bccars

93 octane ? Why ?
My manual clearly states to use 98 octane all the time. And to never go lower, except in emergency, with absolute minimum of 95. also Only use part throttle if less than 98 and be prepared to loose some hp !

stealthboy

We do our octane numbers differently in the States - 93 AKI here is the same as 98 RON over in Europe.

bccars

Ah didn't know that, thx for info stealth :-)

gulrey

I have a 991 MT and I cruise all the time in 3rd gear at 32-35 mph when coming home through my neighborhood.

Note: to say that you should be driving in 2nd gear at higher revs when at this speed is ridiculous in my view given that a PDK in normal would probably be in 5th gear at the same speed.

While I have accelerated from this position, it is never hard or even moderately hard acceleration. Still, no stumbling.

I do notice stumbling when first getting going when the car is cold. This might last for an 1/8 of a mile so, a little longer in colder weather.

duxsi

I also have the dreaded hesitation /stumble at 2500 rpm.
But when I'm in Sport / + it's not noticeable.

You are NOT imagining things and are certainly not alone...

aelia

It is an interesting observation, the fuel, because I was on a long road trip this past weekend and switched to Sunoco because I had to. Following that I noticed this hesitation in the engine at low revs. I then had the chance to mix with Exxon and it was running smoothly again. It may just be me... Btw - C4S 991 MT

meine911

Might be why Sunoco is not on "Top Tier" list.

dodo1porsche

That is VARIOCAM at work. It is obvious in some engines. Nothing to worry about according to Porsche. It was very obvious in my 997. Luckily, my 991 is a bit better.

pfan

Agreed - most likely the VarioiCam system switching profiles. My 991 is not nearly as bad as my 997 was. A bit disheartening that Porsche hasn't perfected the system after over a decade of use on the 911.

mrstep

Yes, but the lectures here are all FREE!

Sorry, wasn't trying to lecture on driving style in any way (which totally reminds me of that joke about other drivers all being either idiots that drive too slow or idiots that drive way too fast), I really was just saying that you may want to downshift if you're trying to accelerate quickly/immediately from cruising speed, but that doesn't address a specific hesitation at the RPMs you mentioned - though you would skip that part of the rev range, so I suppose it sort of 'fixes' that.

I haven't really noticed a hesitation myself, but that may just be because:

1) I don't have a high expectation when hitting the gas at 2100 RPM and haven't paid close attention because of that mental starting point.

2) I'm often in Sport mode as soon as the car is warmed up if I'm anywhere reasonably fun to drive and/or listening to the engine - as duxsi mentioned, maybe it's non-Sport mode that's the difference?

3) Maybe this contributes, but my SUV doesn't accelerate well in any RPM range and has major hesitation from a stop - which has made some turns into traffic nail biters - and with that reference, I may just to see a problem on the 991.

In any case, hopefully you find a resolution to the issue. I would be curious if it's a non-Sport/Sport mapping difference. I've definitely noticed the laggy off-throttle slowdown when in normal mode - seems like they're trying to smooth the driving out, which is annoying since I really expect the car to start slowing down immediately when I take my foot off the gas.

Oh, and regarding 5000 RPM in school zones - think of how much safer that is than with some of the new electric cars where kids won't hear you coming!

stealthboy

Thanks for the reply - I notice a stumbling when just trying to maintain a constant velocity, so it's not *only* on acceleration. Even just holding at 2100 RPM there is a stumbling. But it's very slight.

And when I do downshift to accelerate, it's like the power band just isn't smooth at all until I get well past 3000 RPM. Now, when I'm past 3000 RPM the engine is flawless - it definitely likes to live there.

Again, it could just be "normal", or just a case of bad gas, but it bothered me a bit, so I was just trying to get a feel for whether or not I should worry.

And yes, in Sport mode the issue doesn't seem to be there. I also wonder if it's just a throttle mapping change for Sport that helps.

And free lectures are definitely the best kind! :-)

Cheers,
Mike

TheDatanator

I've got the same thing happening to my 981CS - definitely feels as if the ECU is changing timing attributes in real time. I wrote it off mentally as this but with all the discussion I have to wonder. My instinct tells me it is just Variocam working bit kit as refined as what I had been used to for so many years with BMW VANOS. Above 3K the engine is superb. And that induction howl... Yummy.

Noah Fect

I've felt this phenomenon in my 981BS as well, but only when the engine is stone cold. Power delivery is smooth everywhere after the first couple of stoplights.

With a 6-cylinder engine that cruises at 1200 RPM and revs to almost 8000, you can bet there were some Faustian bargains in the valve timing department to make it work. I'm always impressed at how tractable this car's powertrain is, once it's up to operating temperature.

TheDatanator

Yes yes! Only Happens prior to full operating temp. You're spot on with the assessment of probable bargains to gain this flexibility. The induction noise at WOT is superb.

MerlinsGarage

On another thread," M went to dark side", Coldlist used a upgrade chip from Fabspeed. This could correct some of the rough spots in that RPM range . We have a 7mt ordered, if we run into the same issues I will explore the corrective actions.