Dyno sheet with odd boost drop

[rob77]

As you can see from the dyno sheet my boost drops off immediately around 4600rpm mark and then steadly drops as the turbo loses efficiency, any idea's. I'm using a blitz dual sbc EBC, only thing I can think of is the stock ecu being a a stick in the mud

[adam 32]

something to do with the cam timing? doesnt it change around there??

[rob77]

Yeah, but why does boost drop right off?

[nissaner]

i had this problem too..... after changing the stock wastegate actuator to the hks unit, the problem had dissappeard...

[rob77]

I thought that too, the stock one has a weak spring.

[drifto]

Interesting how the boost suddenly drops and at the same time you get an upward spike in the power curve?????

Did the workshop with the dyno give you any clues?

[rob77]

Nope, its the first one he's seen to do it. I have used this dyno since day 1 when my car was completely stock it dyno'd at 97kw@wheels and the boost did the exact opposite it jumped at that same point. We then put an exhaust on and dyno'd it again, same results with the boost but power jumped to 115kw@wheels. I then had the ebc and fmic installed and we dyno'd it again and got the opposite, boost was now dropping at the same point instead of holding firm and power went up to 235hp@wheels. So I got the dump+front pipe done and power went up to 245hp@wheels but still having the boost issue.

[Steve]

Something just doesnt seem right here, looks like you are dropping 2.5ish psi drop, I would have expected dramatic change in the power curve?????

Those little hiccups, are they the NVCS? about the right rpm isnt it?

Just doesnt add up:confused:

[adam 32]

it may be worth replacing the wastegate spring, i cant imagine itd be an expensive excercise

[sidewaymambo]

The HKS enhanced wastegate actuator is about $150~200 Aus landed..

[Guest INASNT]

your a/f ratios also drop around the same time, which will be robbing u on power!

[rob77]

Yes they do, I'm running very very rich at the top end, which is due to the stock ecu. I will be putting in an aftermarket ecu to sort that out, but that may fix the boost problem, looks like a boost cut. Dunno if I will bother replacing the actuator with a HKS as I'll probably be changing the turbo.

[crooser]

you mention that the problem only occured AFTER installing the ebc.

i'd be looking to rule out a problem with that first.

just a thought

[SlowGTS-t]

My bet is that the dyno operator T'd his boost gauge into the wastegate line. So when either the factory boost solenoid opens up, the pressure in the WASTEGATE line drops closing the wastegate slightly, increasing boost at the MANIFOLD.

A 3psi drop would have shown up as a big change in the power curve

[GTS-t VSPEC]

Nah, it was in the line straight from the manifold, where he always puts it, and no-one elses car does this.

Rob, Could be the spring in the wastegate as others have been suggesting.

[Cubes]

The drop is to sudden and then it holds the boost to flat (approx 1psi) to be a wastegate spring I would think.

I would be checking out the EBC.

Seems almost like you still have the standard boost solanoid plugged in but some how backwards.?!?!