MadDog

Although it hasn't really been discussed much lately, for a while there, the GReddy turbos were failing at what seemed like a pretty high rate. I think a lot of owners were getting them re-built after 10k miles or less! That's not a lot of miles!

My own turbo lasted longer than 30k miles between the previous owner and me. I think that's probably the longevity record so far. But, sure enough. One day that sucker started smoking like a chimney. It was pretty embarassing to drive around town. I even had to apologize for smoking-out a guy next to me at a red light once. He had his window down and before he knew it, the cab of his truck was filled with smoke! I could see people all around me checking their cars to see if they were on fire!!

So, I sent it off to get rebuilt. The really crappy part is that it still smoked after being rebuilt!! I tried cleaning out the intake tract, thinking that there was some residual oil still making its way into the combustion process. But it was dry as a bone in there.

I finally clued-in as to what was happening. The smoke wasn't an indication of a bad rebuild. It was an indication that the turbo was getting WAY too much oil!

HERE'S THE PROBLEM:
That's my postulate. The GReddy turbos are failing at a high rate because they are getting WAY too much oil. The seals and bearings can't take the high pressure for very long. So, they fail permaturely. The symptom is that after sitting at idle for about 30 seconds or so, the turbo begins to smoke. If the seals are still good, it will only smoke out the tail pipes. If the seals are really gone, then you'll get some oil leaking out of the housing and onto the exhaust manifold, and somke comes from underneath the hood, too.

HERE'S THE SOLUTION:
(sorry, I lost my camera so there are no pics)
I used a nitrous nozzle as an oil line restrictor. They come pre-drilled to very small diameters that you need to do this. Plus, they'll fit just perfectly into the oil line tee, letting the hose tighten down on top of it. You just need to dremmel the conical end down to a flat. Use a brass nitrous nozzle. Its soft enough so that it acts like a crush washer when you tighten down the hose. I doubt the stainless nitrous nozzles would work as well.

HERE'S THE RESULTS:
I tried two different nozzle diameters. The first one was an 0.065" diameter. Since the GReddy hose is about 1/8 at the neck-down, I figured that the 0.065" nozzle would cut the flow by a factor of 4. The problem was that this still wasn't enough to stop the smoking. So, I went to a 0.047" nozzle. That seems awfully small, but I did a flow test. At idle, the 0.047" nozzle flows about 0.4 quarts per minute. That's just shy of the 0.5 quarts/minute that Corky Bell recommends. I didn't do a flow rate test on the 0.065" nozzle, but just ratioing the areas seems to suggest that the flow rate for the 0.065" nozzle is close to a full quart a minute and the GReddy hose alone flows close to a gallon a minute!!

I wish I had done a flow test on the 0.065" nozzle. But a quart a minute agrees pretty well with what I observed in the only test I did do on it: disconnect the hose and watch it drain on the floor while the car idled. I was amazed at how much oil came out of the turbo drain with the 0.065" nozzle!


So, that's my advice. Get a ~0.050" brass nitrous nozzle. Dremel the conical end down flat. Insert it in the oil line tee and tighten the hose down on top of it.

You'll save your seals. Plus, its a lot easier to do this than to pull that turbo off!!

rotarygod

The biggest issue is that the drain returns below oil level in the pan. The oil does back up in the line and pressure from the incoming oil hitting the oil in the lines causes excess pressure on the oil seals. The simple fix is to return the oil to above oil level in the pan. I know there are arguments that fluids will not behave this way and that it won't back up but remember it's the viscosity of oil that allows this to happen as it can't reach equilibirum fast enough in relation to the supply amount. This always happens to turbos with drains oriented in the same fashion. Those who say they haven't had any issues just haven't had them yet but will. If you have a proper drain and you still blow out seals, then worry about lowering oil pressure.

epitrochoid

question...does the greddy oil pan have a drain fitting above the oil line?

MadDog

I kind of agree with you - but kind of not. As long as the turbo housing is above the oil level in the pan, which it is, there won't be an issue with this - if the flow rate is low enough! But, if the flow rate is too high, which it is, then the whole notion of static equilibrium of fluids is not at play here. Anyhow, I'm not sure how simple it would be to return the oil to "above the oil level in the pan." It seems like you'd have to return it to the filter or something like that. Maybe a sandwich adapter would work.

Besides, if the GReddy hose is indeed flowing close to a gallon a minute, that is just way too much oil, regardless of the drain level.

Its MUCH simpler to fix the flow rate problem. Then the concept of static equilibrium is more correct, and the fact that the turbo is above the oil line means that it will drain properly. The nozzle costs $5 and it takes all of 30 minutes to install.

MadDog

No.

rotarygod

While I agree that the drainage issue is a flow related problem, I feel that by the time you restrict it down so it is no longer an issue you will have gone to a dangerously low flow volume through the turbo. I think that while you may prolong the issue, you won't eliminate it. I hope I'm wrong on that so good luck with it.

