Why use an air scoop?

[Flatlander]

Why use an air scoop and why do I see them installed in the opposite direction of the air flow?

[boyat68]

Just a guess, but I suspect that the air scoop controls the speed of the air entering the fuel/air feed system. Being mounted backwards renders the ram air effect moot as opposed to supercharging, where you want the cooling effect of ram air to lower the temperature of the air charge before it is compressed.
Just a WAG

[Flatlander]

Been doing some reading since post.

Cart in front of the horse is how I do things.
From what I have been finding is that in the auto world people have been installing ram air on there vehicles and finding 10-15 hp on average increase.

This is because of the temp. decrease of the air entering the carburator, not the air force. This is why, some speculate, Pontiac first called it "Ram Air", and then when oldsmobile wanted to introduce this concept, they called it "Cold Air Induction".

Some people think that cooling the gas temp. also increases hp's, I have found no conclusive info. on that.

Why the backwards scoop? The only thing I can think is that they have found that the scoop does nothing for them, except when she back fires it is in harms way. For example in a boat. What I think might be happening in the backwards scoop though is a vacuum. Not good, on a naturally asperated carburator.

If she goes fast I am trying to make her go faster!

[randy]

In the 60's and early 70's the 'backward' scoop was used because the area where the hood meets the windshield is a high air pressure zone, at least at speed. Your guess is as good as mine if it worked. I had one on my '70 Chevelle SS. That thing would practically do wheelies in factory trim -- who cared about a fancy scoop, but it did look cool.

Crazy fast car, when you floored it, you could hear the FOOMP of the secondary carb barrels pop open. Then it was HOLD ON!

[Guy_b_g]

On boats the backwards scoop creates vacuum to clear the bilge of explosive fumes (it's not attached to the intake system), usually there is also a forward facing scoop to enhance the air exchange.

A rearward facing scoop at the base of a windshield is indeed in a high pressure zone.

A Forward facing scoop can create a ram effect of they are placed properly, useless or even decrease performance if not.

Some bikes (mostly Suzuki 2 strokes) had scoops on their heads to enhance cooling air flow.

NACA ducts can also create a high pressure zone to give increased air flow.

Cooler air is denser, creating a denser more powerful charge of air/fuel mixture at ignition and more HP.

Denser air is why engines make more HP and drag strip elapsed times are lower at sea level than higher elevations.

[81xsproject]

I have heard that there were dyno's to back up Chevy's claim on the "Cowl Induction" hood-intake. Something like 15 ponies.

[Flatlander]

Just don't get it.

"In the 60's and early 70's the 'backward' scoop was used because the area where the hood meets the windshield is a high air pressure zone, at least at speed. Your guess is as good as mine if it worked. I had one on my '70 Chevelle SS. That thing would practically do wheelies in factory trim -- who cared about a fancy scoop, but it did look cool."

Randy what a cool car you had or still have!?!

I pulled some old magazines out that might show this in use and what I am finding is that I see them on both ways, on high perfomance race boats where the scoop is in the full air stream. No engine cowl. These are all naturally asperated, not blown, also. Some are just filters on top. The one's that are backwards may be to keep the water out from other boats.?.

I have found people increasing hp's as much as 20 hp, with ram air on cars. I have found that this is because the intake was pulling air from outside of the engine compartment which is cooler.

$100 One air scoop
10-20 hp increase
Talk about bang for your buck. I have bought alot of snake oil in my life. This all seems pretty logical, but I can not find data supporting it.

On the XS's, imagine a air intake that will improve fuel economy and hp's. I am intrested anybody else? Is there a fabricator? I am trying to do the investigation. If anything I know these bikes are air cooled and the air going into these are on the back side of the motor and exhaust.

[Crazcnuk]

I have a Cowl Induction (the actual name of a scoop that gets air pressure form the base of the windshield) on my Monte Carlo.

It works, but is only really effective at speeds above 70mph.

It does dual duty, first it helps increase intake pressure (poor man's turbo) and it lets the engine breath cold air, rather than the hot stuff off the engine rad and headers. It is very picky about the shape of the car to work. Oh, and it screws up rainX!

The reason the colder air makes more hp is because it is denser and as a result has more oxygen in it. Again, though the results can be varied, and on most cars minimal.

If you live in LA of course this doesn't work, as there is no air!

The Trans-Am, and later Camaro type 'shaker' scoops really did very little, except look neat. On my Z28 the scoop had a little door on the back that was electrically operated from a switch on the gas pedal. It opened up when you stepped the gas to the floor, to let you hear the 4 bbls open!

I would always prop that door open on long road trips to at least get the cool air effect, for fuel economy, not power.

The most effective Pontiac hood scoops were the RAM Air ones on the early Firebirds that were at the front of the hood, facing forward. They actually stuck oout slightly ahead of the grill so as to catch air before it was redirected by the grill and hood


Mopar had one called 'Mopar Pro bolt-on. It faced forward, in the middle of the hood, but it was raised up high enough to catch the air that was deflected upward by the grille. As far as I know it was never offered on a factory car. The other chrysler variations, that were flush with the hood did liittle except let cold air in.

