Venturi Port by David Vizard

[Desmoguzzi]

Dear All, i'm Reading a book of David Vizard where It Is reported the Blow area shaoed as a venturi (see attachment). Some of you have ever tried such shape? Is really effective? If yes what kind of benefit did you find? Thanks in advance for your comments.

IMG_20220928_230317.jpg

[mt-engines]

IMO there should only be 1 venturi in an intake upstream of the valve.

[digger]

The Venturi shown is the valve seat by looks of the diagram , so looks like fairly normal port nothing new.

I think DM recommendation for max effort is for taper from port entry all the way to valve seat region. This isn’t achievable on many ports though

[gruntguru]

Yes, the venturi port will flow more than a multi-angle port especially at low lift.

[digger]

At low and medium lifts the valve head is part of the Venturi but is not shown

[Desmoguzzi]

Yes, the venturi port will flow more than a multi-angle port especially at low lift.

Dear gruntguru what Is strange to me Is that a venturi Port Will have a Blow/valve ratio greater than 0.9 what Is always recommended tò keep among 9.8/0.9

[LotusElise]

Dear All, i'm Reading a book of David Vizard where It Is reported the Blow area shaoed as a venturi (see attachment).

At what are you explicit pointing at? A Venturi like flow shape many ports (shaping a Vena Contracta) have, as this is the way to convert kinetic pressure into partially back into static pressure. That is integrated into the greater seat (down the seat till the curtain area).

The acceleration into that Venna Contracta is designed differently. A few are that extreme like shown above regarding the part c), but the bowl shaped part, Vizard called it "enlarged throat section", exists even in OEM 4-valve heads sometimes, e.g. VW/Lamborghini V10 and Honda K-series utilize it in some kind to improve low lift. It is integrated below the short turn, when the port finds again a straight section.

I believe the flow bench would see that enlarged throat section differently as the engine, because of the discontinuity of flow of the engine process. Just think about the IVC event, where, especially on NA engines, the oncoming peak amplitude of the pressure wave helps to compress the load before close the chamber. What does that section do? It increases static pressure while impluse is feeding it. That may can have interesting effects the bench don't see because of the continuous flow approach.

Otherwise, some race engine even don't have a proper Venna Contracta design. The 320 hp 2-Liter-NA Audi EA113 based race engine with an 5 valve head did have just a port without a throat, giving that torque curve a very peaky shape. Valve throat ratio was 0.96, which means the seat surface was the only part of the seat design. Worked out fine too .

[juuhanaa]

The 320 hp 2-Liter-NA Audi EA113 based race engine with an 5 valve head did have just a port without a throat, giving that torque curve a very peaky shape. Valve throat ratio was 0.96, which means the seat surface was the only part of the seat design. Worked out fine too .

Well, your example probably already hurt feelings So heres my little story of life

Got my hands on top notch engine, which was build into new block, new everything (Renault F4R it was) I cut that cylinder head into pieces... Now other part of the story is when my trusted machinist redid a valve job for my junk engine. He used a Mira and nice single angle blade. Btw this happened, before i got the nice engine... Anyway

So, i was not thinking to buy a performance valve job, because i was just freshing up that head (Renault F7R). Ironically, i forgot that my trusted machinist used to be a racer! Perfect example about "those" things that are not necessarily pretty, but what is worth to be examined!

IMG_20220929_160501.jpg

-juhana

[juuhanaa]

Dear All, i'm Reading a book of David Vizard where It Is reported the Blow area shaoed as a venturi (see attachment). Some of you have ever tried such shape? Is really effective? If yes what kind of benefit did you find? Thanks in advance for your comments.


IMG_20220928_230317.jpg

Hi Desmoguzzi,

Heres a cylinder head i did for Alfa 156 direct injection engine. Now we have to remember this is an engine with a variable length intake manifold and cam timing, adjustable cam pulleys and fuel lines made from PIPE, and all this came from the factory! Chassy parts made of magnesium and aluminum, and the list goes on... so its a good idea to think what might be the limiting factor, what we are trying to improve and how. We redid the valve job as it came from the factory and i only touched the exhaust port, because it got different headers. It turned out to be a good work mule

overal view.JPG

inlet side view.JPG

exhaust side view.JPG

-juhana

[LotusElise]

Got my hands on top notch engine, which was build into new block, new everything (Renault F4R it was) I cut that cylinder head into pieces... Now other part of the story is when my trusted machinist redid a valve job for my junk engine. He used a Mira and nice single angle blade. Btw this happened, before i got the nice engine... Anyway

So, i was not thinking to buy a performance valve job, because i was just freshing up that head (Renault F7R). Ironically, i forgot that my trusted machinist used to be a racer! Perfect example about "those" things that are not necessarily pretty, but what is worth to be examined!

You mean a valve cutting machine? We use a Mira hand driven cutter with expensive cutters . Anyway, that 5-valve head has only 3 x 28 mm intake valves, thence not much room for entrance and welcome as much as possible O2 molecules. But even less then the 2-Liter 4-valve of Opel (Vauxhall) C20XE with 2 x 35 mm valves used for STW and BTCC.

