An In Depth Analysis of The MZR DISI Head
 

Okay, so this has taken me a while but I've finally gotten enough time to sit down and compile my findings to share with everyone. I've spent the past couple of months conducting many, many tests on our cylinder head. Overall, I'm very pleased with the results and I'm going to explain why things are so awesome.

This first post is only going to cover the intake side, I've got lots more testing to do on the exhaust side but the time frame for that is still undetermined. I'm going to start with talking about the port itself before I go into actual flow data because it's easier to see why things are the way they are with a proper image.

So here's what it looks like looking down our ports:

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The Good: As you can see most of the head of the valve is visible, this is a good indicator that the air charge does not have to bend very far to get around the short radius turn on the port. That is good because a sharp short radius (like most old V8's have) will cause the air to detach from the port wall and cause turbulence going into the cylinder. That has a very large negative impact on airflow.

The Bad: Well this isn't really bad, but looking down a port like this doesn't really give a great idea on what the thing actually looks like. It doesn't really give us any apparent weak points in the design of the port shape that could be improved. So, how do we get a better picture? Simple, by making a silicone mould of the port!

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So that is exactly what I did. It took only about 20 minutes to mix it and pour but I gave it 4 days to fully cure. It took me a solid hour to remove it from the port without destroying it but here is what I was rewarded with!

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So, now that we have a 3 dimensional view of what our whole port looks like we can do some analysis of the port shape as well as measure it in certain areas. This should hopefully tell us everything we need to know in order to make a good flowing port. But before I go into any sort of analysis I would like to take a step back and talk about some theory stuff first so you can gain a better understanding of what is desirable for a port as well as why I come to the conclusions that I have.


Here is what an ideal intake port design looks like:

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Theory says that an ideal engine has the port be parallel with the valve, essentially flowing straight down upon it. This is not possible because the valve train components would get in the way. Realistically, it’s not possible to get the port any closer to the valve than ~45*. 45* is still very good because the short turn radius (the angle at the bottom of the port where it meets the valve on the right side in the above pic) is far less sharp than your average V8 port which is the picture below (notice how the port approaches the valve at almost 90*).

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Below is a look at another head, this one is off a 4G63, an engine that is well known for having an extremely good flowing head. Notice how the head port starts in the middle of the head. The reason why it can’t be moved any higher like ours is because the injector has to sit above the port so it can’t be raised any higher. Since our engine is DI we don’t have that issue and the port can start at the very top of the head, giving the air stream a very straight shot down at the top of the valve.

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So now that a bit of shape theory is understood we can examine the quality of our port. To start, on aspect that makes our port great is that it begins at the very top of the head, meaning it can get closer to being parallel to the valve, so it’s right around that 45* angle which is about as good as it gets. Our short turn radius almost doesn’t even exist, and that is because the port angle is 45*. This is great because it means that the air is much less likely to get detatched from the port wall and get very turbulent (a very common effect on most stock V8 engines). Since there aren't turbulence issues going into the port, then more air can make it into the cylinder.

Another thing that is noteworthy is that the port is tangential to the valves. What this means is that the ports do not line up to the valve, but rather they are canted off to the side a little. Here is a photo of what I mean, I've traced the centerline of the cylinder with a red line to show where the center of the cylinder is relative to the center of the port:

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This is important (and beneficial) because of this tangential design, the air charge into the cylinder will actually swirl after passing the valve. This swirl is a form of turbulence, which is good because increased turbulence inside the cylinder leads to better atomization and more importantly, better combustion quality. +1 for Mazda

Here is a side profile of the port:

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In the above photo, the nice steep port angle can be seen. Another thing that can be seen is the shape of the ceiling and the floor of the port. Two important things can be learned from this. One is that in stock form, the floor already has a fairly desirable shape which gradually connnects the port entrance to the valve and really does not need it's shape changed at all. Two is that the ceiling actually lowers further down in the port and this is important to note because the CSA of the port can greatly be increased by raising the ceiling of the port. This is also important because the majority of the intake air charge rides along the ceiling of the port and by raising the ceiling you're actually helping the transition from the port inlet to the valve, which would in theory increase airflow.

Here is something else for you to think about:

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As you can see the two ports are different sizes at the inlet. This is true for just about every dimension between them (large first, small second):

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So now you might be wondering why they are different sizes. The answer lies in something that many people get rid of. The Variable Tumble Control System (VTCS) is often removed from the intake manifold in order to pick up a bit of top end for performance. It's mostly used during light load and cruise events so getting rid of it doesn't really affect too much but what's important is that the flapper is designed to cover the larger port. The reason for this is that all of the airflow during these light load events will have very high velocity because it is only going through the smaller port. This is good because it means that the volumetric efficiency of the engine at lower RPM/low load will be very good, and get better gas mileage because less throttle input is needed.