Greddy should have told everyone to do what even the Atkins supercharger kit for the RX-7's does in regards to oil drain. Tap the front cover for an oil return. This brings it in above pan level. You do this near the oil metering pump. It still requires removing the oil pan but you've got to do that for the Greddy kit anyways and on the RX-8, this is easy. On the RX-7's it is easier to remove the entire engine than it is to remove the pan.

r0tor

iTrader: (1)

Keep in mind oil is used to lubricate AND COOL the bearings in the turbo

MadDog

Again, the only concrete thing I've seen says 0.5qts/minute at idle is good for most turbos - per Corky's book. He also lists a rate under load. But, since the idle test is MUCH easier to conduct, I elected to do it instead.

As another reference, Jeff has been running a 0.0625" restrictor for some time now. I think people are over-estimating how much oil the turbo actually needs. We have evidence in the form of a lot of blown seals that there is too much oil pressure as is. How much it needs is certainly debatable, but I think you'd do well to go at least down to 0.065". I'm certainly experimenting (once again) on my own engine and I'll report the results. But, from the flow rate I measured, I don't have any plans on going to a larger diameter nozzle.

Trekk

I know alot of people that had smoking greddy's on the honda civic's. It was because they placed the turbo oil return line blelow the oil level in the pan. Sadly it said pretty clear in the instructions (on the civic) to tap the pan above the oil level of the pan.

On a side note Ive tested a few turbo's T25's ect around my house. I corked return line then filled them with oil. The only pressure it was under was the weight of its self. Anyways they leaked out the cold side turbine.

guitarjunkie28

*dng ding ding ding*

i just rebuilt a motor for a guy a month ago and he brought it back to me all pissed off because it was blowing smoke like crazy. turned out it was right after he changed the oil. i drained 9 quarts from the engine, and didn't even drain the oil coolers seperately. (what, more isn't better????)

needless to say i got the turbo rebuilt, and wouldn't ya know it, the smoke went away...

Trekk

Does it really need to be rebuilt if your just flooding the turbo with oil?
I've rebuild a t28 and it looked to me like the oil was just suppose to flow in and out at a high rate.
I retapped and welded a few oil pans. After the rest of the oil was burnt out they ran fine.

Thats why I did the test with filling the turbo with oil to see what would happen.

rotarygod

You do if the issue resulted in damage to the oil seals in the turbo. If there was no damage, no rebuild is necessary.

MadDog

It sounds like the turbo was off the car when you did this..?

Yeah, the only pressure on the return should be due to gravity. But, if there is too much flow, it can't drain out fast enough and pressure builds up do to the pressure on the infeed.

MazdaManiac

iTrader: (3)

Sorry Fred, the drain line isn't the issue.
The oil outlet on the Greddy turbo sits above the resting meniscus of the oil in the pan, therefore it can't "back up" until the pressure in the return line becomes positive.

A sleeve bearing turbo requires almost no oil. A bare trickle. Really, all is requires it will pull via capillary action. It is the oil cooling properties that we are realy interested in with regards to flow and anything over a 400 ml a minute is just a waste.

I've been running .065" restrictors in all of my turbos for years and I've never had one fail or smoke.

rotarygod

If it is in fact above oil level, I will agree that it isn't an issue. You should be good. If it is below oil level, you can restrict it all you want. It'll still fail.

MadDog

....

PUR NRG

That's an interesting theory, but seems to fly in the face of the facts. Oil pressure at idle on an RX-8 is something like 10-12 PSI, compared to 30+ for an RX-7. Once you start driving it rapidly shoots up to 30-60 PSI.

If your theory was true then the reverse should happen--smoke while driving but little to none after idle.
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DEPAKOTE SETTLEMENT INFO

MadDog

Yeah. Thank you. I realize that the pressure is higher while under load. But, the "facts" are that turbos with failing seals many times smoke at idle but not while driving. You think I just made that part up? I've never heard a reasonable theory as to why they smoke at idle. I can't explain it either. Have you ever had a turbo that needed to be rebuilt?

Besides, I wasn't saying that the pressure that caused them to fail was the pressure at idle. Merely that was the symptom - the failed bearings and seals caused smoking at idle. Hell, maybe the increased pressure under load causes the seals to seat more firmly. Then, at idle, they relax and leak. Like I said, I don't know the exact mechanism that causes smoking at idle. But, talk to the RX8 folks that got smoke and I'll bet nearly 100% will say it happened at idle only.

Trekk

Only time I've seen some tht needed to be rebuilt, they all had a noticeable amount of shaft play on them.

PUR NRG

Is this part meant to be sarcastic? I can't be positive but it sounds like it. Likewise I'm not sure if you took my post as a put-down, which is not how I meant it.


Nope. I never claimed you were making up the "smoke at idle" stuff.

This is the part that I was questioning and it's the difference between positive correlation and unrelated facts.

