Why use an air scoop?

[Guy_b_g]

this is from Sport rider regarding the ZX9:

THE ZX-9R SYSTEM

Kawasaki's ZX-9R uses a relatively straightforward system compared to the 1995 Honda CBR600F3. Twin vents mounted beneath the headlight channel air via ducts running over the frame beams and into a sealed airbox. Look closely, and you can see two smaller nozzles behind the grilles which connect to the carburetor float bowls. Their function is to equalize the pressure between float bowls and airbox; without them the higher pressure of the incoming charge would upset the carburetion, potentially blowing fuel out of the bowls and tending to push fuel back down the jets, causing mixture leanness. Kawasaki uses much the same system in all its ram-air machines, though the ZX-7 and earlier ZX-11s have a single inlet only.

http://www.sportrider.com/tech/146_9508_ram/index.html

Our bikes may never see high enough speeds to create a problem...but I would still do the venting if I put on ram air.

[Pat Kelly]

Maybe the scoop is backwards on a boat so less water gets sucked in?

[Guy_b_g]

depends what the scoop is for..

I think some boats have air scoops for the same reasons cars do, some for a performance increase, some for cold air, some for looks.

But on the inboard/outboard I used to have there was another reason, 2 scoops on opposite sides of the engine compartment, one facing forward, one back...and it was to create airflow through the compartment so explosive fumes from fuel wouldn't build up in there..they aren't open compartments like in a car...so that could be a real problem without airflow.

A backwards air scoop to the engine itself...I can't answer that one from a perfomance perspective...but it would be less likely to ingest water...mine had no scoop but did have a flash arresting air filter assembly, so carb backfires couldn't creat an explosion.

[Crazcnuk]

Sometimes you'll see diesel piclups with as many as 3 scoops, facing various directions.

One is for cold intake air one is for the intercooler inlet also for cold air, and some have a scoop (or two) to vent out excess underhood heat caused by twin turbochargers..

Often the outlet vents are on the quarter panels in front of the doors, but they can be on the hood as well.

On some cars built for (or built to look like..) very high speeds have vents or louvres in the hood to let air pressure out from underneath the hood becuase at speeds above 150mph, you are getting a LOT of air throught the grille that has to go somewhere, and you do not want it forced under the car as that would adversely affect the handling. These can also be in the quarter panels, or fenders.

Some also have scoops, usually in the bumper or grille that have hoses to direct air onto the front brakes, but a few exotics have these on top of the fenders.

[Flatlander]

I do not know where I am going with this but......

Does anybody allready have the info or willing to attempt getting info on:

1- air temp at the point of intake vs. ambient.
2- static pressure at the point of intake.

Intake temps.
For every 11 deg.F change= 1%hp change
For every 1 deg.F change= 1.5 deg.F E.G.T. change

Static pressure.
170 mph = .5psi = 3.2% air pressure increase
100 mph = .17psi = 1.2% air pressure increase (square factor)
I know these are not typical riding speeds or even obtainable.

But because the XS's intake is behind the motor, in the direction of air flow, it is possible that the turbulant and heated air may be....well robbing power, in all riding conditions. Or add a wind sheild, some leg sheilds, saddle bags and who knows?
Just a thought I had.

[Pat Kelly]

Then the motor (on all bikes) should be turned around.
The carbs should be in front with the air being ramed into the intake, through the combustion chamber, and out the back.
As the curent design is (and has been for 100 years), the air flows in an "S". It flows past half the bike to be sucked into the airbox, back forward through the carbs/throttle bodys, in the intake and out the exhaust (at the front of the bike, curved down and back to the rear of the bike out the exhaust.
Turn the head around and make everything more "free-flowing".
Actually this is something I've pondered since I first discovered the mechanics of motorcycles.

[TomB]

Interesting reading folks, I like your ideas Flatlander.

The carb float bowl vents are already piped to the air box so if you were to ram air pressurise the box would the carbs automatically be vented at the higher pressure??

Since mono-shocking my project I've got to make a new airbox and have been wondering in which direction to point my airbox intake, now I know.

I'm moving all the electrics to under a racing seat hump so all the space under the tank is clear, a couple of 1-1/2" hoses running either side of the steering head under the tank down to the air box could do it.

[AlanB]

Hi Guys,

Back in the day, a rare (but allegedly effective!) tuning mod on triumph twins was indeed to reverse the head!

On the early (8-stud) engines, the stud pattern is symmetrical, so the head turns easily. The cams are a little more complex..........

Once that work is done, the reasons for the "usual" arrangement becomes clear; the carb intakes fill with cr@p, and the exhausts end up two feet behind the taillight............ OK on a drag bike, but no use on the street!

AlanB

[TomB]

The cams are a little more complex..........

Nah, just swap the exhaust for the inlet cam, timings the same

[AlanB]

Hi Tom,

That IS a little more complex than turning the head round!

Most riders had trouble sorting out the dots on the wheels to get the cams timed properly as standard..........

AlanB

[Guy_b_g]

lol..I wonder how many times British neophytes accidently put their heads on backwards...."bloody hell...this can't be right...?!!"

I must be tired...now I'm imagining how hard it'd be t'steer looking over my shoulder...

[TomB]

That IS a little more complex than turning the head round!

It really is as simple as just swapping them Alan

Its been a long while since working on Triumph engines but I think the Unit engine cams are the same part number for inlet and exhaust.

Hey Guy, I'm a bit long in the tooth to be a neophyte any more but still learning new stuff every day

[Crazcnuk]

Theoretically, you are right, the carbs SHOULD be on the front, howeever, there have been a couple of problems.

#1 Dirt, or snow, etc. They had to keep the carbs protected from rain, sleet, mud, snow etc. If you put the carbs on the front of the engine, they are right behind the front wheel.

#2 Cold. The carbs are put where they are partly to get some heat while the bike warms up.

Mfgs have never really been interested in getting every last ounce of power or mileage out of thier bikes, rather they are more interested in making them last past the warranty period, and ease of use/maintenance.

Otherwise hotrodding would never have evolved.

[TomB]

Hmmm warranty! never thought of that.

Dya think my '78 is out of warranty yet?


Joking aside, the thing with the carbs icing is a good point, I ride to work on my '72 CB500/4 and a few weeks ago had the carbs ice up bad, thing wouldn't tickover, lowest revving was 3500rpm....the last thing I wanted riding on icy roads

[Flatlander]

Never thought of turning the motor around.

What an idea, really never thought of that. We'll just add......
I will have to think about that for awhile. In the mean time
thinking two air scoops to the side of the jugs. What do you think?

P.S. Done thinking, my wife won't let me do that.