Home porting? Like Home perm?

[jluetjen]

Scott;
While in concept I agree with Snowman (specifically that the stock T/E heads are awfully good right out of the box), I do disagree with him in degree. I have been hard pressed to find an engine using heads with 32 mm ports which made more then about 165 HP, let alone 200+ as Jack has suggested in the past. In the absence of such an example, I can only conclude that "you can't get there from here". Porsche would seem to agree since they did invest the time and money to develop the S heads and used them for any of the non-race pre-SC engines which made more then ~165 HP. I'm not trying to start anything with Snowman (BTDT! ), I'm just sharing where we have a difference of opinion in regards to the conclusions that we've drawn.

A 2.5 with E cams will most likely be making about that amount. If you are going to be using your car primarily on the street, you could most likely get by quite happily with the stock E ports. If you are going to track or autocross your 2.5, then I think that your approach to "copy exact" the port profile of the S heads would make sense. The same applies since you intend to upgrade the cams and pump in the future without opening up the who engine again.

BTW, are you running "Early E/Solex" cam or the later 2.4E cams? The later cams with the wider lobe angle (ie -- less overlap) will most likely work better with the 32 mm ports then the earlier cam. The difference I would expect to be a slight drop-off in torque at peak RPM's. Conversely, I would expect the earlier cam to maintain its torque a little better at peak RPM with the S style ports. I doubt the difference is huge, but if you are trying to build your engine to be the best that it can be, every little bit will help.

Now that you've heard everyone's $0.02, please let us know what you chose to do and how it turns out.

[911s]

I got a question. What would be better for a 2.7 engine with E-cams and webers? 2.4 E heads, or 2.7 CIS heads? Ported 2.4 E heads, or stock 2.7 CIS heads?

[jluetjen]

Are the CIS heads the "normal" CIS heads or the "S" CIS heads???

[BK911]

911s:
No, I did not polish the heads myself. But I am going to work on them to even out the flows and make them more consistant. I'll start with the worst one and see what happens.

BK

[Scott Clarke]

Believe me, I'd like nothing more than to reach the conclusion that I don't need to do anything at all. The most power I'm aware of coming from small ports is "scruffy's" motor- 33mm ports and 176HP. Porsche never got anything more than 165 from 32mm ports. Note that the 2.0 rally motor that used 32mm ports in conjunction with S cams developed 150. Anyone else have hard data on small port motors? I'd love to see it.

Wayne-
Your point about useable power is well taken. I just don't want to get this thing together and have regrets. Furthermore, once together, I'd reallly rather not take it apart again anytime soon!

John-
My cams are 2.2 E. I think that makes them "late?" If they are late, does that mean porting is less effective or not worthwhile?

[jluetjen]

My cams are 2.2 E. I think that makes them "late?" If they are late, does that mean porting is less effective or not worthwhile?

The best way to tell would be to measure your cam. I assume that you don't have your engine together, so it really is pretty trivial and takes maybe an hour.

1) Assemble your camshaft (along with the gear) into the carrier with a head and the valves installed. Rather then use the stock valve springs, go down to the local hardware store and buy a couple of compression springs which are roughly the same size. The whole process is a lot easier without #100+ of pressure on the cam. Adjust the valves per the manual.

2) Get a piece of paper to record the data. Count the teeth on the camshaft gear and divide that by 360. That is the number of camshaft degrees per tooth. If you divide it it by 720 you will have the number of crankshaft degrees per tooth.

3) Rotating the camshaft in increments of 1/2 tooth (tooth - space - tooth) and measure the lift of both the intake and exhaust valves with a dial guage. If you really want to be precise, you can get yourself a degree wheel, but for our purposes I've found that this method is precise enough.

4) Record your findings.

5) You will then have hard proof (by the lift, duration and lobe angle) of the cam that you have. The Lobe center angle is the number of camshaft degrees between max lift of the exhaust and intake valves.

To answer your question, I believe that the differences will be fairly small (as in not readily apparent to you in the driver's seat). But as far as the combinations go, I guess I'd rank them subjectively as follows...

