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Snoopy0812 04-09-2013 03:38 AM

Intake manifolds understood
First we look at what exactly an intake manifold is and what it does.
An intake manifold is a device that connects between your throttle body and your cylinder head. Itís comprised of four main parts, the inlet, the runner, the surge tank and the fuel delivery method.
Easiest to explain is the inlet, this is the part where the throttle body or carburettor meets with the surge tank or in some cases, the runners directly.
The runners are the individual tubes connecting the cylinder head to the surge tank and in multi-port injected engines (2.0T, MPI 3.8) also house the injector boss, the hole that supports the injector and allows it to deliver fuel.
The surge tank is typically a tank of sorts that acts as a reservoir to feed the runners air. It comes in many shapes and sizes and in some applications is a separate piece such as the 3.8. It usually has the throttle body directly connected to it and connects directly to the runners.
The fuel delivery method can be carburettors, port injection or multi-port injection. I wonít cover these in length but the 2.0T and the MPI 3.8 are multi-port meaning they have a single injector per runner. GDiís deliver the fuel directly to the cylinder, such as the GDi 3.8.
Intake manifolds are only applicable to vehicles that do not have independent throttle bodies. In diesels itís typically called a plenum as they donít have throttle bodies or need to mix the fuel and air prior to entering the cylinder. GDiís would also be more appropriate to use the word plenum as well. This is because of how the function of an intake manifold is defined.
The primary function of the intake manifold is to evenly distribute the air fuel mixture into each port of the cylinder head. Other functions are a mount for fuel delivery devices, sensors and whatever else you can come up with to put on there.
Engines can have more than one intake manifold, though itís uncommon in modern vehicles as itís more efficient and less expensive to share a single unit.

Next we look at different applications for intake manifolds and requirements for those applications.

In naturally aspirated engines (from here on shortened to NA) the runner length of the intake manifold seriously affects the performance of the engine. Longer runners are better for torque while shorter runners are more adept at supplying air at higher RPMís. Some companies go as far as to make variable length runners, these self or computer adjusting runners vary in length to provide the best of both situations at the expense of added complexity and cost. NA engines also benefit from large surge tanks; these are basically air boxes post throttle body that allow the engine to breath between shifts as the throttle plate closes. It also helps with runner balance as the runners donít try to steal air from their neighbour when their time to flow into the cylinder is up.

In turbocharged engines (from here on shortened to TE) the design of the intake manifold differs a bit. This is because the engine is not scavenging for air under load as its being provided by the turbocharger. For optimal performance a TE would have the shortest runners possible with little to no surge tank for maximum performance under load, however when driving outside of load such as cruising, it can cause some decline in performance and responsiveness. When not driving with a positively charged intake (from here on called boost) the engine acts and performs very similarly to a NA engine. Due to the fact that the surge tank is usually reduced in size for under load performance the engine is usually ran at a higher RPM for similar function to increase responsiveness and load the turbocharger readily. This has a negative effect on fuel economy that is usually mitigated by the turbocharger maintaining a small amount of turbine speed to compensate for the extra RPMs demand on the engine, it also helps provide improved low end torque to compensate for the shorter runner length.

In supercharged engines (from here on shortened to SE) you donít want or need a surge tank and runner length is a near moot point. This is because the supercharger reacts directly with engine RPM. The supercharger housing will have a specific volume (unless centrifugal) and that volume will act as a surge tank for the supercharger, air beyond that point is ideally compressed and best acted in a similar fashion to a TE. This type of setup is really only useful to the 3.8 and most setups for the 3.8 modify the existing surge tank and use it to house the water-air intercooler, thus reducing its surge tank capacity.

Now that we have an understanding of the different designs and needs of each induction type we have to look at a few other things specific to our engines.

Snoopy0812 04-09-2013 03:38 AM

Since I’m more versed with the 2.0T, we’ll start there.
Surge tank volume is based on the displacement of the engine, not the turbo that is being connected to it. This is the calculated volume of air required to support the engine between shifts when the throttle plate closes and then opens again. A larger turbo does not mean you need a larger surge tank. A larger displacement engine such as a stroked (longer piston travel) or a bored (larger piston surface) would require a proportionally larger surge tank. Increasing the volume of a surge tank beyond the calculated volume increases the effort required by the turbocharger to compress the air to the desired compression rate, such as 14 psi. This is traditionally called lag, short for latency. While there is often a large amount of debate on this by aftermarket suppliers, this is easily attributed to the additional cost and research required to develop a properly proportional surge tank. Runner length, volume and balance is key to a proper intake manifold for TE’s, more than any other gimmicks that can be had.

Runner length can only be changed with an aftermarket intake manifolds, gains for specifically modifying this length can be troublesome as it usually just moves the power band rather than increasing it. Often aftermarket companies shorten the runners and increase the surge tank volume to compensate for closed throttle conditions, thus costing low end torque or relying in fast turbo spool to compensate and increasing high RPM power.

Runner volume can be changed by porting, a process by which excess material is removed from inside the runner increasing its volume and often resulting in a better flow between the surge tank and the cylinder head. Runner volume can also be adjusted with an aftermarket manifold.

