Davebrossi

Rather than a woe tale, I was hoping for input regarding a conversation my Dad and I have been having. I'm wondering about the differences in roller designs between the 993 and the 986. This stemmed from our conversation about oil weights and ZDDP packages. Any input? I know the engines are very different, but I figure this is how I learn.

Macster

The biggest difference is the 993 engine is air/oil cooled while the 986 engine is water/oil cooled.

Generally an air cooled engine runs hotter, has larger thermal gradients, requires more clearance to avoid metal to metal contact.

Generally larger clearances require a heavier oil.

As for ZDDP based on what I know about this additive it is useless and possibly in some instances harmful.

There are millions of engines running oils with low levels of ZDDP - it is a converter killer so automakers are anxious to get away from oils with too high levels of ZDDP -- and there does not seem to be any significant number of cars around with worn out engines.

And what's worse it appears some owners in order to run an oil that is high in ZDDP select an oil solely based on its ZDDP content and in doing so select an oil that is ill suited to their engines' needs.

Davebrossi

Makes me nervous I put Brad Penn 10W-40 in based on ZDDP content :-). What I really was talking about was the usage of Roller Cams. In the Air Cooled engines it's a machined surface against machined surface between Cam lobes and rocker arms with a thin oil film between them. At high temperatures damage can occur when the surfaces attempt to weld due to poor oil quality (low ZDDP.) I'm wondering if the 986 uses a rubbing or roller design for the rocker system. Means the difference between a continued reliance on high ZDDP oil for me, and using Mobile-1.

flyingpenguin

Most folks in the Porsche world refer to rollers as valve lifters. I found this article explaining the difference between flat tappet and roller lifters: http://www.lunatipower.com/Tech/Cams...tOrRoller.aspx

The 993's M64 engine uses a single overhead cam with rocker arm and hydraulic tappet design: http://reutterwerk.com/forums/showthread.php?t=2356
The 986/996's M96 engine uses a double overhead cam design with flat hydraulic lifters / tappets: http://www.graciecombativeskc.com/Re...tKC/M96/12.JPG

In either engine, load pressure between rocker arm (m64) or lifter (M96) and cam lobes can be significant, and concentrations of 1000 - 1200 ppm ZDDP largely prevent scuffing.

Oil weight-wise, I'd use the thickest Porsche approved oil that is safe for your climatic conditions / time of year. 0W40 for up North in the winter, 10W40 or 50 down South, especially in the summer.

Can't wait for this to spark another oil discussion...

Macster

The 986 engine uses a cam lobe to lifter bucket system. The lobe presses directly down on the lifter bucket to open the valve.

In the 993 the cam lobes press against a rocker which then pivots around a rocker shaft and the outer end moves down to open the valve.

Roller cams (that is cams that operate against a lifter with a roller instead of a flat surface) are generally reserved for high lift/aggressive cams.

Poor oil quality is not determined by the amount of ZDDP the oil contains or does not contain.

Poor oil quality is a factor of the type of oil, its suitability for the application, climatic conditions, etc.

As for loads of ZDDP (or any other additive) know that for every additive in the oil means there is less *oil* in a bottle of oil. In some oils the additive package makes up a substantial portion of the oil representing 5%, 10%, even more of the weight of the oil.

It is the oil, the fluid, that is the first line of protection against metal to metal contact. It is the oil, the fluid, that carries the heat away from the bearing interface and gives it up at the cooler.

The 986 cam/lifter interface is not a rubbing interface per se. There is a thin film of oil between the cam lobe and lifter bucket face.

If there was any rubbing you'd know it pretty quick as the cam lobe would go flat or a depression would wear in the bucket. In either case you'd hear a tick as the zero lash adjuster would not be able to adjust enough to make up for the additional clearance.

BTW, the 986 cam lobe/lifter bucket interface is splash lubed. The oil comes from around the lifter bucket with some coming from the oil that "leaks" from the cam bearings.

