RajDatta

Yes, 3k was the golden rule back in the day when we only had mineral oil. With synthetic, multi-viscosity oils, the intervals can be much longer (depending on use).
For my daily driver as well as my wife's daily driver, I run my oil every 10k miles. For my toys, I never accumulate more than 2k a yr, so I change the oil yearly instead of mileage based.

sccchiii

Unfortunately I'm super sarcastic and was being a wise ***. But yes I have done oil changes at less than 10k simply because of track use only. I drive the snot out of car or at least my "best version" of snot.

Alan C.

KA 991 GT3

The heads are designed different, yes but that's not why the GT3 3.8 is capable of revving higher.
Higher revs are achieved at the bore/stroke level. Bigger bore, shorter stroke provide that on this engine.

Jamie@dundonmotorsports

i knew the GT3 was 102mm bore 77.5mm stroke. Just checked the GT4 and it's the same 102/77.5.

Porsche just uses different Pistons, rods etc in the GT3 engine to reduce reciprocating mass.

Removing mass from valve train is also necessary, or the valves won't be controlled properly, or the lifetime of the valves/valve seats will be short.

From the horses mouth...



991 GT3 Valvetrain




I'll try to post up some pictures of the GT4 and GT3 valve train differences.

Bottom line is the issue with the GT3/RS is unique to the finger follower design.

KA 991 GT3

You are correct as well. But when it comes to physics, geometry and movement of parts, the shorter the stroke, the faster the cylinder can move and the more trips it can make up and down the bore. The heads with the valve design and the springs do place a significant role into maintaining that movement but not create the speed at which it happens. I can draw it for you and show with calculations why... I live math and physics. I do respect your opinion as a vendor and your company's effort into working on this issue and have been reading your posts, please do not take my approach as to discredit you in any way.

m42racer

The CEL in this case (combustion issue) is activated when the engine has a misfire. A misfire is when the engine does not complete a full revolution without stopping. The crank sensor counts the trigger points and the ECU expects to see the number of trigger points. If it loses count, then it knows the engine has "stopped" for some reason and the engine must have misfired and the CEL is activated. The Camshaft sensor can also be included in this as the ECU may be looking for the same count of trigger points between the crank and Cam. If these change the engine must have stopped and the CEL is activated.

As much as we want these engines to be really trick and technical, they are basic ICE power units that require 3 components. Fuel, spark and air. If one is missing or wrong the engine will misfire. Reading the Porsche bulletin speaks directly to the issue. When the CEL is activated, unless there is a direct sensor problem the ECU cannot tell what is the cause. In this case, this is seen by how Porsche are going about the diagnosis. First change the Spark plugs, if no change, change the Coils, if no change, change the Injectors. That’s the Fuel and spark taken care of, so what’s left is air. At some point in time, they removed the valve covers and found the Cam lobes and fingers worn away. Now it’s a matter if sequence as they know there is a problem here.
It is thought that the actual misfire is “set off” by the Spark plugs fouling. If the Valves are not held open and lifted off their seats to the design parameters, then there will be less air pulled into the cylinder, the mixture will be rich and a “rich” mixture will always misfire. DI engines require exact amounts of fuel to be injected so the AFR is correct. Especially for emissions and fuel mileage reasons. Fuel injected directly into the combustion chamber never has the time to heat up and fully vaporize, so any extra fuel per unit of air will stay as droplets and not ignite as it should. Spark plugs foul and the misfire occurs. These engines have Inductive ignition and inductive ignition does not have the energy to fire dense mixtures or fouled plugs.

It is thought that the O2 sensors are not being used to detect and turn on the CEL light under these conditions. If there were individual sensors per exhaust primary them maybe, but it’s thought that the O2 sensors per bank are too non specific to monitor the AFR per cylinder per stroke. But the input value from these sensors is most probably and input in the algorithm fault code.
Getting back to my original thought, once the CEL is activated for reasons of combustion, damage has already happened to your Cam and fingers. The suggestion was not to wait but monitor the condition of these parts before wear starts.

^^^Perhaps if you had taken the time and read this thread a bit you would understand. It has been explained many times.

Yes sir, I did read the all of the posts. failed to read anywhere where is showed the CEL light is activated primarily by the wear on the cam lobes and fingers. If I misses it, I'm sorry.

gago1101

This is where I pause a little. Porsche has been recommending the same oil for a really long time. I'm not really sure, but think it is more than 15 years now. I really think this high revving GT3 engine may be slightly different from the early water cooled engines.

m42racer

I think you are talking about two different engine architectures. Short stroke will allow the engine to accelerate quicker if all things are equal, but has nothing to do with final RPM limit. Many other factors come into play. Valve train parts are huge here. Finger pivot mass allows a higher Valve train speed to be used differently to bucket type followers. Accelerating the masses over a shorter distance helps but once the terminal velocities are reached distance has little of no effect. If you over rev a short stroke engine with the same valve train parts you are going to break parts. Same for a long stroke engine. There are limits and every part in the engine has its limit. The trick is to have all of the limits the same or close as possible.

Also, I'm sure Porsche does not want the GT4 to out perform the GT3. The GT4 engine is limited to final upper RPM by its design, and the components included. Stroke has nothing to do with it.

m42racer

You may be right, but I suggest this to keep your warranty in tact. I'm sure Porsche will find any wiggle room they can to get out of fixing an engine.

ipse dixit

There's the oil that Porsche recommends, and then there are the oils that are Porsche approved. The former (depending on your market) for the 991 GT3 is basically Mobile 1 0W-40, but the latter are many and varied.

neanicu

Each manufacturer has a different name and approach for valve control. Porsche has been using Variocam for years. The Variocam controls the opening and closing of the valves. The electrical control is extremely accurate and detects the slightest anomalies. The DME gets info from the camshaft position sensors in relation to the crankshaft position sensor. The DME can order the Variocam high lift and high duration for maximum power at high RPM. If the Variocam can't sustain that opening because of abnormal wear,the engine will misfire on that particular cylinder or cylinders where the wear is most pronounced,so the DME will know there's a problem and put the engine in limp mode. Forget what you know about electronics of the past. An old system would've never detected this wear. The new one is incredibly accurate!

m42racer

I'm sorry but I must be missing something. Are we discussing the GT3/RS 9A1 engine or another engine. The GT3/RS engine does have variable Cam timing on both cams but does not have any feature that gives it high and low lift control. The fact that the ECU knows where the Camshaft position is in relation to the Crankshaft, it has no idea of valve lift, high or low, good or bad. In the Porsche engines that have high and low lift control they do not have fingers but hydraulic bucket type followers that are a two part bucket with a locking pin to give the high lift control and a tri lobe camshaft. Look at the pic's posted above and it clearly shows how the GT3/RS valve control operates. There is no way there is any control over the lift of the valve other than the finger and camshaft.

m42racer

Actually, from what i understand, the Porsche high /low lift has nothing to do with the variable camshaft control. The cams just go round and round and advance themselves from their home position and retard if required. This make no change to the valve lift. It does change when it happens. The bucket is not connected to the Camshaft which controls the lift. Even in these engines, the cam lobes could wear as could the bucket faces and the ECU would not know until the engine misfired and the exact same approach would be called upon. Start with Ignition components, then fuel parts , then look at the air control.

JasonAndreas

I believe that is the revision number for the mold that was used to produce the intermediate that was then used to cast the parts?