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3 Mar 2008, 14:51 (Ref:2143315) | #1 | ||
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Join Date: Feb 2007
Posts: 48
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inlet port design
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? |
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3 Mar 2008, 18:00 (Ref:2143459) | #2 | ||
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Join Date: Jul 2006
Posts: 4,418
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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. |
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3 Mar 2008, 19:11 (Ref:2143518) | #3 | |
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Join Date: Nov 2007
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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.
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3 Mar 2008, 19:27 (Ref:2143528) | #4 | ||
Racer
Join Date: Jun 2007
Posts: 419
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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. |
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3 Mar 2008, 20:54 (Ref:2143582) | #5 | |||
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Join Date: Feb 2007
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Quote:
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 Last edited by KAM; 3 Mar 2008 at 20:59. |
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3 Mar 2008, 20:58 (Ref:2143584) | #6 | |
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Join Date: Jul 2005
Posts: 1,981
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Quote:
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. |
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3 Mar 2008, 21:05 (Ref:2143587) | #7 | ||
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There there are the differnces between a carberator and fuel injection.
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"When the fear of death out weighs the thrill of speed, brake." LG |
3 Mar 2008, 21:25 (Ref:2143595) | #8 | ||
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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 Last edited by KAM; 3 Mar 2008 at 21:30. |
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5 Mar 2008, 00:43 (Ref:2144574) | #9 | ||
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Join Date: Apr 2006
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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) |
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12 Mar 2008, 00:39 (Ref:2149637) | #10 | |
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Join Date: Sep 2006
Posts: 72
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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. |
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