I have read interesting discussion on this (cant find it now) that the dip is caused by intake harmonics/resonance/standing wave in that rpm range. I do notice that most 996TT have that dip. I've seen some dynos without it, but the people that have solved it aren't open with how it was done.

 

I think I found it, interesting read.

https://www.6speedonline.com/forums/...chart-q-2.html

 

Yeah, that's the one. A few people mention that they've ruled out variocam- which I kinda agree with since the changeover is around/just above 3k rpm, but Im not sure if there is another phase at higher rpm.

Once I have time to get my car back together and can get to a dyno will be interesting to see if the changes I made on intake side eliminate the dip.

 

Thanks for digging this up! I posted my solution to the problem.

 

Good to see. My possible solution is almost identical to yours.

 

I just changed the blue springs to green springs and have some preload on it so that the wg cracks at 11psi. Muuuuch better boost control so far than previously with the blue spring. I've just been incrementally increasing boost. At a low 15psi the 60-100mph 3rd gear pull was as fast as my previous Proto 63vtgs at 22.5psi!!!

 

Glad you got it sorted. The green spring is the way to go unless you're running 30psi. With the green spring cracking at 8.5 and full open at 14psi, I'm getting to my 1.15 bar (17psi) target with 80% N75 duty cycle. 100% duty cycle will get me to 1.4 or 1.5 bar on race gas. This is just about ideal as I am using pretty much the full range of the N75 to control boost which means the ECU has control of boost and not just the spring. Any chance you can run your car on a dyno? I’d love to see the same turbochargers on a 997 engine for a curve comparison. Dynojet would be ideal.

 

I'm not super familiar with the 996 boost control but I do understand it's all done via the tune as opposed to an external controller. I have the Dynojet virtual dyno plots but I don't know how accurate they really are.
There isn't a Dynojet near me but I did do my previous dynotune on a Mustang linked dyno. I may try and get a dyno done there once everything has been finalized...

 

996 boost control is fully closed loop up to 1.5 bar.

Rick

 

Hey Pete, how are things on your end? Hope all is well. I just looked at your dyno graph you posted but I'm a bit confused and maybe you can shed light on it. Your power peaks at 599PS at 5700rpm and falls off above that to about 580PS at 7000rpm never to recover. Instead of a dip it's a continuous drop off in power past 5700 all the way to redline. Maybe I'm overlooking the obvious but something doesn't seem right especially in light of all your intake mods which should allow the engine to breathe better up top, not worse. A significant drop in power in the upper rpm range would indicate some type of large restriction or other issue as I've never seen a turbo Mezger loose power like that. What am I missing?

Every prior set up I've used including my 3.6 and 3.8 had a small dip in the 6200 rpm range but recovered and increased power all the way to redline. My current set up with the stock intake manifold has an increase of almost 80PS between 5700 and redline. My actual power peak occurs at 7360rpm.

 

Why is the quick spool terrible for the track?

 

Quick spool is actually ideal. The problem we had is 49% throttle gave zero boost 50% throttle gave full boost. You have to be able to roll on the power on track or else you will lose control of the car. Smooth is everything. Using a less stiff green spring and allowing the ecu control boost with the n75 allows us to control the output of the turbo. However, when I hammer the throttle, it comes on very fast...

 

We finally go the Xonas dialed in last Friday at the track. In summary they feel amazing. Throttle modulation is fantastic and the engine basically feels like a 700whp GT3 engine. There is no sudden rush of torque down low but instead a nice smooth progressive build as rpms climb very much like a high revving normally aspirated engine. 50% throttle input gives about 50% power, and 100% input gives 100% power in a nice linear fashion. There is simply no comparison to the K16 hybrids I ran before. We tweaked the wastegates on the Xonas by softening the preload on the green spring another turn to start cracking at 7.5psi and be fully open at 13.5psi. We are running 1.3 bar which is achieved at 80% N75 duty cycle and holds all the way to the 7500 rpm redline. 1.5 or 1.6 bar would be easily achievable in this configuration with a race gas file at 85 or 90% N75 duty cycle. It's super easy to drive at the track....

 

John, that is looking fantastic. Come meet me at the glen in september... or next year

 

We have a group of us going to run Road America the first weekend of September. You should make that one! That’s my September road trip.