Advanced Engineering Tech - What accelerates an engine?




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Quickin
01-25-2006, 10:29 PM
I mean, when you push the gas pedal further down the TB plate is the first thing to sense that something has changed, right? What is the next piece/part of the whole system to do something?

Is it the MAF telling the fuel system to spray more because the plate has just moved open more, or does the MAF itself tell the PCM to spray more fuel because it senses increased airflow?

And how does the engine know to speed up at the second you hit the pedal, why doesn't it just bog down from the additional fuel being sprayed into the cylinders, because it hasen't started spinning faster yet.

Maybe a newb question, but I've always wondered this.

.


P Mack
01-25-2006, 10:51 PM
The maf does sense the extra airflow. But also, the manifold pressure sensor senses the increased pressure almost instantaneously and through speed density calculations figures out the increased airflow. The maf and speed density calcs are combined through a calculation to get an airmass value for each cylinder. The pcm figures out injector pulsewidth based on that airmass value. Keep in mind the maf has a little inherent lag because it's based on heat transfer, but the map can respond pretty quickly since the only lag has to do with the speed of sound for the pressure wave moving from the tb to the sensor on the back of the intake.

2002_Z28_Six_Speed
01-25-2006, 11:38 PM
I think P Mack pretty much handled that one!


racer7088
01-25-2006, 11:52 PM
Exactly, as soon as you increase manifold pressure you also instantly increase cylinder pressure and of course torque so you feel in in the back right away and theh car moves out!

Old SStroker
01-26-2006, 08:09 AM
A low-tech explantion:

Think of it as a "demand system". The dumb pistons are moving up and down trying to pump air, but the throttle plate(s) are closed restricting the amount of air those hungry cylinders are demanding. As you let in a little air, and then the smart systems allow the appropriate amount of fuel in, the cylinders are happy to burn it and do some work. If the load on the engine doesn't hold it back (dyno step test), it accelerates and takes anything attached along with it.

Whether it's a mechanical carburetor and a mechanical distributor, or FI and computer controls, those smart systems are just there to satisfy the air pump's demands and yours as you control the throttle. IOW, it always wants to accelerate, we just control (throttle) it. It's a lot like a spirited horse.

gun5l1ng3r
01-26-2006, 11:22 AM
Wouldnt' it be a spirited pony?;)^ (for the fbody)

Old SStroker
01-26-2006, 12:40 PM
Wouldnt' it be a spirited pony?;)^ (for the fbody)

That might be a M**tang, but I don't use that M-word. :)

H8 LUZN
01-26-2006, 01:35 PM
Just an FYI, the "GAS PEDAL" is somewhat of a misnomer..

if we were being technical, it should be called an "AIR pedal" The user controls the amount of air and the computer controls how much fuel... (and when to ignite it for that matter)

Fuel = ENERGY However you need the right mixture of Air with the Fuel to get the most energy extracted into usable form (heat/pressure) and convert it from stored chemical potential energy into kinetic mechanical energy

MadBill
01-26-2006, 01:50 PM
One more element: When you move the pedal, the TPS senses how far and how fast, so that the computer can increase the injector pulse width in anticipation of the greater matching fuel requirement, just like the accelerator pump on a carburetor.

Old SStroker
01-26-2006, 04:10 PM
Just an FYI, the "GAS PEDAL" is somewhat of a misnomer..

if we were being technical, it should be called an "AIR pedal" The user controls the amount of air and the computer controls how much fuel... (and when to ignite it for that matter)


Personally I like "Foot Feed". "Power Pedal" would be my second choice.

"Accelerator Pedal" used to be OEM-speak.

Perhaps "Throttle Pedal" is an accurate description...or "Unthrottle Pedal". :)

Question: With a diesel, isn't it closer to a "Fuel Pedal" than an "Air Pedal"?

NO-OPTION-2002
01-26-2006, 04:21 PM
"Accelerator Pedal" used to be OEM-speak.
Still is in the GM parts catalogs. :)

Quickin
01-26-2006, 06:11 PM
Thanks for the replies. So in short:

pedal goes down
TB plate opens
sensors feel pressure change
PCM instructs fuel system to increase
larger explosions from the already anxious pistons trying to suck more air
rpm's increae

Got it :chug:

92CamaroReallySlow
01-26-2006, 06:19 PM
Just an FYI, the "GAS PEDAL" is somewhat of a misnomer..

if we were being technical, it should be called an "AIR pedal" The user controls the amount of air and the computer controls how much fuel... (and when to ignite it for that matter)

Well on a carb motor too, it would considered a gas pedal, because you automatically let in gas(and air) when you hit the pedal...no computer firing it from injectors. Plus when the term "gas pedal" was coined there probably wasnt too many FI motors around.

