The JCW porting looks like it took all of 15 minutes with a grinder. I've spent over 40 hours porting a pair of cylinder heads before, using only a carburetor synchronizer and shop vac as a makeshift flow bench.

For the price, I would have expected CNC milled to at least be consistent between ports, but it sure looks hand cut.

 

so much better work can be done...last pic is stock cc.

 

Technically speaking, it's not junk. It's CRAP!!

 

ur right!! and i see ur a foundin' member of team craptastic....

i wuz jus being easy on it so thats why i stated "it's fair... for a JCwerks bit
but apparently its a g00d known fact now that it blows

 

The rough surfaces on ported heads are there to get the best air-flow velocity and fuel mixing. This removes the shear friction on the layers of air close to the contact surface (The Boundary Layer). This friction is caused by the zero-flow layer directly in contact with the surface. Then as you move away from the surface, the velocity increases, but due to contact with the underlying layer, there's some friction and velocity differences. The speed function vs. distance away from the wall is a parabolic funciton with zero at the surface.

The rough surface is kinda like a whole bunch of Gurney flaps which causes a vortex on the surface. This vortex acts like a bunch of ball-bearings allowing the air layer just above it to flow at full speed.

1) Each and every head design and layout is different, and every engine design likes & responds to different things.

2) Boundary layer flow control is very important. Observe how many precision pitot tubes a professional head porter uses with his flow bench. Those things are NOT cheap and you gotta have them to see how the heads flow at all valve lifts.

3) Port entry angles, guide boss placement & shape and throat contour, from entry to valve seat, are all things to be tailored to the camshaft profile in use. There is little point in working on flow numbers at .500 of lift, when the cams you will use max at .440.

Engines are to be considered in the context of the whole configuration when deciding on what head flow attributes are needed. A few factors are: Camshaft profile, Displacement, Compression ratio, Bore & stroke ,Rod length, Valve size.

As I hope you can see, this is a complex set of variables and there is no one-size-fits all, so be careful about generalizations,..


GOOD HEAD (One of my 911 RS America Ported Heads w/Big Valves)

David K.

 

911RS...
I hope you are not comparing your head work to the work done on the JCW head shown here on this thread. There is no comparison.

I understand very much what you are speaking of with laminar flows. This is a very debatable area with rough finishes compared to highly polished. I build radio controlled sail boats, and I am of the following that smother is faster then rougher. My boats are amoung the fastest in the world.

(An excuse to show off my boats .... )

 

So thats what you do for a living. I thought you made custom furniture.:smile:


Nice boat. Is that what you meant when you said your going sailing with a buddy.

 

One of the features Larry adds to horsepower optimized heads are dimples to the injector port path surface to create that boundary layer turbulence in order to prevent fuel from sticking and aid in mixing. There is no “polishing” on the interior of Endyn heads.

That’s some really good information to consider. I surely don’t know as much as the JCW engineers, however I don’t think those blunt edges and stock casting characteristics were left there for power effects.

 

We certainly looked at the JCW head, before we started the Cosworth
ported heads. The JCW head "is" CNC machined, which is pretty obvious if you do a closeup "feel" test, put your finger in the exhaust port each port has a small indent in on the right side giving away the automated cnc repetetive
cut it received. Is the head better then stock.....yes, but not much.

peter
Team M7
562-608-8123

 

911RSAmerica, understood.
onasled, understood
I'm sure you guys could both agree on a lot of points on this subject if we could verbalize in a discussion. This is where we are all limited by using text and the misunderstandings that prevail.
May I address those who see this and the comments as a mystery, i.e. what is this all about?
Head work, this is where the power is made, porting/polishing has it's place as part but only in the proper places per each application, that is a given. The ports assist in filling and emptying the chamber. The ideal is application specific.
Am I singing to the choir yet?
I posted those pictures so everyone could see and draw their own conclusion as to what the factory considered acceptable improvement on a stock part. Apparently from my observations there is a combination of machine and hand work in the exhaust ports only. I do not believe any flow work or port comparison flow testing was part of the procedure.
Now if you will consider this, Endyn's approach is the total concept from intake port, injector charge turbulence, flow velocity, combustion chamber swirl and squish to exhaust flow, scavenging. I am sure we could all lean tons from his work, he has been at it for years and has to his credit major breakthrough's it this area. His custom pistons work with the combustion chambers as part and parcel of said combustion chamber to create a efficient swirling mixture for burn propagation. The combustion camber is where the power is created and has to be considered as unit, Piston crown to head squish area with motion to the mixture. Of course the ports are important in aiding this and must be optimized from flange face to valve seat, this includes the backside of the valve heads, stem and guide bosses.

