Why VarioCam off at 5120

[REBible]

As I understand it the VarioCam on the 2.5 turns 'on' as the rpm increases depending on bunch of things and then turns off at 5120.

I would have thought it would stay on through redline. Is this one of the reasons that the horsepower curve falls so flat at 6K.

Anyone play around with this to see effects?

This is my first Porsche. I have always driven trucks. But I don't understand the low redline and big time fall off at 6K. With these bores and strokes it should be happy at much higher rpms.

In college I built a 302 chevy in a PU that pulled strong through 8K. I easily passed 'sports cars' at 7500+ on the straight uphill sections of the mountain roads. They never saw me coming. Of course it didn't idle very well, and cornering was like driving on a dirt track. Ran it 300K miles too.








robert

[JFP in PA]

Originally Posted by REBible

As I understand it the VarioCam on the 2.5 turns 'on' as the rpm increases depending on bunch of things and then turns off at 5120.

I would have thought it would stay on through redline. Is this one of the reasons that the horsepower curve falls so flat at 6K.

Anyone play around with this to see effects?

This is my first Porsche. I have always driven trucks. But I don't understand the low redline and big time fall off at 6K. With these bores and strokes it should be happy at much higher rpms.

In college I built a 302 chevy in a PU that pulled strong through 8K. I easily passed 'sports cars' at 7500+ on the straight uphill sections of the mountain roads. They never saw me coming. Of course it didn't idle very well, and cornering was like driving on a dirt track. Ran it 300K miles too.








robert

VarioCam activates at around 1,500 RPM, advancing the cam approximately 25 degrees on a Boxster. At 5,500 RPM, the cam returns to base timing since at higher RPM's running the cam in the advanced position would actually interfere with resonant intake charging, and actually reduce performance.

[Jake Raby]

Because torque and HP cross mathematically at 5,252 RPM. Keeping the valve timing advanced past this point has no benefit and decreases performance.

Manipulation of the vario cam arrangement past the point where the ECU has dictated is a great way to lose 20HP. I've done it and even allowed my dyno to control the VVT actuation; not the DME. Plotting these things as overlays was very revealing and opened lots of doors early in our program.

[REBible]

Thanks for the quick reply. I figured someone had done the testing. But I couldn't find it referenced anywhere.

I realize that you make your living by selling upgraded engines, and it costs you money to obtain information like this. I appreciate your sharing it.

Why the big drop off at such low rpms? I have read what I can find on the web and there does not appear to be any consensus.

Is it the cam grind.. e.g. is the valve lift and duration too small? Or is it muzzled on the intake and or exhaust?

thanks
robert