The piston drops, this causes the pressure to drop in the cylinder, outside atmospheric pressure is 14.7 I believe, this causes air to rush into the cylinder. I was always told and an engine was a vacuum. Are you talking about air going from the manifold to the cylinder or from the outside into the manifold. I'm not trying to argue with what you've stated I'm just interested in knowing what it actually is.

I'm just wondering....the way I look at it is the pressure drop in the cylinder pretty much creates a vacuum. This creates vacuum in the intake manifold. The intake manifold wants to "suck" air in....what creates the distinction between "sucking" and "pushing". Technically you could argue that the engine is sucking AND that outside air is pushing, cause and effect, you can't have the 1 without the other. I would think that since the engine itself is causing the pressure drop, that the engine is sucking. It just seems odd that if there is no vacuum present in an ICE then why do all carbs work off of vacuum, and why does every MAP EFI system use intake manifold vacuum? There must be vacuum going on SOMEWHERE in the engine if the term is applied everywhere....or is it misused...technically should it be a "pressure differtial" gauge instead of a vacuum gauge....is it the same thign?

 

My physics teacher always said, there is no such thing as sucking, its all pressure differntial.

But I know where Stealth's head is cause I am thinking the same thing....I guess everone just throws terminology around and it messes us up.
This is what I am thinking:
The piston drops and causes a pressure drop...agreed? This causes a pressure differential and air likes to be at an equilibrium, so air will rush into the clyinder to fill this 'void'. Is that not what a vacuum is?

All this damn terminology is messing me up...I am gonna go pull out my engine theroy books and do some reading.... get back to this tomorrow.

Hunter

 

If what you stated were true, a NA engine at WOT could/or would not function. I alluded to this ? in an earlier post. What is the vacuum reading in the intake manifold, on a NA engine, at WOT, with an efficient induction system?

It's not like with a cowl hood the engine must SUCK air in, and with ram air more air can go in because it's being pushed in as opposed to sucked in.

Are you stating the cowl area of vehicles, for which properly matched/designed cowl induction/cowl hood was intended, is not a high pressure area? It's about understanding the areodynamics of the vehicle a person is referring to, that determines where in the airstream a person chooses to position the intake opening, that makes for an effective high/higher pressure air entrance. To blanket a specific area, on the body of ANY vehicle, as being ineffective (or effective), would not be correct. Also, I'm confident those reading this thead understand, the pressure obtained is relative, IOW, it would not be comparible to a FI system. However, as previously stated by another, the correct position of the opening is but a part of the 'equation'. The pressured air entering the ducting, if it must be filtered, will be severely compromised. But again, presure obtained is but relative, and not high pressure per sa. Expect a difference between 'cold air', and the (so called) 'ram air', if properly located. How much? My main intent however, is to focus on the ? above.

 

ouch, a thread about a myth has become all confusing by an even bigger myth! Vacuum. Although in laymans terms the vacuum does 'suck air in', your just describing the effect, not the actual cause.

The word vacuum describes the low pressure side of any pressure differential. It can also mean the total evacuation of air. It doesn't have a strict scientific definition and therefore it gets used in confusing manner.

Vacuum cannot and does not suck. The high pressure side pushes the air in. The only reason air goes into a motor is because the cylinder going down creates an area of lower pressure. The air in our atomosphere is being pulled down by gravity. For every square inch of earths surface area there is a mass of air in the imaginary column above it that results in approxiamately 14.7 lbs of downforce. This external pressure pushes the air into the motor/cylinder.

If this is still confusing, just avoid the word vacuum altogether. It doesn't describe anything that can't be explained in terms of pressure.

Although i don't agree with the way they present space as a vacuum (it's just an empty area), here is a link that may also be relevent.
http://science.howstuffworks.com/question200.htm

maybe all this is being picky, but this is the advanced tech forum

-Brent

 

THANK GOD!!!!!!
Brent that is exactly what I was trying to explain......all these damn terms are screwing us over!!!!

So lets through out the vacuum term....so yes pressure from the atmosphere is pushed into the engine because of a pressure differntial caused by teh faling piston. There its done.

In relation to ram air....I dunno where it all fits in, but I think we have come to the conclusion that ram air will give some power gains, but people still dont agree on WHY we get a performance gain.

Hunter

 

First off, this thread is great! Lot's of good info here. I don't browse the advanced tech section much because some of the info here is a little overwhelming. Anyway, I would like to present something that jumped out at me after reading Jettison's statements-

I'm sure that you are getting a good gain out of the free ram air mod. When you say FTRA I'm assuming you are talking about the mod that a lot of the LS1 guys do which involves cutting the tray that the induction lid sits on, allowing it to draw air directly from the cavity where the radiator sits behind, or doing something similar to this. However, I don't think the ram air effect is what you are feeling. IMO the stock LS1 induction is pretty restrictive, there is not much area for it to actually "draw" air in as it comes stock. If I remember correctly there is a "slit" about 1/3" tall and maybe 10-12" wide that is where the air has to enter, even if the car is equipped with factory ram air. Well, if you cut a huge hole right under the filter, you are able to draw more air in.

Just a thought.

John

 

Well FTRA shows much better gains than FRA (free ram air). FTRA (Fast Toys Ram Air) is a high quality kit made from stainless steel and is a true ram air induction system. The only incoming air comes from directly above the plastic air deflector beneath the car (the deflector that sometimes hits steep driveways). The forced air goes through a duct that goes into the SEALED airbox. This system consistently shows 2 mph and .1 in the quarter.

FRA on the other hand is not sealed and shows little or no gains even though the airbox is less restrictive.

BTW both FRA and FTRA work best with a lid.