Porting & polishing diesel heads

[Fahlin Racing]

Lets clarify what a flowbench is. Its a tool, it is only used for observing flow through any component for finding out how well a piece flows (in CFM), it won't give you the velocities within the port to you. You need other instruments in order to establish that sort of information.

Just because one head flows more than another does not mean that head will perform at a higher efficiency. Its all about what happens in the actual engine during operation. Thats what we use the bench for, trying to simulate actual flow within the engine for optimum power. 'Racing flowbenches' is a waste if you just want to see who can get the highest Cubic Feet per Minute of air through the port or intake or exhaust manifold etc. If you ever are in a speed shop, gasoline or diesel engines, a well flowing port will be quiet, as soon as you hear noise becoming louder as they raise the lift of the valve or valves that means the port, somewhere, is becoming turbulent.

Air is compressible, which means the flow itself doesn't stop here or there or begin flowing again like this or that. There are also pressure waves within our ports as well, but I won't get into the pressure waves in this thread. Too many variables and the calculations are a bit cumbersome if you don't completely understand fluid mechanics, thermodynamics etc. Its a whole new ball game under forced induction as well.

[Fahlin Racing]

For those that want to get in deep here and start tuning. Here is one link to where you can buy parts and build a bench.

http://www.tractorsport.com/

There are multiple companies that produce benches, and there are multiple professionals that you can read what they have written, or, simply ask for some help on establishing your foundation and start experimenting. I am not sure on how much the strictly-diesel shops are with generosity in the porting help, it doesn't hurt to ask. This is where having junkheads around for practicing on is nice. If you want to stick to one engine manufacturer or tune any diesel head out there stick your fit in the door somewhere or take your own way and go from there.

When anyone flows a head, it should be tested with the intake portion if possible. This means tuning the manifold as needed, if needed, along with our head(s). The reason for the intake or exhaust manifold is because our flow doesn't just start or stop at the port entrance or exit! Our flow begins at the air filter, N/A or Turbocharged. Of course its a little easier to establish good flow prior to the turbo, its tuning on the turbo exit side and induction path all the way to the intake valve(s) is what we would like to improve.

Again, since we know air does not like to make immediate turns, or sharp edges within the system, induction or exhaust. Airflow DOES HAVE FRICTION! The air in the middle of the port is flowing faster than the air right next to the wall.

Since unsettled ports produce noise, there are tools out there you can buy to observe the flow seperation where ever it may be. These are called flow-balls. The trick here is finding the size of the disruption within the port area with these. Once you locate an area of turbulence, the flowball should hopefully re-attach your flow. Remember when looking for the exact area the disruption is taking up you must try all directions with whatever testing tool you are using to identify the problematic area.

Make sure you understand HOW to use the tools you have when testing. One book I suggest to begin your testing and tuning. It covers the basics of the internal combustion engine and moves into airflow and testing and testing tools, components etc. Engine Airflow by Harold Bettes is the book if you want to start before you purchase a bench.

If you do buy a bench, there should be literature with the bench itself although I am not sure how much comes with one.

[Fahlin Racing]

The ports themselves will have an area that is more active than the rest of the port. I guess you can call this the main flow path. There is what we call a Effective Flow Area (EFA). How this is determined is by the Discharge Coefficient and the Geometrical Flow Area. Here is an example to give you something to chew on.

The black rectangular shape is the port itself. The theoretical port flow area that is 'most' active in this example in red. Now there may be more flow happening in the corners than is shown in my little picture there. Depending on the where the flow itself travels through the port/runner (high, middle, left or right) is dictated by Where the flow approaches & enters the intake port itself. For example the log style induction box that Cummins casts with the 12V cylinder head. Kustom intakes obviously will influence more efficient flow path than a mass produced cost concerned production piece. Now if you are running a N/A diesel and are going to install a turbocharger, the EFA of the engine during its N/A days will be the same active flow area even when the boost is introduced.

http://www.dieselpowermag.com/tech/c.../photo_02.html

On the link above, I see Diesel Power displays a set of Chevrolet Duramax heads before and after being worked. The thing that comes to mind when I see the taper around the port entrance is there may be a larger port induction manifold. If this is done, it must be done correctly. The pros out there have enough time into this I am sure that they know why the taper has to be done and appear a particular way. This brings us back to the flowbench. Flow separation can happen (boundary layer detaches from our floor or walls or roof) Again, using boost will amplify any turbulence within the port if its present.

When testing a head you must go through all the valve raising and lowering cycles with the intake and exhaust. The valve doesn't go from the seat to full lift right away. Your flow will change at each crank angle of rotation, this means you test in increments and observe the action in the port. We experience low lift flow twice and mid-lift twice and maximum lift once in one intake or exhaust cycle.

The red is higher velocity flow.
http://www.youtube.com/watch?v=mcJWK0N6i-o

[Fahlin Racing]

Here is a snip-it I thought was appropriate. Dealing with any engine in regards to porting, I chose to quote David Vizard.

..The most important thing to remember is to reproduce the correct shape, not to worry about getting a great-looking polish..

This brings to mind if anyone is to clean a head up, just taking down rough areas from the runner to the bowl, don't make it oddly shaped port areas because there may still be viewed as 'rough' areas due to the casting process. Earlier I posted a straight forward drawing of a before & after when porting is done. Granted the change in size in my drawing (on page 3 at the bottom) has no intent to show real measurable size change, its just used for clarity to observe enlargement of the runner.

