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Discussion Starter · #1 ·
*Disclaimer, know what you are saying before you open the yap.

Has anyone tried shrink porting on the GTR heads to get the velocity benefits?
 

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No, but in theory it could be of some benifit. GTR ports are quite small anyway.
 

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will be putting a rb26 head on a flow bench this week to do some tests ,i will ask the guru about velocitys and shrink porting .thehead we are using has mild porting to both inlet and exh.i know he has told me before velocity through the exhaust port is very important on turbo cars depending on turbo size.depends what u aiming for street quick spool or drag lag.ill keep u posted.
 

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Discussion Starter · #5 · (Edited)
^ I don't trust the flow bench.

Cycledoctor

With a flowbench and then get busy with the die-grinder, it's pretty easy to get more flow, because the stock ports aren't very streamlined. The man doing the porting feels good because he's getting bigger numbers, and the customer is happy because he sees smooth, shiny ports. After all, the whole idea of the flowbench is that more flow is supposed to translate into more power; but with a engine, that relationship is weak.
Intake is anything but a steady flow.
 

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Discussion Starter · #6 ·
Please explain the velocity benefits with 1 bar of pressure behind them
Good point. In a NA more VE would be higher with higher velocity and it's duration even after BDC, allowing the valve to stay longer.

But in a turbo'd at 1 bar, you already pushing VE greater than 0.1, which already is pushing more velocity. The only benefit, I would see would be is you aren't boosting 1 bar constantly. So actually I would imagine the benefit would be a quicker or responsive boost time to get up to 1 bar. The added velocity creates more turbulent fuel charge within the chamber.

But again I am just speculating.
 

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dont get confused, turbocharging an engine does not mean you're increasing VE. The efficiency will be the same with the difference that you're forcedly pumping more gas ie. the engine remains as inefficient as before, for example if the the engine pumped out 80% of what it pumped In (being NA) it will be the same or close while turbocharged (80%VE) only that the mass of gas is greater.
 

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Discussion Starter · #8 · (Edited)
dont get confused, turbocharging an engine does not mean you're increasing VE. The efficiency will be the same with the difference that you're forcedly pumping more gas ie. the engine remains as inefficient as before, for example if the the engine pumped out 80% of what it pumped In (being NA) it will be the same or close while turbocharged (80%VE) only that the mass of gas is greater.
Read note in original post please:

Here's a start:
Volumetric Efficiency:* Calculating your cars volumetric efficiency
Volumetric efficiency - Wikipedia, the free encyclopedia
Turbo Engine - Wikicars

You contradicted yourself.

VE is calculated at a reference point, Ambient air density. So the reference point states the an ideal amount of mass that the combustion chamber fills. Density is mass per volume. More density, more mass, more pressure... after all, it has been compressed... don't you think it want's to uncompress itself to match equilibrium with ambient air? Even in a normal N/A motor, streamlining the ports, changing your intake track will change your VE, because you are changing how the actual air is filling the chamber.

VE = Actual Air / Ideal Air

:squintdan
 

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Good links - quote to back your point up:

"Volumetric efficiency in internal combustion engine design refers to the efficiency with which the engine can move the charge into and out of the cylinders. More specifically, volumetric efficiency is a ratio (or percentage) of what quantity of fuel and air actually enters the cylinder during induction to the actual capacity of the cylinder under static conditions. Therefore, those engines that can create higher induction manifold pressures - above ambient - will have efficiencies greater than 100%"
 

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Read note in original post please:

Here's a start:
Volumetric Efficiency:* Calculating your cars volumetric efficiency
Volumetric efficiency - Wikipedia, the free encyclopedia
Turbo Engine - Wikicars

You contradicted yourself.

VE is calculated at a reference point, Ambient air density. So the reference point states the an ideal amount of mass that the combustion chamber fills. Density is mass per volume. More density, more mass, more pressure... after all, it has been compressed... don't you think it want's to uncompress itself to match equilibrium with ambient air? Even in a normal N/A motor, streamlining the ports, changing your intake track will change your VE, because you are changing how the actual air is filling the chamber.

VE = Actual Air / Ideal Air

:squintdan
ok, you're not feelin' me, see if you streamline your ports and change your intake track and other mods you (if done right) make the engine more efficient. In other words, it can pump out more air than before right? because cylinders fill furthermore so increased VE.
Now grab that engine before doing the streamlining and changing your intake track and turbocharge it. You pump more air right, but not because your engine is more efficient but because of a turbocharger forcing more air.
Im not sure if I let myself understand. Its efficiency.
Now if we would like to consider forcing air in as being more efficient... although most would not.
Besides dont always trust wikipedia man, this issue I talk to you about I read from an engine guru I think it was Corky Bell, in his book Maximum Boost if I'm not mistaken, people tend to think turbocharging = increasing VE until they talk to someone that really knows his sh*t.
cheers
 

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Discussion Starter · #11 · (Edited)
Besides dont always trust wikipedia man, this issue I talk to you about I read from an engine guru I think it was Corky Bell, in his book Maximum Boost if I'm not mistaken, people tend to think turbocharging = increasing VE until they talk to someone that really knows his sh*t.
cheers
First link is not wiki, wiki links shows connections as a general information support. Projected general information, wiki does exactly what it supposed to do. But agreed, never should be trusted solely alone. Then anything you read is the same.

