Why did the Factory use different Wur's - same engine

[Tidybuoy]

I'm just curious as to why the factory used the various different wur's on the same 2.7 engine. All of these wur's have different warm pressure specifications.

For example, according to Jim's Primer: #008 = 3.0, #009 = 3.0, #017 = 2.7, 75 911 = 2.2, 76 911 = 2.4. #033 = 3.2.

On my '74S, I use a #033 and have used an #009 with a vacuum enrichment base added. I have found that my car runs better with a warm pressure at around 2.4 bar and it does not run as well when I set it to spec of 3.2. I'm wondering why this would be but this could also be due to the fact that I have a '79 fuel distributor??

Are there any variations in the barrels (i.e., the section that the fuel lines connect to). It seems to me that you could use any model of wur and set the pressures accordingly but this might not work if the restriction in the barrel is different for each model.

I'm just educating myself here.

Thanks

[javadog]

Originally Posted by Tidybuoy

I'm just curious as to why the factory used the various different wur's on the same 2.7 engine.

I think you first have to realize that your premise is wrong. All 2.7 engines are not the same. There were around 10 different versions, not counting the duplicates for use with Sportomatic transmissions. They varied as to power output between models (base engine, S version, etc.) and by market (ROW, Japan, US 49 state, California) and by year, when differing emissions standards were complied with.

It's difficult, and I think pointless, to try and understand (or reverse engineer) why Porsche changed a particular thing, in a given engine specification. The reality is that they changed numerous things in each specification. There WAS a reason, but it may take way too much time to figure out what it was.

I just accept that a CIS system is just that, a system, and that you want to match the components together. In any engine, a given amount of airflow creates a certain amount of airflow sensor arm movement, which creates a certain displacement of the plunger, which opens up a certain area of the metering slits, which delivers a specific volume of fuel. The various fuel pressures involved affect many of these things.

It's just easier to accept that they knew what they were doing and just spend the time optimizing a stock set-up.

JR

[boyt911sc]

Originally Posted by Tidybuoy

I'm just curious as to why the factory used the various different wur's on the same 2.7 engine. All of these wur's have different warm pressure specifications.

For example, according to Jim's Primer: #008 = 3.0, #009 = 3.0, #017 = 2.7, 75 911 = 2.2, 76 911 = 2.4. #033 = 3.2.

On my '74S, I use a #033 and have used an #009 with a vacuum enrichment base added. I have found that my car runs better with a warm pressure at around 2.4 bar and it does not run as well when I set it to spec of 3.2. I'm wondering why this would be but this could also be due to the fact that I have a '79 fuel distributor??

Are there any variations in the barrels (i.e., the section that the fuel lines connect to). It seems to me that you could use any model of wur and set the pressures accordingly but this might not work if the restriction in the barrel is different for each model.

I'm just educating myself here.

Thanks

Vern,

I just spent the day testing and calibrating five (5) WUR-033 for PP members. The WCP for these WUR's are:

2.7 - 3.1 bar (atm)........... no vac applied.
3.4 - 3.8 bar (16" Hg).......vacuum applied.

The 2.7 liter engines come with different specification. For example: S model engines are not the same as the standard model, etc. Where did you get the 3.2 bar WCP? This is too low!!!! Use the Factory shop manual for reference.



The values in my notes are in psi not bar. Look at the upper right corner for the correct WCP taken from Bosch chart 1976-'77 with WUR-033 page (1.1-1/14b).

Tony

[Charles Freeborn]

Originally Posted by javadog

I think you first have to realize that your premise is wrong. All 2.7 engines are not the same. There were around 10 different versions, not counting the duplicates for use with Sportomatic transmissions. They varied as to power output between models (base engine, S version, etc.) and by market (ROW, Japan, US 49 state, California) and by year, when differing emissions standards were complied with.

It's difficult, and I think pointless, to try and understand (or reverse engineer) why Porsche changed a particular thing, in a given engine specification. The reality is that they changed numerous things in each specification. There WAS a reason, but it may take way too much time to figure out what it was.

I just accept that a CIS system is just that, a system, and that you want to match the components together. In any engine, a given amount of airflow creates a certain amount of airflow sensor arm movement, which creates a certain displacement of the plunger, which opens up a certain area of the metering slits, which delivers a specific volume of fuel. The various fuel pressures involved affect many of these things.