Once we progress through the port, of course measuring as you go so you know where the walls, floor and the ceiling are at. Where the port meets the valve seats in 4-valve per cylinder heads will be the more difficult to tune. Most likely more than one way to tune as well

If we look at the convergent side of the valve (backside of the intake) we have our transition into the throat. Between this and the valve itself, there will be the highest airflow velocities. Making our transition into the opening as uniform as possible will increase flow into our cylinder. Although we have a valve to move around as well.

If we can lower any turbulence ANYWHERE, we not only spool up quicker, but make good power on lower boost levels because the amount of work done to make X amount of power is lowered, also reduces our induction charge temp! I remember reading an article that I believe Diesel Power mag had kept turning the boost up until the engine's output actually plateaued and I think we down slightly due to unwanted heating of the intake charge. Make sure you observe your turbo too because increased flow capacity through the ports can overload the turbine's flow capacity and cause some more problems.

The throat, seat and top-cuts are definitely something anyone can test. The people with the seat cutting tools have the advantage in this aspect. If you have a friend with a machine shop, you just might learn a process done by every automotive machine shop. Also, if you look at any diesel head we have the pockets our valves reside in. This is another place we can improve flow, not only for the intake valve but for the exhaust as well.

[dbennett48]

I have not heard David Vizard's name in twenty years. I used his advice on a race engine and that was the last I had heard from him. Good man and great advise.

Dave

[Fahlin Racing]

Yeah, he writes some interesting stuff. There are others out there to follow, but, you also have to watch for the junk tips as well. Verify what anyone says or has written before it goes into any sort of head. Jumping back for a second to our flow within the port, non-turbocharged vs turbocharged engines, our flow area will be roughly in the same portion of the port, in a general sense of putting it of course.

Here is the intake of the 7.3L IDI once again. I have highlighted the valve boss area in both the intake & exhaust. From the factory has some decent size to the valve's guide boss. I believe there is enough meat there to shape it more aerodynamically and hopefully produce more stable flow within the bowl area and not jepordize the strength to keep the valve operating in the position its supposed to. The boss doesn't seem to have much of a gradual slope into the roof of the port. Relieving the severity of this angle creates the better flow path into and through this part of the bowl area. The arrows I have used indicate the point of each side of our valve boss comes into the bowl. Could doing some material removal & radius work in these two areas benefit?


Seeing the exhaust valve guide boss in a highlighted picture as well, you can see the obvious. Going into and out of the cylinder, there will most likely be a generation of vorticies or 'turbulence' if there is immediate changes or of the like in the path. If we improve our exhaust flow starting at the face of the valve, between the valve curtain and seat along the short and long radius, around the valve guide boss. This brings us back to the thought of scavenging of our cylinder. Improved flow should decrease cylinder contamination from reversion on this end. If things flow well up to the turbocharger's capacity, reversion will be reduced without needing to test an tune anti-reversion techniques. There will be reversion on the intake side from the higher cylinder pressure compared to intake tract pressure. Intake air contamination may be reduced as well only if the back-flow characteristics are good. Flowing heads backwards can tell how easily reversion will be.


Looking down into, you can't see too much as far as good definition of the view of the exhaust boss, maybe it was the quality of the camera. Anyways, you could call the shadowed area the top of our boss from how the picture is taken. Again, any head you can do the same basic shaping and clean up as long as your port does not become 'out of shape' compared to how the port itself came.


Since we improve flow stability and capacity through porting (increase in velocities and CFM too) and cleaning up casting imperfections, we produce a stronger swirl action too. Now if you look at the 6.9, 7.3, Cummins 5.9 12V mills you see that the valves are positioned in the center of our cylinder/chamber. Since 2 valve cylinder heads influence swirl naturally, its best to maintain mixture motion in the center area which the valve positions and the piston crown influence this. I hope to get some ported pictures of something on here in the near future.

[Fahlin Racing]

Update, I have not been able to get some heads yet to work with, I will try to by the end of the summer but I am not holding my breath. its been a busy year so far but I will get something up! Sorry for the delay guys and gals!

[Fahlin Racing]

Update, I managed to get some Duramax heads today, and a buddy is going to ship me one of my 7.3L N/A heads at some point in the near future, so there will be somethin' soon! I plan on getting some silicone molding material so we can see the port shape and imperfections out of the head too.

[Fahlin Racing]

For those wanting something to chew on until I get my mold silicone (hopefully in a week or two, maybe), here is the 2011 Duramax head view of the firedeck and closer view of the intake valve bowls. Just so everyone knows I will be grinding and cutting this head apart to see what everything looks like inside the 'outer' part of the casting along with testing the porting limits.





I would say on thing wrong, the position of the glowplug is not centered bwteen the valves the best so going to a larger intake valve or exhaust will only IMO create interference not only in physical proximity but allow more cracking possibilities due to material removal. I could be wrong in some way but that is how I am viewing it.

[Fahlin Racing]

Here is a piece from Jim Mcfarland in chapter of a racing book taking into consideration of equalling out the ports pressure distribution through the runner when flow is occurring.

Whether the "working fluid" is air or air and fuel, air tends to follow the shortest geometrical path between two points of pressure difference. In areas where pressure is skewed to one side of the path to another, low pressure opposite these areas tends to encourage air/fuel seperation or low pressure instability. Intake and exhaust port dimensioning (or modification) should include consideration of these basic features, attempting to keep pressure distribution as uniform as possible across each port section.

Regardless of the shape, as long as the port surface has nothing more than micro-vortex generation, the airflow boundary layer, our cylinder filling will proceed in the right direction. As we enlarge our port, we decrease flow velocity some, in turn we increase the port's flow to a higher rpm level. If we can lighten rotating masses and further improve rpm capability the use of the larger port will become apparent. However we must still take into consideration the proximity of the water ports in the head as well.