But this design is somewhat detrimental when it comes to making power. As I said it's a design that really isn't in use during higher load events. And since it's not in use, it's in the way. So removing it is good and all, but you're still left with one port that is smaller than the other. This isn't a horrible thing (something that I'll brush on later) but it also isn't helping us at all because if the ports were the same size, each cylinder would flow a good amount more airflow. Let's take a bit of a closer look at why I say this.

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Above are a couple of photos of the port bowl area (where the port meets the valve). As you can see, the connection between them has a VERY sharp bottleneck. This is horrible for a couple of reasons. One, it's a bottleneck and that means it will restrict airflow. Two, it's a sharp transition. Airflow does not like sharp transitions as it will cause the airflow to detach from the port and become turbulent which is not desirable.

So the remedy for this would be to smooth it out with some bowl work. That alone will have some very positive effects on airflow without much of any downsides. For those wondering why it is so shitty it's because the head is a mass produced part and making this area smooth is not something that is done by any manufacturer except for high end performance vehicles.

While I'm talking about the bowl area, there's something else I'd like to note. And that is that our head actually has a 3 angle valve job from the factory. It's not anything amazing but it certainly is nice to see. A 5 angle would certainly be an improvement but what we have is a pretty nice start.

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So going back to the mould there are some other things I would like to touch on. One is that the valve guide extends into the port not much really and this is good because valve guides can spilt airflow and cause all sorts of trouble is they're not shaped right but ours are not very intrusive so there isn't much to worry about.

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Also, the overall length of the port is only 5.85". This is important because port length changes things.

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A 6" port isn't very long and short runners are good for high end performance but not so much for low end torque or response. So how does one extend the runner? With a manifold of course!

As some of you know, I've been doing some manifold testing and part of those tests involved connecting the manifold to a head to see how it flowed because the more of the system that is tested together, the better of an understanding that can be gained on it. Yes, it is useful to flow individual components but if you can connect them and test them together, it is even better.

For my testing, I didn't test as many manifolds as before because this testing takes a very long time and I wanted to examine some certain aspects which led me to these manifolds: JMF V2, JMF V1, Stock and the head by itself. No I did not test any ported stock manifolds, it is not worth my time to test these because the results are predictable and I would rather spend my time testing other stuff.

Before I dive into the testing and results I'll give a bit of info on the setup so you can sort of see how it's done. As before, the test pressure was set at 25" of H2O in order to keep things consistent. Please don't compare my tests to other tests that people have done, different test pressures give different results and many people conduct tests at 28" of H2O and the pressures do not exactly convert. I chose 25" because that is what the bench was calibrated at. To minimize leaks, the exhaust valves were installed with their springs to hold them closed and the spark plug was installed as well as the injector bore was taped off. All connections on the manifold were taped off such as the MAP sensor hole and all other holes for vacuum and boost sources. The intake valves were installed with light springs in order for them to be opened easily. A dial indicator is installed above each valve to keep track of the lift that they are at. Lift points were done in increments of .05 L/D and ended at .035 L/D. This was done to give a good idea of how the head performs with camshafts. A bore adapter was used to simulated proper cylinder conditions so the valves would be shrouded properly to keep flow numbers from being inflated. Unfortunately the closest adapter I could find was 3.5" and our bore is 3.44" so bear in mind that my results might be a tad inflated.

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On to the tests! So to set a baseline I flowed just the cylinder head by itself. The results are below and they're really not too bad for a totally stock head. The port itself is restricted to right around 190 CFM but what's important is that they are all exactly the same shape and so they all flow the same amount at pretty much all lift points. +1 for Mazda again.

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Then I moved onto the stock intake manifold connected to the head. I decided to test with the VTCS open as well as closed. What I found is that with it closed, they flow fairly even, which is nice for cruise and low load events but really not useful for making power. When the flappers are open it can be seen that the best the imbalance gets between cylinders is 12%. That is fairly close to the 14% that I found when flowing the manifold by itself. Why is that important to note? It's important because it tells us that despite the head flowing perfectly even, the manifold imbalance upstream from the head will still cause flow imbalances and that in order to have an engine with balanced flow across the cylinders we need little variation between the ports in the head as well as the runners on the intake manifold.

