I can not tell you how much I am enjoying your videos, the opportunity to experience "Data" rather than "tribal knowledge" and the experience of 60 something years is something we would all be foolish to ignore. I look forward to every video and have told all my gearhead friends about your site and never miss an opportunity to like them. Thank you and keep it coming. Please.
@frankromero404810 ай бұрын
I started Drag Racing in 1967... David Vizard's books were my Bibles back then... I'm very glad to see that you're still at it... I'm 73 years old now...I'm still at it too... I've only been building High Performance Harley Engines for the last 20 years... I stopped building automotive, diesel and marine engines back then... CrazyHorse Speed Shop NJ
@tayloralvidrez434210 ай бұрын
High performance Harley... That's an oxymoron
@eddiesheeran57919 ай бұрын
This is literally a free engineering-level course in cylinder head flow dynamics. Thank you for making & sharing this!
@TheDrAkira Жыл бұрын
I took a full course on engine tunning for racing a few years ago and I'm proud to know that my professor explained to us the same as this great man here. This channel is Gold. So many people talking nonsense nowadays, but this man is great!
@UrbanHarvesting Жыл бұрын
Hands down the best book I have ever purchased, cover to cover gold. My 1st port job was after reading your book port & flow test the engine was a dirt speedway ford 6cyl 250ci crossflow for Australia. The car won everything it was entered into for 2 years on the same build until I built a competitor car motor, the 1st race they were both in 1 x new 1 x refreshed they ended up 0.3 apart over the finish line and 3/4 lap ahead of the field. I have always wanted to thank you for all the shared information you have learnt in your many decades of building/racing and shared with the greater racing/engineering community. I have recommended and quoted you many times since, only just found you today on KZbin. Wish you were in Australia I would gladly work for you as a learning experience Looking forward to the next videos in the series Thank you David for sharing
@rodrigograss3580 Жыл бұрын
David, Thank you so much for sharing your knowledge. It is greatly, greatly appreciated. No amount of thanks would suffice I think, but rest assured i'll at least help share your insights with others.
@fernandohood5542 Жыл бұрын
A Guru breaking it all down for you free of cost.
@qoinsmartme1244Ай бұрын
Respect to those that share their acquired skills and knowledge, which most definitely includes you David, Thank you. Had to reply to the malicious keyboard warrior previously, who, I believe is stuck in a world of hate. In reply, today we have an exponential volume of knowledge, led by Dr Google, good bad and indifferent. However principles remain constant and are enduring. Remember over a century ago twin cams, multi valves etc were already being manufactured. In the US mass produced car engines didn't reach a hp per ci till mid 50's. The evolution of fuel, alloys, man made fibres, casting techniques, machining and most of all, in recent times, silicon (as in computing) have revolutionised our world including automotive engineering. I will put my faith in a human being that has honed (punn intended) his skills over half a century and is prepared to share them. Thanks again David.
@mikedearman9630 Жыл бұрын
You wrote your first book 7 years before I was born!! Outstanding, love this. Like watching my old chemistry teacher talk about machining. Thank you!!
@rondye9398 Жыл бұрын
Smoky Yunick claimed the point of greatest restriction is at the valve. So valve/seat angles and the 1 inch above the valve is where to find the power. Of couse much work has been done since he was in the game. I have great esteem for David Vizard and Smokey Yunick.
@johnfairchild3421 Жыл бұрын
Smokey done. Almost genius work
@exploranator Жыл бұрын
Learning more than I knew existed for decades in head flow and porting!
@ferrellvance5565 Жыл бұрын
what a great Wizard, I am a retired 71 years old, and just got inspired after watching this genius give us his lifelong experiences, I just tore my engine down, sent it to the machine shop for my first major rebuild and blueprinting I will be doing myself, thank you sir for all you do, the world could use more gentlemen like you!
@martinfahrni5677 Жыл бұрын
Born in 68 I love your knowledge, churning these lectures like candy, probably never gonna build another small block again, but you are feeding my dreams
@bravohomie Жыл бұрын
It's never too late bro
@TheFarCobra Жыл бұрын
My friend Corky Bell once described David as the best combination of a genius and a practical man.
@johnfairchild3421 Жыл бұрын
He is a Gearhead lol
@billnlori3149 Жыл бұрын
Great info here. DV is a gold mine!!
