inlet port design

[KAM]

I am trying to learn a lot more about engine design as I ready myself to spend money on my new engine. Now I picked up a set of throttlebodies for a good price which were apparently off a 405 supertouring. First thing that I noticed was the inlet port design on the inlet manifold is different to a standard head. The peugeot 16v engines have round ports compared to this



Now if overall port size is kept the same what are the benefits to going to this port shape. Is this to simply help stop charge robbing or is this a more complicated subject regarding airflow characteristics close to the valves?

Only Peugeot seem to stick with round ports out if virtually all other engine manufacturers heads I have seen..

Any good technical books that focus on head design and flow?

[AU N EGL]

This is a common disscussion here in the states as well.

Larger ports allow more air to flow though, smaller ports cause faster air velocity.

Round ports is better for air velocity as water flowing though a round pipe vs a oval or oblong pipe. Air flows quick with no turbulance though round ports.

[sloracer]

I think fundamentals of IC engines has a section on intake/throttle design. It's a fairly complex process involving fluids, getting air and fuel homogenously mixed and combustion eff.

[SidewaysFeltham]

A real can of worms!

As AU already says, smaller diameters can accelerate gasflow.

A number of considerations come into play, here: Bernoulli Effect; Venturi Effect for starters.

Then you need to encorage swirl to provide the best admixture of air and vapourised fuel.

Next you need to promote effective cylinder filling (weight of charge for optimum BMEP): next you need "Squish" to ensure that the charge is as evenly distributed throughout the combustion chamber and this piston crown, to promote even flamefront spread and thus smooth even combustion to avoid "tipping" the piston from an uneven burn.

You cannot separate one requirement from another: no point in having a massive gasflow speed through the first bit of the porting to find it then wants to queue up!

One aspect often forgotten is the reality that the whole intake system from atmosphere creates a "Standing Wave" which is an harmonic of RPM.

This is caused by the inlet valve/s closing when the gas is galloping in and is suddenly stopped; which creates a reverse pressure wave galloping backwards up the pipes!

Effective tuning takes advantage of this standing wave to increase the speed of gasflow.

[KAM]

Originally Posted by AU N EGL

This is a common disscussion here in the states as well.

Larger ports allow more air to flow though, smaller ports cause faster air velocity.

Round ports is better for air velocity as water flowing though a round pipe vs a oval or oblong pipe. Air flows quick with no turbulance though round ports.

I understand the logic of gas speeds due to size, but peugeot seem to be the only manufacturer who sticks with round head inlets on their 16v engines. I'm sure that on all these engines as the port travels further into the head towards the valves they are all round but its the entrance to the head that i'd like to gain an understanding about. No-one seems to cover this little area in detail though it seems a possibly vital point to be looking at.
In effect rather than having four head inlets other engines have 8 in sort of siamesed pairs

I've drawn a crappy diagram!


Now all i can think is that this moves the task of separating the airflow for each cylinder further up the inlet tract, so lessening the impact each port has on the other? This would affect the swirl and ultimately the fuel atomisation. Does moving the separation further from the valves make the separation of the air more gradual process meaning more controlled airflow through to the cylinder chamber

[phoenix]

Originally Posted by KAM

I am trying to learn a lot more about engine design as I ready myself to spend money on my new engine. Now I picked up a set of throttlebodies for a good price which were apparently off a 405 supertouring. First thing that I noticed was the inlet port design on the inlet manifold is different to a standard head. The peugeot 16v engines have round ports compared to this



Now if overall port size is kept the same what are the benefits to going to this port shape. Is this to simply help stop charge robbing or is this a more complicated subject regarding airflow characteristics close to the valves?

Only Peugeot seem to stick with round ports out if virtually all other engine manufacturers heads I have seen..

Any good technical books that focus on head design and flow?

Take a look at where the injectors are located; I would guess that the airflow is being managed by the inlet shape to even up the mixing of the fuel.

Without the dimple in the roof of the manifold I suspect that flow in the top centre part of the port would carry less fuel, as it is in the 'shadow' of the narrowest part of the fuel spray, but by the airflow being directed downwards it will improve mixing of the fuel from the wider spray area available lower down the injector 'cone'.

Just a guess - but an educated one.

[AU N EGL]

There there are the differnces between a carberator and fuel injection.

[KAM]

probably best to stick with fuel injection as thats what I have then lol

Can choosing this


over this


be just due to injector spray pattern as Phoenix mentioned

[Notso Swift]

Do not discount cost of production, either, what is easier to produce is oftent whay is produced! More on topic
A lower, flatter floor usually has more compromises with air speed, as the air tends to stall on the short side turn to the valve. May not be the answer

The Pug motors are notorious for beeing tall, other manufaturers may value a lower profile and are happy to compromise the design (especially if the change is measured in fractions of a percentage point)

[Stocky]

The 2nd head also has the injectors aimed at the back of the valves.

It's common practice to inject onto the back of a closed (hot) inlet valve for good atomisation.

This setup gives good low RPM performance but not so good at high rpm.

Modern motorcycle heads are a mix of both and often have a lower injector aimed at the valve and a 2nd injector higher in the throttle body for higher rpm fueling.