Ceramic Stockies

[Cubes]

I've got a rb20det turbo laying around but not willing to waste it on this experiment, as I don't feel ceramic turbines fail from wheel speed alone.

[bogcock]

I've got a rb20det turbo laying around but not willing to waste it on this experiment, as I don't feel ceramic turbines fail from wheel speed alone.

thats your perogative mate.

i know for a fact that the egt is the cause and all i was doing was offerring a chance to prove it to you all

[Cubes]

I'm convinced its EGT due to empirical evidence, no need to convince me.

[bogcock]

I'm convinced its EGT due to empirical evidence, no need to convince me.

sorry i read ur post wrong, i thought u sed u think they fail from wheel speed alone...

[Busky2k]

Overspeed and EGT are the 2 killers IMO.

Its funny, in the States everyone uses EGT gauges. Here downunder, noone uses them at all!!

[bogcock]

Overspeed and EGT are the 2 killers IMO.

Its funny, in the States everyone uses EGT gauges. Here downunder, noone uses them at all!!

thats because no one likes americans, and no one wants to be like them !!!

[Busky2k]

Well thats not really the point. EGT gauges are very useful and underutilised I believe. Then again I don't have one either lol.

[bogcock]

yeh egt guages are a good idea, but not the most thought of guage...

[GTRgeoff]

I have to agree on the EGT. It should be a heads up guage for track work.

I haven't had time to respond but have been doing some research. Some SAE papers have indicated EGT's as a primary cause of failure of ceramic turbine wheels, because the adhesive is not up to the high temps or through a delta in the rate of thermal expansion. I'm still attempting to source a 1989 SAE paper on Garretts problems with ceramic turbines as that would have direct relevance.

An extract from one..

While this performance advantage [low spool times] is the major factor in the consideration of ceramics for the rotors, the

resistance of silicon nitride to the high temperature exhaust is also. Additionally, a lower coefficient of

expansion can mean a smaller air gap between rotor and housing and more efficient performance.

The major disadvantages of ceramic in this application is the low fracture toughness and the lower Weibull

Modulus. A low Weibull modulus means that the strength data are more widely scattered. Therefore, the

designer is faced with a very brittle material with more poorly defined strength.

An additional problem for the designer is thermal stress at the attachment of the low coefficient of

expansion ceramic to the high coefficient of expansion metal shaft. Finally, due to low volume production

and difficult manufacturing, the cost of ceramic parts remains relatively high.

So even though bog has mentioned the wheel cooling quicker it's close but not quite right. It's the shaft expanding too much causing the increased hoop stresses and failure of the adhesive bond. Some more to explain the lottery of why some turbos fail without warning and some last forever....

Strength

Strength of ceramics is very dependent upon the flaw distribution in the materials. These "flaws" can be of

a microscopic nature and may not be flaws from a normal perspective. For example, the strength of glass

fibers is the highest immediately after manufacture, and simply handling them with clean hands can cause

sufficient surface damage to reduce strength by 30%. Because small flaws can have a very large effect,

the strength data of ceramics tends to be widely scattered.

The most practical way of dealing with widely scattered data is the use of statistics. In the case of ceramic

strength data, the standard statistical model is the Weibull distribution. A Weibull parameter (Weibull

slope, Shape parameter, Weibull Modulus) is often stated when describing the strength of a ceramic. The

meaning and use of this parameter is discussed in Section 2.

Another result of flaw sensitivity is that ceramics are much stronger in compression than tension (it is hard

to open a crack in compression). Testing of ceramics is often done in bending and the failure stress in

bending is often called the Modulus of Rupture, MOR.

And a temp vs strength table to compare the materials used....

An overall useful conversation. I still subscribe to overspeeding being a common root cause and will have to come up with some detail to support it, but admit outright temps are resolving as the critical factor so well done Cubes on a well thought through analysis, making me go and do some reading.

[Cubes]

Awesome research Geoff.

Some solid facts instead my observations + a little theory resulting in a conclusion.

[ranicx]

i still think that if you hit it with a hammer, put it back on the engine, it'd fail then.. and then i'd know exactly what caused it to fail

good research geoff, quite an interesting read too.