It's just easier to accept that they knew what they were doing and just spend the time optimizing a stock set-up.

JR

I'm in this camp too. And will add to it that in addition to the 70's being sort of a moving target with emissions standards, the Bosch K-tronic was used on a bunch of different makes of vehicles, all with different displacements, airflow and so on. Porsche, or any maker, did not warehouse all the components for any given smog year, so by adjusting the various relief valves they could dial in a variety of parts depending on what parts Bosch had "in stock" It's just the way production works.
I think that some mix and match can happen - such as upgrading to the vacuum model WUR, but as said, it's easier to use a single years matched components and using factory settings go from there. The Porsche techs that were assembling and tuning at the factory were using all new parts and lived and breathed CIS. They knew how to balance the system with any given assortment of components. We're using, in some cases, 40 year old parts, with limited experience... but on the bright side we know how to download and install apps....and have the internet for when we get stumped...


-C

[javadog]

I believe the reason is a different one. This technology was new. Porsche had changed from a company that supplied cars that were built for performance first and foremost, to one that had to meet new emissions standards, have greater fuel economy, be able to be run on lower octane gas, etc. That's why the engines grew larger, the compression rations dropped, CIS replaced carbs and mechanical fuel inhection, final drive gearing went up, redlines went down, etc.

During the '70s, Porsche had to meet increasingly stringent emissions regulations. They were also trying to fix some drivability and reliability problems. Each year, they tinkered with the components. Some tinkering was done to meet new regulations. Other new parts addressed one problem area, or another.

You can learn some of what they did, and sometimes why, by reading the service training guides. For instance, in 1977, they made the following changes to the CIS:

Added a leaf spring to the sensor plate lever to hold the CO adjustment screw against the sensor plate lever.

Modified the sensor plate stop, limiting downward movement of the lever.

Added a screw and locknut for the sensor plate height adjustment.

Added vacuum connections to the throttle body for the brake boster and EGR valve.

Added a thermovalve for the WUR to extend the warm-up enrichment.

There were other changes, to other aspects of the motor. Note that all of these changes applied to US 911S models. Turbos and cars for other markets had some of these changes, didn't have the rest of them and might have had changes that were not used on the US 911S cars at all.

JR

[Charles Freeborn]

I completely agree with all of that too. We tend to get "myopic" when addressing repairs or tuning - where the engineers who were designing the systems had to view the whole enchilada...for example adding an accessory that requires vacuum to operate it, such as brake booster, changes the fuel injection balance...Sometimes it's valuable to step back and look at the big picture.
-C

[Tidybuoy]

I understand all of the explanations provided - thank you.

I guess my secondary questions would be: If my '74 originally cam with an #001 wur (which has a 2.8 warm pressure specification) but now the car has a #033 wur. Should I b adjusting the #033 wur to have the same specification as the original wur or do I stick with the specs for the #033?

[javadog]

I would match the WUR to the rest of the CIS components, as it's probably most important to the fuel distributor. Since you are not running the original fuel head (if my memory from the various other threads is correct) it doesn't serve any purpose to run the original pressure that was needed for the original fuel head. Having said that, I'd probably also look at what all of the differences are between the two WUR'S and try to understand if the compatibility is there. Is it just a difference in ultimate pressure, or is the slope of the curve different, or is there an additional function (vacuum for enrichment, etc.)

I haven't looked at either of them in detail, so I can't give you any specifics.

JR

[RarlyL8]

You can learn some of what they did, and sometimes why, by reading the service training guides. For instance, in 1977, they made the following changes to the CIS:

Added a leaf spring to the sensor plate lever to hold the CO adjustment screw against the sensor plate lever.

Modified the sensor plate stop, limiting downward movement of the lever.

Added a screw and locknut for the sensor plate height adjustment.

Added vacuum connections to the throttle body for the brake boster and EGR valve.

Added a thermovalve for the WUR to extend the warm-up enrichment.

This is one reason there are so many part numbers for a given year. You have several engine types and each type is tuned to comply with the standards of the country sold as well as the environment. A Euro 911 WUR will not have the same curve as a CA USA WUR for the same year.

If mixing and matching CIS components you should match the fuel head and WUR if nothing else; USA/USA or Euro/Euro. The -033 WUR most likely was mated with a -017 FD on a 2.7L engine. The -001 WUR is a unique single wire unit so to use the -033 someone has converted to dual wire.