Do we know if the RS runs different valve train and lubrication system to the GT3? Any reason why the RS wouldn't suffer the same percentage failure rate based on the same use and mileage?

 

The lower rpm limit. Much of the wear and potential damage from higher rpm is based on kinetic energy, which is square to speed. So a reduction from 9000 to 8700 rpm means a reduction of 7% of all kinetic energy based on rpm.

That is certainly a significant enough number.

 

I would think that is impossible. There has to be a drop in rpms since the next gear on up shift has a different ratio. That is precisely the instance I am referring to. The exact mechanics of that shift differ from a MT. The bogging down of the motor most likely is more violent than a typical MT up shift because of the speed of the transition. Either way it was just a thought and wanted to lay it out there and see what members think.

 

So you are saying if i regularly shift in my F 2015 GT3 above 8,000 but below 8,500 then there should be no issues ever?

 

Doesn't the RS have the same bore, but longer stroke? For the same rpm, longer stroke means higher piston speed, so you have to do some math to see how the kinetic energy, stresses, etc. compare when considering both rpm and stroke. I recall this being discussed previously in RL, with the conclusion that GT3 and RS have the same max piston speed.

 

Whoa. Way above my pay grade but great point.

 

Jaime: Do we know if all the failures revolve around the cam wipe? I've read there have been other reasons.

Seems each generation from my reading has had issues with terminal failures. The 991 E & F are not alone. Again, they are remedied by PAG and in most cases represent a very small % of total engines. In fact with the E's they replaced all engines even though only a small number failed.

PAG is very protective of their "rep". Rightfully so. These cars are still amazing and predominate at local tracks compared to other high end performance machines for a reason.

 

Load-wise on the things that matter to keep the bottom-end together, I believe that's completely on point. But it is possible that the valve-train turning faster creates lubrication issues. You would probably see higher loads on the valve-train at 9000rpm than 8500, more valve inertia, more force on the cam lobes to control the valve position, friction, heat, not to mention different behavior in how the oil film stays adhered to the part surfaces. Whatever may be the answer, until there are Rs and RSs dropping like flies as is the case with GT3s, it's hard to really know if the lower RPM limit helps avoid the issue. Either way, I find it very surprising given how much development and even automated engine load cell tech they have that this was not identified WAAAAAY earlier. Porsche engineering prowess has definitely dropped a notch in my book for the things I care about (track worthiness).

 

All I'm saying is that it could move it into RS lifetime. You don't have the DLC coating, though.

 

Piston speed, yes.

But the speed of the cam lobe "rubbing" on the finger follower? I bet that whatever is doing the damage there (heat, or stress from repeated impact) is proportional to the square of rpm.

I also wonder about the speed with which the valves move. Valve opening speed should be increasing proportional to rpm increase (which means kinetic energy of the valve is square of rpm). Valve closing speed on the other hand is instead driven by the spring and will not depend on rpm.

I didn't think this through but is it possible that the valve behaves a bit like it is wedged (of course it isn't actually wedged, but something that makes it resist more). And the finger follower presses down on it when it isn't ready to do so when rpms are high?

That is one reason why I would like to get my flippers on a damaged finger follower. I think some easy to do analysis would make us able to tell whether the primary damaging factor is from heat (with normal force and impulse) or from abnormal force. For starters the former would undo some of the annealing. Of course we'd first have to see whether the steel used there is annealed originally. There are reasons why it might not. Those steel geeks can go on and on about that forever.

 

I wonder how much of this is related to the time the engine spends at 8000-9000 rpm as compared to a manual car. Some tracks/drivers may result in a lot of time running at high rpms whereas one would have downshifted a manual car earlier or before a corner previously. The pdk makes it much easier to stay around 8500rpm without worrying about hitting the cutoff or miss-shifting. I wonder if Porsche didn't test on shorter high rpm tracks and under-tested this scenario.

Has anyone driven older and current GT3's on the same track and noticed where the average rpms are?

 

I am looking to purchase a 2014 GT3 with 3175 miles. PCNA said the engine was swapped at the hub before delivery to the first owner. Serial has it as a "E" motor. Car has CPO for another 3 years +/-. Should I pass on this car or is it likely fine with the motor swap? I did not read the entire 141 page thread but these motors going up are concerning for long term ownership.

 

First you need to decide on how you are going to use the car.

 

No track time 4000 miles a year spirited driving on public roads.

 

With CPO warranty, go for it.