Cam Tower Oil Line Restrictors Redux
 

Recently on the Rennlist E-mail exchange, a question came up about wether the Cam Tower Oil line restrictors are a good idea or not. One of the respondents reported that in 2007 he wrote Bruce Anderson on this topic and attached the following e-mail thread:

>>>>>>>>>>>> First >>>>>>>>>>>>>>>>>

Bruce,

The Rennlist 911 forum has been having a long ongoing discussion about the cam oil line fitting for the cam housing that was updated by Porsche for the 1991 911 Turbo (Part # 901.105.361.01). Should or shouldn't this be retrofitted to earlier cars?

What little documentation can be found says it was intended to reduce oil froth and increase cooling. A side effect is increased oil pressure at the cost of less oil flow to the cams. Does the reduced flow result in higher head temperatures.

Can you speak to this?

REPLY:

When the 911 engine was redesigned for its 964 application for 1989 model year introduction the designers determined that they needed less oil for the camshaft lubrication. The design for the 964 engine changed from that in the earlier cars in that the plumbing for the plumbing for the cam lubrication and for the pressure fed chain tensioners is integral the casting for the chain housing.

The reasons given for restricting the oil flow were given as the following:
a. They were getting too much oil in the cam housing with the use of modern synthetic and thinner mineral oils.
b. The smaller sized fittings slightly raised the oil pressure when the engine is hot c. With the better oils the cams require less lubrication quantity.
d. And possibly other reasons of less importance.

When in 1991 the Turbo version was reintroduced the engine utilized a lot of the components used on the previous 3.3 turbo version and Porsche came up with the 901.105.361.01 adaptor which screws into the cam housing to restrict the oil flow. The original part was 901.105.361.00 and the new part 901.105.361.01. To differentiate between the older version and this new version the new part has a groove around the center. The original part had a 6 mm bore while this new part has a 2.5 mm orifice. The reduction of the orifice was intended to reduce oil flow and foaming.

No the head temperature was not hotter.

Bruce Anderson

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I find this interesting since it answers a question that I have wondered about for a while: "What else changed when Porsche went to the restrictors?"

It appears that they had a higher capacity oil pump (964 pump vs previous smaller capacity pump) and they changed the way oil got to the heads.

It is interesting to note the close of this first exchange, Bruce says: "No the head temperature was not hotter". I read this to mean the redesigned 964 motor did not get hotter. From how I read this, this was not in reference to the earlier motors as the previous discussion centered on the new 964 motor. He is silent on this would impact an older motor with it's lower capacity pump.

I also wonder if the problems with the accelerated wear seen with the SM oils had not yet been fully appreciated when this was written.

>>>>>>>>>>>> Second >>>>>>>>>>>>>>>>

Bruce,

Thanks for the additional info. Any opinion on retro fitting these on earlier engines? Those with or without the pressure fed pensioners?

REPLY:

Unless you are one of these old fuddy duddies that still uses old fashioned oils I would change to the new fitting.... Porsche knows best. Probably wont work if you use SAE 30W or SAE 40W oil.

Bruce

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I will concede that he may have been right at the time (2007) but with the advent of the SM/SN oils, this may no longer be valid.

Here are two old threads on this topic that I think really capture many of the issues for both sides:

http://forums.pelicanparts.com/porsche-911-technical-forum/454025-oil-line-restrictors-good-bad-idea.html

http://forums.pelicanparts.com/911-engine-rebuilding-forum/335776-3-0-liter-upgrade-horsepower.html#post3166426.

The retro information is very informative but in the last 4 years I have seen several, many, 3.2 crankshafts wiping the engine because the center rod bearings ran dry of oil, break the rod and wipe the case and the piston it was connected to.
If I can do anything to pressure the crank better, I would rather loose the cam shaft and carrier than the crank and anything within rod range.
Bruce

I installed them under Bruce's premise.

Hi Bruce,

JMHO, but those problems aren't solved by oil pressure: those are oil volume issues to the center of the crank and require different solutions to prevent recurrence. BTDT too many times to recount.

Remember, the #2 & #5 rod journals are the very last parts of these engines to receive oil and the only solution is crossdrilling the crank center main journal, grooving the center main bearings, and modifying the center main oiling passageway to match.

I have these but haven't installed them on my 81 SC 3.0 yet. I just don't feel totally comfortable doing it, yet. I think Henry Schmidt uses these on all the motors he builds?

I've also read on one of the other threads listed above that you can open up the restrictors a little with a drill bit to get a middle ground between original ID and new restrictor ID, I don't have that # with me but it's in the other thread.

I think I'll probably go that route and install them at my next valve adjustment.

One another note, I've seen camshaft wear that some builder attribute to the lack of friction reducers (zddp?) in modern dino oil.... so I don't know if this wear would be exacerbated by restricting the oil flow to the heads or not... part of the info that has kept me from installing these restrictors as I get massive leakage with SM oil so I stick with a good dino oil...

