dirty old airbox sitting on those carbs.

[CaptonZap]

It is very difficult to provide streamlined, non-turbulent, airflow to create superatmospheric pressure at the intake. Also, as with the case with most forced induction carbureted engines, if you do see psi gains at the intake it can severely impact the performance of basic carb functions (especially on motorcycle carbs!).
................
If you take a look at the pictures of the front of my FZR you'll see "ram-scoops" at the front . I laughed when I first saw it because there's no way it does anything with that big dirty old airbox sitting on those carbs.

Right you are, but a V-Max just wouldn't look right without the scoops.

CZ

[SFerinTEXAS]

Just a notion I have (with no detailed knowledge) would suggest CV carbs would not do well with a false atmospheric pressure. Ram air would make them think they were way below Death Valley. I dunno.

[CaptonZap]

Actually, CV carbs are less sensitive to throat pressure.
Bing carbs, a CV design as used on older BMW's, were found to perform well on experimental aircraft, without manual control of mixture, keeping the fuel air (F/A) ratio fairly even, at different altitudes. (Read different air pressures). In fact, Rotax supplied Bings on their aircraft engines.
The reason is that the air flow through the throat is what controls the slide, thus the F/A ratio, not the incoming pressure. The denser air creates a higher suction, and the slide/needle provides a richer mixture.
However, there is still the problems of shaft leakage, and fuel chamber pressure diffrentials.
As an aside, a lot of the today's cheap Chinese come with CV carbs.
CZ