Thanks for the info. A problem with sharp divider is, if the port is not 100% symmetrical, the air could flow in slight angle and that would create a wake at the edge. Round divider is much more forgiving. With sharp divider, margin of error is smaller.
Yeah, that's not really true at all mate, this something we have tested, and something you can easily probe at different pressure drops and confirm for yourself. The air speeds needed to create any sort of detrimental wake with any approach angle
@bobirving6052 No problem, sadly, there are still lots of misconceptions when it comes to cylinder head development and air flow. It's why we started this series to hopefully kill off a lot of the myths 👍
Just found this today , so i have automotive and 2 stroke motorcycle experiance and always radiused the divider on everything due to learning it from years of playing with transfer ports on 2 strokes, i did the same thing on a 4 vave head (bmw motorsport) that had a very sharp divider it still made power but may have caused a choke point as you say and ill try to knifedge the next one to see the difference, so this would mean the flow bench wouldnt have picked up a restriction with the radiused bridge but the way you described the effects this could have affected it to a reasnoble degree, the heads are super special and worth looking at s38b35 bmw head , amazing intake port just a tidy up netted 275cfm @ 10mm lift but dropped off flow after that, im now planning my next port job differntly 😊 thankyou
No problem, just remember a flow bench doesn't measure cfm or flow. Only pressure drop. So it won't test the dynamics well. Also 28" is very restricted. You need to test at different pressures as high as 60" to get more of an idea of the dynamic ability of the port, velocity probing is key here.
That's a low speed to high speed. So, I will suffer separation. So, it's not a great idea. But unfortunately, many manifolds are just too thin. So we shape like a billet head. 60° of the radius to a point.
Have you tested this on a flow bench? What are the actual numbers, or is this just conceptual conjecture. Maybe you can do a head to head dyno comparison. As the great David Visard once said, "I don't have opinions, I have dyno sheets" I personally think that the radis would end up making more power, as it would increase velocity
Yeah, you really need to be careful how you validate what you're testing. And you need to understand the mechanisms at play. Yeah, old Dave, he is a funny guy. For example, flow benches you really need to be careful, as flow data at one pressure drop, and steady state flow with no CSA index. Really won't tell you much at all. This is seen and has been tested time and time again with our winning heads. As they have lost 10-15cfm over the last 2 decades and yet run faster, make more power per PSI and more area under the curve. Remember, a flow bench doesn't measure CFM. It only measures pressure drop and "calculates" CFM. A great example of this we done just recently. A head we did for one of the race shops we supply for their circuit car. It was running a fulling CNC'D head, with radius dividers and flowed 295cfm at 0.450". They had a head failure, and we had to port a new head and put all their gear into this new head. So everything was the same except the port work. Our flow figures didn't even hit 285cfm. And yet the car made 45hp more at the same boost level!! And 35% more mid, and early boost threshold points, nearly 800 rpm earlier! So everywhere was better. And if you understand the relationship between CSA, inertia, and flow. Then this will make sense. Also, when it comes to dynos, you need to be careful. As even the dyno can be misleading when it comes to the track. For example, with our custom manifold program, we have found so many misleading things on the dyno. Plenum volume is a great example of just one thing and area that will make power on the dyno, but cause the car to run slower in the real world. So, you need to look at many aspects to validate what actually works. As I say, the black-track doesn't lie!😉 But yes, sharp dividers have been validated even as far back as the 70's with F1, so yeah, this area has been back to backed many times by us and many other winning cylinder head guys I know and chat to. And no, a radius will create more "dead area," which is energy loss, and it also robs inertial velocity, as we have a great change in CSA with a radius. So this is why it costs you as it can't improve the velocity gradient, as you have a "step" change in CSA. Remember, CSA is what dictates air speed air speed and a "stable" velocity gradient is what feeds oir VE mechanism. If you think about it long enough, you will get it 👌 Cheers for the comment, mate.
It's more to do with relative air speed in front and behind the two points you're referring to. If similar, then sharp is better. If, on the other hand, we have a huge velocity gradient. Then, a radius is generally needed to control separation as the air is accelerating as well as dropping denisty. So we need to control the vena contracta from forming 👌
So this got me thinking, and well maybe overthinking and perhaps even a bit out there😂 so let's say you had a device that could amplify the acoustic waves the engine makes and synchronise them with the motors stroke could this enhance the motors performance hmmmm
Yes, this is what we do when designing intakes. Target the 3rd harmonic. But fixed runners will be limited to a narrow RPM range. But variable runner length like what F1 used in the day allowed a broader RPM range are the runner would get shorter with RPM. But was banned. Some factors bike's a use a lift away runner also. To help improve this mechanism As well as Le mans racing, like the 24 hour's 787B rotary, which also uses a variable length runner system.
Thanks for the info.
A problem with sharp divider is, if the port is not 100% symmetrical, the air could flow in slight angle and that would create a wake at the edge. Round divider is much more forgiving. With sharp divider, margin of error is smaller.
Yeah, that's not really true at all mate, this something we have tested, and something you can easily probe at different pressure drops and confirm for yourself.
