This is untrue with an N/A engine because the air is being sucked in, not pushed in like a forced induction app. Blowing the air in with the head port smaller than the intake port can cause some reversion, but with the air being sucked in the bigger opening on an intake port won't slow down the air. Actually the head port will only suck in the air that it can from the bigger intake port. This has been proven with a BBC "peanut port" head using a huge opening rectangle port intake power was increased over using the "peanut port" factory intake. So anyone not planning on running boost a larger intake port than the head port wouldn't have any adverse effects on airflow. But with a smaller port than the head port airflow can suffer with the intake being the restriction as seen with the factory intake being an airflow restriction as well with an unported TA D/P intake. I hope this helps. GL Derek
Sorry, common fallacy. Nothing is "sucked" into even a naturally aspirated engine. The air/fuel mix is still being pushed in under pressure, even though it's only atmospheric pressure which happens to be higher than the pressure in the intake manifold. It's no different than forced induction, in which the mix is being pushed in at pressures higher than atmospheric. Devon
However you wish to look at it, it's detrimental to air flow, if it's not hitting the ledge, it's loosing the effect of a long runner for filling the cylinder. Again, primarily on the top part of the runner, and in both cases talking about air/fuel inertia near the end of the intake cycle when the piston is near BDC, at BDC and is on it's way back up. The wrong to right setup on engines can be the difference between 85% volumetric efficiency and 100+% volumetric efficiency. One where that face stops the inertia, and one where the air doesn't have to dramatically change direction. And using peanut port heads as an example is..... well an interesting example? It's a choked head with an attached choked intake that is supposed to feed a lot of displacement. Yeah, bolting a bigger intake to them improves the horsepower some, makes the straw shorter, but either opening up the port, or even simply rounding out the edges improves HP even more with a large intake, aka, the head port is still crippling the engine's potential.
The pressure drop in the intake is caused by the downward motion of the piston that makes the pressure drop in the intake because of the suction that is created by the downward movement of the piston SUCKING the atmosphere out of the intake. The air that the atmosphere "forces" into the intake is still drawn in by the piston on its down stroke and at higher RPM even more air is DRAWN in because of valve overlap causing the exhaust movement to help DRAW more air in, this effects is even better with tuned header with a cam with more overlap. Forced induction is different because like the term forced means the air is being forced in faster than the piston can draw the air in. They are NOT the same!!!!! LOL Derek
Very interesting opinions on this! Too bad the 350 Buick hasn't had extensive dyno testing with the few speed parts available to see what the engine wants/needs, guess that's where us guys come in huhou:
Oh, dear. You are really going onward with this??? This is JUNIOR HIGH SCHOOL PHYSICS!!! Do you have any remote concept of why standard atmospheric pressure is rated at 14.7 psi??? Your forced induction is some number above this, that's all. You actually think there is some magical star wars force pulling the molecules toward the lower pressure instead of pushing??? The molecules are being pushed to fill the vacuum by that 14.7. not sucked in by some magic. Fundamental lack grasping this simple concept; seen it too many times before. Devon
Looks awesome! What is TA Charging for them? Will the GS aircleaner fit under the hood with the new intake?
Cool, I should just be able to turn my key to the on position and hit the gas peddle and the engine should start from the air being pushed in! That makes sense, not. What is the vacuum in the intake caused from? Why does the vacuum drop when all 4 barrels are opened and yet even more air enters in the engine as the RPM increases? Why would less vacuum cause more air to be "pushed in" and make more RPM and power if the downward movement of the piston isn't drawing in the air when the intake manifold is no longer at a lower pressure than 14.7 at wide open throttle with the vacuum being zero?
