Venturi Port by David Vizard

[juuhanaa]

Sometimes adding material helps more on the dyno and track as on the flow bench .

Yes, well, some ports are just too big. I recall reading on some motorbike site or another that it was noted that an 80s 400cc 4 cylinder bike had similar port sizes to a more modern litre bike. The takeaway was that unless your 400cc bike was making more than 150hp your ports were probably too big

Adding port volume helps too

Is Big = Velocity or Big = volume?

[BLSTIC]

Big referred to volume/diameter in this case.

And yes, high velocity was the authors war cry...

[juuhanaa]

The 2-valve heads have an advantage on combustion, especially the low inclined angle wedge heads. Here the porter get to a combustion preparation guy while the 4-valve porter just optimize velocity in one direction.

I think open chamber stuff and wrong seat angles are cool. Also open chamber with nice transition between bowl, seat and chamber. Anyway, as one superman said: They shouldn't be treated separately.



-juhana

[modok]

If I remember right the David V illustration was a result of flowbench research, and probably FOR something like a crossflow hemi, something valve size limited, where the valve can flow all the way around. Which isn't a very common situation for what most of us are doing. But I still think it has a lot of important ideas. Like I've said before.... how do you define... what the throat is?
What part is the throat in this illustration?

Does it work better in a real engine? I don't know for sure. THo IMO it's at least not worse, and it can work good on a flowbench in the mid lifts.

[juuhanaa]

If I remember right the David V illustration was a result of flowbench research, and probably FOR something like a crossflow hemi, something valve size limited, where the valve can flow all the way around. Which isn't a very common situation for what most of us are doing. But I still think it has a lot of important ideas. Like I've said before.... how do you define... what the throat is?
What part is the throat in this illustration?

Does it work better in a real engine? I don't know for sure. THo IMO it's at least not worse, and it can work good on a flowbench in the mid lifts.

Static flow: Area which has lowest static pressure, but dynamically area which has highest pressure. Its not all about changes in walls, it comes to how that area is utilized by the flow, so pulsed flow and NA vs boosted make also a difference? Just thinking.

[LotusElise]

The takeaway was that unless your 400cc bike was making more than 150hp your ports were probably too big

Yeap. I have a nice example for that too. One of my Kiwi well known guys built a 2-Liter-V8-NA-engine, based on a Synergy V8 engine (Hayabusa heads, custom block and stuff) which put 460 hp@14,600 rpm down the table on the engine bench and he rocked it on Bonneville to a new 2-Liter-NA-Modified record, of course over 200 mph in a Nissan chassis. You may know him and his team, amazing guys with fantastic enthusiasm. I love these guys passion.

This engine need high revs to come to life as the valve area is huge to be able to inhale enough air at high engine speeds as the peak velocity at the port is somewhere sticking and is very hard to push further. Thence increase the valve area is the way to go, but it sacrifice a bunch of torque level down low, which is quite ok for an 5 mile hunter living between dragy shifted gears hunting for more speed along the run on the salt.

My inline 4 engine will never make it to 460 hp as I can't short the stroke not that much to reach out for even lower 12,000 rpm and I can't put in that much valve area to inhale enough above 13,500 rpm. So the physical wall of restrictions of my 2-Liter-I4-NA-engine are below a 100k budget around 380 hp at around 11,000 rpm. Beyond that the effort increases much for a 5 mile hunter engine.

[Desmoguzzi]

If I remember right the David V illustration was a result of flowbench research, and probably FOR something like a crossflow hemi, something valve size limited, where the valve can flow all the way around. Which isn't a very common situation for what most of us are doing. But I still think it has a lot of important ideas. Like I've said before.... how do you define... what the throat is?
What part is the throat in this illustration?

Does it work better in a real engine? I don't know for sure. THo IMO it's at least not worse, and it can work good on a flowbench in the mid lifts.

That's also my questions: how the venturi Port can be applied on line Angel Port with a ssr very close to the valve Seat?

Moreover i would ask if some of you used the DV venturi Port and found real benefits on dyno.

[LotusElise]

Like I've said before.... how do you define... what the throat is?
What part is the throat in this illustration?

Throat is the smallest cross section of the flow path, it defines to a major part how much oxygen can pass per stroke and it is, in most cases, the last chance to accelerate the air to create impulse = mass x velocity before it expands into the chamber. So my point of view of it.

[LotusElise]

Static flow: Area which has lowest static pressure, but dynamically area which has highest pressure. Its not all about changes in walls, it comes to how that area is utilized by the flow, so pulsed flow and NA vs boosted make also a difference? Just thinking.