UMIRacing
01-26-2006, 09:18 PM
Quicken,
I think you understand now!!!! That was pretty quick for a learning curve. Good explanations everybody.

Just 1 thing to add.
Air is not sucked into an engine, it is pushed!!!
An engine is mearly a pressure drop, therefore, the pressure on the front of the throttle blade is greater than that behind it.
The pressure wants to be equal so the high pressure on the front of the throttle body wants to move in and take over the low pressure on the engine side of the throttle body.

I hope this helps evaluate it a little better for you. Or it may confuse the heck out of you, either way, its all about learning.

P Mack
01-26-2006, 09:30 PM
I guess technically nothing is sucked in any situation, doesn't just apply to air and engines.

VYSSWagon
01-26-2006, 11:30 PM
Quicken,
I think you understand now!!!! That was pretty quick for a learning curve. Good explanations everybody.

Just 1 thing to add.
Air is not sucked into an engine, it is pushed!!!
An engine is mearly a pressure drop, therefore, the pressure on the front of the throttle blade is greater than that behind it.
The pressure wants to be equal so the high pressure on the front of the throttle body wants to move in and take over the low pressure on the engine side of the throttle body.

I hope this helps evaluate it a little better for you. Or it may confuse the heck out of you, either way, its all about learning.

Not to be picky but...

Isn't the "lower pressure" on the inside of the throttle blade caused by the partial vaccuum created inside the cylinder when the piston moves down and the inlet valve is open? The piston kind-of sucks the air in creating the lower preessure in the inlet manifold?

Just my perspective... :poke:

racer7088
01-27-2006, 07:53 AM
It's all in how you understand it but the higher pressure air goes towards the lower pressure region no matter what. If you want to call that sucking that's fine as long as you know what's really going on.

UMIRacing
01-27-2006, 08:58 AM
The reason I say it is being pushed is because for advanced engine development, this is how you approach things. Yes, there is a "sucking" effect taking place. But when analyzing for fuel drop out and true airflow, it has to be thought of as being pushed.
Does this make sense?
The reason it is "sucking" is because there is no air to be pushed into the cylinder.
The pushing is how you can obtain over 100% VE!!!

TheBlurLS1
01-27-2006, 09:07 AM
So what you're telling us is that LS1's really suck? :D

H8 LUZN
01-27-2006, 09:14 AM
The reason I say it is being pushed is because for advanced engine development, this is how you approach things. Yes, there is a "sucking" effect taking place. But when analyzing for fuel drop out and true airflow, it has to be thought of as being pushed.
Does this make sense?
The reason it is "sucking" is because there is no air to be pushed into the cylinder.
The pushing is how you can obtain over 100% VE!!!

Well inertia is how you achieve over 100%... "an object in motion will stay in motion.. etc" So once the pressure is equalized the air is still moving, the energy it takes to slow down the air is put into pressure and achieves a higher density in the cylinder.

You are correct though that air is pushed into the cylinder. because the net force on the air molecules is "pushing" them to the lower pressure.

Nautilus
01-27-2006, 12:03 PM
It's all in how you understand it but the higher pressure air goes towards the lower pressure region no matter what. If you want to call that sucking that's fine as long as you know what's really going on.


My science teacher always said "Science never sucks.... It blows" He loved that line :jest:

BlackHawk T/A
01-27-2006, 01:12 PM
Old SStroker couldn't have said it better...basically the engine is naturally trying to "spin" and will do so freely until the point where it would probably self-destruct...

Which is why we have a throttle blade (and a rev-limiter when the blade is open), to restrict the amount of air it gets and (feed) control it. I like the analogy of taming a wild animal ;)

spy2520
01-27-2006, 01:15 PM
I guess technically nothing is sucked in any situation, doesn't just apply to air and engines.

i know of one situation where something SHOULD get sucked....or blown, yeah i guess it all depends on the point of view.

Quickin
01-27-2006, 02:06 PM
Quicken,
I think you understand now!!!! That was pretty quick for a learning curve. Good explanations everybody.