@captainsledge75548 ай бұрын
Usually I skip over old timers, because some of the guys I've met or watched haven't the slightest clue how things actually work. They just have their ideas and theories. That may have won at the local sportsdrome lol but in today's engines they are lost. "Too many wires blahhh" lol There's still old guys saying 305 heads on a 350 is the way to go. (It's not, you lose so much cfm flow in the runners it's crazy) Then u have those guys who say they tried vortec heads on a sbc. They're junk. I ask em which cast it was. They said it came off a 90 Chevy truck. 😂😂😂 bro that's swirl port. Worst possible head out there. They think the center bolt valve covers automatically mean vortec heads 😂😂 Anyways My point was... this old timer right here knows some shit and I like his channel already. Subscribed.
@goodboyringo971611 ай бұрын
Hi David I just came across this video and found out about your daughter Jacque's passing. Once learning of your beautiful daughter, I need to give my condolences to you and your wife. I read about how she was an engine builder and what a great soul she had. So I just wanted to say that I feel your sadness for her. She is in good hands with our great Lord Jesus Christ !
@michaeltruscott9443 Жыл бұрын
If only these shows were not available in the 80's man do I wish they had been what an incredible amount of dyno time you have outstanding job ol man
@arealassassin Жыл бұрын
They had these things called books back then; one read them, and applied the information gained to the problem. I have as many of the greats as I can get my hands on- Smokey Yunick, Phil Irving, David of course, Carroll Smith...etc. Nowadays people watch something on YT and consider themselves instant experts. This video does nothing more than reinforce the concepts David was writing about decades ago, as he says.
@9psi Жыл бұрын
Very interesting. Especially as back in the day we just used to just port match to the manifold and kid ourselves we were making more powa
@timothyjudsontaylorofficia97869 ай бұрын
When a legend of performance speaks, it is wise to listen.
@KJs5818 ай бұрын
Wow, got so many of your books, the Mini one, and HP books "performance with economy" - from what, 40 years ago???? I learned so much from those books, and it helped so much. Good to see such a legend on here.
@stephenrocque84589 ай бұрын
I saw your KZbin videos - excellent work ...I have some of your original books from the 1960s and 1970s Keep on going Mr. Vizard
@josephrobinson88948 ай бұрын
I’ve been watching your videos this week and have learned so much, your teaching is so spot on. Thanks so much for your instructions 👍🏻👍🏻👍🏻
@kylehill4887 Жыл бұрын
your a loved man David vizard many thousands.... we appreciate you and all you do
@EdBoi18 Жыл бұрын
Pretty educational stuff here. My takeaway is that any work done further up in the port should probably be to provide enough of a straight shot to the valve to utilize more of the "shrouded" short side and reduce turbulent flow up until the air gets to the valve seat and beyond, at which point, inducing turbulence and mixture motion will hopefully even out any pockets of rich a/f mixture and contribute to a quicker/more complete burn.
@DavidVizard Жыл бұрын
Intake ports are totally turbulent from idle up. There is no getting rid of it!
@turbotrana Жыл бұрын
I am surprised David has only got 15000 subs. In a hundred years time this will be the only record of this type of knowledge.
@vikenlink Жыл бұрын
It won’t matter in a hundred years…. One of two things will happen. 1 …No more internal combustion engines will be in service due to technological advances and or 2- no human beings left alive to talk about it because we ported our heads out of existence over oil….destroying any chance of survival by killing our planet 🌎
@vikenlink Жыл бұрын
Sometimes it’s better not to make any comments…. Too many sensitive people out there trying to learn how to port cylinder heads. Fact is every cylinder head is different, every performance engine build is different. Porting cylinder heads is just the tip of the iceberg for horsepower and torque. What’s your compression ratio? What’s the displacement of your engine? Are you running headers and what size? Are you running a performance camshaft and what’s the duration? Are you running a aftermarket intake manifold… which one? Where do you want your power curve for 99% of the performance fans that drive street cars .You can port a cylinder head to perfection and then use the wrong size camshaft or wrong intake manifold because the one you bought looks cool…. But what ever you gained porting and contouring your intake and exhaust ports was lost because you used a bad combination like a sheet metal intake with short runners and a cam that wouldn’t idle below 1000 rpm’s . Great I got 650 hp peak at 7000 rpm’s. But lost 60 foot pounds of torque and 50 hp where I’d prefer to be enjoying it … 2000-6000rpm Headers without considering the primary diameter for your engine displacement and static compression ratio. Lots to consider when diving into a project.