Theses engines don't relay much on low lift flow and are therefore very peaky in the torque shape, so to say almost peak torque engine speed is equal to peak power engine speed. They run even on the 4-valve heads Valve-Throat-Ratios of 0.92-0.94 and seat width's less than 1 mm. These ports need quite a lot of engine speed to come to life as the transfer of impulse into the chamber is quite engine speed depended on those port designs. The Formula 1, one of the V10 NA engine are I know in a bit more detail, did have a bit lower V/T-ratio at the intake.

[juuhanaa]

Got my hands on top notch engine, which was build into new block, new everything (Renault F4R it was) I cut that cylinder head into pieces... Now other part of the story is when my trusted machinist redid a valve job for my junk engine. He used a Mira and nice single angle blade. Btw this happened, before i got the nice engine... Anyway

So, i was not thinking to buy a performance valve job, because i was just freshing up that head (Renault F7R). Ironically, i forgot that my trusted machinist used to be a racer! Perfect example about "those" things that are not necessarily pretty, but what is worth to be examined!

You mean a valve cutting machine? We use a Mira hand driven cutter with expensive cutters . Anyway, that 5-valve head has only 3 x 28 mm intake valves, thence not much room for entrance and welcome as much as possible O2 molecules. But even less then the 2-Liter 4-valve of Opel (Vauxhall) C20XE with 2 x 35 mm valves used for STW and BTCC.

Theses engines don't relay much on low lift flow and are therefore very peaky in the torque shape, so to say almost peak torque engine speed is equal to peak power engine speed. They run even on the 4-valve heads Valve-Throat-Ratios of 0.92-0.94 and seat width's less than 1 mm. These ports need quite a lot of engine speed to come to life as the transfer of impulse into the chamber is quite engine speed depended on those port designs. The Formula 1, one of the V10 NA engine are I know in a bit more detail, did have a bit lower V/T-ratio at the intake.

Yes my local machine shop uses Mira seat cutting tool (that fancy model press button to concentrate). Here we are talking 5 or 4 valve engines, but my hats off for those 2 valve iron dukes who get it work!

Im by no means an expert, but turning air or heavier fuel especially into the chamber near the valve, i can see in some cases is too late. Port stability and flow separation things to consider when changes in velocities. I have my shop vacuum cleaner now, so i can try fix my old porting work I remember i had to raise idle for some odd reason, but no losses in torq and perhaps peak power carried further. I wouldn't say much based on one or too chassis dyno sheets, but yeah something to keep an eye on. On the other hand F7R engine basis with a stock size valves and 3 angle valve job around 45 sealing and .9 valve to seat ratio ---> friend of mine won his first series this year with a OEM near -setup, which i am really happy about.



-juhana

[juuhanaa]

But even less then the 2-Liter 4-valve of Opel (Vauxhall) C20XE with 2 x 35 mm valves used for STW and BTCC.

My rally car has 2 x 34.5 intake valves and i was thinking reverse flow when i did this chamber work. I also installed a complex 4-2-1 header design with chokes fitted every Y -junction starting from "junction of" cylinder head flange and headers. It remains to be seen.. So far i know it idles really well so fingers crossed!

PrtSc.png

-juhana

[LotusElise]

My rally car has 2 x 34.5 intake valves and i was thinking reverse flow when i did this chamber work. I also installed a complex 4-2-1 header design with chokes fitted every Y -junction starting from "junction of" cylinder head flange and headers. It remains to be seen.. So far i know it idles really well so fingers crossed!

Reverse flow can be an significant source of loss, I know that latest since my valve spring attempt came out to weak . The simple approach would be to use not proper flowing seat, what flows bad in one direction flows likely bad in some kind vice versa. A more smart approach would be using shapes which are seen by incoming flow as nicely but really disgusting from the other side. Or you use an interfering fire . Yeap there are different technologies available, socalled pulsator mergers or what HiTech is using and other stuff to solve that on the exhaust side.

[LotusElise]

Yes my local machine shop uses Mira seat cutting tool (that fancy model press button to concentrate). Here we are talking 5 or 4 valve engines, but my hats off for those 2 valve iron dukes who get it work!

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.

Im by no means an expert, but turning air or heavier fuel especially into the chamber near the valve, i can see in some cases is too late. Port stability and flow separation things to consider when changes in velocities. I have my shop vacuum cleaner now, so i can try fix my old porting work I remember i had to raise idle for some odd reason, but no losses in torq and perhaps peak power carried further. I wouldn't say much based on one or too chassis dyno sheets, but yeah something to keep an eye on. On the other hand F7R engine basis with a stock size valves and 3 angle valve job around 45 sealing and .9 valve to seat ratio ---> friend of mine won his first series this year with a OEM near -setup, which i am really happy about.

Fuel separation is an big issue. Wet flow bench flow working is something which is rare in Europe, not many have done experience in that field, but also tumble flow regimes would profit from some fuel ramping. Just think of if EOI and duty cycle are advanced and long then fuel flow down the short turn and once valve opens that fuel is kind of lost. As I also tune engines I developed approaches to reduce that.
My 310 hp 2-Liter-NA-engine, which utilize 182+ ftlb from 4500-8200 rpm, has just stock ports and adapted valve seats, velocity is the key. Many modify the ports, but as long as you can't use an add and take-approach, velocity get maybe bumpy and low. Sometimes adding material helps more on the dyno and track as on the flow bench .

[BLSTIC]

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