Just 1 thing to add.
Air is not sucked into an engine, it is pushed!!!
An engine is mearly a pressure drop, therefore, the pressure on the front of the throttle blade is greater than that behind it.
The pressure wants to be equal so the high pressure on the front of the throttle body wants to move in and take over the low pressure on the engine side of the throttle body.

I hope this helps evaluate it a little better for you. Or it may confuse the heck out of you, either way, its all about learning.

Same as pressure systems in the atmoshpere, High-to-Low. It wants to go towards that low pressure. Same way a wing fly's on a plane, increased speed of the air on top of the wing due to cambered shape lowers the pressure, as compared to the airstream passing under the wing being the same pressure as when the wing encountered it so it stays the same, or higher pressure than the top air. High-to-low equals wing goes upward. I'm a pilot so I can see the same effect going here.

But, isn't the engine really sucking air in, or at least its a sucking process of the pistons that starts the whole process off, therefore we can say that air is being sucked into the air by way of this process, which is Bernoulis.

I'd like to know how high the psi gets from a BBC with 1,000 hp normally aspirated at WOT, I would think it would surpass the ~14.7 psi that the atmosphere has to offer at sea level to keep pushing air into the engine. Therefore isn't there a point that an N/A engine is purely sucking air in to keep accelerating itself to a point that it maxes out even that, red line?

.

P Mack
01-27-2006, 06:46 PM
i know of one situation where something SHOULD get sucked....or blown, yeah i guess it all depends on the point of view.

Haha, i thought about that right after i posted.

BoostCreep45
02-06-2006, 01:50 PM
In terms of this discussion I follow all of the descirptions, and learned a few new perspectives on engine dynamics. However, I find myself wondering what exactly vaccum is. IOW, most mechanical boost gauges read "vacuum" before boost. Is this in reference to the negative pressure differences between an idling/partially open throttle blade? Thanks for any feedback!!

Tommy

white2001s10
02-06-2006, 02:40 PM
A vacuum or boost gauge is simply a pressure gauge referenced to atmospheric pressure. 5" vacuum is simply 5" pressure lower than atmospheric. Vacuum is usually measured in inches/murcury, where boost is measured in PSI.

Re: the original question.
Piston movement in the cylinder expands the volume of the cylinder and lowers the pressure. The atmosphere wants to come in via the intake port to equalize the pressure. The throttle is the pressure regulator. The more you open the throttle, the closer the pressure in the cylinder will get to atmospheric pressure. Air at higher pressure has a greater density and contains much more oxygen. As pressure in the cylinder goes up, engine power goes up.

Fueling or the addition of fuel is simply to maintain the right Air/Fuel ratio as the amount of air/oxygen is changing with throttle opening.

This would be the case even if our atmosphere already had the correct ratio of fuel vapor in it. The power would still be throttled or controlled by the amount of pressure allowed into the engine. IMO you should think of it like this instead of the amount of fuel going in making the difference.

A diesel engine is always WOT and power is based strictly on the amount of fuel or the A/F delivered. This is completely different.

APeteSS
02-06-2006, 03:07 PM
But, isn't the engine really sucking air in, or at least its a sucking process of the pistons that starts the whole process off, therefore we can say that air is being sucked into the air by way of this process, which is Bernoulis.

Not sucking, but atmosphere filling a newly created volume (cylinder on intake stroke). Idea doesn't change with RPM unless you get into harmonics, advanced valving.

And a very good N/A 1,000 HP BBC would still never make much more than a bar absolue manifold pressure (0 gauge) at any RPM.

Steve Bryant
02-07-2006, 06:36 PM
The definition of the word throttle when used as a verb means to strangulate or choke (as in pressing in on the wind pipe a la the Boston Strangler). The butterfly valve or throttle plate regulates the inflow of air by limiting (or throttling) the air flow to something less than its maximum capability at wide open throttle (WOT). Whenever you open the throttle, the you lessen the vacuum or increase the manifold pressure (or manifold absolute pressure (MAP) if you wish) and the engine begins to pick up RPM's or accelerate (which is how the term accelerator derived). This is true whether the engine is a single cylinder Briggs and Stratton or an exotic V16 as long as it is a gasoline/petrol engine (this is not true for a diesel).

Now, the PCM on an LSx series engine matches the fuel flow by regulating the injector duty cycle to maintain the desired air to fuel ratio (AFR). The sensed RPM and MAP are fed to the PCM electronically and are referenced to RPM vs. MAP cells in the VE Table. In Speed Density (MAF disabled) mode, this VE table is the only reference other that the Power Enrichment Table. Also, the mass air flow (MAF) value (if used) is blended with the SD calculation to help get the mixture right.