@theoldbigmoose Жыл бұрын
Excellent CFD visualization David, thank you!
@RichieCat4223 Жыл бұрын
I would like to have seen a before and after picture of that 91% valve seat done on an actual cylinder head to get a better understanding of the theory.
@1967davethewave Жыл бұрын
Excellent!!! I have been "amateur" porting for many years but have kept it simple as not to cause more harm than good. Having the exact contours and a base measurement to shoot for is a really big help in taking my porting to the next level.
@carlosabreu9227 ай бұрын
#1 of the 5 COMMANDMENTS from David Vizard's porting heads! A true Genius "Number$ don't lie, BS does and also walks (takes a hick)"
@alessandroghizzo972 Жыл бұрын
Always the best resource for serious tech info
@stealthynoodle27079 ай бұрын
I've had so many questions recently about 4-stroke engines after doing a fair bit of research on 2-stroke engines in terms of performance and flow efficiency, while it's definitely alot to take in this video delivered well beyond my expectations and already answered alot of questions I had regarding improving said efficiency and flow. Thank you so much for this, I cannot wait to learn more through your videos
@landonthompson5604 Жыл бұрын
Thank you David for the information and direction to improve my knowledge and skills needed to be successful in creating a cylinder head that will improve the overall performance of my project engine. You're a lifesaver and I mean this sincerely, thank you!
@donmilani129 Жыл бұрын
Excellent information and explanations what works and why, instead of just hogging out ports especially in a vortec style head
@annebrown4337 Жыл бұрын
Thank you for the nice lesson.
@thijs728 Жыл бұрын
This is owesome oldskool stuff presentation. Just love it
@peterschofield739 Жыл бұрын
Dave, I did the rule 3 calculation of the weight of air in an average school gymnasium... i came up with 1.6228 tons.
@jamesandannschmitt6835 Жыл бұрын
Thank you David.
@lautburns4829 Жыл бұрын
Thanks again David. ✋🏻👍
@flyingdebree3094 Жыл бұрын
Love how you explain things
@ryanbackstrand Жыл бұрын
Love these videos, but I always change the playback speed to 1.25x
@d.thorpe2046 Жыл бұрын
I wish youtube would go above 2.0x sometimes.
@tonymottram1396 Жыл бұрын
Thanks for the video I really appreciate your time in showing me this.
@Tsxmichael Жыл бұрын
Im very proud of my self to figure this out my self! And see how right i was on my project watching this video now 😌
@nathanbopp6163 Жыл бұрын
Great to get this technical education on KZbin👨🎓🎓🎓🎓🎓👨🎓
@edsmachine93 Жыл бұрын
Thank you David. I really appreciate these videos. Thank you for sharing your time and expertise. Have a good day Sir. Take care, Ed..
@samupk Жыл бұрын
I wish i would had this kind of info around 2004 when i was building CA18DET and RB26DETT engines in my carage shed :D Would have been much more than 408hp from the CA and hell of a lot more from the RB... Well, i guess today its more like plug and play tuning for youngsters with addon parts only.
@Kryndon64 Жыл бұрын
I don't have access to proper tools so I wasn't comfortable with messing the the valve seats on my RB20DE Neo, but what I did do is polish the comb chambers up to 2000 grit completely smooth and also took off material off the short side to help with tumble. Additionally I smoothed out 95% of the entire intake plenum which should help a tiny bit as I did not like the casting on the inside. I just wish I had a proper dremel and bits so I could have gone deeper and more precise. Also lapped the valves which ended up really nice.
@michaelosborne513 Жыл бұрын
Again thank you for videos God bless you sir.
@KerbsideClassics8 ай бұрын
Great channel old school tuning legend
@SteveWright-oy8ky5 ай бұрын
Thanks David for your tutorials as they are very informative .! I Have an issue with the LOUD MUSIC playing while trying to listen to you ! I have TINNITUS , ( ringing in the ear ) and between trying to hear you over the MUSIC and the EAR RINGING is extremely hard to do ! If you could cut the MUSIC VOLUMN by 50 % , it would be much better for anyone trying to concentrate on your talks . The content of your tutorials are far more important than the background music and that is why we're here listening to you ! Thank you again !
@ElvinLeadfoot2 ай бұрын
Harking back and watching once again..