Might be time for a new thread on this. "vacuum" is just a low pressure condition caused by area displacement of the piston, right? What fills the vacuum when you open the valve (throttle)? Atmospheric pressure does, the same 14.7 psi you're and I are breathing right now. It doesn't feel like pressure to you like the deep end of the pool, because your body is at equilibrium with the weight of the atmosphere above your head pushing down on us. But it really is that atmospheric pressure that fills the low pressure above the piston as it's drawn downward. That is the correct explanation of the phenomenon. https://books.google.com/books?id=ClyzQHlQbjYC&pg=PA10&lpg=PA10&dq=throttle+atmospheric+pressure+fills&source=bl&ots=SfScfhV6eb&sig=tkkOIUbnkM-oZ5oegiIgzIFvo_o&hl=en&sa=X&ei=eaNzVeuRGY2wyAT-6ra4AQ&ved=0CCEQ6AEwAQ#v=onepage&q=throttle%20atmospheric%20pressure%20fills&f=false And yes, if the engine is turning, the ignition is on, and the throttle valve is open enough to let some of that 14.7psi air in, it freaking starts! And just because you add five pounds of boost with a blower and call it forced induction, it's not magically something different, its just 14.7 + 5 pushing in the molecules for a change. The concept is really that simple. We can get into it in more detail outside this thread if it's of interest. Devon
"But it really is that atmospheric pressure that fills the low pressure above the piston as it's drawn downward. That is the correct explanation of the phenomenon." Thanks for agreeing with me. Derek
What are you talking about, the sentence that you copied and pasted from somewhere agrees 100% of what I wrote, lets examine it; "But it really is that atmospheric pressure that fills the low pressure above the piston as it's drawn downward. That is the correct explanation of the phenomenon." It is saying that the 14.7 atmosphere is filling the cylinder because of the low pressure above the piston which is WAY after the intake port! ABOVE the piston it says, as its DRAWN downward it says. WAY AFTER the intake port! After the intake port and even after the head port, so a mismatch of a larger intake port with an N/A engine won't cause reversion because the air isn't being pushed in until the low pressure ABOVE the PISTON after all ports! Who is in a coma? LOL Derek
Not going to belabor it. You still don't see the fundamental flaw in your attempt to describe natural aspiration and forced induction when in an absolute sense the physics of airflow due to pressure differentials is the same between them both . Again, vacuum doesn't pull anything. pressure pushes air into it. If you simply want to say that you agree with this, then yes we agree. Back to the topic., it's not important to the discussion anymore. Devon
To beat this dead horse, Look at a simple EFI VE table in KPa. Where are the numbers negative? There is no "vacuum", just lower pressure, and air presses from areas of high molecular density to areas of low molecular density (fixed temperature). All positive numbers, and like all equalizing forces in physics it goes from high to low, and as mention boost is just going from higher to low, no difference in force vectors. This table goes from 20kPa (~18inHg "vaccum") to 265kPa (~20psi boost). As I said earlier, anyway you care to look at it, the lip on the head side isn't going to beneficial over not having a lip.
Induction stroke The induction stroke is the first stroke in a four-stroke internal combustion engine cycle. It involves the downward movement of the piston, creating a partial vacuum that draws (allows atmospheric pressure to push) a fuel/air mixture into the combustion chamber. In a reciprocating engine, it is that portion of the cycle when the pistons move from TDC (top dead center) to BDC (bottom dead center) and the fuel-air mixture is drawn into the cylinders.... A reciprocating engine, also often known as a piston engine, is a heat engine (usually, although there are also pneumatic and hydraulic reciprocating engines) that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types.
Derek, Define "vacuum" as it relates to an internal combustion engine. Discuss throttle plate position vs vacuum. This will help you grasp what Devon is saying.
Please allow me to elaborate: Devon and Derek are both correct. Atmospheric pressure does push air into the engine (so it is pushed), up to a point; when the engine can move more air than the atmosphere can provide, then the engine draws the air in (so it is sucked). This is at full throttle. At partial throttle, the throttle controls how much air is pushed/sucked depending on air demand (CID, VE, RPM, etc.) and atmospheric pressure (dependent on altitude). The reason there is vacuum at partial throttle (the more closed the throttle is vs engine air demand, the more vacuum there is) is because the engine's demand for air is greater than what can be provided, causing the suction. The atmosphere provides the air, and does have pressure. At open throttle, the vacuum disappears and is replaced by pressure provided by the atmosphere. Once engine air demand increases beyond what the atmosphere can provide, it begins to draw it in, which is why there can be vacuum at higher RPMs at full throttle, particularly if the carb is too small. Make more sense? Yes this is oversimplified--for a reason. Keeping the explanation simpler is best when dealing with mixed company. I had to learn this the hard way. Some people have more trouble grasping concepts (particularly if they're abstract) than others. This doesn't make them bad people. Everyone is different and has different learning curves. We're all here to teach/learn from each other. No shame in that. We all have something to offer in our own way. By the way, great thread. Awesome work on the SP3. Great pics! :TU: Gary