 

Although I agree that JCW didn't do much to the head, I'm pretty confident that they DID do flow bench testing, at least. They would be foolish not to have done so, given their funding and access to equipment.

A head shootout between the vendors is definitely in order, since baselines for the stock heads tested by Pilo and Webb varied considerably. Those are the only two baselines I have seen posted.

 

the stock heads are most likely CNC machined, as are the JCW heads; the issue is the amount and specificity of the machining

 

Same reason golf ***** have dimples - keep the boundary layer turbulent as long as possible!

 

different reason; golf ***** don't travel in an air/liquid suspension.

 

I'm not trying to be a wise *** but air is a "fluid" why don't the laws apply?

 

It is the same thing. To reduce drag on a sphere, you create a uniform roughness around it. Even non-spherical surfaces can benefit from this. If you look at olympic swimsuits or even Lance Armstrong's biking suit, they have rough and smooth portions depending on how the air goes by.

By roughening the ports in a head, you create many small vorticies in the intake path which allow the air and fuel to mix but it also reduces the overall drag by reducing the large vortex at the end of the path.

Until you get into airfoils like plane wings do you see a need for a very smooth surface. The airfoil shape itself has a much lower "form drag" compared to the "skin friction drag" that would be reduced by a smooth surface. On spheres etc, they have a high form drag that's significantly reduced by roughening and the skin friction drag increases just slightly.

 

...written in grape vine literature, the JCW folks thought they could get another 15hp or so from the head, but BMW was worried about warranties...

Risk management aside, I would certainly feel comfortable asking the right BMW folk, "why bother?"

 

Kind of like fish scales?

 

I believe you are right.

 

What looks good doesn't always work well. I know Larry (theoldone.com) and many engine builders that are forced to spend a lot of time on port asthetics because of customers expecting a look or finish. You can see on the intake port of the JCW the throats were opened up and the floor and roof of the port have been worked on. On the exhaust port the roof has been done but that's all you can see. The chambers were left alone. It's no work of art but work was done. Without looking at the throats, short radius and examining the valve job is hard to say how well the head works or not.

I don't think you'll find a skilled engine builder that's working with fuel injection that is polishing the ports (the don't flow high volumes of liquid, hopefully none). Anthing more than a catrige roll in the port is overkill. Typically the original finish from the casting flows the best but that's not what customers want to see:smile:

 

like andy said... enough of pictures, etc.. and internet bickering... lets get a shoot out.. well actually maybe the aftermarket could compare their flows to the this jcw head... and then folk can have hard data for beating up the bmw/works parts...

 

What jlm said was that the ball didn't travel through an "air/liquid suspension", i.e. atomized gasoline suspended in an air charge, not that air is not a fluid.

It is a very different concept. The golf ball dimples allow the ball to travel farther because they give the spinning ball more lift allowing it to stay in flight longer. They wouldn't help at all if the ball did not spin, they would in-fact increase drag, limiting the range of flight. You don't see anyone going around dimpling the skin of a 747 to reduce drag because that is an aerodynamic body that does not spin as if flies through the air. Or at least it shouldn't.

Good head work is only dimpled or left unpolished on the intake side to increase turbulence and mixing of the air and fuel, not to reduce drag. Just as k-huevo indicated. The exhaust side should be highly polished in order to move as much air (fluid) as possible without regard for mixing. If our engines had direct injection then both runners would be polished for optimal performance.

 

A: So MINI Dealers can charge 10hrs labor for a JCW install!

 

Ever played golf in Florida's humidity?

 

he he on that one; I played on my HS golf team in Oregon...

larry has said the dimples help keep the feul atomized; that is so it doesn't wet out the walls.