Top one is not stock turbo as you asked for..
Airflow of turbo and exhaust..

 

No, but neither were yours or Mark's answers...

 

it would be nice to know the gear and duration of the run.
for me the posted examples do all look quite different and have a huge random "noise" in it and quite less in common.

 

In these curves the same dip again, difference is just the location at 6k+... Why, oh why?

 

Since you are pulling up non stock turbos now..
There are other Dynos sheets on this forum that do not have that dip,,if you do a Indepth Search..
A good tuner will give you your answer right away.

 

Well, since Markski replied earlier as he did (read below) and also posted the pic above I'm waiting the answer...and if you're so handy with the search -which I'm not, being illiterate foreigner- why don't you show me the correct conversations??

 

Interesting occurrence indeed. It can be fixed and a lot of people/tuners claim different things because they don't know

Stock intake manifold in these 2yr old dynos of my car ...

 

Hey I am in the league of your other below comment ,your post #7
So nice to notice again the lack of aswers from those who know -or pretend to know- when there's no place for shameless plug of their own products....
__________________
Pete

 

did they datalog the run?...to me logs are the most important thing to do.

 

I have the same curve dip between 6000 and 6500 RPM too - 996GT2, stock turbo, GIAC tune headers/exhaust...

Good to know it's common - bad that it's happening.

From my experience with past P-cars, this due to the 'flapper valve opening' inside the intake plenum. It disrupts the airflow as it changes the 'resonate length'. You should be able to 'tune' this out...I'm not sure why it's there on aftermarket 'tunes' - You should be able to adjust the timing of when the valve opens, it's opening 200RPM late.

 

Here's (pic below) the dip again, enhanced with the mods. I'm pretty sure that someone here knows what causes it...

I'm bringing this up again because this seems to be quite unique to M96/7.70 engines. If you google for example STi or Evo X dyno charts you'll notice that Tq drops after peak in quite linear way and the hp rises without dips (or twin peaks) all the way to the redline (or until the turbo runs out of steam).

AMS's turbo kits for Subi:



AMS's tuning for Evo X:

 

Back to this one. Found again a perfect example of the dip mentioned (see below). Yet I have not recieved a clear explanation for the reason.

Facts:
-both 996 and 997 turbos have it
-even stock ones, see below a 997 GT2RS's dyno graph
-happens at different power levels...400 whp and 700whp cars seem to have it
-it might be tuner-dependent
-bottom of the dip is at 5.8-6.2k RPM, about 10% of the "perfect" Hp-curve
-usually the Hp-curve peaks after this dip, so it's not about something choking the engine totally
-Durametric logs' (if available) MAF flow numbers show the drop in flow

So, is it
-intake manifolds (standing wave in there)...runner/plenum size/volume?
-cam timing?
-something in the tune? Ignition advance, CV-adjustment, cam timing, boost adjustment...
-something in the Motronic's Tq-model?

 

Anyone else getting dizzy?

 

From my knowledge the 996tt intake manifold has a dead spot in its flow on higher then stock levels, this is why 2 years ago you see people looking into 997 manifolds, gt3, and WC intake setups.

but that is with everything else tuned well. but each car is different, one could be clutch slip, one could be starving for fuel in that spot, one could have too much exhaust back pressure. there are many causes and yes it can be tuned around and made linear but, first takes someone willing to do that, and two the time and money involved. The tunes you see with the big dips that dont look very well are likely canned tunes, meaning a basic tune not specific to your car, no dyno involved when the flash was created. IE the cheap flash that cost you around 1000$ not a 4000$ custom tune with many dyno hours, and logs of the runs over and over and multiple files for different fuels etc.

 

When I went to the 74 mm throttle body,, it didn't make any noticeable power gain on my 18g set-up but the dyno showed it did help that dip area out..I did a thread with dyno sheets back then.