Regardless of the function of the PCM, any engine will accelerate if you introduce more oxygen into the cylinders and accompany that oxygen with more fuel. The throttle opening initiates the acceleration and the fuel sustains the RPM increase.

Note: with a diesel engine, there is no throttle valve and combustion always takes place with excess oxygen. The fuel flow is metered (or throttled if you wish) to control RPM's. If you introduce more fuel and the oxygen is already there for combustion, the engine will accelerate.

Steve

TranzAm
02-07-2006, 07:05 PM
Sounds like you have just taught Engine Mechanics 101. Nice explanantions guys !

Steve Bryant
02-07-2006, 08:16 PM
I used to be a Detroit Diesel mechanic and at age 56, I'm still a gearhead at heart. My day job is as an avionics (aircraft electronics) engineer. I used to be an technical training instructor, but for avionics maintenance technicians and for pilots.

I really like to help people who want to learn to understand things.

All my best,

Steve

02 Camaro SS
02-07-2006, 11:13 PM
If a diesel is always running with this excess oxygen, why wouldn't it cause the same problems that occur in a gasoline engine while running lean?

Steve Bryant
02-08-2006, 07:22 AM
That's a good question and I don't know the answer right now. I'll do a little research.

Steve

white2001s10
02-08-2006, 10:40 AM
20:1 compression
the fuel doesn't start burning until it's very compressed near TDC.
It also doesn't rely on a spark to start combustion.

If you had to start combustion via a spark at around 30* BTDC you would get the same problems.

Steve Bryant
02-08-2006, 10:53 AM
You are right in that there is no advance for the ignition like with gasoline. With a diesel, the intense heat produced by the 20:1 or so compression means that when the fuel is injected into the cylinder directly (or indirectly via a pre-combustion chamber in older designs) the fuel begins to burn immediately. Also, this beginning of burning begins near TDC. If you want to learn some more about diesels, look at this reference http://en.wikipedia.org/wiki/Diesel_engine. If you want to learn something about a high tech racing diesel slated to run at Le Mans, read this http://www.audi.com/audi/com/en1/experience/motorsport/r10.html.

Steve

02 Camaro SS
02-08-2006, 06:59 PM
But what does it matter how or when it ignites as long as there is all that excess oxygen? I guess what I'm missing here is why does going lean in a gasoline engine cause problems?

Adrenaline_Z
02-09-2006, 07:45 AM
Interesting discussion.

My auto teacher always favoured us using the terms 'high/ low manifold pressure' as opposed to vacuum.

Vacuum in the truest sense is the absense of matter (air/gas in this case),
and you can never have a perfect vacuum...but rather partial vacuum.

As stated by White2001S10, the gauge reading is a reference to atmospheric
pressure at your current standpoint on earth. If you connect a gauge behind
the throttle blade, you can see the manifold pressure become closer to
atmospheric as the blade opens.

Just remember the gauge reading is not absolute.

As for going lean with a mixture, it creates heat. Depending on the extremes
it will cause the chamber to exceed optimum combustion temperatures causing
knock, or possibly component damage over a period of time.

MSURacing
02-09-2006, 09:21 AM
Hummm, this has me thinking. We have always been taught that you can't run a gasoline engine lean.

But here is what I am thinking and someone correct me if I am wrong.
The real reason you can't run a gasoline engine lean is because the fuel burns so fast, that when you start the spark 30 BTDC, the fuel would have expanded to fast and it tries to press the piston down the bore, the wrong way!!!!

So, this would be true all the time. Except, now with electronic timing control, ie, not a distributer, we would be able to reduce the timing at leaner settings and compensate for the quicker burning mixture.

Now, this won't work for emmisions, because it will create more NOx emmissions, I think.

Ok, lets hear what everyone has to say!!!

Adrenaline_Z
02-09-2006, 11:49 AM
If the timing is adjusted to compensate for an improper mixture, then pressure
on the piston is reduced over the duration of the stroke, and/or the peak combustion pressure is not occuring at the best crank angle.

Result is less power.

MSURacing
02-09-2006, 11:58 AM
Yes, you are going to achieve less power, so you will need to open the throttle more, resulting in less pumping losses.
Not sure about the peak pressure occuring at the "right" time, ca50 around 10 degrees ATDC.
I think I need to see some good data on this subject. I am going to do a little research on it.

