The Oldsmobile Connection

[91parkave]

andrewk wrote: 91parkave wrote: really? so youre saying under load vacum decreases? so then what do you call the increase of air flowing into the engine? i always thought that was vacum :roll:

You might find this article helpful-

http://bankspower.com/Tech_SecrettoMakingPower.cfm

The entire article is good, but these paragraphs specifically-

bankspower wrote: Suppose you have a 300-cubic-inch gasoline four-cycle engine. Most of you know how an engine works, but as a simple review, a four-cycle engine has an intake stroke to draw the air/fuel mixture into the cylinder as the piston moves down the cylinder bore, followed by a compression stroke during the following upward movement of the piston. These first two strokes occur during one revolution of the crankshaft (see Fig.1). On the next revolution of the crankshaft, the power stroke occurs as the air/fuel mixture burns pushing the piston down. The following upward movement of the piston is the exhaust stroke. Two revolutions of the crankshaft, four distinct cycles – it’s the basic Otto-cycle piston engine.

By its very design, this means our 300-cubic-inch engine takes in 300 cubic inches of air every two revolutions of the crankshaft. Now here’s the interesting part. It does this whether the throttle is open or closed. But wait, you say. The engine takes in more air when the throttle is open. And while it is true that more air mass flows into the engine when the throttle opens, the engine’s size, or displacement, never changes, so the only actual difference is the density of the air that fills that displacement.

When the throttle is closed, very little air mass flows into the engine, so that small amount has to expand to fill our 300 cubic inches. Thus, the air will be of very low density. As the throttle opens, more air mass can flow in to fill the engine, and the density will increase. This is often called the “charge density”.


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Thats good but remember the whole article you quoted is for forced induction. Theres not really any vacum in a FORCED INDUCTION engine becasue its under pressure. Now weve been talking about this guys N/A engine. naturally aspirated engines make nothing but vacum as load increases
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[andrewk]

91parkave wrote: andrewk wrote: 91parkave wrote: really? so youre saying under load vacum decreases? so then what do you call the increase of air flowing into the engine? i always thought that was vacum :roll:

You might find this article helpful-

http://bankspower.com/Tech_SecrettoMakingPower.cfm

The entire article is good, but these paragraphs specifically-

bankspower wrote: Suppose you have a 300-cubic-inch gasoline four-cycle engine. Most of you know how an engine works, but as a simple review, a four-cycle engine has an intake stroke to draw the air/fuel mixture into the cylinder as the piston moves down the cylinder bore, followed by a compression stroke during the following upward movement of the piston. These first two strokes occur during one revolution of the crankshaft (see Fig.1). On the next revolution of the crankshaft, the power stroke occurs as the air/fuel mixture burns pushing the piston down. The following upward movement of the piston is the exhaust stroke. Two revolutions of the crankshaft, four distinct cycles – it’s the basic Otto-cycle piston engine.

By its very design, this means our 300-cubic-inch engine takes in 300 cubic inches of air every two revolutions of the crankshaft. Now here’s the interesting part. It does this whether the throttle is open or closed. But wait, you say. The engine takes in more air when the throttle is open. And while it is true that more air mass flows into the engine when the throttle opens, the engine’s size, or displacement, never changes, so the only actual difference is the density of the air that fills that displacement.

When the throttle is closed, very little air mass flows into the engine, so that small amount has to expand to fill our 300 cubic inches. Thus, the air will be of very low density. As the throttle opens, more air mass can flow in to fill the engine, and the density will increase. This is often called the “charge density”.


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Thats good but remember the whole article you quoted is for forced induction. Theres not really any vacum in a FORCED INDUCTION engine becasue its under pressure. Now weve been talking about this guys N/A engine. naturally aspirated engines make nothing but vacum as load increases
---------------------------------------------

The first part, that I pasted here is a theory review, and the principles discussed are first being dicussed as a NA engine, then the concept is applied to forced induction. No matter the engine, the theories of operation are the same.

If there were no vac in a forced induction engine, you would have a few problems, including the engine pushing oil out of itself.

[91parkave]

under boost there no vacum present andrew. At idle and off the gas pedal is when vacum is present in forced induction engines. N/a like i already said is all vacum air is being pulled in which is the definition of vacum so please quote another source or something cause you not making any logical sense to me.