That's an interesting point. Pulsed flow has a much lower dependency to wall friction as to inertia. A simple experience of that is, if you test headers on mostly straight piping on engine test bench level and go with the optimized dimensions into the chassis, but you need 10 bend to fit it, the results will be almost the same on the rollers. Just because wall friction is way lower affecting losses as the inertia of the gas. The fluid is undergoing a highly dynamic change of its thermodynamic status, that is common knowhow in fluid dynamics for immediate vented high pressure tanks or gas pipes like Nordstream 1 and 2 after the explosion. Same is valid for alternation of load parts. Of course there is a dependency of pressure amplitute height and time scale, but even IM system follow that recognition.

The effect of wall roughness is way lower as the effect of cross section changes. Every change there creates a loss, but if designed right some of the kinetic energy can be converted back in static pressure, which is the one accounting for density in the chamber. Kinetic pressure or impluse is important for the combustion process, but should be not driven to far as density losses will follow that. But as the inhale process is highly dynamic each phase has it own rules: low lift opening, low lift acceleration, low lift to high lift and so on till low lift closing. The last phase need an high impulse which can be reflected at the valve back as a high static pressure to crump as much as air as possible.

So finally the inflow process is connected to all processes before and after. Therefore bench flow port development follows requirements of hole process not just flow numbers. The cylinder head market unfortunately doesn't work like that, if follows straight flow numbers, which is an indicator but says not much about the power output.

At the engine forum I am Admin of we have a nice example regarding port velocity. A head ported by the top dog in drag racing in the K20-scene compared to a stock near head, which get material added in the port (increasing the short turn radius and increasing the length of the high speed section). That top dog head had cuts in the bowl and inflow area as well as on the divider (typical knife edge cut). Of course the top dog head lost everywhere as the flow velocity was too low for a 2-Liter engine, we talk about 7-15 ftlb and peak power was about a handful ponies offset'd. Later on that top dog CNC company released a much smaller port, seems they learned their lesson . BTW, that guy adding material to ports was from Finland. I am sure you will know him, as the scene here and there is too small not to know some essentials.

[juuhanaa]

Static flow: Area which has lowest static pressure, but dynamically area which has highest pressure. Its not all about changes in walls, it comes to how that area is utilized by the flow, so pulsed flow and NA vs boosted make also a difference? Just thinking.

That's an interesting point. Pulsed flow has a much lower dependency to wall friction as to inertia. A simple experience of that is, if you test headers on mostly straight piping on engine test bench level and go with the optimized dimensions into the chassis, but you need 10 bend to fit it, the results will be almost the same on the rollers. Just because wall friction is way lower affecting losses as the inertia of the gas. The fluid is undergoing a highly dynamic change of its thermodynamic status, that is common knowhow in fluid dynamics for immediate vented high pressure tanks or gas pipes like Nordstream 1 and 2 after the explosion. Same is valid for alternation of load parts. Of course there is a dependency of pressure amplitute height and time scale, but even IM system follow that recognition.

The effect of wall roughness is way lower as the effect of cross section changes. Every change there creates a loss, but if designed right some of the kinetic energy can be converted back in static pressure, which is the one accounting for density in the chamber. Kinetic pressure or impluse is important for the combustion process, but should be not driven to far as density losses will follow that. But as the inhale process is highly dynamic each phase has it own rules: low lift opening, low lift acceleration, low lift to high lift and so on till low lift closing. The last phase need an high impulse which can be reflected at the valve back as a high static pressure to crump as much as air as possible.

So finally the inflow process is connected to all processes before and after. Therefore bench flow port development follows requirements of hole process not just flow numbers. The cylinder head market unfortunately doesn't work like that, if follows straight flow numbers, which is an indicator but says not much about the power output.

At the engine forum I am Admin of we have a nice example regarding port velocity. A head ported by the top dog in drag racing in the K20-scene compared to a stock near head, which get material added in the port (increasing the short turn radius and increasing the length of the high speed section). That top dog head had cuts in the bowl and inflow area as well as on the divider (typical knife edge cut). Of course the top dog head lost everywhere as the flow velocity was too low for a 2-Liter engine, we talk about 7-15 ftlb and peak power was about a handful ponies offset'd. Later on that top dog CNC company released a much smaller port, seems they learned their lesson . BTW, that guy adding material to ports was from Finland. I am sure you will know him, as the scene here and there is too small not to know some essentials.

Thank you LotusElite, i appreciate. Yeea, i may like the hole process too much.

Folkrace is a class where we cut some metal to make things fit. As far as headers go, maybe we have done stupid things..

IMG-20210905-WA0012.jpg

[LotusElise]

Yeea, i may like the hole process too much.

