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AIR SPEED

Started by EunUCh , Aug 28 2007 03:49 PM

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#76 _oldjohnno_

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Posted 15 March 2015 - 09:12 PM

Thanks oldjohnno ,"Bernoulli" might have been "onto" something ?

And in this case Henri Coanda.

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#77 EunUCh

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Posted 16 March 2015 - 04:05 PM

Interisting ! if we were to apply the same principle to the long side and around the throat, would we find that not such a large valve throat would be needed ? but given that there are physical restrainsts/shrouding etc. that a slightly larger valve increases the "Coanda"

effect on the short side without the real need to "worry" about the long side so much,and would introducing this effect in the port be

beneficial or detrimental ?

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#78 _oldjohnno_

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Posted 16 March 2015 - 04:58 PM

Interisting ! if we were to apply the same principle to the long side and around the throat, would we find that not such a large valve throat would be needed ? but given that there are physical restrainsts/shrouding etc. that a slightly larger valve increases the "Coanda"

effect on the short side without the real need to "worry" about the long side so much,and would introducing this effect in the port be

beneficial or detrimental ?

The Holden port is a bit of an odd one - by todays standards anyway - because it has such a sharp angle and such a pronounced difference in the lengths of the floor and the roof. Theoretically you shouldn't have to do anything special with the roof because it curves down "into" the flow, so it should be easy to keep it attached. But because the flow near the floor is going so much faster than the flow above it the upper layers are already turbulent before the roof starts to sweep down. It's hard to get it calmed down enough to manage it and some of the things that are commonly done - like widening the roof to square up the port and make it look nice - are exactly the wrong thing to do.

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#79 EunUCh

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Posted 16 March 2015 - 06:10 PM

Very interisting stuff , so cyclones or part thereof play an important part in life after all :dontknow:

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#80 EunUCh

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Posted 17 March 2015 - 03:34 PM

b2.jpg 39.52K 1 downloads b4.jpg 33K 1 downloads

large radius/smaller radius

Obviously a bit different on an engine with a valve in there,but considering the wing and the theoretical increase in speed over the top!

Do we liken the air speed to that close to the center of the eye of a cyclone where the low pressure is and expect the high pressure area of air to tend to follow,up to a point?

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#81 _uctorry_

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Posted 17 March 2015 - 05:37 PM

great thread guys learning a lot here

stupid question .. so vl vn group a manifold with the longer runners or trumpets help speed up the air ????

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#82 _Bomber Watson_

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Posted 17 March 2015 - 05:54 PM

No the VL/VN grp A mani misses two cylinders and directs half the air and fuel to four spots somewhere around the passenger side front guard for no known reason.

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#83 _uctorry_

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Posted 17 March 2015 - 06:20 PM

mmm k I think lols

so as a manifold they are no good ???

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#84 _Bomber Watson_

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Posted 17 March 2015 - 06:30 PM

For a six, no.

dont know what everyone raves on about them so much for.

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#85 _oldjohnno_

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Posted 17 March 2015 - 07:23 PM

Don't get fixated on or distracted by airspeed too much. With our old engines the main thing is just to get every damn gram of air we can into the engine.

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#86 _duggan208_

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Posted 17 March 2015 - 10:57 PM

I've allways wondered that if you fill the floor of the port at the opening just a couple of mm to match the roof if it would be effective and even raise the roof a little higher, so that the port opening is higher, sort of like the Ford XD,E alloy head.

regards

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#87 rodomo

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Posted 17 March 2015 - 11:28 PM

9 port or 12 port? Work better on a 12 port I'd reckon?

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#88 N/A-PWR

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Posted 18 March 2015 - 03:01 AM

As some names were used to describe the port,

here is a short turn or long side diagram:-

http://en.wikipedia....er_head_porting

and this yellow picture is close to what the little six head port would look like:-

So now I am understanding more about the terminology's.

Edited by NA-PWR, 18 March 2015 - 03:06 AM.

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#89 _oldjohnno_

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Posted 18 March 2015 - 05:55 AM

I've allways wondered that if you fill the floor of the port at the opening just a couple of mm to match the roof if it would be effective and even raise the roof a little higher, so that the port opening is higher, sort of like the Ford XD,E alloy head.

regards

I've spent many happy (?) hours with a tin of bog and a die grinder testing things just like that. As is typical for a 12 port, it doesn't behave as you'd expect. They really are an odd port (not necessarily bad, just odd) and the only thing I've seen that's similar is the old small block Chrysler intake port. They have nothing at all in common with ports that look superficially similar eg. SBC.

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#90 EunUCh

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Posted 18 March 2015 - 06:04 PM

I think i "see" why leaving the roof/guide boss area alone might affect things in conjunction with the short turn radius would upset things a bit ?

Bit more happening in there than meets the eye?

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#91 _duggan208_

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Posted 18 March 2015 - 11:12 PM

The diagram above is what i'm trying to describe, the yellow path, trying to lessen that nasty abrupt turn into the bowl area by raising up the mouth of the port. The blue path is just like my Duggan, downdrafted port design. The floor on the 9 port seems to angle up hill, making the nasty turn even tighter.

regards

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#92 _Agent 34_

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Posted 21 March 2015 - 05:39 AM

I have started to re-read " steve vizards " book again last night on " how to port " or how to build horse power ( I have both) there is so much info in this book it will make your head spin in this area.

