RF5BPilot

Was recently perusing some of the articles at pedrosgarage.com

In one article he notes:

I've heard of a lot...but never this. Anyone else hear of this or is this just more fantasy piled on the engine?

Flat6 Innovations

Odd, I purposely keep my engines at 3K RPM and prescribe that driving to all the owners of my engines.

b8_rdc

I keep the RPMs up in that range as to never bog the engine when shifting. The M97 engine had a poor design on the piece on top of the oil pressure spring which would whine at 2k rpm. Never heard anything around 3k in either M96 nor M97.

Zanzibar Red 996

Can we hear from Pedro ?
I would like to know how he arrived at his theory

b8_rdc

There could be some truth around the lifters locking and unlocking at certain RPM which could accelerate wear.

perryinva

That is right around the RPM where the variocam+ kicks in and out so I can see not going up and down through that short range constantly. That is the only vibration I've ever heard or felt.

Barn996

At an indicated 79 mph in my 99' C2 my tach is at 3k RPM, and that is usually the speed I drive on the highway. According to my wife's GPS, actual speed is only 74 MPH. My Porsche seems happy at that speed.

Imo000

Lifters lock?

b8_rdc

Variocam Plus intake lifters operate at two levels. I believe 3mm and 11mm depending on RPM.

See below @0:52 onward pin shown as red/green for locking tappet. (gosh that robot voice is hard to listen to....)

Macster

Think this arose because the resonance flap is activated at 3K rpms and then deactivated at 3K on the way down.

Going up one might notice a bit of the engine coming 'on cam'. Going down there can be a bit of engine reaction. It is hard to describe and my experience is the behavior depends upon other things like the road surface.

Seems like on smoother roads the reaction is more pronounced which suggests to me it is a factor of engine and drive train harmonics more than anything related to the resonance flap.

VarioCam timing changes and low lift take place at lower 1400 (or thereabouts) rpms and timing only at IIRC 5K rpms.

Anyhow, I've driven my 02 Boxster lots of miles and sometimes 3K rpms in 5th gear is just perfect. While I pay no particular attention I suspect the engine has spent hours over the years operating at 3K rpms.

With no ill effects I can detect.

RF5BPilot

Yep. I know the vario-cam plus effects -- particularly under light throttle. But I've never felt nor heard anyone else talk about inherent harmonic issues. Some small airplanes have small RPM ranges noted on the tach that you avoid because of harmonics. So, the concept isn't new....but just seems confused or misguided when applied to the M96/M97 engines.

KrazyK

Its more commonly known as "gimbal lock" and the 996 will tumble off into blown engine space.

Seriously, the safest RPM is "0".

perryinva

Thanks for that Macster. I had forgotten about the resonance flap! That makes more sense. I'm surprised it has such a pronounced effect, but then, I guess that's why they put it in. I don't remember where I thought I read that VC+ occurred at around 3k, but I swear that's been circulating around for a bit.