From another old thread:

Here's an article in favor:

Untitled Document

March 2002
911 Camshaft Oiling Update
By Steve Grosekemper

One of the benefits of writing a monthly article like this is the great input I get from the readers. From time to time, readers will send me interesting technical bulletins or articles to evaluate. One such article was written by Lee Rice and appeared in the September 2001 issue of Pandemonium, the Orange County Region newsletter.

The article discussed the existence of an updated cam oil line fitting for the cam housing on pre- 3.6L 911 engines that restricts oil flow to the camshafts by nearly 50%. I thought the article was quite interesting, but I still had some questions that Lee did not answer in his article. I decided to go straight to the source, and sent the first of several e-mails to Lee to get all the facts.


After several conversations and some additional investigations by both of us, here is what we came up with. 911 engines after late 1966 and all the way up to the last 1989 3.2L Carrera and 1990 3.3L Turbo all use the same adapter piece connecting the cam oil line to the camshaft housing. (Part #901.105.361.00). See Figure #1.

Starting with the 1991 911 Turbo this adapter was replaced with a new updated adapter with a reduced center orifice. (Unfortunately, Porsche did not give a great deal information as to the reason for the update, other than to reduce oil foaming.) The new adapter (Part # 901.105.361.01) has a groove around the center to differentiate it from the older adapter when installed on an engine. (See Figure #2)

Oil foaming is caused when there is too much oil in the crankcase and it gets "whipped up" by the rapidly rotating internal parts. You might be wondering, much like I did, if such a large reduction in orifice size would still deliver enough oil to the cam housings. To find out, I installed these adapters on several cars with greatly varied oiling needs and scenarios.


One of weakest oiling systems I installed the adapters on was a 1975 911S. This was a high mileage car that had no front oil cooler, a small early style oil pump, was still running the original 5-blade cooling fan and the thermal reactors were still in place. As you can imagine it did not take long to see 220-230 degrees of oil temperature and no idle oil pressure in this car. I figured that if the updated fitting worked in this car, it would work in anything.


After installing the adapters, I pulled the top valve covers and had someone start the engine. Oil vigorously sprayed from all of the holes in the camshaft spray bar, which told me there was no need to worry about low oil volume to the cam housing. The surprise bonus was that the car now showed about 10 psi on the oil pressure gauge instead of a bright red warning light due to low oil pressure. All this for two $5.10 fittings!


The next test was on my 914-6 race car, which has an interesting camshaft/cam housing setup. The cam housings are later '74 cam housings with a central oil spray bar. The camshafts however, are '66-911 cams with internal oiling (oil pressure from the cam journal exits holes at the heel of the cam). Porsche used one or the other, but never both types of oiling in the same engine due to the inevitable loss of oil pressure at idle. I installed the updated fittings and ran the same valve cover test.


This time I was amazed to witness what could only be described as a very messy geyser of oil coming from the right side cam housing. With 210-degree oil temperature, the oil pressure was almost 30 psi due to the engine's turbo oil pump. Pressure with the old fittings was closer to 10 psi.


After all our tests, we came up with the following conclusions:
- The new fittings decrease oil to the cam housings and decrease oil foaming.
- The decreased foaming allows the scavenge oil pump to transfer oil out of the case and into the storage tank much faster. This in turn keeps the oil - tank level more consistent and causes the oil level gauge to react quicker.
- Less oil foaming will lead to less consumption of oil through the engine breather system.
- The smaller orifice creates higher oil pressure at the main and rod bearings as well as at the piston squirters. The increase we noticed varied from 10-20 psi.

All in all, these fittings seem to be a great addition to any early 911 engine. With an extremely low cost and huge lubrication benefit, I am sure that even the most frugal 911 owner will be eager to spend a little and gain a lot in performing this update. Special thanks goes out to Lee Rice for his help and initiative regarding this article.


Good Luck!

I put the restrictors in a number of years ago and because I had only purchased 4 washers instead of 6 I initially installed one a couple weeks before the other.
This brought a couple things to mind...
- Installing just one bumped up the hot idle pressure to the point where it was reasonable.
- What would you see on teardown if you just ran one restrictor on an engine throughout its life?

Anyone want to try a "back to back" test on an engine they are building that will see a lot of miles and perhaps you know will see cam changes?


I've been thinking that if I ever get around to actually putting the 3.5L together that I would drill out the restrictors to 3mm because that would be still more restriction then is needed for really good idle and main circuit pressure. The the conservative increase in cam oiling pressure/flow would be good for the cams and the head temp.

Yet another take on this topic:

http://forums.pelicanparts.com/porsche-911-technical-forum/580133-peter-zimmermann-again.html