911SC-L (3.1L) Fuel Distributor question

[GTT]

Question for the group: I am rebuilding my 82' 3.0 and have upgraded to the 3.1L Engine Leistungsgesteigert pistons/cylinder kit recreated by Henry at Supertech. I want to keep CIS on the car, and am now at the stage where I am going through all my CIS components and rebuilding/replacing worn out parts. As background, the car sat for 25 yrs so it needs everything. I've read several articles on the factory 3.1L upgrade that indicate an "upgraded fuel distributor" was used.

Since both my fuel distributor and WRU likely need to be rebuilt, does anyone know what fuel distributor was used or what the specs were? I've been reading everything I can find on the CIS system and have a good understanding of how all the components work, but I am just trying to get my head around what changes, if anything, I should make since I've now changed the displacement, or should I just have my fuel distributor and WRU rebuilt to the stock specs for my car?

Currently I have the 3.1L P&C, 10:1 compression, 964 cams, SSI exchangers and a sport muffler. I live in a state that does not have emissions testing so I'm not concerned about keeping all of that stock.

Thanks!

[Henry Schmidt]

If your engine is a US version, you have a challenge to maximize this set up.
You would want an early (78-79) SC big port air box and plenums. The early 031 fuel distributor and ported heads. There is a Euro fuel distributor that is better 098(?) but it's hard to come by in the US.
The challenge is with the Lamda system. It is designed to create a lean burn condition to meet smog requirements.
The early system doesn't have that equipment. The warm up regulator is adjustable so your stock one will work.
The next challenge is to clean up the CIS. It has a decel system that is prone to air leaks and vacuum failures. The cleaner the system the better performance is available.

You might note that there is no breather from the oil tank. This removes an air leak and make vacuum pressure more consistent. The new breather attached to the air filter portion of the air box. This one even has the auxiliary air valve removed because we retrofitted an early hand throttle.

[GTT]

Thanks Henry! This is exactly what I needed to know, and appreciate the pictures as well. Yes, I have a US engine, so looks like I need to start searching for some parts!

[PeteKz]

Let me add to the redoubtable Henry's comments.

I strongly advise to first get the CIS running with the original parts. Don't complicate things by throwing different CIS parts into the mix. After you have it running properly, THEN consider changing things. It will also be less expensive that way. You probably don't need to "rebuild" the WUR and fuel distributor, but you do need to clean them out with carb spray. There's plenty of other discussion here about how to do that. I caution you to be very careful handing the FD, to make sure the plunger does not fall out and get damaged.

Some people say that the various CIS parts are calibrated to that year engine, etc., but in my experience, they work across many engines. Merely increasing the displacement 4% will not require a different setup. The OXS (lambda) system does lean out the mixture at part throttle, but that actually increases cruising fuel mileage. It does not hurt power, because the throttle switch on the throttle body signals to the OXS that you are at full throttle (actually past about half-throttle), so the OXS goes to full enrichment open-loop anyway.

Your 1982 WUR should be a 090. Henry referred to a 089 that was used on the RoW cars. The main difference is that the OXS equipped cars do not have WUR vacuum enrichment, because the OXS system controls the mixture. If you decide to ditch the OXS for simplicity, then you will need a WUR that has vacuum enrichment. I have swapped back and forth with several vacuum WURs on my car (without OXS), and I can't tell much difference between them--maybe during warmup, but after fully warm, they work the same. A WUR 033, 089, 069, or 045 will work for you.

Henry also referred to the large intake manifold runners and heads with larger intake ports used on the early SC and RoW cars. Sourcing those can end up being an expensive slide down the slippery slope, and good luck finding them. If your budget allows, spend the money, but you won't notice a difference below 5000+ RPM and full throttle. If you're not satisfied with the CIS system you have, tweaked for best performance, then you will probably end up looking at a new fuel injection system with ITBs anyway.

Let me beat you again--get it working well with the setup you have BEFORE you try different CIS parts!

I don't remember offhand what the 3.1 piston domes look like--please post a picture.

Like Henry's engine above, I removed the decel valve, AAR, AAV, and warmup plumbing because my car has a hand throttle. I like to keep things simple.