[andrewk]

91parkave wrote: under boost there no vacum present andrew.
At idle and off the gas pedal is when vacum is present in forced induction engines.

The same is true in NA engines too, Marshall. Under load, or at WOT, the throttle blades are open and vacuum decreases. Difference is, forced induction forces the air in, instead of the pressure differential that the engine creates in NA applications.

Quote: N/a like i already said is all vacum air is being pulled in which is the definition of vacum

Definition of a vacuum is a pressure lower than atmospheric, in physics. (In astronomy, it would be absence of all matter)

At WOT, it is the pressure differential, not an increase in manifold vacuum that draws air/fuel into an engine. A larger cam does not create more vacuum. Bigger cam, larger intake runners, head work, etc, remove the restrictions in the intake system so that a more dense intake charge can be obtained by the displacement of the pistons, as talked about in the Banks article, and DECREASE manifold vacuum.

Even if these things did create more vacuum, it would not be before the throttle plate, as you said, but it would be after. Thats why I say, and will say it again: You couldn't be more wrong.

Forced induction is not some magical step away from traditional means where the rules of physics and dynamics do not apply. The same processes are used, and the same theories hold true, regardless. For some reason you seem to think that this is not the case, that because an engine has a blower or a turbo on it, that its a whole different ball game. It's not.

Quote: so please quote another source or something

I don't understand how you can not see the N/A examples in this article. Have you been reading any of this, or just scanning?

But, here is one from "Super Chevy magazine"- The article is discussing valve train and street-able power, and they briefly mention the effect of cam size and its relation to engine vacuum.

SCM wrote: An engine with an efficient intake tract will not need as much overlap to work well, while a restricted intake tract is stingy with its air, and an engine equipped that way would suffer from a cam with too much overlap. When you boil the valvetrain events down to their most basic levels, it's the closing of the intake valve that has a huge effect on power. If you close it too late you'll lose power because as the piston moves up the bore it'll force the incoming fresh intake charge right back out due to an effect known as reversion. If you close it too soon you'll choke off the engine from all that fresh air that is rushing into it. In a perfect engine we would close the intake valve precisely at the same time the air/fuel column stops moving in. Determining that point is difficult and the entire intake tract-from the air cleaner to the cylinder head and even the exhaust system-all have an effect on when the air stops moving in. Engine vacuum is also directly related to overlap, and our street engines need vacuum. Typically, with street and mild performance cams, the lobe separation will directly affect overlap. A wider separation figure (i.e. 114-116) means less overlap, while a narrower separation provides just the opposite. But giant race cams can have a wide lobe separation angle like 114 and still have a lot of overlap because the intake valve begins to open very early--sometimes way before the exhaust valve has closed on the exhaust stroke. That's what makes a hard-core race motor sound the way it does. You're hearing the intake and exhaust tracts working together to give it that raspy, wicked tone, especially at idle. See our story on cam lobe separations in this issue ("Separation of Power," pg. 56) to find out a bit more on how overlap can affect power.

Article in full length can be found here

Wikipedia also has an article on the subject-

http://en.wikipedia.org/wiki/Manifold_vacuum

Specifically:
Wiki wrote: Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere.

Manifold vacuum is an effect of choked flow through a throttle in the intake manifold of an engine. It is a measure of the amount of restriction of airflow through the engine, and hence of the unused power capacity in the engine. In some engines, the manifold vacuum is also used as an auxiliary power source to drive engine accessories. Manifold vacuum should not be confused with venturi vacuum, which is an effect that is exploited in carburetors to achieve a fixed mix ratio between fuel and air.

The rate of airflow through an internal combustion engine determines the amount of power the engine generates, and most engines are controlled by limiting that flow with a throttle that restricts intake airflow.

Quote: cause you not making any logical sense to me.

I have yet to see where you demonstrate that you even understand logic, much less make sense.