Balance is by far the most important; it’s the volume of flow in relation to the other runners. Volume of flow is usually measured in CFM or cubic feet per minute of air.
Runner balance has nothing to do with overall flow in terms of its effectiveness.
To split this down into easier wording, if the head will flow 250 CFM per cylinder (example number only) that limits the engine to 1000 CFM. The intake manifold flows 1200 CFM total, thus it outflows the head. However, you actually need a turbo that can produce 1000 CFM to outflow the head. A T72 turbo flows roughly 1000 CFM at 40 PSI on a 2L engine, stock turbo on a 2013 is roughly 460 CFM on a stock tune. So that 460cfm gets roughly divided across the 4 cylinders, I say roughly because it's not perfectly even because the timing of the GC actually double taps the intake valves as part of the EGR system on the 2.0T. So the stock turbo doesn't even come close to maxing out the head or the intake manifold. This means that balance is more important as it allows proper equalization of air dispersal since the flow is unrestricted.
Very important to note, only diesels can operate with a turbo at full boost 100% of the time, because they have no throttle plate. Because of this characteristic of gas engines we have to cycle boost, meaning we can't keep the intake manifold charged all the time, further pushing the need for it to be equalized as we have to operate in vacuum as well as pressure. Uneven runners in vacuum cause cylinder starvation, as the engine can't compensate for the cylinders individually (we would need four O2 sensors in the manifold alone) the engine pushes the fuel and aggressively fires two of those cylinders; this can cause cylinder washing and harms the longevity of the engine. Once boost is applied that's no longer the case for those cylinders, however it creates an issue for the other cylinders, they now receive too much air and are running lean, very hot which can cause a whole different set of issues.
Runner balancing is much more important than any other function of the intake manifold in regards to flow and safe operation of the engine.

An additional process called gasket matching is when the runner port is matched to the gasket port in size. This is a very tricky process because done wrong and it can cause rapid expansion of the air and result in pre-cylinder pressure loss. Poor atomization of the air fuel mixture can also result. Gasket matching is mainly important to high RPM TE engines or when the head inclines into the runner port in which case you would gasket match the head so the step goes down and not up impeding the air flow.

Polishing and deburring or extrude honing* ģ the casting marks from a TE intake manifold is not heavily important, at least not as important as it is for NA engines. If the event occurs where you’re nearing the max flow of the intake manifold or the engine is set up for high RPM, then this becomes important as it will aid in laminar air flow, further improving efficiency. However, when the flow demand is not nearly as high as the maximum potential, this will have a negligible effect and the added runner turbulence may actually benefit atomization of the air fuel mixture. More than likely though, it will have no noticeable effect other than looking good when it’s all apart. If the engine primarily spends its time out of boost, extrude honing will have a benefit then as it’s operating similarly to a NA engine.
Due to copyright and patents this process is typically called “port and polish” by other companies that don’t have the rights to use the term.

RedRaspberry wanted to know the internal volume of the stock 2.0T intake manifold. Using my spare 100% internally stock manifold I taped the inside of the manifold using thin aluminium tape, this takes the boss volumes out of the equation and focuses on the intended volume. I also taped the injector bosses from the inside as well as I don't know the exact displacement of the injector nozzles and again focuses on intended volume.

I then filled the intake manifold with water after blocking off the throttle body port with the same aluminium tape. I filled the manifold until the water was level with all four runner ports at the head mount and then held the manifold over a basin and poked a hole in the tape and let the water drain into the basin. When the water flow stopped I removed all the tape over the basin and allowed it to drip dry. I then measured the volume of water in the basin by pouring it into a measuring glass with 25mL increments and came up to the volume of 1975mL. My method is not the most scientific however it gives a very good approximation of the internal volume and it would be fair to say that the intake manifold is roughly 2 litres, the same displacement as the engine itself.
I will redo this test when my manifold gets flow balanced.

Snoopy0812 04-09-2013 03:38 AM

Again, the surge tank is sized to the engines displacement. The 3.8 has nearly twice the volume of the 2.0T and thus, has over twice the volume in its surge tank. Partly because the 2.0T has a reduced surge tank because it’s TE and mostly because the 3.8 is NA. The 2013 GDi engine received a smaller surge tank compared to the 2010 MPI engine, this is most likely due to the added torque benefits of GDi, allowing them to shorten the intake length, rely on GDi for compensation in that regard and improve top end output of the engine. MPI engines willing to sacrifice some low end torque or have modified to turbochargers or centrifugal superchargers could consider this as an easy way to gain some top end and rely on their forced induction to compensate.

The runner length on the 3.8 is fixed, by definition the runner assembly is Hyundai’s official intake manifold as the whole assembly is separated into two parts, the upper surge tank and the lower intake manifold. On MPI’s the intake manifold holds the injector bosses and the surge tank connects directly to the throttle body. On the GDi’s the intake manifold is nothing more than runners and the surge tank connects directly to the throttle body. No aftermarket solution has been provided to change the runners on the 3.8 as of this writing and would more than likely provide a negligible benefit for the cost.