[Flatlander]

Might be interesting to some.

I came across this,

www.electricsupercharger.com

They explain in their "F.A.Q." question #1 that this is only used in wot position.

My conclusion so far is that a air scoop does two things:

1- Allows cooler air from outside the engine area for more dense air which increase hp across the board at all throttle possitions.

2- Increases intake pressure at wot for maximun air flow.

And for the VET guys I found www.vararam.com some pretty intresting stuff directly related to this. They claimed up to 30 hp gain at 115 mph.

[Flatlander]

CRAZCNUK your Z just helps prove that the air scoop does what I have found at wot. Where did it get its air when you where at part throttle? Did it just leave the gate partially open? If it did that helps me and my conclusion.

[Crazcnuk]

No the gate was open or closed, no part open. It had two of the 'normal' type snorkels inside the engine compartment, which made no sense to me at all.

The scoop was all for show. It only opened when you pushed the gas pedal to the floor.

[Guy_b_g]

Flatlander.

If we were to get enough ram effect to make a difference, we would also have to route our carb vents to the sealed ram air duct in such a manner that the carb bowls are pressurized to the same degree that the intake is, otherwise you would run lean, possibly lean enough to burn a piston (at speed when the ram air is in effect).

These bikes would be really hard to put a duct on, newer bikes have the cylinders canted forward, and nearly straight intake tracts leading up to downdraft carbs or fuel injection. Most of them have hollow aluminum frames which make good ducts, leading to a sealed airbox under (or tucked into) the tank. They have water cooling so you don't have to worry about ducting obstructing airflow away from the cylinders.

We have little room above the cylinders to work with, and it would probably obstruct airflow to put ductwork there. Our airboxes are waaaay far back and not sealed, and you can't get effective ram air from the sides of the bike...even if the ductwork didn't take away your legroom.

I'm not saying it is impossible...just saying I sure wouldn't know where to start.

Also, there's no free lunch..any time you increase charge density and horsepower...you have to add more fuel...so you would actually decrease fuel mileage any time the ram air was giving increased horsepower.

[Flatlander]

Crazcnuk
Did the "normal snorkle" duct to an area where it was getting air where it would be cooler than behind the radiator or effected by the exhaust at idle or low speeds? All the cars that I have worked on from that erra, the ducting system had either been removed or damaged to the point to remove it and not replaced. Or had been removed for the idea that it hampered performance due to restricting air or something else.

Guy
I think I read at 100 mph = .1128 PPSIG. Does anybody know that forumla? Dosen't the float bowl vent, vent into the intake side of the carburator? I am not too sure.
Yes I know that this idea would take the help of engineers, inventors, annalists, faborcators, mold makers, schetchers, CAD designers, project managers, and back yard tree mechanics. Did I miss anybody? Not trying to hurt anybodys feeelings just trying my humor out. !

[Crazcnuk]

No, if you know the standard air cleaner on a 70's chevy, the round thing with a snorkel, that is what my Camaro one looked like except it had 2 snorkels. Only 1 hooked to the thermactor hose, for cold weather starting.

The Lid of the air cleaner was what was different, as it mated against the hood, under the scoop. Theonly time you got any air from the scoop was when you put the gas to the floor, and the electric switch (same as is used for kickdown on a TH-400 tranny) would pop the scoop open.

I would put a wood chip in there to hold the door open when travelling on the highway, to get some benefit from the cold air.

As for leaning out, none of this will affect your carb settings. All you are doing is preloading the intake charge slightly above the normal air pressure in your area. The carb will supply X amount of fuel with y amount of air, either way. Just think of it as a blow-thru turbo, rather than a draw-thru.

Normally aspirated engines are fed with atmospheric pressure of 14.696 psi (at sea level). Using different kinds of scoops you can get up to another 2psi or so, depending on how fast you go.

Turbochargers usually start around 6psi boost and go up from there, Superchargers can be anywhere from 6psi to 20psi or more depending on application.

[Guy_b_g]

I'm certainly no expert...but I do know that at least some of the more modern sportbikes with sealed airboxes and ram air have the float bowl vents routed to the intake ducting at the point of highest pressure for the ram air....

The ZX7 is a case in point..here is a page from a zx7 forum where a guy is having carb leaning out problems when he reinstalled the ram air after making mods.

Quote:

"No you dont need bigger jets. The problem is the carb bowl vents need to be pressurized with the same pressure as the intake side of the carb. Your bowl vent tube iether fell off or is plugged. Did you take off the air diverter valve? If you did you need to redirect the bowl vent to the aircleaner."

http://www.motorcycle.com/forum/showthread.php?t=6250

Doesn't take much to cause the carbs to lean out...