cam oil line Restrictor/Adapter

[PeteKz]

Correct. That's why I increased the hole into the oil tube substantially when I last rebuilt my engine. Now I can change the restrictors to change oil flow and not be limited by the hole in the oil tube.

[proffighter]

So I made a restrictor of 3.3mm (shrink fit) into the adapter

[PeteKz]

Has anyone measured the size of the squirt holes in the tube? If they don't add up to at least the area of the restrictor orifice, then they will limit flow and the restrictor size will be moot, above that size.

[Oregon 911]

Hello everyone I am in the process of starting to rebuild my 1974 2.7 engine. A long time engine rebuilder, machinist and mechanic told me not to go with the restrictor update his idea is that it will not supply enough oil for the camshafts. So how is that idea? will there be less oil and more ware on the camshafts?
I have updated my oil pump to a four rib oil pump and I have the oil bypass modification done to the case, Also I had the Carrera chain tensioners update in the engine before starting this rebuild. This is my first time rebuilding any kind of engine and I realize this is a very complicated engine to rebuild. Any and all advice will be greatly appreciated. Thank you Marion Fisk

[Henry Schmidt]

Originally Posted by Oregon 911

Hello everyone I am in the process of starting to rebuild my 1974 2.7 engine. A long time engine rebuilder, machinist and mechanic told me not to go with the restrictor update his idea is that it will not supply enough oil for the camshafts. So how is that idea? will there be less oil and more ware on the camshafts?
I have updated my oil pump to a four rib oil pump and I have the oil bypass modification done to the case, Also I had the Carrera chain tensioners update in the engine before starting this rebuild. This is my first time rebuilding any kind of engine and I realize this is a very complicated engine to rebuild. Any and all advice will be greatly appreciated. Thank you Marion Fisk

That is a statement without foundation. The factory determined that the flow to the top end was excessive. The reduced the flow to the heads in 964/965 engine. They reduced the flow by 30%.
Holding oil pressure in the lower end and also reducing the amount of oil cam towers and eventually the crank case is where it has the potential to create drag on the crank was the goal.
Porsche engineers are not always right but this was the correct move.

[reclino]

Many different manufacturers began to carefully control cylinder head temperatures due to emissions reasons in the 90's and 2000's. The Hemi combustion chamber is known for being difficult from an emissions point of view. Is it possible Porsche was making this change for emissions reasons rather than performance? On 935 heads they drilled / milled holes right over to the exhaust guide to better cool that area..... This would never work on a car with emission controls.
I am just think out loud here, don't have any data to even generate this idea

[PeteKz]

The 935 heads have the oil passages to cool the valve guides, and thus the valves. Remember, these are OIL cooled engines. Without water cooling, the 935's needed all the oil cooling they could get.

As for hemi combustion chambers and emissions, yes, they produce more unburned hydrocarbons, because the wide narrow chamber has cool edges and a long flame travel distance. Look at the combustion chambers in all newer cars--they are more compact. Also look at Henry's "peanut chamber". It makes the combustion chamber much tighter and more efficient.

If you want proof that the cams get plenty of oil, take the valve cover off and run the engine.

[Henry Schmidt]

Not to beat this horse to death but holding oil pressure in the bottom end during all running conditions is paramount.
The most common failure in air cooled 911 engines is connecting rods oil starvation.
At 40psi the piston oil squirters are open and they use a lot of oil. They are regulated because Porsche engineers realized that below 40psi, crankshaft oil pressure was critical.
As soon as the engine rpm is reduced, residual pressure drops quickly. The larger the cams feed volume the quicker the pressure drop. The 30% reduction in cam feed volume substantially reduces oil pressure drop and as far as we cam measure, has no affect on the head temperatures.
Trying the compare the oil requirement of a 700hp 935 to a performance 911 street engine is a fools errand.

[ahh911]

Thank you Henry,
I suppose this applies to road cars as well. What you say makes sense, the pressure is regulated at high rpm's, when most of the heat is generated, therefore no difference in head temps.
Hmm, so I should never rev below 5000? Seriously, I was tentative several years back, but it's on the list of to do.

81 sc.
Phil

[PeteKz]

Henry, thanks for that. So you measured the head temps in an engine with and without the cam oil restrictor? If so, then I expect that my increased oil flow to the cams and valves doesn't do much. But since I put a 930 oil pump in it, I might as well route the excess oil somewhere other than back into the return or supply lines. It doesn't seem to cause the valve covers to leak, and it might help control head temps.

[mikedsilva]

For those with a fresh engine, and the restrictors fitted, what does your pressure gauge show at idle on
- cold startup?
- fully up to temp?

curious
Mike

[Jeff Alton]

Originally Posted by mikedsilva

For those with a fresh engine, and the restrictors fitted, what does your pressure gauge show at idle on
- cold startup?
- fully up to temp?

curious
Mike

And further, if a non believer in what Henry had to say, could you also do the same test with the original large orfice part in place and report? It will take you around 10-20 mins to make the change and 4 crush washers.