[GTT]

PeteKz, thank you for taking the time to respond and I appreciate your advice. Yes, just checked and my WUR is a 090. As I was cleaning the years of grime off the various components this afternoon and contemplating what it would take to backdate my CIS so to speak, I had pretty much convinced myself to just put it back together with the original parts and get it running first. Your comments just confirmed my thinking. I have been bitten by the Porsche bug hard, so I suspect I'll have plenty of time to tweak it and experiment in the future. For now, I just want to get it running well and drive it like it's meant to be used.

And here is a picture of the 3.1 dome - sorry didn't take a picture before I installed them.

-Troy

[Henry Schmidt]

With the stock O2 sensor system you risk lean conditions under off cruise acceleration. This is the major cause of damage in the 81-83 SC engines. A large percentage of the SC engines we've rebuilt of the last 30 years have had piston damage due to detonation.
Leaving it stock and expecting performance at speed is a formula for disaster.
We've done this a few dozen times and the modification I recommend is the best option for performance CIS. Track proven and well worth the effort.
This kind of piston damage is /was never seen in the high compression big port euro engines or the low compression big port 78-79 US engines.

What that old saying:Not enough money to do it right but plenty of money to do it over.

[G450X]

Great discussion! These discussions reach out way beyond the recipient and help innumerable enthusiasts.

When I have time to get back to my project 3.0 “Max Moritz” setup, I have better guidance now.

I have accumulated numerous early 3.0 SC CIS parts (and heads) and now have a clear direction on my pending build. I need a hand throttle setup, so I am now on the hunt for those parts and info on how to add this to my early CIS setup.

I’m all for simple is better, and I want more high rpm power. The fact that my relatively stock ‘82 SC (SSI’s & M&K 2/1 on a stock 3.0) falls off cam around 5500 rpm drives me nuts. A common small block Ford engine revs higher with pushrods and ancient tech. I know some people love to putt around with a torquey engine and not changing gears, but not me.

Many Thanks - I know I’m not the only one out there that many of these discussions help.

[GTT]

For the benefit of anyone else following this thread, Henry and I emailed each other last night and I'm attaching our discussion (with his permission) as I'm sure it would be helpful to others:

Hi Henry, I’m reaching out as a follow up to the question you answered for me on what fuel distributor I should be using with my 3.1L set up on the Pelican engine building form. I actually have a lead on a early (78-79) SC big port complete CIS system with a 031 distributor, but since I didn’t port my heads in your opinion is is still worthwhile to use the bigger airbox, plenums, and the early 031 fuel distributor? I guess I should have done a better job of planning this all out before I started assembling my motor, but this is my first 911 so it’s been a learning experience.
Hi Troy
In general, an engine project like yours can take many unique directions.
For what it's worth: If you built a solid bottom end and the piston and cylinder set offer reasonable performance, the only thing holding your back from going crazy is the port size. with larger port size and your bottom you open the possibilities in many directions without much disassembly.
Some possible directions:
Carbs with a simple cam change,
MFI with injector adapters and cams
EFI with large butterfly.
All these including the early /Euro big port CIS
That said: If i understand your current build state, removing the heads for big port modification is only a few hours away and only a few hundred dollars.
That simple modification done now gives you a plethora of future possibilities.
The essence of the Porsche 911 is evolution. It makes sense to make evolution as painless as possible.
The next question: is she a keeper. Do you plan to pass it to someone in the family.
Many of these cool old cars live in families for generations.
I hope this helps
Cheers
Henry

[PeteKz]

Edit: I posted my reply at the same time as GTT's previous reply. So, at this point, I defer to what Henry said.

GTT: Let's say that you eventually go to CIS with the larger intake manifolds, or ITB's or carbs. If it's in the budget, have the heads ported out to the larger size now, before you put them on. Otherwise, you will have to remove the heads later to replace them with the larger port heads, or get these heads ported then. There's not much advantage to swapping to larger intake manifolds or ITBs or carbs, if you still have small port heads. Whereas, you can run the smaller intake CIS manifolds with the larger or ported heads until you change the intake.

[Jesse911]

I'm changing my '77 Carrera 3.0 to ITBs and EFI. If you want I can check the numbers if you are interested. Send me a PM.

[Henry Schmidt]

Originally Posted by Jesse911

I'm changing my '77 Carrera 3.0 to ITBs and EFI. If you want I can check the numbers if you are interested. Send me a PM.

Your system should be a big port, rich running, enhanced delivery, fuel distributor.
These engines were low compression (8.5:1) 200 hp. This was about 20 hp more than the US delivery 78 SC.