Turbo K24 shaky dyno plot

K24z7 turbo. Skunk 2 cams. Link G4 ECU. Pulsar turbo.

Dyno plot is very shaky and getting worse with each pull. Everything seems to check out. 10-11psi of boost. Sounds good. Runs well. Just not making the power it should and revving lazily. It has started to get a bit richer than at the beginning. Injectors are new and have used many times for same setup. We’ve gone through all the scenarios and can’t seem to make power after vtec hits. Timing is good. All sensors are displaying correct info. Really stumped on this one. Tomorrow we pull plugs and do compression and leakdown. Any thoughts? What causes that shaky dyno plot?

Is the base timing set correctly?

What's the trigger doing there? No ignition drift?

Any EGT info?

Oil pressure instabilities?

What's the VVTi doing?

No exhaust leaks? Or other air leaks? Busted coils/plugs? Hoses not bolted down....?

Base timing is good. Afr’s are good. No EGT info. Oil pressure is spot on. Vtec solenoid and VTC are good. Exhaust is new, no leaks. Coils/plugs/injectors are all new. Turbo is new. Valve lash is spot on.

Leakdown was perfect. We bore scoped the cylinders and they’re perfect

We found the brand new Skunk 2 stage 1 drop-in exhaust cam was made wrong, when pinned at the back the timing was off. We swapped out the exhaust cam for a stock cam, timing lined up perfectly and no change to the dyno runs. So now we’re starting to suspect the Skunk 2 intake cam is no good. When we adjust the vtc, it seems to be a bit better but still produces this shaky dyno plot and down on power. And it’s always around 4500-5500 where it goes bad. Even if we engage vtec early or late, it’s always the same result.

The car starts, idles, runs great. Sounds strong, but way down on power compared to other cars with the same setup.

Does the data logging from the Link show any variation in engine speed?

If that data is smooth, I would suspect the dyno may have a failing speed sensor (or wiring problem).

If the speed sensor is ok, then is there any indication of traction problems with the dyno -- was it strapped down the same way? Even tire pressures, etc.

Agreed on link data verification in terms of stability.

If all is sound and verified mechanically as well as on the ECU side...

It's either something very simple being missed or something not directly related to the car.

Any way to verify?

Also try to get a scope above 4500 rpm to see what the triggers do...

Thanks for the replies. After going down every troubleshooting route we finally realized we were dealing with an “EGR” effect on the dyno. This is a Honda K24z7 swap into a Porsche 997 so the exhaust and turbo intake are close to each other and we realized after watching the recordings of the dyno runs and verifying by looking into the intercooler, turbo and air filter and finding an excessive amount of soot that the turbo was ingesting exhaust gas and because we ran the Link in closed loop, the ECU was trying to “fix” the issue which is what the up/down was on the dyno plot. We ran the car again with a fresh air intake to the Pulsar 6262 turbo and it made 411whp at 10psi on stock cams. At that point we were maxing out the stock Porsche fuel system. This was one of the toughest issues to nail down and one of the easiest fixes not including all the work we did trying to find the problem. A great lesson was learned.