MadBill
02-09-2006, 07:23 PM
With typical engine components and geometry, gasoline won't sustain a reliable spark-initiated flame in uniform mixtures leaner than perhaps 17-18:1, the "lean limit" of flammability. Even a slight misfire greatly impacts emissions and fuel economy. "Stratified Charge" engines provide a richer mixture near the spark plug and the resulting large flame front can propagate into much leaner regions of mixture, but the high combustion temperatures create a lot of oxides of nitrogen, which are very hard to 'clean up' in the exhaust. Hence, this technology is virtually unused in the USA, which has the most stringent standards in the world (especially CA)

MSURacing
02-09-2006, 07:59 PM
Ok, did a little research on it, called a very reliable source. And he said the same thing that MadBill did. The fuel mixture would not be consitant across the volume of the chamber therefore causing a misfire.
He also said there would probably be pre-ignition even before you could reach the lean limit of the fuel. Although he did say that moving the timing back towards top dead center may delay this, but probably not by much.

Good job MadBill.

bdc95ta
02-10-2006, 01:02 AM
Interesting discussion. But what about formula one engines, no throttle blades!
-b

Old SStroker
02-10-2006, 07:05 AM
Interesting discussion. But what about formula one engines, no throttle blades!
-b
Most current F1 engines use barrel throttles. Different mechanism but the same results. Throttle-by-wire is used and some engines have one bank of throttles open slightly before the other bank to "shape" the torque curve for driveability. I suggest that the lag-time could be programmed for the different turns in a circuit. When the throttles are closed, the program changes which bank leads to keep wear the same. This was used about 4-5 years ago and still may be.

Adnectere
03-31-2006, 12:20 AM
This has been a concept in the thread that has bugged me for a few months. I haven't been able to put it straight in my head.

Hit the gas and more air/fuel are recorded/metered and the engine burns more a/f creating more bmep. So is it the addition of bmep that makes the motor spin up higher? For instance if I'm at 1500 rpms and making 100 bmep and I open the throttle and make 110 bmep, is the motor going to spin up? How do we know how much? By 10 rpms? 100 rpms? 1000 rpms? Is it as simple as a bmep increase making the motor spin faster by pushing the pistons down harder?

Old SStroker
03-31-2006, 07:00 AM
This has been a concept in the thread that has bugged me for a few months. I haven't been able to put it straight in my head.

Hit the gas and more air/fuel are recorded/metered and the engine burns more a/f creating more bmep. So is it the addition of bmep that makes the motor spin up higher? For instance if I'm at 1500 rpms and making 100 bmep and I open the throttle and make 110 bmep, is the motor going to spin up? How do we know how much? By 10 rpms? 100 rpms? 1000 rpms? Is it as simple as a bmep increase making the motor spin faster by pushing the pistons down harder?

Thoughts:

BMEP is Brake Mean Effective Pressure, which means the engine is actually driving something other than itself. If the engine is free reving in neutral or with the clutch disengaged, it is only producing enough torque and power to overcome it's own friction and that of the trans in neutral or to spin the converter and trans pump. It's not trying to move the vehicle or load the dyno so there's no Brake torque/power an no BMEP. There is however Indicated MEP or what the engine is producng internally. The engine friction is the FMEP and as you know, BMEP = IMEP- FMEP. Now in this case FMEP = IMEP so there is 0 BMEP. All the torque/power (or MEP) being produced is consumed overcoming internal losses.

Because IMEP (or BMEP) is directly related to torque/cubic inch (or cc), it might help to think of torque or power being produced instead. FWIW, a V8 free reving to 1500 may be producing something like 25 lb-ft (7.1 hp) to ovecome it's own friction. On a 350 thats about 11 psi IMEP.

If you let more air/fuel in, the engine will free rev until the torque/power generated equals the internal friction at a higher rpm. You suggested a 10% increase, so I'd guess just about a 10% increase in free rpm because friction torque/hp is almost linear at low rpm.

Clear as mud?

Adnectere
03-31-2006, 10:32 AM
Ok then ignore the above and go with IMEP, it's what I mean at the root anyways. I'm imagining pressure on the cylinders sans losses of any type so IMEP is what I mean and should have said.

So it's as simple as the motor will have a certain IMEP needed to overcome its losses at various rpms and these losses will increase (vague statement) as the rpms increase so to rev the motor you need more force in terms of IMEP.