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After that my next curiosity was between the two JMF manifolds. From my bare head test and the flow tests of the JMFs I knew that they would easily outflow the head but what I wanted to find out was how much the runner divider in the V1 made a difference compared to the V2 which didn't have one. My results were a bit surprising in the fact that there really wasn't much different. My guess was that the longer divider would aid in low lift flow but it seems I wasn't quite right on that. More importantly, what was learned from this is that the flat face on the head of the runner divider really doesn't impact flow much at all. So contrary to belief, it's okay to run a manifold that doesn't have a divider on a stock head. Another thing that was learned is that the JMFs don't flow evenly at low lift and are decent at high lift. I believe it tends to smoothen out at higher lift is because the runners are so short and the air has a higher velocity. One other thing that I just feel inclined to say about the JMF manifold(s). While yes it is far better than stock, it leaves a lot to be desired. The JMF flows enough air for 1200 horsepower. So yes, it's pretty oversized and not only that but the runners are extremely short. This is fine for high RPM power but it doesn't do anything for low down torque and doesn't really help spool a turbo any faster. Flow results are below:

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So after looking at the results I'd like to go back quickly to the topic of cams. Our stock cam has a max lift of 0.372". That's right around the area where flow levels off so what this tells me is that the stock cam is matched nicely for a stock head. It also tells me that there's no point in dropping in a hotter cam without putting in larger valves. The issue with larger valves is that airflow gained is minimal because they will be shrouded even more by the cylinder wall and the other valve. So IMO there's not point in upgrading cams unless you are opening the ports up UNLESS you are moving to a fatter profile grind that offers similar lift but has a greater duration at those higher lift points.

Some other things that I would like to brush on are once again the difference in port sizes for each cylinder. The reason I'm going back to this is because it is not desirable in terms of power to have these be different sizes. The reason for this is because the larger port can actually start to pull air from the smaller port once it has reached its max flow potential. I know this to be true because at high lift on the bare head tests the noise was unbearable. This noise is from the larger port pulling air across the divider and out of the smaller port. The two remedies to this would either be to eliminate the divider or make both ports equal in size.

One last note before I wrap this up is that the single greatest quality about the stock head is how evenly it flows. This is EXTREMELY critical because an engine can only make as much power as its weakest cylinder. The only way around that is to have one of each sensor for each cylinder (not something really feasible). So if all the cylinders flowed the same but one *cough* cylinder 4 *cough* flowed 20% less, then the rest of the cylinders will be forced to make 20% less power. That is why balance is paramount when it comes to airflow through an engine.

I've attached the results for all of my tests in case anyone is interested to see the whole numbers. Unfortunately I left the swirl tester off for all but one of the tests. I didn't want to run short on time for testing (which ended up happening anyway) but I was still curious about the numbers. I didn't have time to test port velocity and I might try and go back and do it but that might not be for a while.

Thanks again to @maisonvi; for loaning me the manis

Thanks for your time gents. Let me know if you have any questions.

3/18/17: Exhaust side results added. Will add observations/theories/notes when I don't feel so lazy.
3/20/17: Wall of text notes added with observations on exhaust side and valvetrain.

Finally got time to get the exhaust side flowed on the bench. I'm really happy to see that the exhaust side flows almost as evenly as the intake side. The modified port changes consisted thinning up the valve divider a bit, touching the ceiling a tad, and smoothing everything out. For the small amount of work I'm happy with the gains. There is still a good amount to be had but I've got some testing to do with exhaust manifolds before I come back and port the exhaust side further. After I get through the manifold testing, I'll be cutting the head apart to check wall thickness and find where all the water is in the head. I've got some things to say about the exhaust side which I'll share later.

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Feeling lazy at work so figured I might as well throw some brain cells here. Some things to note about the exhaust side (some of this may or may not have been said already, too lazy to reread the whole OP):

