Sixshooter loses another CHRA but doesn't know why
 

I noticed power and spool was down on the GTX2867R and so I checked the internal wastegate to make sure it was closing and checked the preload. All good. Bosch BOV was still good (need to upgrade). I pulled the air cleaner for an inspection of the spinny bits and found quite a bit more play in the wheels than it had when I was new. I am disappoint. But thankfully no wheel contact when I push and pull and twist.

I pulled the oil feed line and restrictor from the CHRA and dropped the end into an empty jug to see if the oil supply was blocked. In the 15 or so seconds I ran the engine, it pissed a very powerful stream and put about 1/4 quart into the bottle. Seems plenty good.

The water lines for the CHRA banjo fittings come from the front of the head and go to the mixing manifold. Should be good on coolant flow.

I went through a couple of chinese journal bearing turbos prior to dropping in the Garrett, blaming the first failure on plastic dipstick pieces getting in the feed line. The second I attributed to very high temperatures due to using a turbo blanket.

I'm very cautious with cooling down prior to shutting off the engine, so I don't suspect hot shutdowns killed it.

Engine temps and oil temps (has oil temp gauge) never crest 215/245

I'm wondering if my tune has too much retard in the boosted cells, thereby making more heat than normal in the turbo? Running 8.4cr Supertechs and Crower rods, 1.8na stock cams, pump 93, boundary non-vvt oil pump assembly. About 14-15psi max. I'll attach a timing map.

https://www.miataturbo.net/attachmen...ine=1435430944



I'm also wondering about the oiling and whether it truly is enough. I only get about 40-45psi hot at higher RPMs due to my engine builder building the bottom end a bit loose (because racecar engine builder?) Maybe I should have a larger opening in my restrictor to compensate? But, damn, it sure seems like plenty of oil at cold idle.

I am going to send the CHRA to get rebuilt/exchanged but don't want to do this again next year.

Please offer ideas / direction / something I missed.

What size oil feed line? What size restrictor? What size oil drain and does it have any sharp bends? What viscocity and type of oil do you run?

Almost a guarantee these repeated failures are a lubrication problem. You're not even pushing the turbo that hard with only 15 PSI. It should last a longggggg time.

Your timing map looks ok to me.

If it were me I'd make sure my oil drain was large and free of sharp bends, and it dumps into the oil pan ABOVE the oil level. Then I'd run a 4AN oil line to the turbo with no restrictor. And run it. If it proves to push oil past the turbine seals, and I was CERTAIN my oil drain was an well-designed as I could make it, then I'd start with a large restrictor and find the largest one that makes the oil burning go away.

I'm having severe déjà vu right now with this thread. I swear I almost read this word for word a few months ago. Feels like I stepped into a time warp, mind is blown.
Do you think it's bearing failure due to oil starvation? Or is the oil simply not circulating fast enough and getting way too hot?

Lack of lubrication causes excess bearing wear. The oil oil lubricates and cools the bearings. Some oil, but not enough, results in higher friction and more bearing wear, so while it won't immediately fail, it will wear out a lot faster. Which is exactly what he is experiencing.

Which is either, 1) oil drain restriction, or 2) lack of oil feed...right?
This is why I'm so dead set on journal bearing turbos...

Yes, it's simple. Something is causing not-enough-oil to get to the turbo. He said he runs a restrictor and has toasted 3 turbos, so that would be my bet but he should check everything I mentioned.

Oil lubricates and cools. Both functions are important. A compromise in the feed or drain will reduce both. A smaller drain line can cause oil to back up into the turbo, forcing you to run a restrictor to prevent the backup causing smoke. Of course less oil means less cooling, and less lubrication, so bearing life will decrease. The right fix is to fix the drain. Miata people commonly run small drains. I ran a 12AN drain on my Garrett journal bearing and had no sharp bends, it worked great.

Nice. I run -10 with all straight fittings.

drain restriction would cause too much oil and leaking
this sounds like a feed problem. perhaps the restrictor is a tad small or something

Sixshooter loses another CHRA but doesn't know why
 

I use Rotella cut 50/50 with Valvoline VR1 50wt to keep the pressure up since the rebuild is so loose. The feed line is large 1/8" but the restrictor is the small hole recommended for ball bearings. The drainis 1/2" with no tight bends. It empties at the front corner of the oil pan beneath the a/c compressor.

The mobile app doesn't let me refer back to the posts while typing so I'll have to make another post but I really appreciate everyone's questions and advice.

Sixshooter loses another CHRA but doesn't know why
 

I'm thinking of removing the restrictor since my oil pressure is somewhat compromised, though my volume seems fine.

That's really thick oil. That's gonna result in more pressure, but less volume.

Also, is that a typo or do you really have a 1/8" ID oil feed line? Cause that's tiny. A 1/4" hose would be more common and certainly better since you already have low oil pressure to start with.

What size is the restrictor?

If you are going to run that high of viscosity, I would completely remove the oil restrictor.

Also if you can easily run a larger diameter hose for your drain, that would be a good idea too since running without a restrictor will make it more likely to backup without a large drain.

Sixshooter loses another CHRA but doesn't know why
 

1/4 was what I meant. Flows a ton cold when unhooked.

<p>https://www.turbobygarrett.com/turbo...oil_restrictor</p><p>Sounds like ball bearing turbos want 40-45. So your restrictor might have made that lower.</p>

^That says this:
Well... fuck. I've probably been cutting it short on oil.

have same turbo/same sad end result. how many hours on CHRA?

Sixshooter loses another CHRA but doesn't know why
 

IDK how many hours but less than 6 months of very rare usage.

Yeap. You should post what size restrictor you ran when you can so others will know what not to run if they have similar oil pressure that you had.

When I killed my T25 running too small of a restrictor, GPopShop told me it takes less than 10 seconds if you REALLY deprive it of oil significantly. I ran a ball bearing restrictor in a journal bearing turbo.

I would urge you drop the restrictor and change to a 20/50 oil.

When using a restrictor, it's good to check oil p after the restrictor. Takes a little work.

You suggest heavier wt oil due to loose clearances, but were these bearings of which you talk? I doubt it.

Pistons don't give a hoot what oil you use.

Corky

Sixshooter loses another CHRA but doesn't know why
 

I'm going to ditch the restrictor. I'm not going to measure the pressure after the restrictor because it would be unnecessary if ditching the restrictor.

I'll probably run straight 50wt in the summer from here out. The rod bearings are the biggest reason I use heavier oil to keep the film strength up.