Honda Power Unit Hardware & Software

[godlameroso]

You could have just said miller/Atkinson cycle is on the intake valves, but the whole condescension works too I guess.

Don't pay attention to much you say, afterall you were completely wrong about intake port dimples making power. Like completely and utterly wrong

[PlatinumZealot]

Why would it?

Because the exhaust valves are partially held open during combustion, instead of the normal combustion cycle which has the exhaust valve fully closed during combustion. This allows the valve face to absorb the combustion heat and radiate it directly to the cylinder head. If you hold the valve open and allow combustion gas to escape you don't get this direct combustion heat convection to the head, forcing the valve guide to handle the task on its own. Perhaps with different materials and engineering this issue can be largely avoided.

I'm sorry to be blunt but that's complete and utter rubbish.
First of all Miller cycle is all about the inlet valve timing (late closing typically). Why would the exhaust valve even be open during combustion ? That is just plain nonsense.

Secondly, you don't really seem to understand what the different heat transfer mechanisms are and how they work.
First, you say "This allows the valve face to absorb the combustion heat and radiate it directly to the cylinder head."
There is no such thing as valve radiating heat to the head. The heat transfer mechanism between valve, valve seat and head is conduction. The heat transfer mechanism between valve and guide is also conduction.

Then you say " If you hold the valve open and allow combustion gas to escape you don't get this direct combustion heat convection to the head, forcing the valve guide to handle the task on its own."
The primary heat transfer mechanism between the combustion gases and any part they come into contact with is convection. If the exhaust valve would actually stay open during combustion (it doesn't though!) the convective heat transfer would actually increase (there is flow across the valve and the heat transfer coefficient is a function of Reynold's number). Either way, there is a convective heat load on any surface in direct contact with combustion gases, regardless of whether the exhaust valve is open or closed.

And finally, exhaust valves in these highly boosted engines are guaranteed to have sodium filled stems. In such case the heat transfer along the valve stem is greatly increased and hence heat input into the valve guide is also high compared to a conventional engine. Luckily water cooled valve guides have been in use since around WW2.

Radiattion is considerable in combustion though. It really is. Thats one of the things i remember i had to calculate for when i was in school long ago.
Something with radiation length.. And emissivity of soot particles... Anyway.. Radiation is considerable.

[63l8qrrfy6]

You could have just said miller/Atkinson cycle is on the intake valves, but the whole condescension works too I guess.

Or you could have just googled it before posting and spared us all.

Don't pay attention to much you say, afterall you were completely wrong about intake port dimples making power. Like completely and utterly wrong

I have never said anything about port dimples. I assume you are talking about this discussion:
viewtopic.php?f=4&t=28447&start=15

It was gruntguru who contradicted you and I think he is right to do so.

[63l8qrrfy6]

Radiattion is considerable in combustion though. It really is. Thats one of the things i remember i had to calculate for when i was in school long ago.
Something with radiation length.. And emissivity of soot particles... Anyway.. Radiation is considerable.

Not in SI engines though. Have a look here:
http://web.mit.edu/2.61/www/Lecture%20n ... transf.pdf
Even in a diesel it is only 20% of total heat transfer.

Either way, he said radiation heat transfer between valve and head. The only heat transfer mechanism between valve and head is conduction regardless of engine.

[PlatinumZealot]

Radiattion is considerable in combustion though. It really is. Thats one of the things i remember i had to calculate for when i was in school long ago.
Something with radiation length.. And emissivity of soot particles... Anyway.. Radiation is considerable.

Not in SI engines though. Have a look here:
http://web.mit.edu/2.61/www/Lecture%20n ... transf.pdf
Even in a diesel it is only 20% of total heat transfer.

Either way, he said radiation heat transfer between valve and head. The only heat transfer mechanism between valve and head is conduction regardless of engine.

Recent studies suggest that soot radiation is not the major cause of heat loss by radiation but molecular radiation. This is new to me I admit. Anyway, this has caused researchers to take a second look at spark ignition engines which should have even higher molecular radiation since there is less shadowing from soot. The figure I am seeing is approximately 10% which is quite significant!

I remember reading tuner magazines about people polishing the combustion chambers to a mirror finish... It might actually have made sense looking back on it.

[Rodak]

Recent studies suggest that soot radiation is not the major cause of heat loss by radiation but molecular radiation.

What are you talking about?

[godlameroso]

You could have just said miller/Atkinson cycle is on the intake valves, but the whole condescension works too I guess.

Or you could have just googled it before posting and spared us all.

Don't pay attention to much you say, afterall you were completely wrong about intake port dimples making power. Like completely and utterly wrong

I have never said anything about port dimples. I assume you are talking about this discussion:
viewtopic.php?f=4&t=28447&start=15

It was gruntguru who contradicted you and I think he is right to do so.

The real world trumps all theoretical arguments. Port and polish jobs are just better with dimpled intake ports and some other modifications. It's been proven countless times, the drag strip and dyno doesn't lie.

