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Just Some Dude in Jersey
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Let's say you made an air scoop out of a 3" diameter pipe, bent into a 90 degree elbow, sticking out of your hood and onto your carb as a baseline. How fast would you have to go to ram double the atmospheric pressure(2 atmospheres) into your carburetor?

I've always wondered if all those scoops and vents some cars have, including racers, actually increase the amount of air going into an engine enough to meaningfully offset the increased air resistance. Or do they just look cool.

How much pressure does a "typical" turbo or supercharger create?
 

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Mid-West Opeler
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I've always wondered if all those scoops and vents some cars have, including racers, actually increase the amount of air going into an engine enough to meaningfully offset the increased air resistance. Or do they just look cool.
If it's on a real race car, then chances are it's very functional. Either to bring in cooling air or to vent out hot air. There are a lot of systems on a race car that need temperature control: the engine's coolant system, oil system, intercooler (if forced induction), power steering fluid, brake system, transmission, and differential.

If it's on a street car chances are it's for the bling...

How much pressure does a "typical" turbo or supercharger create?
Define 'typical'. Street car? OEM's can range from 4 psi (above atmostpheric) to 20+ psi.

For a race car? If the rules allow it, as much as possible. In the turbo F1 era (mid 1980's), they were pushing 55-60 psi of boost into 1500 cc engines. And making well over 1000 hp.

http://www.gurneyflap.com/bmwturbof1engine.html

But pressure is one thing, and volume is another. A small turbo making 15 psi of boost might might 150 hp, while a large turbo pushing 10 psi might make 500 hp.

Compare pressurizing a soda can @ 5 psi to pressurizing a 55 gallon drum @ 5 psi...same pressure, much more volume in the drum.
 
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Just Some Dude in Jersey
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Discussion Starter · #8 ·
there is some good info here on things you can do to help

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Hey!!! I've got one of those Magnahelic gauges that are talked about in the second part of the article. I can go wild looking for negative vacuum! He's an entertaining author. I used to do a little writing and critiquing of writing and the author practices his craft well.

The area just under the front screen is said to get around 1.5 bar at 60mph which is why most cars have the ventilation inlet there.
If that's true, then I'm 3/4 of the way to 2 atmospheres, right? 1 atmosphere = 14.7 psi = 1 bar. I guess atmosphere was an old fashioned word for me to use.

So, if I run my pipe out to just under the grill and drive 120mph I'll make my goal!
 

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Opeler
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In the turbo F1 era (mid 1980's), they were pushing 55-60 psi of boost into 1500 cc engines. And making well over 1000 hp.
And they were silly enough to bring them to Dallas one year, to run a race in August, in the Texas Heat. It didn't help that the track was lined on both sides by concrete barriers, which only held the heat in.

They set a record for blowing those little motors up that week, and I still have a fond memory of watching Alain Prost stomping back to the pits after he blew up like his eleventh engine the day of the race. Somebody got his helmet that day as a race souvenior when he flung it, and I don't know exactly what he was saying, but you didn't have to speak French to know he was cursing!

They never tried that silliness again.

back on topic, pressure in the intake is nice, but temp is just as important, because after all, lower temp equals higher density. But you knew that.
 

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Just Some Dude in Jersey
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Discussion Starter · #15 ·
Leaf blower turbo

even easier....graph.
Perfect! That answers my questions! It seems to say that at about 170mph undeflected air pressure at a scoop or ram inlet is at double the atmospheric pressure at sea level of 14.7 psi.

I'm led to believe, from what my friends tell me, that all blowers, turbos, and superchargers introduce air into the system post-carburator and after some gizmo in a fuel injected engine. Is this true?

I'm told that this requires that there be pressure relief valving and some way to alter the air/fuel mixture.

If some of that stuff is true and rammed air CAN achieve the psi increases close to that of a modest turbo(5 psi) at less that 100mph, why don't you see fans or blowers or whatever in cars' cold air intakes, filter chambers, or at the very front of people's air intake systems? In other words, can I attach my leaf blower to the inlet of my cold air intake and make my car go faster?
 

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Mid-West Opeler
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Perfect! That answers my questions! It seems to say that at about 170mph undeflected air pressure at a scoop or ram inlet is at double the atmospheric pressure at sea level of 14.7 psi.
From what I see on that chart, at 200 mph you would have about a .7 psi increase above atmospheric.
 

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I'm led to believe, from what my friends tell me, that all blowers, turbos, and superchargers introduce air into the system post-carburator and after some gizmo in a fuel injected engine. Is this true?
No, air filter box -> turbo -> intercooler -> air metering device -> inlet would be the correct sequence for a fuel injected engine, for a carburettor engine the turbo can be either before or after the carburettor but if it's after you can't use an intercooler

If some of that stuff is true and rammed air CAN achieve the psi increases close to that of a modest turbo(5 psi) at less that 100mph, why don't you see fans or blowers or whatever in cars' cold air intakes, filter chambers, or at the very front of people's air intake systems?
You're answering your own question :), if it was that simple you would see it on just about any car you can imagine. You never see them on regular cars and the few high performance cars that have scoops in some form have them to channel cold air to the intake and not for the ram effect

As for fans or blowers in the intake, for every revolution of your 2.0 engine it gulps up one liter of air, yes I know it's not accurate but let's just keep things simple, at 6000 rpm your engine needs 6000 liters of air pr minute and that's without any boost .... that's one heck of a fan :)

A fan capable of pumping in excess of 6000 liters pr minute would consume quite a bit of power, which is why we have turbos, they use "waste" energy.
 

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There are systems which use the forward motion of a vehicle to produce compressed air to generate power for the vehicle. It is called a "ram jet." These have been worked on for nearly 100 years. The problem is that the ram jet must achieve very high speeds before it can produce any thrust. They seem to work best between Mach 3 and Mach 5, a bit fast for terrestrial vehicles. Bill

Ramjet - Wikipedia, the free encyclopedia

Ramjet Propulsion
 
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