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.

divots??? :confused:

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.

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.

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

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.

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.

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. http://forums.pelicanparts.com/uploa...1076737150.jpg http://forums.pelicanparts.com/uploa...1076737193.jpg

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.

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

-Wayne

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.

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.

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.

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.

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.

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

-Wayne

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.

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.

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.

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?

I'm a little confused now too. Where does the factory measure the diameter of the port? Right at it's entrance, or further inside at some point of taper?

Cheers

John;
They are referenced by the port's diameter at the manifold face.

Thanks John

Hey guys, I got a question. Say I wanted to open up my MFI head intake port from 32mm to 36mm. Would I open it up, being careful not to mess with the short side of the port too much?

See the picture I've included. Assuming the original port size is 32mm and the red line represents 36mm, is this the way one would set out to accomplish opening up the port to 36mm? Anyone have a 'S' head, that can measure the distance between the manifold stud and the short side port opening? Or how about from the other manifold stud to the long side port opening, for that matter? Possibly some pics of a 2.0, 2.2, 2.4 'S' port to reference?

http://forums.pelicanparts.com/uploa...1077072897.jpg

Anyone with other comments on how to go about accomplishing this (not 'don't do it')? I'm thinking of trying it out on the 32mm CIS heads first and trying it on an engine I have. If it works, then I'll consider doing it on the MFI heads. I'll still have a stock set of 2.7 'S' CIS heads available, if all else fails (and actually, if the 32mm CIS heads don't fly, I won't even bother trying to open up the MFI heads). Any info or opinions are appreciated (including the 'don't do it's' - with appropriate explanation).

Thanks.

Wow, what happened to my picture. I'll try uploading it again.
http://forums.pelicanparts.com/uploa...1077073983.jpg

Help! I'm not able to post picture. Can anyone help? What to do?

Sorry guys. To get the picture, highlight the "http://forums.pelicanparts.com/uploads2/MFI Intake (e)1077073983.jpg", and paste it into the address box above. This will take you to the picture, but you won't be able to view it with the text.
Sorry!

911s,
Paint the area around the intake port with Dykem, temporarily install the S manifold gasket, then transfer the gasket ID onto the head with a scribe.

It doesn't look like your picture below corresponds to the above.
http://forums.pelicanparts.com/uploa...1077094844.jpg

BTW, to successfully upload, your file name must be without spaces or symbols.

Sherwood

911S-
My thinking is that it would be important to get your hands on a S head. I think that it would be possible to glean 3D information from that head so that you can insure that your ports share all of the nuances with those originally having larger ports. It seems that someone must have an otherwise unuseable S head lying around that could be purcheased for a reasonable price (cracked or otherwise damaged). When you done, you can sell it to me so that I can do the same!
-Scott

The last heads I looked at had the "S" diameter everywhere but at the manifold connection. There the port size reduced to the smaller 32mm size. Seems like Porsche started with S heads, and marketing said we need lower performance versions, so what do we do to mess up the performance a bit. Neck down the port at the interface and mess up the cam seems to have been part of the answer. About all one would have to do with the port I have seen is to open up the area at the manifold so it matches the rest of the insides of the ports. Of course the heads must match the manifold runners.

An even more important observation I have made is that the 32 mm heads flow more than enough air to support more power than possible with this engine, so why bother porting them, thats unless you intend to rev them past 8000 RPM. The ammount of power gained at lower RPMs is maybe one or 2 PERCENT!
I have based this observation on a VERY limited sample of Porsches heads, and it may not be true for all fo them. Anyone else seen the same thing???

Snowman,

My intention was to open up the port without disrupting the all-important short side, as you mentioned earlier. The only way I can see doing this, without touching the short side, is to do it the way I've illustrated in the photo, assuming that the S port is also round.

I'd love to get my hands on a S head, but until now I have not been able to do so (guess I'm not trying hard enough). I'll try putting in a wanted post in the classifieds section. Now, should I be looking for a 2.4 S head, or will a 2.2 or 2.0 serve the purpose?

I donno Jack. Here's a comparison that I've done between the early S heads that I have (2 different years) and a set of 2.4TK heads. I don't see any similarity.

Distance in.............2.2S............2.4TK...........2.2 E
from Manifold
Face

0 inches...............36x36mm.....30x30mm.....32x32 mm
.5 inches..............38x38mm.....31x31mm.....33x33m m
1 inch..................39x39mm.....32x32mm.....34x3 4mm
1.5 inches............40x40mm.....35x35mm.....35x35mm

Note that 1.5 inches in is where the throat transitions into the bowl. I don't see where there is any overlap. I've got a 2.2E longblock in the garage in which I can measure the port dimensions and I'll post them after lunch.