Fact: turbos smoke oil at idle.
Fact: oil pressure is extremely(?) low at idle.
Fact: lower oil pressure means lower flow volume.
Unproven (at least to me) hypothesis: greddy turbo fails due to "way too much oil at idle".

There's a story about a scientist measuring how far a frog jumped after the hearing a loud noise. He then cut off one of the frog's legs, made a loud noise and measured how far the frog jumped again. Each time he cut off a leg the frog jumped less and less until after all the frog's legs were cut off it didn't jump at all. The scientist's conclusion? The more legs you cut off a frog the worse its hearing.

There's also the difference between a symptom and a cause. Taking painkillers for a toothache removes the symptom but does nothing to address the cavity which is the source of discomfort.

That sounds more plausible to me. And it may be the restrictor you put in place merely masks the symptom by having less oil present during idle to leak past the seal and produce smoke.

This does not sound right. Haven't other people rebuilt smoking turbos and put them back in with no other changes? Shouldn't they have immediately started smoking as well?

I have a turbo running 12.5 psi that I've autocrossed for a year now. I also have a recirculating BOV, oil catch can and greddy oil pan that I added in part to hopefully improve reliability. The turbo hasn't started smoking yet and if it never does I won't know if any of the extra bits I added prevented me from blowing smoke as well. Knock wood.
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NSR150

SpeedForceRacing

You are absolutely correct in your statement.However, we find that even if you return the oil above the oil level in the pan it will still back up if the drain is lower then the return coming out of the turbo.

Tim

MadDog

You missed the entire point of my last rant. I never once said "way too much oil at idle". I said "way too much oil" and spearately I said it smoked at idle. The flow rate at idle is just a way to gage that the flow under load is also 8 times too much!

Not really. Did they start smoking immediately when they were new? No. I'm sure there are lots of statistical parameters adding up here.

I fail to see how these things would aid in turbo longevity. The oil pan has the drain in exactly the same spot as the stock pan.

Jumping Jesus people! I've offered up TWO pieces of evidence here.

1) The only flow rate specification I could find after an extensive search: 0.5 quarts per minute at idle.

2) The flow rate of the GReddy hose: somewhere near 4 quarts per minute idle. (based on scaling my flow rate test)

Its a KNOWN fact that too much oil will cause the seals to fail. 0.5<4. Therefore its not unreasonable to say that there is probably too much oil flowing to the turbo. It is not unreasonable to speculate that this is probably the reason for the high failure rate of the GReddy turbo on our cars!

Anyone else care to offer-up any measured evidence? Or perhaps just indulge in more speculation that the flow rate isn't too high?

Yes, I fully realize that its just speculation on my part that the flow rate is what's causing the high seal failure rate. It is, however, a plausible explanation. It is NOT speculation that the flow rate as GReddy delivers the kit is much higher than necessary. Given that its apparently 8 times too high, its not unreasonable to speculate that this would damage the seals - since it is known that too much oil pressure can damage the seals.

Anyone else care to offer an explanation for the high failure rate of the seals on this turbo setup?

PUR NRG

Sorry, my misinterpretation on "way too much oil at idle". However...

Flow rate is not equal to high pressure. A garden hose flows much less at a higher pressure than a river.

Sure. But the obvious one seems to be if most people who rebuilt turbos did not experience smoking @ idle immediately after reinstall, then the fact you did seems to indicate something besides flow rate or pressure was the culprit.

A BOV eliminates surge which can cause compressor stall. Compressor stall can cause the bearings to make contact with the carriers because the oil flow rate slows and because of the excessive vibration from the opposite forces on each side of the shaft. The oil catch can eliminates oil blowing into the intake and the greddy oil pan has an extra quart capacity. Extra oil and increased surface area help keep oil temps down.

I haven't read Corky Bell's book so I can't say much about it. So I'll ask you this question: does Corky say PSI is irrelevant when it comes to flow rate? 'Cause my garden hose/river analogy seems to say otherwise.

Can someone with a mathmatical understanding of flow rates vs. PSI chime in here?
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Og Kush Seeds

Trekk

Well look at these to get an idea of what you looking at.
http://photo.platonoff.com/Auto/2005...Turbo_Rebuild/

If the oil backs up to the point it reachs the shaft height it will leak reguardless of pressure.

Failure could be a few things.
Did you break in your turbo few hundred miles before you started to boost it hard? I dont know if its a proven fact but some people swear by it.

You watching you EGT's?

I'd blame bad installs (bad drain exc..)and over heating before to much oil pressure.

On a civic its 10psi @900RPMs and 50PSI at 3,000RPMs

r0tor

iTrader: (1)

You sure the seals aren't failing due to large clearances developing in the bearings - which would allow the shaft to move around and wear out the seal?


For the record, if your return line plumbs into the oil pan under the level of the oil, the weight of the oil above the line will cause added backpressure in the return line... may or may not be significant