Ask yourself, Why did the Porsche engineers make this change? It was not for emmissions of fuel economy or to save money (the largest drivers to re engineering), so why did they make the change? What did they learn since 1965 that made them think it was a worthwile change in production? All the while understanding that oil pumps gained folow and capacity along the way.

If you are happy with the original orfice size, continue as you are. If you think the smaller orfice is benefical, continue as you were. End of story.

I am not sure of the answer, but would love to know the thoughts out there...

Cheers

[Rosco_NZ]

Info highlighted above makes me wonder whether this whole thing is a non event for early engines as all early engines up as the spray bar hole is the same size as the late restrictor hole.

Therefore there may be no change or benefit fitting later restrictors. I have seen an engine where this played out in practise … no apparent change in idle oil pressure before and after fitting restrictors. It did have an old mag pump and no bypass mod mind you. Would this change the results?

It would’ve been simpler for Porsche to rationalise parts where one could suffice for all air cooled engines.

Anyone whether oil spray bar feed hole sizes change across the years?

[manbridge 74]

I attended Porsche Classic training taught by an experienced gentleman who started with Porsche in 1969 and went on to write the DME test plan for the new for 1984 911. This was back in 2017 and I asked why the change was needed? The answer was something along the lines of: keeps more oil where it’s needed, specifically the lower end and piston cooling jets but also the cam tensioner circuit was found to have improved operation with the restrictors. Apparently if new tensioner updates were installed at a Porsche dealer back in the day it came with restrictors. I have been looking for the bulletin on this which would show the parts list to confirm….

Now for the caveats. Steve Weiner was never a fan and his reasons can be searched on here, mainly due to Porsche insisting on 0w40 for years. But the Euro 0w40 Mobil One was a different formulation than what the USA got so maybe the Euros had no issues. Also, I believe Henry has stated he drills these out to a size midway between old and new and that changes oil pressure a lot compared to an unaltered new type restrictor.

[PeteKz]

Very interesting about the restrictors helping keep pressure in the oil-fed tensioners.

[Henry Schmidt]

Back in the mid-late 70s the 2.7 liter 911 came from the dealers running at 260 degrees. We worked at lowering those temperature by removing the thermal reactors,replacing the fans and adding front coolers. Cost concerns being what they are, we looked for ways to help these cars survive, but the time most of these cars got upgraded the mag cases were already distorted. Many had low oil pressure at hot idle [idiot light on] so holding oil in the bottom end became paramount. We made these oil control fittings and the result was always increased oil pressure at idle. Generally the light went out and stayed out.
On a side note: around that time Porsche changed the oil temp sending unit on engine and remove the numbers on the temperature gauge. Drivers had become hyper-aware or temperature issue and Porsche sought the mitigate those concerns.

[Martinlassmann]

There is also the change from 3 to 4 bearings for the cams in 1977. The leakage rate increase and so more oil went through the cam housing with the early Adapter

[hannu_911]

I have Porsche 911 SC 1981 that has a replacement engine that was built by Porsche early 1990. Engine number is 930/10 AT63D6576 (AT=AusTausch=Replacement).

When Porsche built this engine it got few upgrades on from later 3.2 carrera and 964 engines.
-Oil pump is the same that was used in 3.2 Carrera
-Hydraulic chain tensioners from 3.2 Carrera
-Camshaft housing from 964.
But Porsche did not use the restricted oil flow fittings on the camshaft housings. I don’t know why.


Yesterday I installed these 2.5mm restricted oil flow fittings to my 1978 930 turbo engine that I’m rebuilding. This engine has GT3 oil pump, front fender coolers both left and right side. Engine mount oil cooler has been replaced by 965 oil filter console.
So let’s see if I want to open these up or not based on this thread.

Originally Posted by Rosco_NZ

Anyone whether oil spray bar feed hole sizes change across the years?

All 930 based engines have the same oil splash tube, including Carrera 3.0 and early turbos. 964 engines had also the same oil splash tube as 930 engines.

[Cloggie]

I must admit I love these kinds of threads as they really span the range of thoughts, opinions and history of our beloved engines.

It still makes me believe that the combination of Turbo pump and a slightly drilled adapter will be a good balance for my normally aspirated street 3.4 with PMO ITB's

Thanks guys!

D.

[Packin4]

Several posts suggested this Cam Line Oil Restrictor upgrade. Maybe the spec exists somewhere, however, I couldn't find a torque spec in Bentley, Porsche spec book, or other searched posts other than "snug". So, used my torque wrench and increased torque in 1nm increments until I got movement on my original installed cam lines. Here's the result:

Restrictor: 40nm or 29.5 ft/lbs
Oil line bolt: 27nm or 20 ft/lbs