The use of a oil viscosity that deviates from the viscosity of an approved oil runs the risk the heavier (or lighter) oil may not have the same splash characteristics and this could lead to substandard lubrication of this vital area. All the ZDDP in the world won't help matters if the oil is slung off too soon or too late and the cam lobe/bucket interface runs short of oil under various operating temperatures or rpm ranges.

For instance a 10w-60 oil could have the cam lobe/lifter interface short on oil at both cold engine start -- courtesy of that 10w -- and at operating temperature -- courtesy of that 60.

A 10w-40 oil perhaps just at cold engine start and while the engine (and oil) warms up.

I do not understand why there is all this over-thinking (I would hazard an opinion it is wrong-thinking) on oil. There are a number of approved oils to choose from with a number of different viscosities: 0w-40, 5w-40, 5w-50; and of different groups: IV and V; that barring one living on the moon a suitable oil is available for use in one's Porsche.

Thus one could spend more time thinking about other things, like maybe where to drive his Porsche.

gfl

You have , IMO, the consistently best quality answers here.

But on this one i don't think i agree - or maybe i don't understand.

During hydrodynamic lubrication ( normal oiling) ZDDP is not useful

When HD lubrication fails and you enter a state of barrier lubrication, such as with older style valve trains (before 993s), ZDDP provides a physical protection barrier and is generally thought favorably of by lubrication formulators.

Except, as you state, that it fouls cats. But, on a car that does not burn any oil, or much, who cares?

As for weights, viscosity selections should follow the use/application. For normal, day-to-day driving, i agree - simply use the recommended weights, but maybe don't leave them in as long as suggested (even Porsche revised its drain intervals). But for track, where cars are rarely cold, and often much hotter than normal, i strongly urge people to consider thicker oil (incidentally, 10w40 is thicker at temp than 0w40, read the curves). I'll also note that major lubrication blenders concur.

Most OEMs trade off three objectives:

1. low maintenance cost
2. CAFE fuel economy requirements and penalties
3. wear and long term motor health

Guess which is compromised?

Educate me!

Grant

Joe-B

Jake Raby (Flat Six Engineering) and LN Engineering both recommend Joe Gibbs 5W/40 oil, which is high in zinc.

Macster

FlatSix/LN do not have to warranty engines -- unless of course one is running a FlatSix engine then run whatever oil FlatSix recommends ... it is a FlatSix engine -- nor warranty converters.

Macster

Track usage is usage for which in some form or another is not approved of by Porsche.

(All the owners who think they can buy a modern Porsche and drive it to the track and then drive at the track and at the end of the day drive home again are woefully mistaken.... the techs all lament that this era of Porsches is long long gone. This is not necessarily a bad thing for continuing to build that kind of car might have resulted in the demise of Porsche and its very very fine high performance road cars would be absent from our lives.)

Anyhow, track usage... so since one is using the car in a way that is not sanctioned by Porsche he can use whatever oil he wants to use selected based on whatever selection criteria he think applies.

As for ZDDP... If one goes through the history of this it comes into play in engines that have very high valve spring pressures. Our engines have around 170lbs psi valve seat pressure which is kind of low. It can be low because the valve hardware is light. I mean even with that low valve spring pressure my 02 Boxster's redline is 7200 rpm. That's darn high considering it is a street engine.

When ones gets up into the higher valve spring pressures that are commonly used (required) by after market cams/high performance cams to allow the valve to follow the contour of the lobe then ZDDP can act to protect against metal to metal contact.

But there is a downside.

The ZDDP can react with the base metal and cause spalling of the cam lobe.

In stock engines exceptional cam lob or lifter wear was initially blamed on lack of proper lubrication but over time metallurgy was found to be the real culprit.

Some years ago -- not that long ago -- cam lobe wear raised its head again and the clamor was about the crappy oil. Turns out it was the crappy imported cams/lifters that were popular because they were cheap. But as it turns out crappy.