If it fit the purpose, way not.

We all like to work on that stuff, it is part of it. How knows the optimum if not experienced the non-optimum? A fast way to optimum causes somewhere else some effort. My first NA engine exceeding the 130 Nm/Liter boarder had 5 years of part time preparation, development software build up, learning the NA engine, designing it, searching parts, deciding where to prototype, building and tuning it. In that time others built 20 engines and my come to another optimum .

Folkrace is a class where we cut some metal to make things fit. As far as headers go, maybe we have done stupid things..

As my wife says, the inner values count. What was the redline and what were the pipe lengths?

[juuhanaa]

As my wife says, the inner values count. What was the redline and what were the pipe lengths?

Info regarding headers can be found at page 19, and it was little scary how it turned out to be.

viewtopic.php?f=15&t=55767&start=270

And here at page 6...

viewtopic.php?f=1&t=50975&p=920577#p920577

thanks,



-juhana

[modok]

Like I've said before.... how do you define... what the throat is?
What part is the throat in this illustration?

Throat is the smallest cross section of the flow path, it defines to a major part how much oxygen can pass per stroke and it is, in most cases, the last chance to accelerate the air to create impulse = mass x velocity before it expands into the chamber. So my point of view of it.

Ok, so to you... throat is MCSA. Fair enough.
IMO if all headporters used drawings we would have advanced a lot faster, clears up a lot of misunderstandings
I've got a 88% throat at the valve seat and a 86% throat slightly upstream in my picture, so, two throats
But anyway, just in my mind the "valve seat throat" is the distance across the 90 degree angle of the valve seat, or at the bottom of the 75 degree if there isn't a 90.
i do agree with David V's book that the valve seat angles do tend to end up very near a radius, not exactly a radius but usually pretty close, and if that is true the valve seat throat% is linked to how tight that radius is. For instance in general a 90% + throat then the radius is too tight and thus you lose flow, or at 85% or less you lose flow because....well, maybe the throat velocity is too high and the air can't make the turn, or I think of it as making the path to the curtain too tight and maybe that's not right, in any case the velocity at high lifts is too high and that does more hurt than the gentler radius helps. but whatever it is... you can find it yourself easy on a flowbench testing valve jobs made of epoxy, and find the same thing he found. Good luck finding anything different but if you do we want to know too.

ONE interesting idea in both these illustrations so far is that this radius does not have to stop at 90 degrees, it can keep going! so then we have like a 105 degree angle upstream of the 90... I would say.
Joe Modello and Kay Sissell and David V all have at ONE time found such a thing improve flow, and so have I, and you might too. But it doesen't always work so maybe situational.

Right near the valve the angles must be concentric to the valve by nature, but as you go farther upstream then less and less so. IMo upstream of the radius of the valve angles it's open season, try whatever.
If you want to accept that the valve seat angles should always be a certain way, always an 88% throat, then you can be more creative elsewhere, decide exactly how to feed that 88% throat most effectively. What heresy!
but hey, maybe, at least an idea to try.
The term -venturi port- has been used to death but in MY mind it means contracting to a smaller size about 1/2 valve diameter upstream of the valve and then expanding out again, what this does is direct the flow at the valve such that the velocity in the center is high but the velocity at the walls is lower. This can allow the flow to go around the radius of the valve seat more efficiently because....., high velocity for the long path following the valve and low velocity for the short path hugging the seat angles. David V's illustration is NOT that, so I think it's not a venturi port, but it is what it is. A venturi port like i described does for sure work, trouble is that it really only works at mid lifts, or at particular lifts. say... with a 88% seat throat and a 86% venturi upstream controlling the airflow onto the back of the valve right you should be able to flow more at .25 lift than if it had just a 86% seat throat, for example. But if looking only at 0.3+ lift(valve size to lift ratio) lift you won't end up with that. but if you focus on .25 or so then it might be the the ticket. And both ways can make power. Look at popular engines, not many are valve limited and use high lifts, does that prove anything? not really, but what is the goal anyway? whatever you want it to be.

Earland Cox years ago did a clean sheet kind of study on ports with slices of tubing, and one thing he found that I thought was very clever was that 'the flow should be aimed at the valve". ok sounds dead simple right? But all real ports are always angled and curved so that can't be maintained at all lifts. The only way for the flow to always be centered on the valve at all lifts was if the port was perfectly straight of course So depending on how things are, sometimes you can use a smaller area just upstream of the valve to aim the flow at it ideally, and other times you can't, with some designs it becomes impractical. Venturis don't really work around curves.

BTW not aimed at anybody in particular and just what i think about remembering that illustration.