- The exhaust ports are mirrored over a vertical centerline through the head ie cyl 2 mirrors 3 and cyl 1 mirrors 4 but they're curved in the opposite direction (look at pics if my shitty explanation doesn't make sense)
- The gash cut in the end of cyl 4 for EGR doesn't affect flow at all. READ -> (this is a preliminary observation and very well may change after testing is performed with a manifold attached, it will also affect exhaust pulses and any reversion that may occur, so in other words it may not affect flow on a bench but that doesn't mean it won't affect engine performance.)
- The outlet of the ports at the head flange is MUCH smaller than the exhaust mani gasket and most aftermarket manifolds, this is good because it means this bottleneck can be shaped to work with nearly any manifold
- The short turn of the ports is cast extremely well and does not need to be touched at all besides giving it a smoother surface finish. I REPEAT, DO NOT FUCK WITH THE SHORT TURN
- The long turn is a bit larger than what's needed for the valve throat size so once again, don't make it any larger, just give it a nice surface finish if you feel like putting effort into the head.
- The ceiling is a tad low and could use a tiny bit of raising (this is an observation and I could be wrong about this).
- There is water in the valve divider on the exhaust side. If my thinking is right it's a steam relief hole (even if it's not, water is still flowing through there). Until I can cross section the head I don't know how thick it is there but there are some small gains in thinning the divider up.
- Cylinders 1 and 4 ports are longer than 2 and 3, something to think about for those making manifolds.
- I *think* the floor could use for a bit of raising near the outlet at the head flange. That or lower the opening of the outlet at the flange, though that may or may not be a good idea depending on your manifold.
- Overall, the exhaust side is about as impressive as the intake side. I am content with results but not enough to leave it unmodified, hehe.


Other notes about valvetrain stuffs (once again, some of this might be a repeat):

- Our stock valvesprings are beehives. This is good because they don't have nasty harmonic issues like straight spiral springs do. This is bad because it means we have to run a different retainer if we want to run aftermarket springs.
- Our stock valves are pretty awesome. The intake side doesn't need to be taken any larger as it's already past the point of diminishing returns. The exhaust side would benefit from a +.05mm or +1mm valve but the cost of doing so might not make it worth it.
- Our valves use a single groove retainer which is much more desirable over multi groove retainers.
- Our valve stem diameter is 6mm which is on the larger side of the spectrum for 4 valve engines but that's good because it means greater heat sink-ability and the exhaust side is half inconel and has hollow, sodium filled stems so they can really handle heat (something you won't find on aftermarket valves except for the uber high end stuff). Lastly, the downside is the stem is 5.5mm on the tip so aftermarket retainer/keeper options are greatly reduced. Also if you want to move to aftermarket valves, you'll have to change to 5.5mm guides since all aftermarket valve options (that I've seen) use 5.5mm stems, and thus you'll also have to have your seats ground which = $$$.
- The stock exhaust valves have thick margins. This is good because thick margins help to reduce turbulence as the exhaust gas leaves the cylinder and also gives the valve more heat sink-ability.
- Our valves are a bit tulip shaped, good for our application.

Thanks for the work testing this Austin.

yes indeed. must take some time to digest :)

Does your bench have a velocity probe so that can highlight the air separation from the port wall at the junction of head and manifold? The fatal flow of this manifold.

@Mazdazilla6; will any of your upcoming test be including a single runner intake side and ported exhaust side head? would love to see the results of that.

I'm curious if the Flow evens out on the stock intake Manifold if the Stock exhaust manifold is on, as it doesn't flow evenly either.

Also I think if you were to run a cam with more duration vs more lift you would still see gains with stock ports/valves

It has pitot tubes but they will not work with the manifold connected to the head.


I'm going to try to but that will be a long ways away.


The exhaust flow will not change the intake flow. They are separated from each other by valve events. There is no overlap on stock cams.

You will not see more gains in port flow but you will see more gains in cylinder filling.

I've read a few of your threads and I must applaud you for the time and effort you take with them.

I must also say that, you sir, are insane, and I mean that in the best possible way. Keep up the good work. :biggthumpup:

Tapatalk says "fuck this post."

Good work.

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Fixed for you.

http://www.mazdaspeedforum.org/forum/foru...ap-closeup.png

Source:
http://www.mazdaspeedforum.org/forum/foru...ml#post3042652

Yea I remember that thread. My statement still stands though, porting the exhaust will not bear an effect on the intake flow.

this is some impressive info, but you said PnP stock mani's are predictable, what would you predict the gain over stock is and compared to a jmf

Not suggesting it would.

A gasket matched stocker flows roughly 20% more than stock and is a good match for a stock head. The JMF flows over twice as much as stock and wouldn't be a restriction until quadruple digit power numbers. So it's a tad oversized for most applications lol


I know. Just stating it to avoid any confusion from anyone else :)

At what point would you say a pnp stocker becomes a restrictor for more power due to its limitations?

Great info. Have to finish reading later but just curious in this
Is it just held like that cause the silicone is limp? Or am I confused. Its still pretty steep when I rotate. Pretty much 45* like you said shown by 2nd line in 2nd pic

tl/dr

I think that's just because the mold doesn't have a base capable of standing on its own given where the center of gravity is.