@anthonymilano691 Жыл бұрын
When porting the cylinder head one should note concentrating on having the highest port flow average rather than peak, and know that it’s just part of the equation
@user-id9ft8qv4x Жыл бұрын
Thanks for knowledge!
@YerkitRacingChannel Жыл бұрын
Thanks for sharing the illustrations! With the cfm from the cutouts in mind makes you wonder if it's worth touching the rest of the runner lol. Would be interesting to see something similar on a stock casting for comparison
@bullitautorepairsmobile4989Ай бұрын
Are you the same David vizard of Mini Cooper fame, I bought your mini book years ago forgot the name,but I remwmber the lotos engine on a mini gearbox, I even moved my clocks t o put a 45 Weber on my mini 1275,reborded it out to 1330 if I remember correctly but the battery box in the dash good old days building my 1275 gt clubman .i remember now how to modify mini,by David Vizard ,definitely a new subscriber,
@diesdasa Жыл бұрын
Thank you David Vizard!
@richardmoerke9329 Жыл бұрын
I can’t wait till then. That’s was a great job .
@mikemoore5929 Жыл бұрын
David Vizard was th einspiration for my career in modifying cars and engines . I bought '' How to modify your Mini '' in the seventies . What alegend !
@herseem Жыл бұрын
I got his 'A' series engine book. It's encyclopaedic. I spent a fortune modifying my allegro estate, and it was all worth it
@fraud3647 Жыл бұрын
Always learning something new when listen him unique knowledge how to modify ports, seats, valves and chamber. Probably he is one off the best headmaster what I know.
@clarkmcmahan1595 Жыл бұрын
Sure wished you had finished by your explanation on areas of efficiencies of the seat .can't wait to see how this works out ..
@bcbloc02 Жыл бұрын
I would love to see a series on home building flow benches. I am about to get a shop vac and a manometer and go to town testing!
@billshiff2060 Жыл бұрын
Built several. If I did it again I'd consider a leaf blower or 2. The best is a roots blower.
@spleno1 Жыл бұрын
Love the great information your making available for the public. You're being a true gentleman. Unfortunately when describing the seat angle, your hand was blocking all the important pick work you were demonstrating! Also we want more on polyquad heads. Who still drives boring old 2 valve heads?
@raymondguzman5083 Жыл бұрын
Lmao i drive 2 valve heads and tons of other people do as well
@freshkryp69 Жыл бұрын
Back in the 90's, when 'Roadsters' was the end all be all website/hub for performance companies it lead me to Vizard! He's a badass dude! I printed out all the 'Performance Professor' articles! Felt guilty I didnt have to pay for them! Best freebees ive ever got pertaining to race engine!~
@BigEsGarage Жыл бұрын
The minuet I saw the lightning I hit the subscribe button, like. This has to be good!!
@danieldonahue3293 Жыл бұрын
Great science-based info ...thanks for posting !
@jasonbirch1182 Жыл бұрын
Good info but I'd like to see what a non race prepped head does in that computational simulation and how much cleaning up the sharp edges from cast to machined accomplishes. Showing where a restriction in a fully prepped head is doesn't tell me much about the garbage I want to improve.
@nathanbopp6163 Жыл бұрын
Sharp edges will crack easier than rounded edges.
@alleyoop1234 Жыл бұрын
Have patience, I'm sure he'll get around to that stuff eventually!
@garlandjones77094 ай бұрын
@@nathanbopp6163he's not talking about shaping rough edges into a port. He's talking about casting flash and roughness in OEM ports and tracking improvement as you go on OEM stuff. Not improving already prepped heads
@disolejunk Жыл бұрын
Go until you hit water jackets...🤣🤣
@fraud3647 Жыл бұрын
There is no any reason open port too much, velocity is King!
@PhilipUnderwood-oy9tv10 ай бұрын
I agree with you 100%
@gregquinn6827 Жыл бұрын
Thanks a bundle sir! So many myths dispelled! So much data!
@IronmanG74 Жыл бұрын
Point 3. 7 port heads. A massive weakness
@notbuyingit8047 Жыл бұрын
I’d love to see what Mr Vizad would do to a Gen 5 LT1 head
@user-cg1jg9mi5c9 ай бұрын
great graphics from the Port Velocity at different lifts.
@ebbonemint Жыл бұрын
Well, I wish I’dve watched this before I spent 5 weekends porting and polishing my heads.
