|
This article was first published in 2006.
|
In the first part of this series we compared the design of sleeve and ball
bearing turbochargers and their pros/cons. Well, now it’s time to raise the
curtain on an innovative Australian-built turbo bearing system...
Gold Coast based turbo specialist Mark ‘Mr Turbo’ Kitchen offers a range of
turbochargers which employ an in-house developed silicon nitride bearing system.
Mark says the biggest advantage of silicon nitride bearings is their ability to
tolerate very high shaft speed and load - which means you can safely run more
boost/power. The majority of Mr Turbo’s silicon nitride bearing systems are
installed within a custom built carrier assembly and a CNC machined aluminium
centre cartridge.
At the time of writing, Mr Turbo manufactures cartridges from relatively small
T3/T4 size turbochargers all the way up to drag spec monsters capable of hundreds of kilowatts. The new cartridges are CNC machined from billet aluminium to
accept off-the-shelf shafts, wheels and housings.
Mr Turbo manufactures a stainless steel bearing carrier tube which is
inserted into the aluminium cartridge. On its inner surface, the carrier
incorporates machined shoulders to locate a ball bearing race at each end
while, on its outer surface, a grooved section along the top collects oil
supplied from the engine. At each end of this groove is a small hole that lets
oil drip onto the turbine shaft (to help remove some heat) and, more
importantly, lubricate the ball bearings. Oil can escape through a large
diameter outlet at the bottom of the cartridge.
Like an OE ball bearing turbocharger, the turbine shaft is supported by two bearings. However, a Mr Turbo turbocharger employs silicon
nitride balls which are extremely hard and perfectly round, giving advantages in high rpm/load durability. The bearings are retained in
NSK-manufactured inner and outer races and the cageless design contributes to further
improved high rpm/load durability.
The inner bearing races spin at around turbine shaft speed while the outer
races are able to turn relatively slowly. As seen here, a coil spring is fitted
inside the bearing carrier to apply some preload and keep the bearings
apart.
The complete bearing carrier assembly is slid into the custom machined centre cartridge and
is locked into position by a bolt in one of the side water passages.
Note the large cooling passages around the bearing carrier – it’s important
that any ball bearing turbo has significant cooling capacity because
compared to a sleeve bearing, less heat is conducted away by the oil. In a Mr
Turbo centre cartridge you can configure the coolant flow from left to right or
vice versa.
Performance and Price
The biggest advantage of the Mr Turbo silicon nitride bearing turbo is its
high rpm/load durability thanks to the harder and rounder ball bearings and
cageless design. Mr Turbo has successfully pushed one of his silicon bearing
turbochargers to over 300,000 rpm (calculated), which is significantly more than
you’d achieve using a typical ball bearing unit. Depending on your intended
application, you can either push more boost into your engine with greater safety
or opt for what would normally be considered a ‘too small’ turbocharger – the
extra high rpm/load durability will let you push it harder in the top-end while
enjoying the driveability benefits of a small turbocharger.
Another advantage is the superior visual appeal of the Mr Turbo billet
aluminium centre cartridge which can be anodised (as seen here). Perfect for
show cars.
So what are the drawbacks of the new bearing system?
Well, the silicon nitride bearings shouldn’t be exposed to excessively high
temperatures – the recommended maximum is 300 degrees Celsius. It’s for this
reason that Mr Turbo emphasises the use of very large cooling passages within the
centre cartridge. The other disadvantage is cost...
To purchase a complete Mr Turbo silicon nitride bearing turbocharger in a
small T3/T4 size you’re looking at AUD$2300 – AUD$2400 (including housings and
wheels). The largest versions will set you back just over AUD$5100. We suggest
contacting Mr Turbo for prices on your specific requirements.
All complete turbo assemblies are supplied with a 12 months warranty on
parts/manufacturing and long-term durability appears very good - the longest
running example has so far lasted more than two years in a 22 psi boosted street
car.
Verdict? A Mr Turbo silicon nitride bearing turbocharger is certainly worth
considering if you’re searching for a new large capacity turbo – the claimed
benefits seem reasonable and the extra cost is modest. It could well give you
that all-important edge.
Silicon Bearing Conversions for OE Ball Bearing Turbos?
Although not Mr Turbo’s primary focus, it is possible to convert your
existing ball bearing turbocharger to employ silicon nitride bearings.
A IHI VF-series turbocharger (from a Subaru) has recently been converted by
inserting a machined bearing carrier assembly. The rest of the turbocharger
remained untouched and, according to dyno graphs, spool-up was improved.
As a guide, you’ll pay around AUD$700 to convert an IHI turbocharger or
around AUD$1300 to convert a Garrett type turbocharger. These prices assume
there is no other repair/modification work necessary.
|
Contact:
Mr Turbo +61 75596 1079
Did you enjoy this article?
Please consider supporting AutoSpeed with a small contribution. More Info...
|
More of our most popular articles.
|
|
|
Email a friend
Print article
|