Planet 9

I have finally gotten past the break in miles and have started to explore the higher reaches of the RPM band on my CS.

I am underwhelmed!

The torque curves show a big jump in torque from 3500 to 4500 RPM. During a foot to the floor acceleration in second gear I feel no noticable surge going thru this range. Good pull, but no surge. Is this normal or is my "plus" on the VarioCam Plus not working?

I've never felt a "surge" either, some of the descriptions in other threads make it sound like a drastic/turbo like change, but I never found it to be that noticeable. But I will say that once I hit about 4000 I do feel and see the Revs start to climb faster and the engine note starts turning into that mechanical flat 6 melody.

In 2nd, try doing some WOT at 2500RPM, then at 4500RPM I think your car should respond differently.

Well as Blitzkrieg said, its not a "turbo" surge, but there IS better response on that range

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"Sir! We're surrounded!" - "Excellent! We can shoot in any direction!"

Most reviews of the Cayman S refer to a power surge at 5000 RPM to redline. However I've never experienced that surge. The power does seem to build linearly with quicker(as expected) engine response at higher RPM.

You need to see that graph a little closer. The "big jump" you refer to really isn't that big at all. This is no v-tech style on-off situation, don't expect some stone-age style "once past N RPM it's a monster" deal. The control on both functions of both cams is a lot more detailed and smooth than that. Instead of a step-up, what you get is increased, smooth, consistent torque. Through most of the range.

This is a read-drive car that's big on ballance, the whole point is having a smooth power-band. How terrible would it be if you're ballancing on the throttle in a curve, and suddenly through 200rpm you gained 30lb-ft? Your cams are working fine, they're not supposed to bump.

The fact that you're not feeling a surge suggests that Vario Cam Plus is doing it's thing. The fully variable nature of valve overlap (0-40 degrees) allows the system to be very transparent, especially when compared to something like the V-Tec setup.

The bump you see on the Torque curve looks exaggerated because of the scale chosen on that graph.

I feel a dead spot in the 3,500 area, and a slight surge around 5,200.

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Gator Bite
PCA Cayman Register Advocate

Be happy you don't feel a surge. As Pint-of-Brew points out, surges are not good on the track near the traction limit. Also notice the linearity of the power curve. It is indicative of a flat torque curve that is a real plus to drivability because it means that you will get quite similar relative thrust response for the same relative pedal movement throughout the ~4,000 - ~6,000 band. Being able to repeatably control one of the variables in total traction means that the car is easier to learn and that a practiced driver can operate more consistently at the traction limit.

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Kenny

2006 Arctic Silver CS 6M, PASM, Sport Chrono,, short shifter, 19" wheels, Pirrelli tires, Milltek Catbback, Softronic SRP and 4.2 Flash.

If you look at the 996 board over at Rennlist, there are frequent threads about surging at 3000rpm. I've just come to a 987 from a 996 and it really is much smoother on the newer car - I think the Variocam system on the 9x7 motor is more subtle than on the 9x6 unit.

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Simon
Another Brit in Delaware

Thanks for the replies folks. My understanding is that the VarioCam affects cam timing while the Plus affects lift and the lift change is not gradual. That's why I was expecting a noticable torque bump between 3500 and 4500. However, sounds like my car is acting just like everyone elses so that is good. Or at least not bad.

Suggest SprintBooster if you do not have the Sport Chrono.

You are correct, the phasing is graded but the lift is not, though with so detailed control it's rather trivial from an engine desing point of view to make change-over subtle. They would have "dialed-out" the step-up at the cam lift-change points, even if it means having to reduce the output for the first few degrees by inferior timing. This'd be done specifically to give as smooth a torque output as possible.

The graph in the car's presentation booklet does seem deceptively missleading, I was expecting a major drop and a major surge too; In fact you should think of the graph really compressed in the X-axis and elongated in the Y. It's almost the same torque from very low (and part of the deception is the high low-end torque), just has a small, almost imperceptible dip and a slightly larger bump after it.

It's much more noticeable in the 2.7, and by much more I mean: Rather than "not there" it's "barely there".

All the intake tom-foolery and cam work really is to dial-out the dip. Porsche boxter engines (and other boxters for that matter) have a dip in the middle of their band, almost certainly due to some physical resonance. Even tuners have some moderate trouble dialing it out, though it seems certain mods which relate to induction/exhaust tuning do a good job of removing it. Others don't and make it worse.