40rwhp has gone walkabouts, brain trust needed.
 

Hey guys,

Ive got an NB2 with a log, GT2560r, 3" turbo back, big intercooler, ID1000, Haltech Elite, rods/pistons/studs/gasket etc

It made 280ish @21psi odd previously with the VVT disabled. The VVT was disabled due to being worn out from a pre-rebuild oil starvation.

The car was given back, driven for a few months and returned to fix some coolant temp issues, nothing bad ever happened it just needed some ducting and a once over.
During this time I decided to weld the VVT actuator in its resting position (full retard) to reduce the engines mechanical noise. The decision not to replace VVT was because it had made good power without it, and everything seemed to be working ok.

The car was retuned and I didnt go hard on it resulting in around 250-260whp. It was given back, but the owner wants his other 30 odd rwhp back. Back on the dyno after he has had it a further month to turn it back up and it makes 240 and not a hp more.

Dyno sheet attached to show the shape of the curve.

Im really stumped.

Tested:

Boost leaks, no.
BOV leak, no.
Exhaust blockage, no.
Intake restriction, no.
Intake cam advanced, worse.
Compression 140+-140+-140+-140+-, static compression unknown, likely low comp but the builder doesnt remember.
I literally ran it sans intake, sans catback, and with the bov port blocked and all other joins tested for leaks and it wont make any more power/boost than this.



The compressor wheel has some damage, but not missing chunks or blades, Im removing the downpipe now to check the turbine wheel.

Thoughts?



You can see it come on boost, then boost control keeps it around 15, but at the top it wouldnt make any more than 15 no matter what. With the wastegate duty cycle at a constant 95% it hit boost cut (22psi) around 4500rpm then died back down to 15psi.

https://www.miataturbo.net/attachmen...ine=1466930813

https://www.miataturbo.net/attachmen...ine=1466932885

40whp?

Turbine side is undamaged.

Turbine side.

3mm of preload on the WGA, and only thing to note is that where the actuator shaft goes through the housing there is some play, something ive never noticed before, Id say close to 1mm.

https://www.miataturbo.net/attachmen...ine=1466934096

Compression seems way low. What are the leak down numbers?

Check if it's leaking the wastegate, like if the valve won't close well

I havnt done a leakdown, it made 40whp more just a couple of months ago and all cylinders are even. Ill leakdown test it tomorrow regardless and post results.

Wastegate closes nice and smooth, flapper goes flat against the housing every time.

is the VTSC stuck closed or something?

those compression numbers are low but consistent and not quite in the DANGER ZONE...

You try bypassing and running allofit?

"You can see it come on boost, then boost control keeps it around 15, but at the top it wouldnt make any more than 15 no matter what. With the wastegate duty cycle at a constant 95% it hit boost cut (22psi) around 4500rpm then died back down to 15psi."

Seems like if you troubleshoot this part it will lead you to the answer. 15 isn't 21 is it? Sorry to be master of the obvious...

other reason is not enough flow through head.. brain is smarter than I and I do not know vvt/vtsc. so i'd start there. vtsc restricts instake i guess according to my searhcing reading. i'd go with that.. hah

I digress...


so i guess i'd run allofit... just to test if it still didn't fix anything then i'd pull the intake and remove the butterflies? someone else opinion?

he means vtcs
but that'd kill like 95% of the power, not 40

That compressor wheel looks awful to me.

looks beat up. like something went through it

That's what I thought. Looks like it ate 36 grit flap disk.

How are the AFRs?

--Ian

The thing that worries me is the compressor wheel damage. Was he running the car with no filter or screen between the outside world and the combustion chamber? Did the crud that chewed up those compression wheels have a go at the rings as well? What would have stopped that crap from getting into the engine? What about the aluminum from the wheels themselves?

Disabling valve control because oil starvation- that line is solid fucking gold. How fucked up is this car? How bad was the oil starvation? How hard was the car run while the car had low oil pressure?

Eh, I've made 312hp on a similar looking wheel, as long as it makes the boost, it makes the power.

Did you log boost or afr? That would tell you if it's an issue with the turbo.

This is where I am at, where is the last 6 psi. Flat top manifold no butterflies.

Mid 11's.

Its unlikely that anything that damaged the wheel caused completely identical low compression on all cylinders. Thats pretty much ruled out, the compression is low but it doesnt indicated any damage.
The car had an oil starvation event 50,000+ miles ago, the long engine was rebuild but the VVT gear not working was only discovered after I tuned it and it had made a perfectly healthy 285whp on 21 psi.

This has been my experience also. Boost is logged on the above dyno sheet. AFR's in the mid 11s.





Ok so Ive replaced the VVT gear with a new one, and I will retune it, then I will swap to a brand new wastegate actuator, then ill wire the wastegate closed to eliminate 3 port solenoid EBC failure. Then Ill let the customer decide if he wants to fork out for a new turbo or not.

Thoughts?

If the VVT actuator was busted, was it set at full advance, or full retard? Is it possible it flipped from one to the other? That could explain a significant difference in power.

--Ian

OP stated that the boost is falling off to 15 from 21. That wheel is not making the boost, so it's not making the power.

I'd at least try to smooth that damage. That's what's done with FOD damage on jet engines . . . dye penetrant inspection for cracks and then smooth out the damage with a file.

couldn't it be possible that whatever went through might have damaged/clogged some of the intercooler causing the top end choking?

ken @ oracle recently had a thread where a 2560 was doing this exact thing and the conclusion was the old school fm fmic was choking flow after he tested it.

So, it was the cam position.

Turns out that the cam must free float in a different spot to a normal NB and the position I chose to lock it in was FUBAR.

Fitted VVT, tuned it, tuned the fuel and spark, and viola, 290rwhp. Its what I expected but still I was so sure I was wrong.

Dann