BG

I have an 02 TT-X50 and have noticed that under WOT there is a pretty noticable flattening of power as I accelerate past 5000 RPM. There is definitely an abrupt difference in pulling power once past 5000. I think it might be the wastegates opening to lower boost but its happening so fast that I can't look at the boost guage to verify. The published torque curve of the X50 motor does show a dropoff after approx. 5000 RPM. Is this the normal workings of the computer controlling boost or is there something wrong.

Bill S.

Could you have bad gas or low octane (i.e., less than 91)? The knock sensor could be retarding the timing when the power comes on, causing the symptoms you mention.

BG

I live on Long Island in New York and use either Exxon/Mobil 93 Octane or Sunoco 94 Octane however it does feel like it could be a timing issue now that you mention it. I'm going to switch gas stations and see what happens. Thanks, Hopefully that's all it is. <img src="confused.gif" border="0">

Bill S.

cjv,

Interesting point you make. I've always wondered about the long-term durability of the VarioCam given its narrower cam lobes and actuators. Now you have me wondering about its short-term reliability. Have you heard this happen to many cars? Do you know if other parameters, like oil level and temperature, affect the system?

Nissan and Infiniti use something called CVTCS (Continuously Variable Valve Timing Control System). It uses the traditional heavy-duty cams, but uses a special hydraulic/electronic actuator at the end of the cam to advance or retard the cam. It seems to be a very durable and reliable system. I'm not sure why Porsche decided to use a different type of system.

BG

Hmmmmm!!! You guys make an interesting point. I wonder how that could be checked. I doubt the computer would show a fault because of a variocam pump/valve problem. I'm going to try different fuel and if that doesn't help I guess it's off to my friendly Porsche service dept. Thanks, it's nice having knowledgable people to talk to. CJV, what's happening with your dyno run. Like everyone else I've been following your quest.

Jack

[quote]Originally posted by BG:
<strong> I doubt the computer would show a fault because of a variocam pump/valve problem. </strong><hr></blockquote>

BG: Actually, I've been told that a failure of the pump/valve may throw a "check engine" light and a fault code stored in the ECU. Also, if the variocam/lift is really "out of whack", your car will idle poorly and overall drivability will suffer, not just a 5000 rpm hiccup. This variocam/lift issue has not been a common problem according to my sources, FWIW.

jb1

I have an '02 996TTX50 and have also noticed similar characteristics. The thing that made me think there's nothing wrong is the relative performance of the car to others... it will leave a regular 911 turbo behind on a 1/4 mile straight.

I guess I'll find out whether anything is wrong today as I just had the car taken in to the shop from the track... the car simply cut out on me and stopped (permanently!)... no fluids, no bangs, no electrical failure (basic functions inside the car atleast). totally mystery.

BG

jb1 Good luck, keep me posted please. I'm trying a different brand of fuel this weekend so I'll find out whether it's the timing being retarded due to bad fuel or not. As soon as I pass 5000 RPM at WOT the power drops abruptly about 15% or 20% and remains that way to redline.It's like I flipped a switch. Is this the same thing you are experiencing. I would love to see a boost graph of the X50 motor. I have the one for the standard motor which doesn't indicate anything like I'm experiencing. <img src="confused.gif" border="0">

BG

Thanks guys for the all the input. Other than the drop in power over 5000 RPM the motor is smooth and idles right at 750 RPM. I filled up with Sunoco 94 Octane at a different station and the problem remains however the suggestion of a timing issue started me thinking. Here in the Northeast from October through April all fuel is oxygenated. In the owners manual on page 142 it states the car will run on this type of fuel but there might be a deterioration of drivability and performance. I wonder if this is what's causing my problem. I might have to wait until May to find out. Unfortunately I'll be putting it away for the winter in a few weeks anyhow.