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911s · 02-13-2004, 06:03 AM

What about the 'divots' at the entrance to the intake port? Will this not create a disruption to the intake flow. This is why I was considering porting MFI heads, so as to create a port that doesn't have this divot.

jluetjen · jluetjen's Garage

divots???

William Miller · 02-13-2004, 06:48 AM

Can anyone confirm the size of the intake ports on the 930/10
Euro engine? Were they originally smaller than the intake runners like the specifications written in Waynes book.

I have the little spec book, but that's about the only thing I can't find in there.

Tim Walsh · Tim Walsh's Garage

There are divots on CIS heads where the injectors poke out (probably to avoid spraying the walls of the intake runners. I've seen a few of these heads floating about my machine shop (well really a race shop) and they don't seem to mind them at all. If you're really worried about them I'm sure someone who can weld aluminum can weld in something there.

William Miller · 02-13-2004, 07:02 AM

When I opened up the throat of my heads to match the runners the diviots were almost all gone.

snowman · 08:05 PM

If there are divots in an intake and the factory put them there, DO NOT MESS WITH THEM! They are likely very important factors in the intake flow. NASCAR and others have played with specialized divots and things like them and as a result have been able to make more power than thought possible. What divots do is to act like a source of ball bearings for the air flow, improving it significantly. If you want technical referances look up something called Ribblets, a mathematical thing. If you know what they are you already know to much. They used these things on a special skin developed by 3M for the Americas Cup racing boats. IN that case they looked like record grooves or grooves seen on the side of a shark. THese special features are still very very hush hush due to the competative nature of racing, but they will admit to using them and People I know have actually seen them in NASCAR intakes. Unfortunately these are in the realm of world class math wizzes or which they are VERY few. Sort of like trying to find out how to build a nuke only that would be easier.

911s · 02-13-2004, 08:08 PM

The divots are specific to CIS engines. I see them on SC heads, as well. They are there to allow the CIS injector nozzle to introduce fuel to the intake port. Obviously, the problem here is that now I can't port match the intake manifolds to the port. So, there's going to be this 'divot' on the intake side of the port, which I'm guessing will slow the flow down as in enters the head (much as water flow decreases as a stream enters a pond). If I have to weld up these 'divots', then I may as well just port the MFI heads.

911s · 02-13-2004, 08:40 PM

Ok, for those who haven't seen a CIS port before, I ran out into my garage to get some photos so you guys can see what I'm talking about.

911s · 02-13-2004, 08:45 PM

Sorry, need to explain. The first photo is of a MFI head (2.4E), the second is of a 2.7 CIS (I believe this is not an S head, as the intake ports appear to be the same size as the E head, only with the divot in it). The engine I currently have in my car is a 2.7 S, which 'should' have the 35mm intake ports, with similar divots in them. Wayne's engine book illustrates the divots in the ports, as well.

Wayne 962 · Wayne 962's Garage

Quote:

Originally posted by William Miller
Can anyone confirm the size of the intake ports on the 930/10
Euro engine? Were they originally smaller than the intake runners like the specifications written in Waynes book.

I have the little spec book, but that's about the only thing I can't find in there.

Port sizes are listed in the master engine table in Appendix A...

-Wayne

jluetjen · jluetjen's Garage

Ohhh, I don't have a clue -- but if you are not going to be useing the CIS, why not just fill the "divot" with epoxy or have it welded up??? I could picture that it would cause some disturbance to the air flow in the port. But then maybe not. This would be the perfect thing to test on a flow bench.

350HP930 · 02-14-2004, 02:11 PM

The divots are there to clear the spray pattern of the injector.

The injector is aimed at the head of the valve and that part of the head is in the way of the best shot down the hole. Its not there for any type of air flow advantage but its not really disturbing the flow that badly either.

If you had no CIS it would make sense to get rid of it but there are downsides to the solutions.

I would be cautious about filling it in with epoxy since fuel exposure and heat cycles could cause it to come lose with disasterous results. Welding is more difficult and would add some odd latent stresses to an otherwise seasoned head. Unless you are really pushing the limits on a motor I wouldn't bother filling it in.

snowman · 06:13 PM

Now I see what you ment by divots, its the "s" that got me going on the wrong track as in more than one divot per port. The divots I referanced, that improve air flow are spots like you see on the surface of a golf ball.