1) Early E cams, 36 mm ported heads
2) Late E cams, 32 mm ported heads
3) Late E cams, 36 mm ported heads
4) Early E cams, 32 mm ported heads


Given your original objective of upgrading the cams and MFI pump at some point in the future without opening the engine, I would agree that it most likely makes sense to port the heads to 36 mm's now.

[Tim Walsh]

John,
I'll soon be running the same cams.. 2.2E and they are more agressive than the 2.4E cams but have less overall lift compared to solex cams. I don't have any #'s since this is off the top of my head though.

[jluetjen]

Hi Tim;
It would be interesting if you could check them because my understanding is that the Solex cams became the '69E Cams after they added a drive for the MFI.

[Tim Walsh]

John,
I'll do some pocking around and try to figure out where I learned that..

[snowman]

I will rephrase what I said earlier to clarify why the heads do not need to be bigger. To get the Hp that I stated the heads would support requires much higher RPMs for this size engine. The reason Porsche had trouble had more to do with RPM limitations than head flow. In other words, if your RPM is limited to say 7000, then your HP is also limited to say 165 or 170 and the heads flow more than enough to support this. Above 7000 RPM the 36 mm ports will add a very small ammount of power over the stock 32 mm ports of the T version up to 8500 RPM. In fact the 32 mm ports will work here almost as well. The power is still limited by RPM for the given engine size. MOre power means even more RPM, unfortunately the engine starts to blow up at higher RPMs, consequently Porsche never acheived the full capability that the heads could support. A limitation of the bottom end, not the heads.

[aigel]

Why would you want the exhaust runners rough and not polished? The intake I understand, but the exhaust???

George

[snowman]

You are correct, exhaust can be polished. Benefit, small. Intakes not polished, benefit relatively big.

[aigel]

Jack:

How do you feel about polishing valves and head chambers?

All flat six heads I ever saw really are pretty smooth already from the factory. (Compared to a cast iron job from Detroit).

George

[William Miller]

OK, just jumped on because I wanted opinions on what I did. (Myself on my engine)

I bought a $4,000 bastard case (Not a basket case but a bastard case!)
It's an 83SC ROW 930/10 but the PO had a 82US 930/16 "rebuilt" engine installed in it in 1996. I rebuilt the engine last summer. Prior to that it hadn't run right since the engine was installed in 96. Because of the new engine code the CIS was "BASTARDIZED". Part original, part 83US. (Remember K-basic was used on ROW thru 83.)

I believe I read somewhere (I think Anderson) to make sure the intakes on the heads matched the size of the runners. "CIS intakes should be rough to help swirl the air and mix it with the fuel being injected. Exhausts should be polished, but not made larger." My Euro intake runners (manifolds) were the larger size 39mm? (Same ones used on the 78-79 US) The intake ports on the head were smaller 34mm. This created a step choking the air flow. My mission was to eliminate the step.

In looking closely inside the intake port I noticed that the port opened up a bit as it reached the bend and where the air goes arround the valve guide.I also noticed that the hole was perpendicular to the gasket surface. The exhaust gasket mounting surface is parrellel to the intake.

Some of you might get squeemish here:

I took a 2x6 and drilled 2 holes to accept the exhaust studs so the head could lay flat on my drill press. (The little bench top kind.) On the intake side I made a guide out of a piece of solid Coreon (Solid plastic counter top that's 1/2" thick.) I marked a center and 2 holes for the intake studs. I drilled the holes for the intake studs tight and the big hole with a hole saw. (1-1/2" is about 38 mm 1mm smaller then the 39mm ID of the intake runner.")

The guide was put over the intake and held in place with the nuts.
The whole thing put into the little drill press and the intakes were bored out to the new diameter. (Slowest speed on the press with lots of oil to help keep the chips away.) As I cut deeper into the port it gradually opened up to the wider diameter (matching the new hole) just near the bend.

Next I chucked up a ball end cutter into a die grinder and cleaned up the far end up against the valve guide. This is what takes some practice but i got pretty good after the first one. I finished with a little (rough grit like #80 sandpaper cylinder on the die grinder. When finished I'm sure the port is just about 39mm.