PS: I've just added the 2.2E data above.

Jack, have you seen enough SC heads to answer my earlier question?
The 79 heads have larger ports and runners. The US 82-83 ports and runners are smaller. My Euro CIS has the big runners so I opened up the 930/16 intake ports to match my larger runners. I'm trying to confirm if the original 930/10 heads on this engine were the same as the 79 with the larger ports or were the ports the size of the US 930/16.
Waynes book shows thatthey are smaller which wouldn't match the runners. To me this doesn't make sense.

When I opened up the intake ports it seems simular to what you observed the 930/16 ports just narrowed to the smaller diameter "Necked down" as you mentiomned near the interface.

What do you suppose the reason was for reducing the size of the runners and the intake ports on the 81-81 US cars.
The only thing I can think of is that if you make the tube smaller the air velocity would increase. (Maybe this was an emissions thing.)

Emissions was not as big a deal with the ROW cars so they kept them big?

John, that is what I observed on my 82 SC heads. (I didn't measure them, but when I bored them with the 1-1/2" hole saw they opened up to that diameter somewhere about 1 - 1/2 Inch down. That's why the transition was pretty smooth. It didn't really effect the inside corner that much if your careful. 1.5" = 38.1mm (It was probably about 1mm larger by the time I cleaned it up.

William;
I suspect that the reason that the ports of the CIS cars were reduced in diameter is to increase the air velocity. Keep in mind that downstream of the air meter, the induction system will be operating in a partial vacuum (the pressure will be less then ambiant). With the larger ports and the reduction in pressure, I could picture the velocity dropping below a level that Porsche desired to keep the fuel from the constantly spraying injecters suspended in air. By reducing the port diameter, the intake velocity increased which would have increased the turbulance, both of which help to keep the fuel from settling on the port walls, especially in low rev situations such as when emissions are tested.

Ultimately the smaller port size didn't hurt the peak HP of the CIS engines since the real gate to peak HP is airflow, and as I mentioned, that is constrained by the CIS's airflow meter. If you change from CIS to Carbs or MFI, then I believe that the smaller ports will be an issue as far as generating peak HP.

John, I agree with you on the probably reason the ports were reduced in size probably to improve emissions on the US cars.

However I also believe this probably had a marginal effect on power.
No reason to keep the large intake ports on an engine that would be later restricted by the cat in the exhaust system.

The ROW 930/10 engine didn't have that restriction and they kept the larger intake runners (My guess is that they also kept the larger intake ports. My quest is to have someone measure and confirm this)

My guess is that the Euro engine 930/10 engine was more powerful mostly because it had no cat and flowed better both exhaust and intake next is the bump in compression and lastly cam timing was retarded which I understand does not actually increase a lot of power but pushes it up more twards the top end.

Can anyone confirm the intake port size?

Just don't discount the affects of the CIS airflow meter. If you can't flow the air into the system, nothing you do downstream of the airflow meter's obstruction will allow you to flow more air then the CFM allowed through the meter. Besides, with the non-existant overlap in the valve timing, it's not like there is a huge amount of exhaust tuning going on.

Did the Euro/ROW 930/10 use the exact same CIS system as the US version? What specifically are the differences?

I just updated the data above with measurements from the 2.2E that I have in my garage right now.

I apologize for coming to this thread so late, and not reading it in its entirety - this is very interesting because "home porting" is something I've been grappling with...

The 204 hp ROW 3.0 engine had the large 4R intake runners and appropriate intake ports. This assembly was used in the U.S. '78-79 3.0 engine. As John says, for the '80-'83 3.0, these runners and ports were shrunk to the 2R size, most probably for reasons toward an increase low-end torque and thus better traffic friendliness.

This home porting, however, is an effort I've been highly interested in. To enhance eventual use of 20/21 camshafts in an '83 3.0, it has been said that the larger ports and runners will be a better match than the 2R-style ports. Yet, my concern is whether or not the camshafts might damage the valves, etc. And from what I know of the 911 cylinder heads to change the valves, springs and all else, the heads have to be removed. At that point, it might be a better deal to simply port the heads in the usual manner - off the engine.

The hindrance is the need for valvetrain modifications. If this were not needed, I'd be very much in favor of home porting.

Any thoughts?

For all those interested in home porting I would encourage it. My first suggestion is to get all the books on porting you can find, there are several English ones that are very good. These books also cover how to build a home made flow bench, a must for any porting, other than port matching. Don
't be scared of a home made flow bench, one can be made with a typical shop vac, a couple dollars worth of tubing and wood, thats all. You may not get absolute flow numbers, but you will find out if you made it better or worse.