Let's say we have a throttle at 25%. And another at 100%. I would assume the latter to make 4x the IMEP of the first, ignoring losses that complicate. Is this true?

Old SStroker
03-31-2006, 05:22 PM
Ok then ignore the above and go with IMEP, it's what I mean at the root anyways. I'm imagining pressure on the cylinders sans losses of any type so IMEP is what I mean and should have said.

So it's as simple as the motor will have a certain IMEP needed to overcome its losses at various rpms and these losses will increase (vague statement) as the rpms increase so to rev the motor you need more force in terms of IMEP.

Let's say we have a throttle at 25%. And another at 100%. I would assume the latter to make 4x the IMEP of the first, ignoring losses that complicate. Is this true?

Without a load on the engine from the dyno or the vehicle, it takes very little throttle opening to free rev the engine to it's electronic or mechanical limit. 25% opening would be way too much. If you loaded the engine and picked an rpm the difference in power between 25% throttle opening and 100% would depend on the rpm you selected. At 2500 rpm, for example, the engine's demand for air might almost be met by 25% throttle opening, so 100% wouldn't necesarily produce 4 times as much power.

At power peak, say 6000 rpm, 100% vs 25% opening would make a lot of difference. The 25% would act like a very small restrictor, so you might see a 40% or so loss of power from 100% opening. IOW, the 100% opening might show 50% or so more BMEP and torque/power than the 25% opening. You could simulate this nicely on something like Engine Analyzer PRO if you want to see realistic numbers.

Adnectere
03-31-2006, 07:08 PM
So basically an easy way for me to think of this is...maybe you need 10 psi to power the motor at idle, maybe 25 psi to run it at 2500 rpms, maybe 50 psi to run it at 6000 rpms. All speculative pressure numbers, but is that the theory? Are we basically saying that as the piston gets forced down harder it swings back faster than the next time and so the engine climbs rpm?

Old SStroker
03-31-2006, 07:49 PM
So basically an easy way for me to think of this is...maybe you need 10 psi to power the motor at idle, maybe 25 psi to run it at 2500 rpms, maybe 50 psi to run it at 6000 rpms. All speculative pressure numbers, but is that the theory? Are we basically saying that as the piston gets forced down harder it swings back faster than the next time and so the engine climbs rpm?

I think it's even more basic than that: for a given mass of air & fuel taken into the engine, it will produce a certain about of force on the pistons (power). If that is more than the internal friction on the engine, and there is no load, it will accelerate until it reaches the point where the power it is producing just equals the total resistance or engine friction.

The same thing happens when you are cruising on the freeway. You control the amount of air/fuel into the engine so it produces just enough power to overcome the friction and drag of the entire vehicle. Your foot, or your cruise control, is the feedback device that makes the minute adjustment of the amount of air/fuel the engine receives.

Don't overthink this.

Quickin
03-31-2006, 10:22 PM
Look what I've started, and I still don't have a clear answer.

The way I see it so far is: As you sit idling at a light, the pistons are struggling and wanting more air, but each cylinder is being deprived that air because the throttle plate is not open. So, the second you push the pedal down and open that plate you just allowed those pistons to have what they're craving, so on each ensuing compression stroke for each piston that just got that extra gulp of air, along with the fuel injectors following suit immediately with more fuel........PRESTO.....the crank is turned faster than it was 1 second ago.

Can it be that simple of an explanation?


.

Wild Willy
04-05-2006, 07:40 AM
The sucking/pressure thing may be seen a little more clearly by considering- the airflow through an opening is only controlled by the size of the opening and the pressure of ambient air. Doesn't matter if it is a Hoover vacuum cleaner or a Hemi 426 doing the drawing (sucking), what determines how much air goes through that opening is the size of the opening and the atmospheric pressure- period.
That is why the 'old-school' first mod was more carburetor- more barrels, more carbs = more opening. Now days, bored throttle bodies. Engines are just big air pumps that happen to burn fuel, but, to get more power you have to pump more air. Better flow along the whole chain; heads, exhaust, intake-

racer7088
04-08-2006, 09:59 AM
acceleration is caused by force. This force is caused by the air fuel mixture exploding in the trapped space above the piston on the power stroke. when the throttle is opened you fill the cylinder with more air and cleaner air and fuel is added and the cylinder pressure increases and so does the force on top of the pistons. When the force on top of the piston pushing down on them increases so does the engine rpm and so does the vehicle as well if it's in gear and the clutch is out!