Planet 9

Hi guys.

I have noticed that my Boxster S (3.4) performance is quite inconstant. Somedays I will start her up and get blown away from the amazing performance and responsiveness, other days she feels somehow lagging and way less responsive, also the sound is somewhat washed up and weak.
Usually the performance is very good at cold engine, but as soon as it gets hot it diminishes. The same applies to external temp. If it is at around 12 °C (53 °F) she performs the best, when it's hot (30 °C - 86 °F), however, she feels like she is not breathing.
I have tried to redline her everytime I feel she's lazy but it doesn't change much. What really makes a difference is going very fast (like 200 kmh - 124 mph) on the highway for a sustained period of time.
What really kills performance is driving in traffic. Even if I keep a low gear.
A friend of mine who has a 3.2 experiencies the same variable performance.

Is it something you have experienced yourself? Can you fix it?

Thank you!

I think that is expected when the engine has been running for a while and becomes hot especially in situations like heavy traffic.

Do you have an auto or a manual?

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2010 Porsche Cayman S PDK

It's a manual w/ short shifter.

do you service the car regularly?

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2010 Porsche Cayman S PDK

make sure in the hot conditions that your air conditioner is off. the a/c zaps the power.

to enter intake system? This leak would be *before* the MAF so the hot air is metered thus no CEL but being hot really brings down engine performance. Cause it's hot engne controller will dial back timing to avoid detonation and this really can sap engine peformance.

(Bought a new '01 Camaro Z28 and checked intake air filter and found it not installed properly and allowing air in from engine compartment, not enough I recall to make a diff in performance but it can and does happen.)

Another possibility would be coolant or intake air temp sensor malfunctioning and causing engine controller to dial back on fueling or timing with engine performance taking a hit.

Give engine intake a good checking out. Be sure air filter installed correctly and not blocked with some piece of paper or plastic.

If ambient temperature real high engine performance will naturally suffer some. To make matters worse is if hot enough electric radiator fans will be on as can the engine compartment fan. If you have the A/C on the compressor presents a parasitic load along with the fans. Under these conditions the car's performance is a bit subdued. Nothing real serious but there is a noticable difference in the car's peformance.

Sincerely,

Rockster.

You had artificiality more performance than normal when its cold.
Just expect less.

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2010 Cayman S, special build.

I have just spoken to the mechanic of the local Porsche Center.

He told me that the catalytic converters are very restrictive and if you don't rev enough your engine it won't get rid of the particles it gets filled with. The best way to clean it is to run at very fast speeds for a while (like on the highway). The resulting higher temperatures allow the cat to get rid of the particles. This also means that the best way to fill it up is to start revving the engine without moving.

The particles dramatically restrict the airflow, the lambda senses that the cat is being filled up and further reduces the engine responsiveness. I am no technician so I just tell you what he told me.

OT:
He was quite upset to learn that I have installed lowering springs. He started shouting at me (he is has become a friend over time):"Good work Jack you have transformed once of the finest cars on Earth into a coffin on wheels."
He claims that since I kept the stock dampers cornering at high speed will make the front lift making it difficult to control. It sounds BS to me. Fortunately warranty has not been voided with such a light modification.

I'd tend to agree with him if you lowered more than 25mm or so. You'd also better re-allign your wheels if you lowered as it'll be out. Your mechanic is totally Italian. I don't think you can make a very good coffin out of some lowering, unless you dropped something idiotic like 55mm, which will totally change handling without correct shocks, tyres, wheels, and allignment.

What you're experiencing deffinitely seems temperature related. Not moving in heat, goes away when cold and at high-speed.

I don't think your car is old enough to have clogged catalysts. The theory about cats is correct, but cats don't build-up over a few hours; the amount of build-up you can burn off is really very small, and so is the amount of build-up you gain. If you commute a lot, for long hours, at very low engine load (eg. slow traffic) then yes, over several months it'll build-up, but three or four seconds on the red-line and a few spirited full-throttle accelerations will clear most of it off.

I do absolutely not expect catalyst build-up to change that much over a drive as you mention. I think something's overheating in your car and causing it to run in a Safe (Limp) Mode when it's slightly hotter. Check your coolant and have the OPC hook up your car's log to see if it's been running in Safe Mode recently.

Having said all that, be aware that lower performance when hot is normal. Heat affects both air density (meaning less air quantity for the same volume) and in-cylinder temperature (meaning less energy can be produced without overheating). Unless you're feeling a lot less power, there's nothing wrong with your car. It's also very unlikely the engine is affected at low load. If at low speeds around town you feel it's dead and lifeless, it's probably a Safe Mode. If in the middle of the Italian Summer it just feels "a little slower" than a cold November evening, it's the same as every other car in the world. My old Subaru STi would gain 0.3sec in 30-160km/h rolling starts if it was cold and the air was very humid, and lose about 0.7sec in 0-100km/h in the Greek summer around 35deg C. Temperature does that kind of thing.

He gave a look to car's log today. He didn't mention Safe Mode.
There were a couple of PSM faliures, he said those were quite normal. And a nasty level 5 overrev (176 misfires) I made many driving hours ago, according to the on board computer. (I remember about it).
The difference in performace I notice is definately normal and related both to hot air and heavy traffic, start-stop driving style, then. It is noticeable, yes but it's not a night-day difference as I would experience in Safe Mode. I didn't know that hot air was responsible for these performance variations. I thank you for the exhaustive reply Pint of Brew.

The car has been lowered exactly 25 mm. That was really funny because a crowd of people gathered around my car at the dealer. "What have you done to this car?!? She looks like an Alfa Romeo now"

BTW I have this level 5 overrev to cope with now. My warranty is voided and cannot be restored. Now that's a problem. I am not going to keep an out of warranty car.