The air speeds needed to create any sort of detrimental wake with any approach angle
@bainracing
Wow! Thanks 👍
I can re-read this slowly several times
@bobirving6052 No problem, sadly, there are still lots of misconceptions when it comes to cylinder head development and air flow.
It's why we started this series to hopefully kill off a lot of the myths 👍
CSA stands for??
@@Baard2000 CSA=Cross Sectional area, the CAS of a port dictates the air speed and targeting this air speed is what makes HP👌
Just found this today , so i have automotive and 2 stroke motorcycle experiance and always radiused the divider on everything due to learning it from years of playing with transfer ports on 2 strokes, i did the same thing on a 4 vave head (bmw motorsport) that had a very sharp divider it still made power but may have caused a choke point as you say and ill try to knifedge the next one to see the difference, so this would mean the flow bench wouldnt have picked up a restriction with the radiused bridge but the way you described the effects this could have affected it to a reasnoble degree, the heads are super special and worth looking at s38b35 bmw head , amazing intake port just a tidy up netted 275cfm @ 10mm lift but dropped off flow after that, im now planning my next port job differntly 😊 thankyou
No problem, just remember a flow bench doesn't measure cfm or flow. Only pressure drop. So it won't test the dynamics well. Also 28" is very restricted. You need to test at different pressures as high as 60" to get more of an idea of the dynamic ability of the port, velocity probing is key here.
Very interesting. What do you feel about applying the sharp runner divider in the plenum of typical single 4bbl manifolds?
That's a low speed to high speed. So, I will suffer separation.
So, it's not a great idea. But unfortunately, many manifolds are just too thin. So we shape like a billet head. 60° of the radius to a point.
Have you tested this on a flow bench? What are the actual numbers, or is this just conceptual conjecture. Maybe you can do a head to head dyno comparison. As the great David Visard once said, "I don't have opinions, I have dyno sheets" I personally think that the radis would end up making more power, as it would increase velocity
Yeah, you really need to be careful how you validate what you're testing. And you need to understand the mechanisms at play. Yeah, old Dave, he is a funny guy.
For example, flow benches you really need to be careful, as flow data at one pressure drop, and steady state flow with no CSA index. Really won't tell you much at all.
This is seen and has been tested time and time again with our winning heads. As they have lost 10-15cfm over the last 2 decades and yet run faster, make more power per PSI and more area under the curve. Remember, a flow bench doesn't measure CFM. It only measures pressure drop and "calculates" CFM.
A great example of this we done just recently. A head we did for one of the race shops we supply for their circuit car. It was running a fulling CNC'D head, with radius dividers and flowed 295cfm at 0.450".
They had a head failure, and we had to port a new head and put all their gear into this new head. So everything was the same except the port work. Our flow figures didn't even hit 285cfm. And yet the car made 45hp more at the same boost level!! And 35% more mid, and early boost threshold points, nearly 800 rpm earlier! So everywhere was better. And if you understand the relationship between CSA, inertia, and flow. Then this will make sense.
Also, when it comes to dynos, you need to be careful. As even the dyno can be misleading when it comes to the track. For example, with our custom manifold program, we have found so many misleading things on the dyno. Plenum volume is a great example of just one thing and area that will make power on the dyno, but cause the car to run slower in the real world. So, you need to look at many aspects to validate what actually works. As I say, the black-track doesn't lie!😉
But yes, sharp dividers have been validated even as far back as the 70's with F1, so yeah, this area has been back to backed many times by us and many other winning cylinder head guys I know and chat to.
And no, a radius will create more "dead area," which is energy loss, and it also robs inertial velocity, as we have a great change in CSA with a radius. So this is why it costs you as it can't improve the velocity gradient, as you have a "step" change in CSA.
Remember, CSA is what dictates air speed air speed and a "stable" velocity gradient is what feeds oir VE mechanism. If you think about it long enough, you will get it 👌
Cheers for the comment, mate.
If its 2 into 1, a sharp would be best. On a 1 into 2 a convex radius is beneficial due to Bernoulli's principle. Agree? Disagree?
It's more to do with relative air speed in front and behind the two points you're referring to. If similar, then sharp is better. If, on the other hand, we have a huge velocity gradient. Then, a radius is generally needed to control separation as the air is accelerating as well as dropping denisty. So we need to control the vena contracta from forming 👌
Good breakdown, thank you sir
Very welcome
Legit teachings
👌 cheers
clear and to the point, learned something, good video
Good stuff, mate 👌😉
🔥not bad
nice R31
So this got me thinking, and well maybe overthinking and perhaps even a bit out there😂 so let's say you had a device that could amplify the acoustic waves the engine makes and synchronise them with the motors stroke could this enhance the motors performance hmmmm
Yes, this is what we do when designing intakes. Target the 3rd harmonic. But fixed runners will be limited to a narrow RPM range.
But variable runner length like what F1 used in the day allowed a broader RPM range are the runner would get shorter with RPM. But was banned.
Some factors bike's a use a lift away runner also. To help improve this mechanism
As well as Le mans racing, like the 24 hour's 787B rotary, which also uses a variable length runner system.
Is that a port or a lady with hairy legs 😄
A lady with hairly legs, of course 😂👌