A bit off topic but worth the throw in, the book talks about scavenging of the cylinder is just as important but this is directly related to LSA ( lobe separation angle) which leads to exhaust tune lenght !

This book also talks about air speed in detail and what it goes onto say is that just make the runner wide (larger ) and then putting a bigger valve will not necessarily give you a efficient combustion chamber.

but i feel that you all know this, but get the book it worth the read.

there is another whole threat on LSA angle and " filling the cylinder " once i have scanned the pages will upload and start a topic for discussions.

Edited by Agent 34, 21 March 2015 - 05:40 AM.

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#93 _oldjohnno_

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Posted 21 March 2015 - 07:25 AM

I bought and read a few books on porting, including Vizards. I don't think any of them really explain the fundamentals in a really useful way, especially to someone new to porting and flow testing. Of all the "hotrod" books I read Harold Bettes (VP of Superflow) Engine Airflow would be the best I think.

Once you have enough experience to be able to improve ports consistently you realize that a lot of what's in the books is just padding or filler, and that no matter what port or runner design you are working on you follow the same basic principles every time. And these have just two or three aims and could be described in a few pages. I'm not saying you shouldn't read the "hotrod" books but there's generally a lot more quality information in the generic flow dynamics texts.

Something I would highly recommend is searching for CFD images - eg. google "CFD intake port". These show graphically the flow paths, pressure, velocity etc. in a way that is infinitely more understandable than pages of text. And if a picture is worth a thousand words an animation is worth a billion. Animated CFD GIFS of finite pressure wave activity in ports are an eye-opener.

Everyone likes to think that they know what it takes to make air flow - I know I did. Until of course you buy or build your first flowbench, at which point you suddenly learn that most of what you've been doing is either wrong or a waste of time.

Edited by oldjohnno, 21 March 2015 - 07:31 AM.

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#94 EunUCh

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Posted 22 March 2015 - 07:30 PM

Maybe the "upturn" on the floor is there for a reason,considering the way the ports are configured and which way the stream needs to go into the chamber ? ...9 port...12 port is not much different.

Maybe the downturn on the roof is there for a reason considering the valve and low side/valve/chamber relationship configuration?

dunno,interesting though.

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#95 _oldjohnno_

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Posted 22 March 2015 - 08:52 PM

The floor on the 9 port seems to angle up hill, making the nasty turn even tighter.

Maybe the "upturn" on the floor is there for a reason,considering the way the ports are configured and which way the stream needs to go into the chamber ? ...9 port...12 port is not much different.

Maybe the downturn on the roof is there for a reason considering the valve and low side/valve/chamber relationship configuration?

dunno,interesting though.

You're onto it. When is an 80 degree port angle better than one at 90 degrees? When it allows you to use a larger short turn radius, which in turn allows the flow to stay attached to a higher speed. Those "lump port" inserts are the same - looked at from a port angle perspective they do the "wrong" thing but by making the short side radius effectively longer they provide a net gain.

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#96 _oldjohnno_

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Posted 23 March 2015 - 01:37 PM

Here's something else about airflow that isn't always apparent - the walls of a port don't usually have much in common with the path that the flow takes unless the port is just a straight tube. One way to think of it is to imagine the port as being a racetrack and the port walls as being the Armco on each side. The fence doesn't dictate the line that the cars take, it just sets the limits as to where the cars can go. The majority of cars - at least the fast ones - will all be taking much the same line and on the other areas of the track there won't be much happening at all. And the shape of the racing line may be completely different to the shape of the fenceline.

It's the same with airflow; the vast majority of the mass of air will be taking a path that may be less than half of the ports height/width. If air particles were cars and the port was a racetrack there'd be a continuous stream of fast moving cars on the racing line. There'd be cars on the other parts of the track too but they'd be further apart, moving much slower and less orderly. Some would be spinning out, some moving backwards and all the chaos would severely limit the flow of traffic in these areas. That's what turbulence would look like.

You could make the cars that are on the racing line go faster in order to increase the traffic flow, but eventually you'd get the point where the cars become detached from the track in the corners (flow detachment) and they too start to spin out and slow the traffic (turbulence). You'd try to fix this by making the radius of the corner larger and making the changes in track angle of direction stay within certain limits.

I guess the point I'm trying to make is that you can't expect to alter airflow in a port by moving walls any more than you'd expect to change the course of cars by moving a fence. The only time it really has a big effect is when the flow is hugging that wall - or the racing line is hard against the fence. Once you understand this you'll understand why the port doesn't care a whole lot about what you do with 3 of the 4 port sides but reacts strongly to changes in the 4th side.

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#97 _Bomber Watson_

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Posted 23 March 2015 - 02:00 PM

That is probably the clearest explanation i have ever read.

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#98 _oldjohnno_

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Posted 23 March 2015 - 02:17 PM

Thanks Bomber.

Anyone who's messed with BBC's knows that the intake ports have some odd kinks in them (that the flow mainly ignores). There's a story about Keith Duckworth, who on being shown a BBC head, suggested that the factory cast arrows into the floor "so the air will know which way to go"...