Engine issue: stock 2015 BRZ power dip @ 6100 RPM
 

Summary
Stock 2015 BRZ with 71k miles loses power at roughly 6100 RPM and peaks at 125 whp. Mechanic suspected detonation with ECU cutting power, alternative insights appreciated.

Details
I took my stock 2015 BRZ to a baseline dyno before starting to do any upgrades on it. The car was pre-owned (single owner) and had about 65k miles on it. Leasing car, don't know much about previous owner. Regular service done by dealership, had them change spark plugs a month ago. Spirited driving on my part, all on European 98 octane, the previous owner might have used 95 or 98.

The dyno graph shows a clear cutting of power at roughly 6100 rpm. The same dip happened in all pulls but with +-200 rpm. The peak power also comes out at just 125 whp which seems a tad low. Dyno was Rototest.

The mechanic suspected detonation and the ECU cutting off power to protect the engine given how harsh the drop was. He sold me fuel line cleaner and engine cleaner (to be mixed with oil) which seemed like a good first step. He also suggested E85, which I'm planning to do later, but I'd like to see if I can fix this on 98 octane first.

Opinions and ideas on how to fix it?

It ain't liking something. Cats still in one piece?

I don't see how E85 can "fix" this. Sounds like it has some issue with the AVCS. Maybe the solenoid has gone bad? Toyota Part # is SU00300096.

Datalogs would really help

Do you feel the dip when doing WOT pulls? A drop like that should be fairly noticeable.
The overall WHP number looks low but at the end of the day its just a number.
Do you have any acceleration numbers to compare? If your doing 0-60 in under 7sec and don’t noticeably feel a loss of power/hesitation at 6k it could all be fine.

A data-log would make things 10times easier to diagnose if/what the issue is.
The best place to start would be to clean the maf, and double check all hoses, clamps, fittings etc.. for any vacuum leaks, and check for exhaust leaks.
Also no CEL?

This sounds like a reasonable next step.

I'm new to the platform, what would be the highest quality logger for the BRZ given I'm fine for having a laptop in the car? Does the OEM Techstream app/cable suffice or does one of the tuning devices like EcuTEK offer better resolution/data?

I'm planning to rebuild the intake and exhaust paths so everything should get cleaned out naturally. Surprisingly I hadn't noticed the dip that much, perhaps because it does happen in a pretty narrow band at the top. I also suspect that the 3k-4k dip distracts enough during a WOT pull that this issues simply was masked.

No CEL.

I don't see how you wouldn't be able to notice that dip, I would think it'd be like having a strong headwind blast you.

For tuning N/A, I would recommend the openflash tablet. If you're dead set on using a laptop, a Tactrix cable and Romraider/BRZedit would suffice. I think a one time use BRZedit personal license is only $50 bucks and it works well enough. I still recommend openflash tablet for ease of use and the availability of support using it.