Printable Version of Topic

Posted by: DennisV Sep 4 2022, 06:23 PM

Is this a correct Oil Cover Lid for a 1970 914-6? It appears to have a threaded port for a temperature or pressure sensor / switch. I can't find that part number in the 914 or early 911 parts catalogs.
901.107.701.3R

Posted by: rgalla9146 Sep 5 2022, 05:59 AM

Hmmm....
Picture taken this morning of maybe the last greasy, rust free, unrestored 1970 914 6
# 1467
I think the switch is to trigger the throttle position pot for cold start.
Along with raw gas squirters in the air filter usually disabled to avoid engine fires.
The different part number is curious.....the switch is moved rearward.
I'll get a look at my other car
Rory
Edit; pic of second car # 1095


Attached thumbnail(s)

Posted by: nditiz1 Sep 5 2022, 06:36 AM

I thought all 6s were carbd which would mean no TPS. A hand throttle up front to set the choke when cold. Not sure what that port would be for.

Rory, what is that plug hooked to?

Posted by: SixerJ Sep 5 2022, 07:50 AM

My -6 engine which happens to be on the floor at the moment. Built 450 odd away from yours

.2R same as Rory's initial pic

Posted by: johnhora Sep 5 2022, 08:10 AM

The "TPS" was used as an early emissions solutions.
On the 914-6 it was a set up that used a vacuum positioner to kept the throttle open for "over run"
What is throttle overrun?
Over run is where the throttle is fully closed and the engine is slowing down.

Rory's second picture shows the vacuum pot. That's also why the original 914-6 DR side intake manifold had the vacuum ports.
Also the throttle cross bar was unique having a fitting to connect the vacuum pot.

Posted by: rgalla9146 Sep 5 2022, 08:18 AM

Original equipment on our cars was a temp sensor switch (in pics) that activates a throttle position arm on the throttle shaft (using a vacuum pot and hose from from the 1-2-3 intake)and opens a fuel valve that feeds squirters in the OE air filter housing.
At least that's the way I think it works.
Usually eliminated (maybe by Porsche service update) due to frequent fires.
Not too many cars still have those parts.
Not too many OE air filter housings are not melted.

Posted by: johnhora Sep 5 2022, 08:33 AM

914-6 Throttle Valve Positioner....the vacuum "pot"



914-6 Cold Start Valve
The fire starter that dumps raw fuel into the air box

Posted by: johnhora Sep 5 2022, 08:39 AM

914-6 intake manifold with vacuum ports



picture from the shop manuals 914-6 fuel system volume

Posted by: davep Sep 5 2022, 08:43 AM

You are confusing casting numbers with part #'s. The basic part # 901.107.701.xR is supplemented by the revision # "x", so 901.107.701.3R could be the fourth revision (0, 1, 2, 3) of that casting. There could also be 901.107.701.00 or .01 for the earliest aluminum versions. Some of these covers have no switch port, some have one and some have 2. The casting #'s often bear no resemblance to the finished part #.

Posted by: rgalla9146 Sep 5 2022, 01:10 PM

Holy Cow Visual aids aplenty

Posted by: DennisV Sep 9 2022, 10:09 AM

Very interesting! Thanks for the visual aids. Do you know if those ports were threaded?

Our engine was missing the carbs. What we have now is a set of Zenith. The intake manifold has openings, but they are are not threaded.

Posted by: sixnotfour Sep 9 2022, 10:57 AM

TVP was annoying, pull up to stop light with high idle to burn off left over fuel .... not Cool , but.. the beginning of emissions...probably better than an air pump..

Posted by: fixer34 Sep 9 2022, 12:20 PM

Had me curious so I went to look. March '70. Oil breather is the 2R with the sensor hole toward the front. I put an aftermarket temp sensor in there when I pulled the cold start pieces long ago. Left the pipes in the air housing. A couple rubber caps on the manifold took care of the removed vacuum hoses.

Posted by: fixer34 Sep 9 2022, 12:27 PM

I have wondered for a while what the sensor was that was 'floating' around by the breather. I obviously took it out a long time ago, but I don't remember why. It has been connected all this time, but has 2 contacts on the top under the rubber cover unlike the first picture. I got the p/n if anyone can reference it.

Posted by: rgalla9146 Sep 9 2022, 01:30 PM

I think that switch (two wire) was the trigger for the fuel supply to the air filter gas
squirters.
The switch that has the 90 degree male connector is for MFI as I recall.
It was like that due to tight space (IIRC)

Posted by: rgalla9146 Sep 9 2022, 01:49 PM

Dennis those carbs and manifolds are from a '70-'71 2.2 911T
Two year only combination.
Not drilled for the vacuum ports....but could be.
How serious is your restoration ?
Those manifolds will be just fine on your 6 unless you insist on the absolute correct
parts.
The only difference is the vacuum ports which you will likely never use.

Posted by: DennisV Sep 9 2022, 04:12 PM

Thanks for sharing this. The devil in the details with the sharing between and evolution of these Porsche cars.

Very fair question. It is an original 914-6 in quite good condition, but not numbers matching (i.e. the chassis came without engine or transmission. We have number range appropriate replacements). So for things that are missing or need replacement, I plan to go stock config with Porsche or OES parts. The exception might be if we have to get new pistons and cylinders. Anything that we already have (e.g. carbs) that will work without requiring modification I will continue using till they need replacing. Or my obsessive tendency doesn't allow it to remain.