Google is for cowards. I rather be wrong.

[godlameroso]

Recent studies suggest that soot radiation is not the major cause of heat loss by radiation but molecular radiation.

What are you talking about?

Fuel kinetics, the heat loss and heat release is due to free radicals decaying. Free radical propagation is the real cause of combustion, the ionization of fuel by the spark plug breaks hydrocarbon bonds and releases free radicals which bond with carbon and release energy in the process. The benefit of air is that it can be compressed increasing the statistical probability of the correct free radical compounds to be released by the spark within the A/F mixture.

[63l8qrrfy6]

You could have just said miller/Atkinson cycle is on the intake valves, but the whole condescension works too I guess.

Or you could have just googled it before posting and spared us all.

Don't pay attention to much you say, afterall you were completely wrong about intake port dimples making power. Like completely and utterly wrong

I have never said anything about port dimples. I assume you are talking about this discussion:
viewtopic.php?f=4&t=28447&start=15

It was gruntguru who contradicted you and I think he is right to do so.

The real world trumps all theoretical arguments. Port and polish jobs are just better with dimpled intake ports and some other modifications. It's been proven countless times, the drag strip and dyno doesn't lie.

Google is for cowards. I rather be wrong.

I the real world F1 engines and any serious racing engines do not have dimpled ports.

Well, you are wrong but I would rather you weren't so that we could have constructive discussions.

[godlameroso]

Or you could have just googled it before posting and spared us all.



I have never said anything about port dimples. I assume you are talking about this discussion:
viewtopic.php?f=4&t=28447&start=15

It was gruntguru who contradicted you and I think he is right to do so.

The real world trumps all theoretical arguments. Port and polish jobs are just better with dimpled intake ports and some other modifications. It's been proven countless times, the drag strip and dyno doesn't lie.

Google is for cowards. I rather be wrong.

I the real world F1 engines and any serious racing engines do not have dimpled ports.

Well, you are wrong but I would rather you weren't so that we could have constructive discussions.

Then they're missing out, because they work.

I assume they use solid valve trains in F1, where the camshaft acts directly on a rocker arm that pushes down on the valve. I wonder if anyone thought about using hydraulic lifters, probably not, probably too many issues, both legal and mechanical.

[Rodak]

The benefit of air is that it can be compressed increasing the statistical probability of the correct free radical compounds to be released by the spark within the A/F mixture.

Okay, I see where you are going with energy release, but the 'statistical probability' from increased density increases all the probable reactions. How would that preferentially affect the desired ('correct') reactions?

[trinidefender]

The real world trumps all theoretical arguments. Port and polish jobs are just better with dimpled intake ports and some other modifications. It's been proven countless times, the drag strip and dyno doesn't lie.

Google is for cowards. I rather be wrong.

I the real world F1 engines and any serious racing engines do not have dimpled ports.

Well, you are wrong but I would rather you weren't so that we could have constructive discussions.

Then they're missing out, because they work.

I assume they use solid valve trains in F1, where the camshaft acts directly on a rocker arm that pushes down on the valve. I wonder if anyone thought about using hydraulic lifters, probably not, probably too many issues, both legal and mechanical.

You should probably take the time to read what people write more carefully and actually comprehend what they were trying to say. Here is what GG said;

A well designed port does not need dimples (ever seen dimples in an F1 port?).

Furthermore, in a port, dimples would not be the most appropriate method to initiate a turbulent boundary layer (which is what the dimples do). The flow orientation in a port is known unlike a golf ball which is (spinning) constantly presenting a different face to the flow direction.

From what I can tell, GG is not saying that dimples can't and won't achieve a power increase over a badly or cheaply designed port (which when done for mass production is the case 99% of the time). He is simply saying that it is not the most optimal way of introducing a turbulent boundary layer.

If you take a generic road car engine and are tuning it, sure adding dimples will work to add to a port and polish job. However almost no person or tuning shop has the CFD and bench equipment capable to design the most optimal design which will use some other shape. I.e. A generic dimples shape that is known to work is used.

[godlameroso]

There are engines which are already highly tuned from the factory. Engines which are notoriously difficult at extracting more power without resorting to forced induction. These engines already have heads that flow ungodly amounts of air. Even porting and polishing them, or using ITBs makes little if any gains. Mostly limited to the midrange. Yet time and time again significantly more power is made by dimpling the intake ports. Even a rough job done by hand, no CNC, made power everywhere.

I've seen it happen too many times to call it a coincidence.

[godlameroso]

The benefit of air is that it can be compressed increasing the statistical probability of the correct free radical compounds to be released by the spark within the A/F mixture.

Okay, I see where you are going with energy release, but the 'statistical probability' from increased density increases all the probable reactions. How would that preferentially affect the desired ('correct') reactions?

That's where fuel chemistry comes in. It's why fuel is so important to these power units. And why the fuel is developed in tandem with the engine.

[Snorked]

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