@aviator79; ^ That. It's not super rigid so that was the easiest way for me to support it and take the pic at the same time. Also because 4am typing my 25 page term paper the morning that it's due lol.

I either disagree with some of these assertions, don't understand them correctly, or you are not explaining them right.

1. If flow on the small port is chocked, then the larger port cannot suck air from the smaller one.
2. Where in the air charge tract do you imply that the big port pulls air from the other one? at the start of the divider of the stock manifold? or inside the combustion chamber?
3. If the two ports were the same size, and they would flow equally at the higher flow rates, you would not have a swirl effect in the combustion chamber. The two masses of air would just collide with each other upon entering the combustion chamber. As you point out, swirl is inhibited at slow air speeds by the VCTS. At high speeds however, when the flapper valve opens, air speed would be equal unless the ports were of different size. What I believe happens at high air speeds is that the air from the small port entering the combustion chamber travels at a higher speeds than the one in the big port and thus creates swirl in the combustion chamber by pulling the air coming out of the big port. Both of these air masses then. twist, or swirl, inside the chamber.

@Ziggo;

1. Was in reference to manifolds without VTCS or when the VTCS is open. I observed this when I tested the head by itself. The bench makes a horrid shrieking noise because the air is being pulled across the divider.

2. It would be at the beginning of the divider. Unfortunately it's not something I can observe with a manifold mounted on the head.

3. IMO the primary cause of swirl on our head is the offset port design. Creating swirl is very very tricky on a 4 valve head because the flow from one valve will interfere with the other. What actually ends up happening is that the flow from one will disrupt the other and reduce turbulence in the combustion chamber, which is bad. The bench has pitot tubes on it which allow me to measure flow velocity, and while I didn't have time to do those tests I can assure you that the small one flows faster but as to if it is "pulling" air out of the large port I cannot say. My educated guess would be no, simply because of the reason that the valve from the large port would get in the way and disrupt the swirl action. When I was first calculating valve efficiencies, I was curious as to why they were so low. As a small test I closed one and left the other open. Not to my surprise the efficiency went up about 15-20% simply because the other valve wasn't shrouding it. Now while 4 valve heads don't make great swirl, they inherently create good tumble. Unfortunately I cannot measure tumble like I can swirl but based of the swirl numbers I was seeing I'd say that our head makes plenty of tumble.

Awesome post, thanks for the time you've invested and sharing the results.

It makes me feel a little better about cheaping out on a JMF V1 too :P.

Nice, thank you a lot for taking the time to do this research!

Any new data to share?

Haha yes, currently rushing to catch a train. Will update when I have time and internets.

Sweet! Hopefully see you in a few hours to go racing. If not, we'll be doing hoodrat shit in the garage tomorrow if you'd like to swing by.

doing hoodrat shit = some sort of new game involving the human anus?
I wanna play.

Hey did you ever plan on flowing the exhaust side of the stock head?

I recall Justin commenting in regards to portwork on the head, that the intake side was pretty good but the exhaust ports needed a lot of work. Interested to see any flow bench results on stock or otherwise.

I was going to get to doing that this semester but ended up taking the semester away from school to pursue an internship. Fortunately, where I'm working at has a badass machine shop and an equally badass flow bench. If I can find the time I will throw a head on to do some exhaust side testing. I want to do some ported testing as well but without a good air supply to run my die grinder I won't be able to get to that for a while. Maybe I can squeak it in after hours but I'm not sure I really want to commit my free time to that right now.

you who has good air supply, die grinders and carbides? @WetzMS3; and I. Come visit.

In for grinding of things and head.

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I'll be home in two weeks. I really want to go to Hofbrauhaus while I'm in town. What kind of air supply do you have?

Bigger 2.5 hp HF. I've done porting work it already, it works well, lots of flow (helped by the fact that I use 1/2" hose and milton G fittings).

Chris has a dual tank setup with the same compressor.

You're welcome to come open up holes anytime

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Interesting, my 3hp 12gal couldn't keep up with my die grinder at all. Literally grind for 2 minutes and it's spraying water out of the grinder from condensation. I was going to get a moisture separator but decided against it because the motor gets hot as hell anyway and I don't want to kill it.

I'd love to work on my experimental head some more but we'll see!

Reserve tank helps with that. And patience.

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I have no patience lol. I love porting at school because we have a central air system. All the grinder all the time!

Either you have very dull grinder tools, or you've put holes in whatever you're working on.

2 minutes of straight work in any once place is a lot of material removed if you're using the right tools.