[s-cars] installing a hybrid turbo
djdawson2 at aol.com
djdawson2 at aol.com
Tue Aug 1 12:36:21 EDT 2006
To supplement Jeff's comments with some Garrett speak...
Ball bearings have a bad time dealing with vibration. A turbo that surges, subjects the bearing to some "bad stuff" typically leading to a short life. A floating journal bearing can deal with it much better, as it typically has 2 "layers" of fluid to dampen the vibration or disturbance. A ball bearing is rigid in its design, and vibration will make it die quickly.
As the turbo wears, some things happen that *will* make it out of balance. Objects in the intake will chew up the blades on the compressor wheel. At that point, both surge and vibration are working against the ball bearing.
What Garrett has done... create a ball bearing system that has the advantages of both a ball bearing, and a journal bearing. The ball bearing cartridge itself is damped by fluid. The cartridge is pinned in place (it can't spin), but there is clearance between the bearing housing and its bore, and oil pressure is present in the clearance, providing some damping ability. It is, in essence, a floating ball bearing.
Ball bearing attempts in turbo applications have failed on every attempt in the past. This latest and greatest from Garrett seems to be doing OK... provided you do not have surge. My first GT30R used a .63 turbine housing. As a result, I had too much boost... too soon for the characteristics of the compressor. As a result, I had substantial surge, and the turbo lived only 22k miles before the bearing literally fell apart. I have changed to a .82 turbine housing. Surge is nearly eliminated, but it can happen under certain circumstances. This turbo now has about 26k miles on it, and honestly, I'm simply waiting and expecting its failure.
The sad part about these new turbos, is that Garrett has elected to make them non-servicable. You can not replace the bearing, or service it in any way. If the bearing was replaceable, I would be much more likely to suggest them to anyone willing to take on the additional maintenance task of periodic bearing replacement. As a result, when the bearing does fail, it ruins every component of the turbo. When the shaft comes free, the compressor and turbine blades chew up the inside of both the turbine and compressor housings... rendering your $1100 - $1500 turbo 100% totaled.
They are great performing turbos, but you have to decide for yourself if they are worth the additional effort and expense. If you're thinking you're going to bolt up a GT ball bearing turbo and drive it for 200k miles (like a journal bearing KKK), you will be disappointed.
Dave
-----Original Message-----
From: Jeff.Postupack at analog.com
To: s-car-list at audifans.com
Sent: Tue, 1 Aug 2006 8:31 AM
Subject: [s-cars] installing a hybrid turbo
Further to what Dave wrote..
I consulted with a machinist who worked in the aircraft business his
entire life.
Having seen ball bearings, bushings in various applications.he told me .
"A journal bearing is a cylinder which surrounds the shaft and is
filled with some form of fluid lubricant Journal bearings can have
unlimited life, compared to a ball bearing."
->. For the more complete write up, seek
http://www.reliabilitydirect.com/appnotes/jb.html
He (the machinist) also commented that journal bearings are much
tighter tolerances composed of particular material much better suited to
the
Hot side and cold side of the turbo charger., than a ball bearing will
ever be.
All the fascination with ball bearings may be misguided for a long life
expectancy, turbo application.
Truth be told a journal bearing can be machined to very close fitment,
which means the shaft will not wobble.
Isn't that what the Audi R&D actually specified also?
Which means when I get around to selecting a turbo, for long life and
higher boost, it shall have a journal bearing.
Posto
------------------------------
Message: 2
Date: Tue, 01 Aug 2006 00:48:31 -0400
From: djdawson2 at aol.com
Subject: Re: [s-cars] installing a hybrid turbo
To: calvinlc at earthlink.net, tedebearp at yahoo.com,
james.pasqualoni at gs.com
Cc: s-car-list at audifans.com
Message-ID: <8C8833CDFAF9FD8-D28-A04D at FWM-D43.sysops.aol.com>
Content-Type: text/plain; charset="us-ascii"
1) the journal bearing units are inexpensive
2) I haven't seen the journal bearing units fail (genuine Garrett, not
ITS, etc...)
3) I *have* seen many of the GT units fail
4) if your hp goals are 400whp or less, why bother with a ball bearing
unit?
5) a 50 trim allows a lot of boost at low rpm without surge issues
6) the GT units seem to be much more prone to surge
IMHO, there's a lot of trouble-free hp available from a 50 trim T3/T4.
Great drivability, low boost threshold, low cost. In fact, the 50 trim
compressor is about the most versatile thing I've ever experimented
with.
OTOH, I run a 30R... but I wanted "more." But, as a result of this
choice, I'm on turbo # 2 in 50k miles, and under certain circumstances,
I do have surge.
Dave
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