@spyker_aileron8 ай бұрын
So basically. High-ratio rockers and camshafts go first before i ever think about porting. Just get the valve out of the way of the air.
@raffiki22211 ай бұрын
David Vizard is on youtube!?!?! Thumbs up!
@knickebien1966 Жыл бұрын
an interesting perspective
@theblackhand6485 Жыл бұрын
@David Vizard: Could you make a 3D animation of the different radius's of the valve seats? Then it is more clear what you mean with the 92, 93, 88 radius along the valve seats. Thank you.
@danmaycock92383 ай бұрын
Are you from that lil part of America where their accents mixed with Cornish?
@TheMoghrabimahmoud11 ай бұрын
Vizard the porting wizard ❤
@yzScott Жыл бұрын
Too bad I didn't find your stuff years ago (except much of it didn't exist yet). I am playing with LS engines these days. But all the principals still apply.
@edmitchell9307 Жыл бұрын
I hope you do a whole episode on offset seat profiles
@chriscimino7854 Жыл бұрын
Mr. David Vitter I can't tell you how much I enjoy watching your videos. I never ported heads before. I have a pair of Pontiac #13 heads I would like to street pocket port but not ruin them. I am nervous and need to watch as many of your videos as I can to gain confidence. I am trying to build a 400hp 400 cu.in. Pontiac. I am running reproduction ram air three exhaust manifolds and stock four barrel quadrajet intake what do you think?
@hotrodray6802 Жыл бұрын
1) Back about 2005 a guy needed new head gaskets so he ported the heads too. He showed me a pair of mid 70s SBC 350 heads he ported (his first try) and I was aghast. Worst mess I ever saw. At least he didn't gouge out the seats. He put them on this ragged out 75 Camaro and it ran like a scalded dog!! Surprised me beyond words. 2) 1970 had a 292 Y block that chunked out an exhaust valve. Got a junk head for $5. Must have been a 239 or 256" with tiny quarter sized valves and tiny chambers. Put it on and it ran perfectly smooth for the next 25 years. Go figure. Never went over 4000 rpm I'm sure. SMH.
@TIMEtoRIDE900 Жыл бұрын
Chalk one up for "rough" port finish ?? Some guys are trying to carve golfball pips in. An engine builder told me SBC heads don't need any exhaust port work for the street.
@jasoncampbell4723 Жыл бұрын
Cutting pips do help but you need to know where to put them, if you do the whole port it doesn’t work.
@1crazypj Жыл бұрын
That's something new, offsetting the throat diameters!
@stevesadusky8634 Жыл бұрын
Thank you David for this video! I'm still trying to understand the porting process as in the past my brother would do all my heads for me because he knew the process inside and out but, he was killed by a drunk driver and I'm on my own now trying to learn the porting process. Do you also have books that I can purchase from you?
@mcintyretyler89 Жыл бұрын
I'll be back for the bowl🥣
@dannykim596910 ай бұрын
i really appreicate your informative videos. thank you sir!
@christinenevistiuk79067 ай бұрын
Hi David . I get asked a lot about the valve Guide . And is it ok to cut the part level with the port . Is it ? Thank you your knowledge is a gift to us all !!!
@davidciesielski8251 Жыл бұрын
Thank you
@martiniv89249 ай бұрын
Legend 🙌🏻
@buschenterprises4788 Жыл бұрын
restriction to cfm on flowbench and restriction to rpm and power capability do not necessarily go hand-in-hand the pushrod pinch may not be a cfm restriction, but it is an rpm and therefore power restriction…depends on cubic inch and desired power level (be reasonable here).
@jamest.5001 Жыл бұрын
I was just swiping through, and saw the Chevy head from the chamber, and thought, what if the valve angle were to be reversed? So intake would be similar to the heads being installed backwards, using the intake as exhaust, and exhaust as intake, with the valves reversed, seems high lift flow would be higher, possibly, low lift could be hurt, with the valve opens, the air should have a straight shot into the cylinder. The swirl may be hurt also, but tumble should be greater, but with optimized chambers could inverted valve angles in a wedge chamber, any thoughts?