[Godzilla32]

Im sure i read they used ceramic because it handled the heat better and as mentioned is lighter. Still i guess 15-20 years of use is pretty good. Ive had 2 come apart on stock boost.

BTW: while reading my post take into account i didnt realise there was more than 1 page already on the topic lol..

Edited June 13, 2008 by Godzilla32

[GTRgeoff]

Yep, plenty more good research and opinion in here Deren.

Ceramic stockers are not your friend...as you know.

[allthewaytotheskyline]

Well thats not really the point. EGT gauges are very useful and underutilised I believe. Then again I don't have one either lol.

i totally agree with what your saying ive got a EGT gauge and im currently running 15psi all day every day on my rb20det and its been almost 3 months and hasnt missed a beat....when it was being tuned we went off the pyrometer to see as to whether it was running rich or lean, more importantly exhaust temps and so yes i definately recommend one for longetivity of turbo.

Edited June 14, 2008 by allthewaytotheskyline

[335]

Where can I get these gauges from? Are they known by another name? I live in Japan. I have a R32 GTS-T with a RB25 turbo on my engine. What is the highest safe boost I can run for this for day driving and highway driving?

[den001]

i have popped a wheel on my old gtr, after a quater mile run, on the way back it decided t pop, not whilst i was into it....

so who's theory is correct

[NWR31]

Ceramic stockers are not your friend...as you know.

anyone have any knowlege of the ceramic turbines used in the apexi RX6 & AX53b70 turbos?

i assume they are of a far better design/composition, being fairly recent compared to the rb stockers?

thanks

[tommis85]

Hi all, I have read thru this entire thread and it has some excellent content. Excellent work guys and thorough research. From the above I too have developed a question and that is:

"How do 1995 R33 GTR stocko's compare?"

They are a smaller turbine and hence should, as stated, cope with slightly higher (raised) rpm's than say, a GTST turbine of the same year.

I currently run a 3 inch system, although only from the CAT back (with hi-flow 3" cat). I have also taken out the restrictor after extensive discussions on here saying that it's OK to do so. A combination of the higher flowing exhaust and removal of restrictor have raised the boost up to around 13.5 to 14 pounds.

I always let engine warm up and warm down (with turbo timer) as I'm aware that it does a world of good for engine and turbos. So, in other words I'm giving the turbos time to cool down and contract SLOWLY which should somewhat make life easier on them.

However, what does concern me is track days. I've had one on stock boost, but my next one will be with the higher boost level. Will the smaller GTR stockies put up with extended thrashings? The track is Queensland Raceway, so for those who know it has the front long straight while the rest of it is a series of small squirts from corner to corner where your brakes and tires experience more wear than anything else haha!

Any advice would be much appreciated guys - thanks!!

Tom

[Duncan1]

Hi all, I have read thru this entire thread and it has some excellent content. Excellent work guys and thorough research. From the above I too have developed a question and that is:

"How do 1995 R33 GTR stocko's compare?"

They are a smaller turbine and hence should, as stated, cope with slightly higher (raised) rpm's than say, a GTST turbine of the same year.

I currently run a 3 inch system, although only from the CAT back (with hi-flow 3" cat). I have also taken out the restrictor after extensive discussions on here saying that it's OK to do so. A combination of the higher flowing exhaust and removal of restrictor have raised the boost up to around 13.5 to 14 pounds.

I always let engine warm up and warm down (with turbo timer) as I'm aware that it does a world of good for engine and turbos. So, in other words I'm giving the turbos time to cool down and contract SLOWLY which should somewhat make life easier on them.

However, what does concern me is track days. I've had one on stock boost, but my next one will be with the higher boost level. Will the smaller GTR stockies put up with extended thrashings? The track is Queensland Raceway, so for those who know it has the front long straight while the rest of it is a series of small squirts from corner to corner where your brakes and tires experience more wear than anything else haha!

Any advice would be much appreciated guys - thanks!!

Tom

Yeah second that, i Also am planning on taking mine to QR shortly. Should I be ok to run 1bar? I know 34 turbo's still have ceramic wheels, are they less prone to throw a wheel at all??

[R31Nismoid]

i have popped a wheel on my old gtr, after a quater mile run, on the way back it decided t pop, not whilst i was into it....

so who's theory is correct

Damage was possibly done on the run, then worked loose there after