Like the 2.0T, runner volume can be changed by porting, a process by which excess material is removed from inside the runner increasing its volume and often resulting in a better flow between the surge tank and the cylinder head. The added benefit of this is more volume during closed throttle applications improving throttle response when it’s opened again after a shift.

Runner balance is just as critical to NA engines as it is to boosted engines and is often times not noticed until too late. The passenger side ports on average are quite a bit worse for flow than the drivers side ports are, up to 11% in some cases. The 3.8’s intake runners can flow roughly 320 CFM on average in stock form. Some individually as high as 335 CFM while some as low as only 300 CFM. Like the 2.0T this is a lot of variation that can be easily remedied by porting the low flowing runners and in some cases not touching the high flowing ones to help keep everything even as possible. A proper runner balance can bring the lowest flowing port up to 325 CFM and even the rest out considerably, that means no lean cylinders or overly rich cylinders.

Gasket matching is even with runner balancing on the NA 3.8. Due to how a NA engine naturally operates gasket matching allows a very laminar flow between the surge tank, the runners and the cylinder head. This laminar flow allows the air to travel faster with less restriction allowing more air to enter the cylinder prior to the valve closing. More air that enters the cylinder the more efficient it operates the more power it can produce and the less fuel is wasted. Any steps between the components will disrupt the flow and slow it down.

Polishing and deburring or extrude honing* ģ further improves on the benefits of porting and gasket matching by making the intake runners as smooth as possible maximizing laminar flow. The two part intake manifold of the 3.8 makes this relatively easier to do than on the 2.0T.

If I've missed anything or further explanation is required just ask and I'll fill in the gaps. Just trying to make this as layman’s as possible.

* Abrasive flow machining or extrude honing is a registered trademark of Extrude Hone Corporation and is used in reference only.

Red Raspberry 04-09-2013 03:44 AM

So what are the volumes intakes?

Snoopy0812 04-09-2013 11:04 AM

Don't really understand your question can you reword it?

Unstablementaly 04-09-2013 12:40 PM

Snoop, have you been getting bored again lately? Great write up and explanation by the way.

Snoopy0812 04-09-2013 01:02 PM

kids were having a rough night so I thought I'd fill in the gaps and make a straight forward explanation of things and benefits for everyone. Seems like a pretty hot topic on the forum these days.

Mooseman 04-09-2013 01:05 PM

After that thread that got locked yesterday, I love this writeup. Thanks alot snoop. Good info.

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Tyr 04-09-2013 01:05 PM

I'm worried about reading this. I just bought the Elite manifold and was gonna put it on either this weekend or next. I don't wanna find out it's bad. Someone read it for me. Which thread got locked?

Mooseman 04-09-2013 01:08 PM

Oh nothing important just stubborn QQ'ing. Basically tyr snoop says he loves you long time. Read it urself lol

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cjd82187 04-09-2013 01:13 PM

Too many threads of yours to subscribe to...

Tyr 04-09-2013 01:24 PM

I read it anyways and I'm sticking to my strategy of putting my fingers in my ears and screaming, "I AM THE GREATEST!"

And I think you're talking about that guy who got his IM balanced and then did a chargeback because #1 and #4 weren't honed.

Red Raspberry 04-09-2013 01:32 PM


Originally Posted by Snoopy0812 (Post 1460745)
Don't really understand your question can you reword it?

What is the intake manifold volume? How much water will it hold?

Mooseman 04-09-2013 01:34 PM

Just keep telling yourself that lol.

It may or may not have been that thread. I dont want that nonsense coming to this thread. So who knows. All I know is these are not the droids you are looking for.

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TVONE2 04-09-2013 01:53 PM

lots of modern EFI engines do have plenums.. IE that big thing on the top of a fox body 5.0 mustang is a plenumn.. bolted to a set of runners.. the big thing on a 3.5L Chrysler motor with 2 throttle bodies '93to present with the long and short runner flaps.. is a plenum..

Speedos623 04-09-2013 02:11 PM

God, Snoopy, I have such a man-crush on you right now

Snoopy0812 04-09-2013 03:03 PM

second post updated for you Red. Anyone who has an unmodified 3.8 manifold could follow my steps and find the volume for that as well it would be interesting to see.

Short of it, the intake manifold for the 2.0T is measured by me at 1.975L, nearly identical to the displacement of the engine.

Snoopy0812 04-09-2013 03:07 PM


Originally Posted by TVONE2 (Post 1460936)
lots of modern EFI engines do have plenums.. IE that big thing on the top of a fox body 5.0 mustang is a plenumn.. bolted to a set of runners.. the big thing on a 3.5L Chrysler motor with 2 throttle bodies '93to present with the long and short runner flaps.. is a plenum..

by definition, they're using the term wrongly.

Plenum chamber; a chamber intended to contain air, gas, or liquid at positive pressure.

Key to that is at a positive pressure, hence why it's more suited to diesels where the boost is constant in terms of never needing to enter a state of vacuum.

jhan 04-09-2013 03:08 PM

You need to school me in cars snoop o_o

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Stewjoe 04-09-2013 03:43 PM

Has there been any flow balance testing on the 2013 manifold to see if they have fixed the imbalance?

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