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Intake Discussion (Warning, this will be really long write-up)
Good morning Evom members!
I want to gather everyone's thoughts about boosted air intake in our evos so we can all better understand how it works and why many mods don't quite work. There is no dumb question as long as someone learns. I'll start with my understanding and my thinking behind it and hope with everyone's comments that we get a nice and complete picture at the end. Let's all add pictures of what we can find to aid in our discussion (most of mine could be from online searches).
Demand Side:
Engine cylinders are all the same volume and valve durations (although they vary depending on cam) are the same between each cylinder. I would think that if one of the cylinder air passages flows 10% better, this cylinder is not going to get 10% more air since cylinder volumes are the same and valves are open about 1/4 of the time.
Head Design:
This is where air gets into combustion chamber to be used to make power. Valves will allow air to enter during the suction stroke and stays closed for other 3 strokes (compression, power/ignition, and exhaust). Air will have be stationary and once valves open, begin entering cylinders. At this point the pressure drops behind the valves (bowl). Each bowl will provide an intial certain volume of air and give time for rest of system to ramp up and flow air to fill the bowl. The half up in the head is the fuel mixing/necking passage. This part needs to mix the fuel and minimize the amount of fuel droplets reaching the floor (if it reaches the floor, fuel may not make it into cylinder, which means that combustion cycle will run leaner than planned). This part also supplies air to fill the bowl, so its design need to be able to flow enough air with minimum restrictions to support the cylinder demands.
Together, the bowl acts like a cushion for the on and off air demand of the cylinder while the necking provides the air/fuel mixture. The reason we don't want to completely open up this necking is because we don't want air to stop. We need air to keep flowing as continuous as possible so that more can get into cylinder in any given amount of time (depending on RPM). The necking should be sized to bounce between the lowest bowl pressure (when valves are open) and the highest bowl pressure (when valves are closed). This neck should be sized to minimize and stabilize the pressure changes causee by the valves without stopping the flow of air (and losing all its energy).
Intake Manifold:
First up (from head) is the injector. If air isn't moving, fuel will spray out the injector forward-down and some liquid fuel could hit the floor. With air movement, it will help to evaporate more of the fuel before reaching the floor in the head. These runners need to stabilize flow throughout the RPM range as much as possible.
The plenum needs to stabilize demand flows of all the runners into one stable flow. The plenum needs to be designed to evenly distribute the same amount of air to each cylinder and should be designed to adjust for any differences in runner lengths and inner diameters. Realize that temperature differences do affect the volume. So if air starts heating up from throttle body to the end of plenum, the last runner will need to flow more air to make up (on top of the energy loss from the additional length of plenum). But if the plenum can cool the air, it can help make up for energy loss due to longer length of plenum before getting into runner.
Throttle Body:
It's only purpose is to stop air flow when it isn't needed. Problem with this is the butterfly valve which causes flow rates and angles to become turbulent behind it into the plenum. The position of this isn't ideal since it's on one end instead of the middle of all 4 runners.
A little more on head:
when valves are closed, the neck has the opportunity to fill the bowl and compress the air as flow rates in the neck start slowing down. The higher the pressure it can build in the bowl without completely stopping the flow rate in the neck, the better. By having extra pressure in the bowl, it has energy to jump inside cylinder once the valves start to open.
The tricky part is finding where the trade off points are since modifying these parts would be good for a limited range of RPMs at the sacrifice of rest of RPMs.
A little more on plenum designs:
I've read about how bell horns extending the runners into the plenum helps. Take a look at the areas affected by varying pressure/flow rates of runners cause by demand pulses of cylinder. I marked it in red to show how much more cushioned area there is on bell horns and how that helps to better stabilize the pressure and flow rates inside the plenum. The problem is the difficulty in building these where each runner benefits from these equally.
Seems like when i see a fully built 4G63 (proper build) the Magnus IM is utilized. Would like to see what their design incorporates to achieve high flow (not sure if laminar flow is used here?)
Seems like when i see a fully built 4G63 (proper build) the Magnus IM is utilized. Would like to see what their design incorporates to achieve high flow (not sure if laminar flow is used here?)