After figuring out the set-up each head took about 30 min.

This made the intake port match the diameter of the runner with a slightly rough finish. The transition at the guide end was very smooth.

A while after completing my rebuild I happed across the engine specifications in Waynes book. It lists 34mm as the intake port size. It doesn't make sense to me that the step was part of the original 930/10 engine? Were the intakes intentially choked down ti increase the air speed. Maybe there is a typo? 930/10 was just a continuation of the 79 US engine. It still had the air pump, but no Cat.

Anyway, with this setup I could easily repeat the results. I think it would work for anyone with a drill press and some patience. The results looked like it was done by a shop, however who knows about the performance. I'm not sure my description was that great on the guide, but if you need more detail let me know.
Jack, have you had the oppertunity to compaire a the later ROW head against a US?

[Scott Clarke]

William-
You have GUMPTION! You left one thing out: how does your car run?

[William Miller]

Scott,
I like it now! After a year and a half of battle, I've got the engine and the CIS sorted out. Low budget piece by piece. It ran like crap until I finally found a rebuilt Euro fuel distributer to match the rest of the CIS.
Unfortunately I have nothing to compaire it to. It's the only P-car I've driven in probably 15 years. I have to say I was ashamed of how it ran. Now I'm just ashamed of how it looks. Body and paint work comming next. I have driven it daily and it now has a little over 256K on the dial.

[jluetjen]

[911s]

"Are the CIS heads the "normal" CIS heads or the "S" CIS heads???"

To answer Jluetjen's question from his earlier reply (sorry, I forgot to answer it), I have the 'S' CIS heads from a 2.7. Is the 2.7 S heads better for use on a 2.7 w/E cams & Webers than the 2.4E heads are? How about with 2.4E heads ported to 36mm (Andersen's book says to use heads opened up to 36mm when using E cams in a 2.7 w/Webers).

[snowman]

Matching intake ports is always a good idea, as far as I know, exhaust may have an exception for something called an anti reversion step. Thats where the header is bigger than the exhaust port. For the most part it isn't likely part of the design, but a possibility. In general porting should be kept simple, ie taking out flashing junk and matching port sizes. The bottom line is an old saying, "to flow is to know". That means you use a flow bench to make changes. A flow bench can be homemade, using a shop vac and home made manometer. or a commercial Super Flow Bench. A home made flow bench is most useful for differential measurements, ie is it better than before, a commercial bench will also yield numbers that can be used in calculations.

On intake ports, the "short side radius" is most important. Use your finger to feel for any roughness or bumps on the short side radius of the intake port. If there are any make them smooth to the touch. How important is this? Well on a typical Chevy small block head the intake flow may be in the range of 160cfm, but with just the removal of casting flashing on the short side radius, the flow will increase to 225 cfm, thats a WHOLE bunch of power. How much, well just proportion the flow rates. The Porsche heads are much, much , much better than Chevy heads, stock, so don't expect as much gain. But if you can feel a bump, and most likely you will, then the flow increase will be significant after you smooth it out. There are other sources for flow iimprovemets, but for a typical Porsche, thats NOT where the extra power is, as they have already done a very good job at the factory. Just play around with a program like Dyno 2000 to see where the biggest bang for the buck is.

The next biggest bang for the buck is to radius the exhaust valves. The outside edge of the valve must be radiused to acheive maximum flow. All the other "tricks" have already been utilized by Porsche, ie 3 angle valve job, (a 5 angle job will only acheive something a real racer could appreciate) Porsche just did not leave much for the home mechanic to monkey with.

Finally I do apologize for the attrocious spelling ( I am an Engineer, who are not known for good spelling) but this stupid thing will not let me utilize this function., sorry.

[jluetjen]

911S, The CIS-S heads have intake ports of 35 mm, which should be just about perfect for a 2.5 with E cams. I doubt there is anyone alive who will be able to feel the difference between 35 mm intake ports and 36 mm intake ports (from either a stock S head or from porting your E heads) in your engine.

I'd just use your CIS-S heads and get on with the rebuild.