[juuhanaa]

Like I've said before.... how do you define... what the throat is?
What part is the throat in this illustration?

Throat is the smallest cross section of the flow path, it defines to a major part how much oxygen can pass per stroke and it is, in most cases, the last chance to accelerate the air to create impulse = mass x velocity before it expands into the chamber. So my point of view of it.

Ok, so to you... throat is MCSA. Fair enough.
IMO if all headporters used drawings we would have advanced a lot faster, clears up a lot of misunderstandings
I've got a 88% throat at the valve seat and a 86% throat slightly upstream in my picture, so, two throats
But anyway, just in my mind the "valve seat throat" is the distance across the 90 degree angle of the valve seat, or at the bottom of the 75 degree if there isn't a 90.
i do agree with David V's book that the valve seat angles do tend to end up very near a radius, not exactly a radius but usually pretty close, and if that is true the valve seat throat% is linked to how tight that radius is. For instance in general a 90% + throat then the radius is too tight and thus you lose flow, or at 85% or less you lose flow because....well, maybe the throat velocity is too high and the air can't make the turn, or I think of it as making the path to the curtain too tight and maybe that's not right, in any case the velocity at high lifts is too high and that does more hurt than the gentler radius helps. but whatever it is... you can find it yourself easy on a flowbench testing valve jobs made of epoxy, and find the same thing he found. Good luck finding anything different but if you do we want to know too.

ONE interesting idea in both these illustrations so far is that this radius does not have to stop at 90 degrees, it can keep going! so then we have like a 105 degree angle upstream of the 90... I would say.
Joe Modello and Kay Sissell and David V all have at ONE time found such a thing improve flow, and so have I, and you might too. But it doesen't always work so maybe situational.

Right near the valve the angles must be concentric to the valve by nature, but as you go farther upstream then less and less so. IMo upstream of the radius of the valve angles it's open season, try whatever.
If you want to accept that the valve seat angles should always be a certain way, always an 88% throat, then you can be more creative elsewhere, decide exactly how to feed that 88% throat most effectively. What heresy!
but hey, maybe, at least an idea to try.
The term -venturi port- has been used to death but in MY mind it means contracting to a smaller size about 1/2 valve diameter upstream of the valve and then expanding out again, what this does is direct the flow at the valve such that the velocity in the center is high but the velocity at the walls is lower. This can allow the flow to go around the radius of the valve seat more efficiently because....., high velocity for the long path following the valve and low velocity for the short path hugging the seat angles. David V's illustration is NOT that, so I think it's not a venturi port, but it is what it is. A venturi port like i described does for sure work, trouble is that it really only works at mid lifts, or at particular lifts. say... with a 88% seat throat and a 86% venturi upstream controlling the airflow onto the back of the valve right you should be able to flow more at .25 lift than if it had just a 86% seat throat, for example. But if looking only at 0.3+ lift(valve size to lift ratio) lift you won't end up with that. but if you focus on .25 or so then it might be the the ticket. And both ways can make power. Look at popular engines, not many are valve limited and use high lifts, does that prove anything? not really, but what is the goal anyway? whatever you want it to be.

Earland Cox years ago did a clean sheet kind of study on ports with slices of tubing, and one thing he found that I thought was very clever was that 'the flow should be aimed at the valve". ok sounds dead simple right? But all real ports are always angled and curved so that can't be maintained at all lifts. The only way for the flow to always be centered on the valve at all lifts was if the port was perfectly straight of course So depending on how things are, sometimes you can use a smaller area just upstream of the valve to aim the flow at it ideally, and other times you can't, with some designs it becomes impractical. Venturis don't really work around curves.

BTW not aimed at anybody in particular and just what i think about remembering that illustration.

Super!

And i was too hard about less than .25 earlier this year for a guy who afterwards helped me personally. My "smallest cam" and old style valves gives me .265 lift to valve ratio.. Just thinking, higher port angle could also limit some cross flow

IMO Sweden guys just make better and nicer racing cars than we here in next door.. That said, i could just cut bonnet and make a box or something for it. I mean if its needs a better fit But think i have to ask couple more detailed questions if i get to that point.

Cheers,



-juhana

[LotusElise]

Just thinking, higher port angle could also limit some cross flow

A higher port angle changes everything. You can run bigger throats and valve sizes to gain the same port efficiency. You remember the example of the I5 Volvo head for BTCC?! Yeah, you do. It changes also the tumble number as the main lever arm to control tumble without complex valve back sides and flaps is the short turn radius flow. The steeper the port the lower the tumble number as the short turn flow increases and counteracts against the bigger brother of above's flow.