Even "brand name" cams were caught up in this. I researched then bought a name brand aftermarket cam for my Datsun 510 engine. My choice received nothing but praise in the mag articles. This was before the 'net and even BBS and car forums.

I took care to ensure the cam lobes all contacted the rocker arm pads in the center. In fact when I took the head to an engine builder in Campbell CA (I can't remember his name now) and explained to him what I wanted he at first didn't understand. Rocker arms with pads were I guess rare at that time. All USA engines that used rocker arms had a push rod working one end with the arm pivoting around a rocker arm shaft and pressing on the valve stem.

Anyhow, the engine builder did the head right. When he did the valves he took the same amount of of each seat and I can't remember now if I replaced the valves or used the old ones but in the end the valve stem heights were correct and I blued each pad and confirmed the contact patch/wipe area was located smack dab in the center of the lifter pad.

Also, I followed the cam makers instructions for installation, pre-assembly lube, break in, the whole nine yards.

Ok. Some time later -- maybe not quite a year -- I had an offer from someone to buy the car. My business needs had me looking for a truck so I sold the car and immediately went out and bought a used truck.

The guy that bought the car I ran into him - at a store nearby -- he worked in the area where I lived at the time -- and we got to talking about the car. He liked it, like the dual side draft Weber carbs, etc, but mentioned he found a cam lobe flat shortly after he bought the car from me. Thinking he thought I sold him the car knowing that I started to say something -- I do not recall what now -- but he told me not worry, he just replaced the aftermarket cam with a factory cam -- the rocker arm pads were ok -- and the engine was just fine.

My exposure to a crappy aftermarket cam...

As for the 3 OEM objectives you listed

1. low maintenance cost
2. CAFE fuel economy requirements and penalties
3. wear and long term motor health

There is a number 4: Stay in business.

It is just your opinion that one or more of your 3 are being compromised.

Certainly each is important but to obtain low maintenance costs at the expense of engine longevity.... an automaker would have to have death wish.

CAFE is what it is. All companies have to deal with it. Can't believe automakers from A-Z with the exception of Porsche have figured this out.

Porsche new car warranty -- in the USA anyhow -- is 4 years 50K miles.

That's pretty darn good. My '89 Tempo warranty was 2 years, 24K miles (and really needed 100K mile warranty... what a crummy car).

My '96 Mustang warranty was 3 years, 36K miles (and was in the shop right up to and a bit past the 36K mile mark with issues.. another crappy car). Ditto my '01 Camaro warranty and my '06 GTO warranty. The Camaro accumulated 28K miles in around 4 months' time. Not one warranty issue. The GTO accumulated nearly 40K miles in under 3 years' time with just a door handle issue.

My Boxster warranty was 4 years, 50K miles. I can't recall now the warranty time on my VW Golf.

My 03 Turbo (bought used) came with a 2 year, 100K mile warranty which expired of course 2 years later but with nearly 60K miles on the car, 50K I added in that time.

Ignoring the IMSB issue which is probably not directly related to engine oil performance or servicing shortcomings I do not see a scary number of Porsches with worn out engines. In fact, I do not see a scary number of any automaker's car with worn out engines.

Automakers from A-Z have managed to deliver vehicles with good better than good engine longevity.

As an aside, my info is that for an engine to be certified to be sold in the USA it must run 100K miles with no more servicing other than scheduled oil/filter services. Not even cam timing belts can be changed.

Additionally the EPA constantly pulls in used cars to check their emissions, even cars that are long out of their new car warranty time, long past the federal emissions warranty time, to ensure random samples of cars comply with emissions.

If any car maker, and Porsche would be treated no different, were to have a too large a number of examples fail these spots checks there'd be heck to pay.

Emissions requirements come in for some real negative comments but one thing they have done is forced the automakers to up their engine game and modern engines are not only clean running, they produce good HP -- an honest 217hp from my 2.7l Boxster engine when a 1960 Ford station wagon (my dad's) with a 3.8l (233ci) 6-cylinder engine struggled to produce 145hp -- and last a long time.