911 996 3.6 performance ??

Pepi1677 · Mar 30, 2009

I have a couple of questions relating to the performance of my 911 996 3.6 with the PSE switchable sports exhaust. I only test drove the car with the standard exhaust on. I have noticed 2 things one is that there seems to be a step in performance at around 2800 rpm under faily light acceleration, if pressing on you do not notice it.

The other thing is at around 5500rpm the car seems to sort of hold back for a few hundred rpm the pulls again up to 7000rpm.

I have not had the mod done which removes the quite spot. I remember when I had bikes that they seemed to have a flat spot which had something to do with helping the bike meet noise/ emission test.

Any one any ideas?

adrian996 · Mar 30, 2009

Hi David. I have a standard 2003 996 C2 Manual car. Mine has always had that noticeable "lump" in the engine response at just under 3000 rpm. I think that it has something to do with the vario-cam system kicking in at those revs - which it is designed to do. I believe that the valves lift slightly providing quicker expulsion of exhaust gases and a more rapid inlet of fuel. I found it odd at first but then just found it to be characteristic of the engine. I find it more noticeable on some occasions than others. It is probably effected by the outside air temperature, etc. Eg. Cold morning air = higher density of air and increased combustion.

I may not be sport on here but I'm sure that Richard or someone will be along soon to confirm, or otherwise.

I can't really comment on the higher revs characteristics that you've noticed but I'm pretty sure that there's nothing wrong with your engine.

Adrian.

Richard_Hamilton · Mar 30, 2009

I agree with Adrian that the 3000-ish rpm 'bump' sounds like the normal variocam switching point. Not sure about the 5500 rpm one though. Usually, hesitation at this sort of rev range is attributed to the MAF sensor, or sometimes O2 sensors.

Did Peter Morgan report any fault codes in his report?

http://www.renntech.org/forums/index.php?s=&showtopic=422&view=findpost&p=1645

http://www.renntech.org/forums/index.php?s=&showtopic=12366&view=findpost&p=60705

Diesel130 · Mar 31, 2009

Mine pulls strongly across the entire rev range ... but then its a 3.4, not 3.6.

Richard_Hamilton · Mar 31, 2009

ORIGINAL: Diesel130

Mine pulls strongly across the entire rev range ... but then its a 3.4, not 3.6.

The 3.6 has Variocam Plus, which has switching points at around 1400rpm and 3000 rpm. The 3.4 Variocam only has the 1400rpm switching point, and it is much less noticeable.

Hugh Ross · Mar 31, 2009

For what its worth, when pushing hard my 3.4 has a noticeable hesitation and then power surge at around 5k which I assumed was a variocam thing. Had occasion to notice it a couple of times this weekend. I had variocam solenoid work done around three years ago after emissions light came on.
Hugh

Grant · Mar 31, 2009

Don't forget the 996 has a two stage induction system, but this creates a slight step as it opens rather than a flat spot.
If its a "serious" flat spot I agree with Richard about the MAF!

Diesel130 · Mar 31, 2009

ORIGINAL: Richard Hamilton

ORIGINAL: Diesel130

Mine pulls strongly across the entire rev range ... but then its a 3.4, not 3.6.

Click to expand...

The 3.6 has Variocam Plus, which has switching points at around 1400rpm and 3000 rpm. The 3.4 Variocam only has the 1400rpm switching point, and it is much less noticeable.

That's great ... so I've got a better engine than the 3.6 boys have

I always wondered why evo mag had the 3.4 996 down as 4.6s to 60 and 5 star rating, yet only 5.1s and 4.5 stars for the facelift

Peter_Bull · Apr 1, 2009

ORIGINAL: Diesel130
I always wondered why evo mag had the 3.4 996 down as 4.6s to 60 and 5 star rating, yet only 5.1s and 4.5 stars for the facelift

We always knew that tho.................[

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Pepi1677 · Apr 11, 2009

Thanks for the response. Peter found no error codes. I am having it looked at just to check all is well. I will post response when I get back of Hols

Pepi1677 · Apr 11, 2009

Richard, thanks for the links. The info will help me when I take the car back to the dealer today. I am getting it looked at while I am away. Thanks again

Ian W · Apr 11, 2009

ORIGINAL: Pepi1677

I have a couple of questions relating to the performance of my 911 996 3.6 with the PSE switchable sports exhaust. I only test drove the car with the standard exhaust on. I have noticed 2 things one is that there seems to be a step in performance at around 2800 rpm under faily light acceleration, if pressing on you do not notice it.

The other thing is at around 5500rpm the car seems to sort of hold back for a few hundred rpm the pulls again up to 7000rpm.

I have not had the mod done which removes the quite spot. I remember when I had bikes that they seemed to have a flat spot which had something to do with helping the bike meet noise/ emission test.

Any one any ideas?

The 3.6 has always had a 'flat spot' at 5000-5500rpm. If you look at the factory power/torque curves (or any tuner's dyno plots) it's clearly visible. It's also carried over (quite noticeably) into the 3.8 Carrera S motor too. It's a characteristic of the engine and one Porsche tried to overcome with the resonance flap in the second crossover pipe in the inlet manifold - using a resonant effect to bump up the torque curve at that point in the rpm band. Unfortuntely it didn't remove the dip in output completely and that is what you're experiencing - perfectly normal for this engine.

The 'bump' at ~3000rpm is the variocam plus switching from the low-lift inlet cams to the high lift ones and again is perfectly normal. It's usually more noticeable at part throttle.