@dale116dot710 ай бұрын
The main reason that the valve sizes are what they are is that the intake valve has atmospheric pressure pushing the air into the cylinder and on a naturally aspirated engine any restriction at all in the intake system generates a power loss. The exhaust valve has pressure from the piston pushing the exhaust gas out, and exhaust valve restriction mostly generates internal EGR and reduces scavenging a bit both of which creates a power loss, but not by the same amount. Intake needs to have priority in a naturally aspirated engine. In a turbocharged or supercharged engine it is possible that reversing the valve sizes might be helpful but with the exception of I think some race-prepped nailheads, I don’t think it’s a common way of doing it.
@robertjohnson4401 Жыл бұрын
When you said 91%, which measurement is the numerator and which measurement is the denominator. You left that undefined here.
@michaelau5159 Жыл бұрын
Percentage is metric it is based on 100. Take whatever your width is and divide it by 100 times by 91 3.g. 2.02/100 x 91 =1.83.
@ArmySigs9 ай бұрын
Great insights!
@russellanderson746 Жыл бұрын
Great video Mr. Vizard!! But, I must confess, I don't have a total lock on the percentages and what they mean. Please elucidate sir! Thanks again for the very interesting and valuable information. Also eagerly awaiting more on the Mazda 4 valve porting!
@DigiMannen Жыл бұрын
If it is Concentric. Imagine 90% of valve diameter in the pinch points furthest to intake runner if you have a 2" valve it should be 1.8", 92% is 1.84", 88% is 1.76" so concentric hole where the inner seat width is 1.82" at pinch points and 1.76" seat width perpendicular.
@russellanderson746 Жыл бұрын
@@DigiMannen Define pinch point. I'm not hip to all this porting nomenclature. By pinch point do you mean the area in the seat that is directly adjacent to the exhaust valve on one side and cylinder wall on the other? Thanks for the reply, BTW.
@DigiMannen Жыл бұрын
@@russellanderson746 You did not watch the video?
@DigiMannen Жыл бұрын
@@russellanderson746 The red areas! kzbin.info/www/bejne/m32thmSeYteUi8k
@ElvinLeadfoot2 ай бұрын
Going ba k and watching again King David:)
@rickyhenson49069 ай бұрын
Love all the info
@gf845 Жыл бұрын
I can remember 25 years ago now (maybe more) reading your A series tuning book over and over (it was like a bible to me at the time). At the time I had a very slow mini 1000 and a very crashed mg metro 1275 With the A+ engine in. I remember fitting the entire top end from the metro onto the 998 block and it ran and produced so much torque it was always spinning the wheels up in the wet through it’s open diff. I’m sure you said in the book the 12g940 head wouldn’t work on the 1000 block (especially the mg version with the bigger valves). Am I mistaken. The 998 had its standard cam still in it and the engine ran with no problems at all. It was t the most high reving 998 I’ve had but I remember the torque made it great to drive.
@senghornphon6100 Жыл бұрын
Thanks for your sharing
@ziggassedup Жыл бұрын
Thanks DV.
@hotrodray6802 Жыл бұрын
🔔😎 The name of the game is RESULTS !!!
@chrispompano Жыл бұрын
What firms do Computational Fluid Dynamics for the a mature to send their heads to for analyzing?????????
@racerd9669 Жыл бұрын
CID does.
@chrispompano Жыл бұрын
@@racerd9669 Are you referring to Competition Induction Designs?
@ForceEngineering Жыл бұрын
Is your CFD data doing an engine simulation? As in changing the differential pressure across the valve as a result of the % of cylinder filled for a given valve lift. Or is it not taking that into account and is strictly looking at flow with 28" of depression over the lift range?
@MrKentaroMotoPI Жыл бұрын
Doesn't matter unless the CFD result is intended to produce quantitative total airflow results. The solution shows the relative velocities and overall flow distortion (pretty bad, but typical). That's sufficient information to act on.
@ForceEngineering Жыл бұрын
@Mr. Moto The air speed in the port and the direction of flow won't change as the pressure delta is affected by the cyilinder filling?
@MrKentaroMotoPI Жыл бұрын
@@ForceEngineering The pressure difference across the head will affect mass and volumetric flow, and velocity. It won't effect the flow field structure much. Yes, velocity change will change the Reynolds number - which can change the flowfield - but these flows are fully turbulent, so it's a weak effect. It is very important that the CFD model uses a turbulence model, and that it is operating correctly. This flow has a lot of boundary layer separation (blue regions). While the turbulence increases pressure drop, it actually suppresses the separation and helps overall. Poor turbulence simulation is one of the most common problems encountered with CFD.