Corky Bell - Maximum Boost. Good book. Only mentions VE twice in the book when he is trying to example how to calculate airflow rate, he just state that it's volumetric flow rate with no explanation of how to calculate that. Then the glossary. VE - "This is the ratio of the number of molecules of air that actually get into a combustion chamber to the number of molecules in an equal volume at atmosphere pressure. For atmospheric engines, this ratio is almost less than one. Supercharged engines are capable of operating at ratios greater than one."

VE isn't about how the air is packed in the cylinders, it's just a measurement based on it's reference point, chamber maximum volume, rpm, and atmospheric density. It's often used in thermodynamics to determine how much work is produced by the engine, and even it doesn't care how the air is packed in the cylinders.

Maybe you are confusing the fact of off boost the motor is still cranking it's NA VE until the boost is developed.
 

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well, it wasnt in maximum boost but I remember it was a heavy weight, just cant recall who and where.
Anyways, I guess it all comes down to thinking that forcing air through an engine's cylinder head makes the cylinder head-pistons-etc more efficient OR it is modifiying these parts that make it more eficient, perhaps I'm confusing the term but I think everyone would agree that an efficient engine is one that handles best the losses while it works, and forcing air through it doesnt eliminate or reduce (bacause its imposible to totally eliminate) these losses because the "inefficient" shapes of the cylinderhead-pistons-valves-etc are still there.
 

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Discussion Starter · #13 · (Edited)
Motor makes roughly 1/3 of power, 1/3 goes in coolant and conduction, and 1/3 of heat expelled out the exhaust. (Don't quote me on actual fractions)

Turbo car utilizes the exhaust gases to compress air and forces it to the system. So overall efficiency is higher.

There isn't a natural efficiency. There's efficiency that you design it to utilize. Where the shapes of the ports come to play is when the engine isn't utilizing the extra energy input, but one would have to determine if focus in that area is necessary for their application. Boosting air has a different air flow dynamic than ambient air flow, so one would need to design where it fits their application. There isn't one true design that fits all applications.
 

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Please explain the velocity benefits with 1 bar of pressure behind them
Thats more or less how you get more power with an engine without forced induction. I have been quite fascinated about what might happen with over an atmosphere or pressure being forced into the engine.... does the engine realise that it has air being forced into it, or is it just that in reference to the intake manifold we've got a pretty heavy day going on?

What a boost gauge presents is manifold pressure versus ambient air pressure - the boost level is a concept based on what we are used to, the reality is we rarely have "1atmosphere" of ambient pressure anyway.....

I think the way people often look at how air gets into an NA engine might be a bit misleading. The way I look at it, an NA engine doesn't really suck the air into it - it creates an empty chamber and opens a valve and lets the air pressure in cache outside it (inlet manifold) equalise using the new open space. Port, cam, manifold etc design (as you of course know) tunes the way the air can flow through a port into the empty chamber so that it can operate most efficiently under desired situations - taking into account various tricks to keep velocity up etc where applicable.

How does that change when we are talking forced induction? I do know that all the tricks Honda used on their NA VTEC engines to get them breathing really well still apply when turbocharging is brought into the equation... they don't suddenly lose their hp and lbft/l advantages against other motors when the air gets forced into them a bit harder.

To keep this closer to topic, I wouldn't have a clue about the requirement of shrink porting on an RB26 - presumeably if the person porting the head is switched on enough, they would be able to determine what is required of the head and decide what needs to be done to get it to do its job best. Maybe some cases will require shrinking the ports, some may require bringing them out, argueably many may just require the ports to be cleaned up to get rid of bottlenecks.
 

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The real question would be whats the balance between, speed gained in velocity by making the ports smaller and smarter vs the restriction at WOT situations from the ports being smaller?
You cant make the intake work better at all valve lifts and all piston speeds either.
There will be a point where they cross over.
 

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gasoline has an energy content.... so extracting 100% of its energy content per power stroke would mean our engine are 100% efficiency but they aint...


so if you inject 200lbs min of a fuel that has a certain amount of energy yet your car only produce half of that fuels energy cappacity then your at 50% vehicular efficiency... there's no other way to calculate it .....



the amount of air ingested means nothing...... its actually the gasoline that explodes and creates a pressure from the expansion of gas to push the piston down that creates power ... and the more energy extracted by our mixture of air/fuel ... so people overfuel and put bigger turbo's .... but instead we could make more power by having less fuel and more air .... but we would be running dangerously lean......




now if someone can have a way to run high compression + ultra lean charge like diesels then hed have a more efficient design then what he has now ......






normal 87 octane has a 32.0 MJ/L energy content... now convert it into KW/L


fuel molecule has to bind to oxygen molecules..... so if there is more air molecules then fuel molecule wont affect the efficiency ... but might allow to extract the most out of the fuel injected.... but all that fuel need to be mixed in properly + it also need to be atomized perfectly.... wich are obstacle that head porting wont do to increase volumetric efficiency .....
 

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Er, are you trying to say that more power can be made either by using more air & fuel, or by burning the same fuel more efficiently (i.e. there are two ways of getting more power)?

I got a bit lost.
 

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the amount of air ingested means nothing...... its actually the gasoline that explodes and creates a pressure from the expansion of gas to push the piston down that creates power
What ?
So using that analogy, we should just direct inject 100 % fuel only directly into the cylinder ?
 
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