Ceramic turbos.

[KiwiBacon]

I've heard lots of stories about the ceramic turbos which came in several nissan cars.
But does anyone here have first hand information about exactly what they are and what they can take?

Here's what the internet has spouted so far:
Probably a T28
Ceramic exhaust wheel which loses all the fins after about 14psi boost.

[2.2 Straight six]

they're very lightweight, so they spool up fast. which is Nissan's reason for using them in the GT-Rs. the problem is that in the event of being over-loaded, having too much backpressure or a backfire (i think) can cause them to shatter. not a problem if the broken parts go down the downpipe, but it's not unknown for the pieces to go back into the cylinders and cause a lot of damage.

they can support mild mild boost (ie just turning up the stock boost a few psi with a flashed chip) otherwise, they're not rated for much. you're far better off with a ball-bearing turbo like a Garrett GT-Series.

yes, they are T28s and they were made by Garrett.

[drunken monkey]

not sure if this helps but if my memory serves me correctly, the turbos in the Skyline GT-Rs R32-34 are ceramic garretts and the T28 are used in various nissan cars.

Make of this what you will but another random bit of informantion that I have in my head;
most toyotas that have aturbo in them as standard tend to have ceramic turbines in them for the home market and steel ones for the UK market.

The other good thing about them is that they can deal with a hell of a lot of heat and they also radiate very very well. Means you don't have to give your engine that cooling down period.

[2.2 Straight six]

Originally Posted by drunken monkey

The other good thing about them is that they can deal with a hell of a lot of heat and they also radiate very very well. Means you don't have to give your engine that cooling down period.

the cooling-down period isn't for the benefit of letting the turbine wheel cool, it's to keep oil flowing through the turbo as the bearing unit cools. this prevent oil from coking and damaging the turbo. keeping oil flowing as the turbo cools prevents any damage.

[drunken monkey]

ahhh....
i always figured it was the turbine cooling too slowly and seizing up that way.
it never occured to me that the bearings also get hot.....

on a side note, don't they also use ceramic bearings?

[2.2 Straight six]

nope, they're either wet plain bearings or wet roller (ball) bearings.

at least, i've never heard of ceramic bearings in turbos.

[KiwiBacon]

Originally Posted by 2.2 Straight six

the cooling-down period isn't for the benefit of letting the turbine wheel cool, it's to keep oil flowing through the turbo as the bearing unit cools. this prevent oil from coking and damaging the turbo. keeping oil flowing as the turbo cools prevents any damage.

The ceramic wheel will have a benefit there.

The problems can occur shutting down a hot turbo where the steel turbine wheel (big heat sink) has a lot of stored heat but the bearings are still cool.

The heat soaks out of the steel wheel, conducting back along the shaft and cooking the oil in the bearings.
If a ceramic wheel holds less heat, then it can't heat the shaft up as much so the danger of cooking oil is less.

[KiwiBacon]

Turns out my new turbo has a steel wheel.
Shame to miss out on the hi-tech ceramic, but I gain reliability, resale value and ease of rebuilding.

[2.2 Straight six]

steelies are better for power and reliability. ceramics can't hold the same boost levels and have fairly low limits. for example, GT-R owners can only turn the boost up a few psi on the stock turbos, because the ceramic wheels shatter under higher boost levels.

[drunken monkey]

to be fair, if a skyline owner wanted more boost, they usually get a bigger turbo (if garret, it would probably just be a bigger ceramic turbine).

[KiwiBacon]

Originally Posted by drunken monkey

to be fair, if a skyline owner wanted more boost, they usually get a bigger turbo (if garret, it would probably just be a bigger ceramic turbine).

A bigger turbo is just a bigger turbo, boost is set by the wastegate.

[drunken monkey]

but the physical size limits the amount of pressure the whole thing can sustain, no?
doesn't a bigger turbo mean you have more pressure in the system?

[2.2 Straight six]

well, yes. there comes a point where the exhaust flow can't make the boost any higher, but that's usually past the point of engine damage (except in diesels, usually) if a turbo is slightly oversized for the engine, the back pressure will be limited because of the good flow ability.

most turbos can reach a point, where if the exhaust gasses aren't vented they'll make a lot of pressure. but wastegate springs are usually soft enough on stock cars that they open at ~8psi in the intake.

if you're talking performance diesel, intake pressures can be pretty high. my friend's drag diesel runs at a max boost of ~61psi with a twin-stage setup. some very high-performance petrol engines can run upto ~35psi with water/alcohol injection and a lot of fail-safe gear.

generally speaking, the wastegate controls the boost, unless it's fixed shut or it fails.

[drunken monkey]

sorry, left out a word (can)

it should've been
"doesn't a bigger turbo mean you can have more pressure in the system?"

[2.2 Straight six]

yes and no. it's dependant on a few factors.

think of it like this, take an engine that flows X amount of xhaust gas over a constant period of time.

a big turbo can flow this gas in that time, with the turbine wheel moving slowly (because it has larger capacity) and therefore the intake side moves slowly and there's low pressure.

this is reversed for a smaller turbo.

of course, there's far more to this than boost pressures, they're just used for rough workings. what's really important is volume flow (cfm and the like) because it tells you how much air the turbo can flow. this is shown in compressor maps.