The "divot" providing clearence for the injector spray pattern is in a relative dead zone of the port, ie small and possibly even large changes in it will not do much of anything to the air flow. The opposite side, the short radius is VERY sensitive to anything done there. A small bump there could make as much as a 30% or 40% change in air flow. Thats just a guess, but I have seen similar results on a number of differen't heads on the air flow bench.

I suspect that matching the ports, as well as possible, ignoring the divot, will do the job. Only an air flow bench will tell for certain.

911s · 02-14-2004, 10:12 PM

The way I'm looking at it is, if I were porting a head, I would not make such a pocket at the entrance to the intake port. Therefore, why would I accept such a pocket, even if it were introduced from the factory? Precision seems so critical for other things, such as tapping and plugging an oil relief passage, and yet we should be able to accept such an abnormality in an intake port? I mean, if it's ok to leave the divot there, then what's the big deal on port matching manifolds to heads? Anyway, that's the way I would feel, and why I think that using an MFI head would be a better alternative.

350HP930 · 02-15-2004, 07:11 AM

Port matching gets rid of blockages to the flow which is critical to good flow. That divit is a void which should to little to nothing to block or restrict the flow.

Wayne 962 · Wayne 962's Garage

I personally doubt it would show much difference on a flow bench, assuming you had a straight-through manifold mounted on top...

-Wayne

snowman · 02-15-2004, 06:06 PM

Quote:

Originally posted by 911s
T... Precision seems so critical for other things, such as tapping and plugging an oil relief passage, and yet we should be able to accept such an abnormality in an intake port? I mean, if it's ok to leave the divot there, then what's the big deal on port matching manifolds to heads? Anyway,...

Your concern is true in general, but with experience porting heads on a flow bench you end up finding out some things are important, and some are not. It happens that Porsche introduced the injector at a point in the port where there is little likelyhood of much interference with the flow, which is probably NOT an accident, as Porsche knows what they are doing. So to summerize the divot may look pretty awful and appear to be a big mismatch, however the air is flowing, in this very specific spot, in a way that it will tend to ignore the presence of the divot completely. THis in not true on the opposite side of the port where ANY little disruption, in or out can harm the flow. Again a flow bence is the way to prove this. You should have this done to both prove that the divot is insignificant and set your mind at ease. While at it have any minor porting changes done to enhance the flow.

911s · 02-15-2004, 07:08 PM

I would think that they would want to introduce the fuel at the point where the velocity is high, so as to ensure that the fuel stays atomized, and doesn't fall out of suspension before it hits the cylinder.

At the same time, I can't see the factory putting something in the port that would slow the velocity of the charge going in to the combustion chamber. I would like to examine a CIS runner, just as it meets with the cylinder head. The way I'm looking at it, if the CIS runner is round, as would be a Weber manifold, then it should be ok. But, if the CIS runner has a similar divot, which matches up to the divot on the head, then I'm going to have to re-think how I want to approach this whole thing (which would be to use the MFI heads, as originally intended.

snowman · 02-15-2004, 08:06 PM

The injector sticks out in the port, just a little. but the SPRAY is, well SPRAY, and extends well into the port and the airflow. The divot insures that the SPRAY PATTERN isn't disrupted. Think momentum, ie the spray will not be dormant because it is directed in the direction of the air flow and into the stream, but the injector itself does not interfere with the stream. The point where the injector is placed IS dormant and fuel would and likely does drop from suspension at this point, thankfully the injector is providing enough boost to keep the fuel going in the correct direction. Hope this helps.

William Miller · 02-17-2004, 07:22 AM

Wayne-"Port sizes are listed in the master engine table in Appendix A..."
I saw them and that is what I am looking for some one with a 930/10 engine to confirm the specifications in your appendix.

If the specifications in the appendix are correct then the intake port was smaller than the diameter of the runner. This was what I found because the long block was replaced in my car with a 930/16 long block which had the smaller intake ports. (The runners were smaller on that engine as well.)

I would think that Porsche would have matched the port size to the larger intake runner size on the 930/10 engine. If not, why not?