I would think it helps a wide range of popular engine build flow rates. Everything affects flow rates, even same size engine builds. For example, 2.2 liter, larger bore vs longer stroke. Both have same cylonder volume, but the bore would flow better. The additional stroke will allow a bigger pressure drop on top of piston at the end of the suction cycle. So the power advantage from better flow would go to bigger bore (my guess without calculating anything ).
Unless an engine build has all the dimensions and have tested each at different flow rates, RPMs, & boosts, it's all a shot in the dark. If a build has all this info, they can find an IM that would fit the flows better.
I spent several years professionally building engines and porting cylinder heads. I have done numerous bbc, sbc, ls1 and dsm heads.
Most of how you believe it all works I do not agree with.
Several of your ideas I’ve actually never heard before.
Nice head pictures tho
I spent several years professionally building engines and porting cylinder heads. I have done numerous bbc, sbc, ls1 and dsm heads.
Most of how you believe it all works I do not agree with.
Several of your ideas I’ve actually never heard before.
Nice head pictures tho
Please share your real world experience. I'm looking at it from an engineering view (not all theories pan out). As for the pictures, I stole it from someone's site with Google's help.
Wait, I stole those head photos from your thread!!!
I’m on my phone so I’ll keep it brief.
The bowl isn’t a reservoir, the plenum is
runner length is a thing. The runners are a single entity, you want them as smooth as possible as they transition from the plenum to the back of the valve. All your talk of the bowl stuff is way off. It’s just a different shaped area of the the runner to flow around the valve. Valve throat area ratio is also a thing.
Why would Mitsubishi spend more money to cast 2 shapes instead of a single port? I don't plan on spending the money (or time) to test that theory
But I am curious at the volumes of each portion. Calculations are free
Originally Posted by TrendSetter
I’m on my phone so I’ll keep it brief.
The bowl isn’t a reservoir, the plenum is
runner length is a thing. The runners are a single entity, you want them as smooth as possible as they transition from the plenum to the back of the valve. All your talk of the bowl stuff is way off. It’s just a different shaped area of the the runner to flow around the valve. Valve throat area ratio is also a thing.
UPDATE: intake manifold opening is 56mm by 28mm. So OEM IM ports are already really well matched to head intake ports! And same thing with throttle body, both are at 60mm!
Just found a thread where someone measured the head intake port:
"At the cylinder head the port measures 58mm wide by 28.5mm tall with roughly a 12.5mm radius in the corners."
Last edited by 2006EvoIXer; Mar 14, 2018 at 07:03 PM.
I've yet to see a list of various volumes for various parts of the 4G63 head.
There's more than just one head casting.
Intake port volume
Exhaust port volume.
Combustion chamber volume.
Those numbers are quite often quoted re SBCs and SBFs, not so with any japper engine.
The 4Gs bigger brother, the 6G has those numbers available (one person measured several heads) if you take the time to look.....just as an example.
Originally Posted by 2006EvoIXer
Just found a thread where someone measured the head intake port:
"At the cylinder head the port measures 58mm wide by 28.5mm tall with roughly a 12.5mm radius in the corners."
A measurement like that is meaningless because you can't measure the whole length of the port.
Bowl and neck down runner (reminds me of a funnel). They could have easily cast with straight runner.
its because the shape of the runner has to change to flow around the valve. with a poppet style valve, you cant just swing it out of the way, you have to flow around the outside diameter of the head.
laminar flow requires smooth transitions between runner cross sectional shapes, and the venturi affect dictates that the runners overall shape taper down for the most efficiency and effectiveness. the bowl is just an extension of the rest of the intake runner but it is used to coax the air around the head of the valve in the most efficient way possible.
Its great how enthusiastic you are, but your theories and understanding of cylinder head flow are way off. Ill see if i can find any books to recommend you. There might be some good info on speedtalk. i havent really dabbled in the cylinder head world in quite some time.
Those numbers are quite often quoted re SBCs and SBFs, not so with any japper engine.
runner volume is only useful in quoting heads for the same platform, because you dont include the length. a 200cc sbc runner doesnt compare to a 200cc dsm runner because the dsm runner is a different length.
A measurement like that is meaningless because you can't measure the whole length of the port.
there are ways to measure the length of the port. its really not that hard.
Mar 9, 2018, 09:55 AM
Intake Discussion (Warning, this will be really long write-up)
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