GT3's have variable intake valve timing. The Turbo's variable intake valve lift mechanism apparently adds too much weight to the valve train to go much over 7300 RPM.

 

sticky,

The 996tt has variable lift and timing. The GT3 motor does not have variable lift, It does have variable timing. On the KA motor we eliminated the variable lift and have variable timing. Just like the GT3 motors.

 

I understand that it is difficult for the 996 turbo motor to go much higher than that and keep the variable intake and lift but when they do the motor for the 997 I don't see why even if they decided to do an 8k redline they could not make it work when starting from a new motor and re-engineering all the parts. I'm sure now they could make it much lighter and able to rev, what would stop the factory?

 

Isn't that only due to you using ther GT3 head though? If you kept the 996 turbo head you would still have variable lift and timing wouldn't you but you would not be able to rev as high as a result correct?

 

sticky,

The variable lift can be removed from the 996tt by installing a non variable cam. removing the lift accuators and deleting the variable lift segment of the ECU program. You can eliminate the variable lift and use turbo heads.

 

I understand you can eliminate it with software but it is impossible to have variable lift if you go with GT3 heads but if you port the turbo heads and rev higher you can still retain it and there would be no need to disable it, correct?

 

sticky,

It is not just the software you need to change.

I'll try to explain it this way. The main difference between the turbo and GT3 heads is the size of the ports and the valves. You can take the turbo heads and enlarge the valves and port the intakes and exhausts so the turbo head basically becomes a GT3 head.

At thus point you still have variable lift because you have a variable cam. The GT3 exhaust cam will fit in a turbo cam housing, however, the GT3 intake cam will not. The turbo cams are variable lift and have two sets of lobes, the GT3 cams are not variable and have only one set of lobes. If you go to the GT3 cams you must use the GT3 cam housings. These housings are beefier and will accept the bigger cams. I believe you can install either cam housing on either set of heads. The GT3 cam housings also accept both the GT3 intake and exhaust cams. The GT3 cams have taller lift and longer duration.

So to answer yor question (if you want to keep the variable cam), yes it is possible, however you can get the same results for alot less money if you modify the stock turbo heads and stay with he turbo cams and cam housings. If you changed the rods, oil pump, amd ECU (for power gains) this would prettty much give you a motor that would safely provide good usable power to a 7400 redline.

Hope this helps.

 

You guys know much more than me but this is my thought. I think high reving motors are cool too. However, if you giet a high torque motor down low that will pull nicely to 6500 or so then the higher revs are not needed. When the car shifts gears and drops back to 4000 or so it still pulls like a freight trane. This is what I always liked about big block muscle motors. Hugh torque down low and with a littel intake and head work they would pull to 6k or so. When you boost a car, high compression becomes the tricky enemy. I like a car that runs smoothly, effeciently and has some nice longevity built in to it. The turbo motors purr at modest throttle levels but you can boost em up good with tuning. Remember a tweaked out high compression motor is always that even when you are not hammering it. Just my thoughts. I don't want to wait untill 4 plus thousand to pull hard. Even iff I can turn 8500 it just is not for me.

 

Ummm, the m3 stock sucks. When I was stock I was demolishing stock m3s, with some some work I have beaten AA turboed e36 m3. A e55 stock against a m3 wouldnt even be race.

 

Chad, let me clarify.

The reason that making changes is expensive to you and I is because they are changes.

Forgetting the CGT, Porsche now offers four basic motors- M96 (Boxster/Boxster S/Cayman S/Carrera/Carrera S/Carrera S X51), 964/GT1-Derived (GT3/Turbo/X50-GT2), V6 (Cayenne) and V8 (Cayenne S-Turbo). These four different motors have about twelve different setups- in other words, more engine choices than Nissan or Honda in our domestic market.

In an ideal world, a bean-counter's dream, manufacturers would only offer one motor that would be inexpensive to build, with different performance envelopes available simply by selling the prospective consumer different software packages. Given the laws of thermodynamics/chemistry/physics, such a scenario is impossible.

However, taking as an example the Turbo S/X50/GT2 version of the 964/GT1 derived motor, there are varying outputs but the motors are mechanically identical- the difference is simply programming. Taken a step further, it would probably SAVE MONEY for Porsche to dump the variable valve lift and make this entire line of motors identical save for forced induction plumbing and lower compression setups for the forced induction models. Currently, I can't imagine that Porsche is saving much if any money by putting a different oil (single outlet) pump into the standard Turbo than it puts into the X50/Turbo S/GT3/GT2 (dual outlet).

In other words, by changing the logistics of engine building, we could see engine envelopes be a little more flexible at a decreased manufacturing cost with consequent increased profit. To some degree, the day is coming.

 

Wow, interesting info guys

 

Agreed. I stand corrected. I meant compare non-supercharged AMG V8s against the M3.

 

Silver: the latest variable cam and timing technologies allow for just that. Maximum torque down low as well as up high, with incredible low end pull and top end power. Add a turbo and you can see how even a lightly bosted, low compression GT3 can easily make 500HP while out-accelerating cars with similar specs but lower redlines.

 

Dock,

PM'd you. Thanks.