[andrewk]

Still confused? I can elaborate if needed-

Andrew

[91parkave]

Andrew i appreicate the reasearch you did but when you compress everything you quoted it comes out just like i said before. when air is "pulled" into another orfice, its called vacum, if you increse the amount of that can be pulled into that orfice then you create a deeper louder "intake" sound. its that simple :twisted:

[andrewk]

91parkave wrote: Andrew i appreicate the reasearch you did but when you compress everything you quoted it comes out just like i said before. when air is "pulled" into another orfice, its called vacum, if you increse the amount of that can be pulled into that orfice then you create a deeper louder "intake" sound. its that simple :twisted:

Sorry, Charlie.

Quote: Manifold vacuum is an effect of choked flow through a throttle in the intake manifold of an engine. It is a measure of the amount of restriction of airflow through the engine, and hence of the unused power capacity in the engine.

If vacuum is the effect of the "choking", and it is, how can removing the restriction create more of it? It is not vacuum, at least in the mechanical sense of the word. What happens is that enlarging any part of the intake is allowing the engine to breathe better, and easily suck in a bigger and denser charge, but it is not an increase in vacuum that does this, as I have mentioned earlier.

"Like you said before" was this-

Quote: that [increasing vacuum] would happen if you got a biger throttle body, ported your upper intake and/or cylinder heads, cams etc.....

I don't follow how you think I am proving your point.

[91parkave]

we wont agree on this then. you got anything else to say

[andrewk]

91parkave wrote: we wont agree on this then. you got anything else to say

Yeah, you still couldn't be more wrong.:laughing: :laughing:

[88delta88]

:eat: ....




:beer:


Ahhh... Thats better.



Anybody got any recommendations for my first prototype air box?

[88 Coupe]

Andrew: As always, your input is appreciated by all.

88delta88 wrote: ........ How do you think a tuba can take a person's lips buzzing rapidly, and produce such a loud, deep sound? Or an antique record player... etc ........
Not with a "tuned box".

The "airbox" design was used to muffle intake sound, with as little loss in airflow as possible. It does it very well.

Replacing it with a "ricer pipe" eliminates the the "sound deadening" effects, and will produce the sound you are looking for. The "cone filter" muffles that sound, and is the reason you have what you have, now.

If you replace it with an exponential horn, you should hear a significant difference.

The Tuba is an example of an exponential horn.

Norm

[andrewk]

Felt the need to clarify one point-

Quote: when air is "pulled" into another orfice, its called vacum

You are right. Vacuum is used to pull air into the engine. But when you add a bigger cam, or port the heads, or any of your above mentioned things, you do not increase vacuum that the engine creates, you merely make it easier for it to use the existing vacuum to suck in the air.

[91parkave]

i will agree with you on that

EDIT: forgot the rest of my reply,
MY wording must have been off this is back to what we first talked about though. So if the engine is able to draw more air "in" i would say thats increasing vacum then. say if your heads flow 229CFM stock you get bigger valves and such port job etc... and now you flow 406CFM at the same RPM as before. Are you telling me theres going to be no increase in vacum just more air "being pulled" into the engine?

[andrewk]

91parkave wrote:
MY wording must have been off this is back to what we first talked about though. So if the engine is able to draw more air "in" i would say thats increasing vacum then.

Nope.

Quote: say if your heads flow 229CFM stock you get bigger valves and such port job etc... and now you flow 406CFM at the same RPM as before.

That's an increase in flow (Velocity/Volume). No more vacuum is created by the engine.

[quoteAre you telling me theres going to be no increase in vacum just more air "being pulled" into the engine?[/quote]

Yes.

[91parkave]

andrewk wrote: 91parkave wrote:
MY wording must have been off this is back to what we first talked about though. So if the engine is able to draw more air "in" i would say thats increasing vacum then.

Nope.

Quote: say if your heads flow 229CFM stock you get bigger valves and such port job etc... and now you flow 406CFM at the same RPM as before.

That's an increase in flow (Velocity/Volume). No more vacuum is created by the engine.

[quoteAre you telling me theres going to be no increase in vacum just more air "being pulled" into the engine?

Yes.[/quote]


so vacum dosent increase as more air is entering the engine? how do you come to this conclusion even though you said you agree when i said air being "pulled" into another orfice is reffered to as vacum.sothe ability to "pull" in more air would still be desribed as vacum as well. so please clarify to me what youre saying.