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YOUR RESEARCHWHY 2800 RPM
Leading reported evidence
Replace around the 1400 rpm level
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Now my info is that for some engines the valve timing is changed around the 1400 RPM level and then again at a bit over the 5K RPM level.
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i ran fister modded mufflers for a while and noticed the switch at about 2800 rpms but with stock exhaust it was nearly seemless.
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Suggestion
The stroke of the intake valves changes from 3.6 mm to 11 mm.
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Suggestion
However, later M96 engines with VarioCam Plus may have a different cam timing change profile.
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Suggestion
My wife has been instructed to run the motor 3K RPM's or more.
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I read a few days ago on here a post that Jake wrote. Can't remember what the topic of the post was. Jake said 2800 rpm was the hardest rpm on the cam chains. WHY?
Maybe this -
http://en.wikipedia.org/wiki/VarioCam
For more detail -
https://rennlist.com/forums/996-foru...-a-primer.html
However, these explanations do not say anything specifically about 2800 RPM being a changeover point, so maybe ask Jake directly.
What DBJoe996 said: Ask JR directly.
I suspect it has to do with when the intake valve timing is changed.
Now my info is that for some engines the valve timing is changed around the 1400 RPM level and then again at a bit over the 5K RPM level.
However, later M96 engines with VarioCam Plus may have a different cam timing change profile. After a quick search of my references I can't find any specifics on this.
the only explanation that I can think of is only for vehicles with "variocam plus". At approx. 2800 rpm to 3200 variocam plus switches from small lift to large lift. The stroke of the intake valves changes from 3.6 mm to 11 mm. The timing chains will be required to do a little more work in this mode.
Yes, your 3.4L engine didn't come with VarioCam Plus, just plain ol' VarioCam.
My info is timing is changed at around 1400 RPMs and again at something over 5K RPMs.
Even with VarioCam Plus my info is the transition from low life to high lift occurs at a much lower RPM than 2800. More like half that, around 1400 or so.
Interesting that the Variocam-Plus 3.6 engines is when the IMS failures make a big jump. If fact it could be that it is the cam chain end of the IMS shaft where the failures begin.
The M96 does have a harmonic imbalance at about the 2800-3000 RPM level that is inherent to the engine design.
Perhaps this is also related to cam chain vibration/slapping??
you may be correct, the switch to large lift is not at an exact rpm and it occurs at different rpms depending on several factors. the attached is for the 996 turbo, i could not find anything for the carrera. i ran fister modded mufflers for a while and noticed the switch at about 2800 rpms but with stock exhaust it was nearly seemless.
Hartech mentions this on one of their documents as well, but I want to say they specify 3K RPM's. I do believe they say its related to the Variocam change over point
The list of documents is here -
http://www.hartech.org/porsche_996_9...ers_guide.html
My wife has been instructed to run the motor 3K RPM's or more. Never lug it (had to explain). and Every on ramp should be done in 2nd gear until she reaches freeway speeds. 1st time she did it she called with OMG!!!! this car can get a ticket in 2nd gear!!!!!!!!!!!
I went through the same thing. I did the FisterD mod, and now at (or around) 3000RPM as it's reving up i get a slight jerk forward, like somebody taps your rear bumper at 3 miles and hour. What about the FisterD's causes this? Lack of back pressure?
i think you are correct, it is the lack of back pressure. i also noticed a small loss in low end power which i attributed to back pressure. i ended up going back to stock. i think you feel the surge when variocam plus goes to large lift because prior to switching there is a less power than with stock cans and the difference is more noticeable.
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