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.