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Old 01-22-2006, 02:35 PM   #1
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4k rpm the sweet spot?

Why is the Box very happy at 4000-4500 rpm and 100 mph? The reasonance is perfect, the ride is smooth, and the engine almost feels twitchy and ready to go. Is seems like this is the sweet spot...kind of like the when you make contact with the golf ball and you can just tell you schwacked the hell out of it. Is it purposely geared this way, or does it have to do with cams...?
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Old 01-22-2006, 02:45 PM   #2
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Every engine has a point where the HP and Torque curves are pretty much in synch.

My guess is that this is the spot for the box.

Anyone else?

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Old 01-22-2006, 03:31 PM   #3
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isn't that the rpm that VarioCam kicks in?
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Old 01-22-2006, 04:05 PM   #4
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Originally Posted by tqtran
isn't that the rpm that VarioCam kicks in?

I don't think it is just the VarioCam. Since the VarioCam varies the timing of the intake camshafts to optimize performance at any engine speed or load. The camshaft angle is continuously varied by the twin rotary valve vane adjusters.

On the 987, at about 4500 RMP, the torque curve is at about optimum- 191 lb.ft. (Max being 199)

And for the 987S, at about 4500 RPM, the torque curve maxes out at 236 lb.ft.

Last edited by bmussatti; 01-22-2006 at 04:37 PM.
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Old 01-22-2006, 07:01 PM   #5
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That makes sense thanks!
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RC-7 Crazy Hawk

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Old 01-22-2006, 08:46 PM   #6
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Quote:
Originally Posted by bmussatti
I don't think it is just the VarioCam. Since the VarioCam varies the timing of the intake camshafts to optimize performance at any engine speed or load. The camshaft angle is continuously varied by the twin rotary valve vane adjusters.

On the 987, at about 4500 RMP, the torque curve is at about optimum- 191 lb.ft. (Max being 199)

And for the 987S, at about 4500 RPM, the torque curve maxes out at 236 lb.ft.
Hi,

VarioCam's job is to increase/decrease Valve Overlap to maximize Torque and Power. In the past, selecting a Cam was always a compromize between these two.

By Advancing/Retarding the Valve timing, you can increase Torque, Power, and lessen Emmisions. Retarding the V Timing in the Low-Mid Ranges increases Torque, while Advancing the V Timing at Idle and Low RPM Range increases Power and reduces HC Emissions.

There are 2 versions of VarioCam on the Boxster. Only on the Latter version is the adjustment Continuously Variable.

The 1st version - '97-'02 used an Electric Solenoid which Advances the Intake Cam 13, the limit of this system is that it is either ON or OFF at a pre-set RPM controlled by the DME.

The 2nd version - '03-'06 eliminates the Solenoids and uses an Oil-filled Stator. This allows for infinitly variable V Timing within a 40 Range. This is where much of the HP/Torque gains are had over previous MY. Also, a Synchronizing chain between pairs of Cams is eliminated probably eliminating a 1-2 HP Parasitic Loss.

Happy Motoring!... Jim'99
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Old 01-23-2006, 09:52 AM   #7
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I at first thought that the punchy feeling I got at 4500 RPM was the variocam changeover point, but someone (I believe on here) told me a long time ago that it was the torque peak, and that variocam didn't switch over until like 5200 RPM.

I haven't seen the charts, but I'd be inclined to believe it.
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Old 01-24-2006, 06:16 PM   #8
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MN Boxster, my head just exploded.
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'05 987 Basalt Black/Sand Beige
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RC-7 Crazy Hawk

"If the wings are traveling faster than
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Old 01-24-2006, 06:25 PM   #9
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I didn't know the 03+ vario was infinately variable throughout the range. That's cool. I still feel a surge right about 5,200 rpm that is accompanied with a great intake sound. You'd think if it was infinately variable there woul be linear power delivery thoughout the rpm and no spikes at about 5,200. Don't get me wrong..I love the power surge
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