[DaveGTA]

Im purchasing a pair of s/h standard GTR turbos for a biturbo project on another car, but what I wan't to know is WHAT is the reason for the ceramic wheels packing up on the GTR at just over 'a bar'..?

Is it the total turbine RPM, based on the fact that you lot are holding a bar into very high engine RPMs, so the turbo has to overspeed or run at high rpms to sustain airflow...?

Is the turbine inlet pressure too high, is it shearing it off the shaft?

Is it EGT related, on this engine, at these revs, at this boost level...?

Which part of the wheel is breaking, the vanes or the core..?

So basically, what I want to know, it is 'a bar' that is killing them, or something else, so in theory, in a different application, they could be run at more boost..

Thanks in advance..

Dave

:wavey:

 

[toddrb30gtr]

they shear off at the base of the exhaust wheel, because at higher boost the wheel spins alot quicker to produce the boost,, and when you back off and the sudden slowing down of the turbine, the enertia ( if thats how its spelt :nervous: ) of the turbine has greater force than the shaft so it stresses the weakest point....... think of it as if you have a pensil with a push bike wheel attached to it,,, if you start turning it slowly, speeding it up more and more....... NOW TRY TO STOP IT QUICKLY!!!!!!!! what happens?????:thumbsup:

 

[DaveGTA]

they shear off at the base of the exhaust wheel, because at higher boost the wheel spins alot quicker to produce the boost,, and when you back off and the sudden slowing down of the turbine, the enertia ( if thats how its spelt :nervous: ) of the turbine has greater force than the shaft so it stresses the weakest point....... think of it as if you have a pensil with a push bike wheel attached to it,,, if you start turning it slowly, speeding it up more and more....... NOW TRY TO STOP IT QUICKLY!!!!!!!! what happens?????:thumbsup:

If it is centre related, it more likely to start to break at the point of maximum load (ie high revs, high boost), not when you back off as exhaust output will be very low, and it is a ceramic wheel on a steel shaft, the inertial mass is very low..

Just sounds like the exhaust turbine pressure combined with the inlet pressure is just to much, cheers.

 

[tath]

Also thought it was at very high rpm the ceramic wheel detaches and much hilarity ensues.

 

[toddrb30gtr]

ive had plenty of turbine wheels go on skylines when ive been driving, always go when i backed off, and on dynos,,,, complete the power run fine back off!! SEE YA also have the same explanation from customers,,,,, another big factor is play in the shaft,, if that turbine wheel hits the housing,,kiss it good bye.... im just going off what i have experienced:thumbsup:

 

[toddrb30gtr]

another reason that it can happen when you back off is,, you turn the boost up so your pumping more pressure into your intake pipes, back off throttle body shuts off, and if your standard bovs cant get rid of the pressure quick enough it stalls the compressor wheel,,, and once again the enertia of the turbine wheel puts stress on the shaft...

 

[NISFAN]

Surely the torque required to produce pressure must increase with increasing pressure. Eventually you get to the limit of the joint between ceramic wheel, and metal shaft (the weak link), and they go thier seperate ways.
I'm sure vibration, heat, and speed play thier part in it too.

 

[toddrb30gtr]

Surely the torque required to produce pressure must increase with increasing pressure. Eventually you get to the limit of the joint between ceramic wheel, and metal shaft (the weak link), and they go thier seperate ways.
I'm sure vibration, heat, and speed play thier part in it too.

yer im not saying it doesnt,,,,, just going off my experiences mate,,,, what it come down to is,,,,,,, THEY GO BECAUSE THEY CANT TAKE THE PRESSURE!!!! no matter where it comes from:thumbsup:

 

[tath]

Anybody know if they're more likely to go on stock dumpvalves than good aftermarket ones? Maybe a gentler run down would protect them a bit better.

That said, you shouldn't really need to wrap them in cottonwool.

 

[toddrb30gtr]

luck of the draw mate, yes it would help.... but so would getting turbos with little shaft play,,,,, but to save heart ache just use a turbo that will take the punishment.... doing things twice sux!!!!!!!:thumbsup:

 

[moosedoog]

as you say toddrb30gtr the highest pressure on the turbo shaft and compressor wheel is as the throttle is backed off. the compressed air travelling through the intercooler etc hits the butterfly and has nowhere to go causing a spike in pressure, which in turn manifests itself as more drag/pressure on the turbine parts. thats one of the main reasons for the dump valve, to release this pressure and prolong the life of the turbo.

thats my understanding anyway:runaway: :runaway: :runaway:

 

[tath]

What's involved in changing them for steel internalled ones then? AKA How much?

 

[toddrb30gtr]

What's involved in changing them for steel internalled ones then? AKA How much?

around £600 each mate:thumbsup:

 

[toddrb30gtr]

as you say toddrb30gtr the highest pressure on the turbo shaft and compressor wheel is as the throttle is backed off. the compressed air travelling through the intercooler etc hits the butterfly and has nowhere to go causing a spike in pressure, which in turn manifests itself as more drag/pressure on the turbine parts. thats one of the main reasons for the dump valve, to release this pressure and prolong the life of the turbo.

thats my understanding anyway:runaway: :runaway: :runaway:

yer,, i think the ceramic wheels just cant stand up to the constant sudden changes in load when you turn the boost up...:thumbsup:

 

[tath]

around £600 each mate:thumbsup:

What, to change the wheel? Blow that, Garretts from the states aren't much more!!

 

[toddrb30gtr]

What, to change the wheel? Blow that, Garretts from the states aren't much more!!

no thats to put new bigger turbine wheel and shaft, new bigger comp wheel, machine out housings to fit and rebuild....

 

[Warpspeed]

The whole turbo needs to be rebuilt and balanced, it is really not an economic proposition to fit steel wheels to original turbos.

Much better to get something new from Garrett or HKS.

 

[Cornhoolio]

I was just quoted £625 + VAT from a reputable UK company to fit "steel" internals to my std. GT-R turbos Like you say, better off I think with a pair of HKS GT-SS's at that price. At least you will have brand new units not reworked old ones

Cheers
Ian

 

[roguepi]

Something we have noticed on customers cars:

Even though they are running stock turbo's and are running 14 psi or so (1 Bar) at the inlet, the actual pressure before the intercooler is more like 18-19 psi due to the pressure drop across the core.

The interesting thing is, some of the cars have replacement intercoolers, such as ARC, greddy and apexi. These cars are still seeing 14 psi at the inlet. All of these cores have a larger pressure drop due to increased core size and they often think "hey, I can run 14psi so I will just turn the boost up to 14 psi" without thinking that they have a higher pressure drop across the new IC. Obviously on stock boost they make more power, torque and have better responce, but actual pressure before the intercooler is more like 20-22 psi! And most are fine! We have been told by a couple of customers they they Shat their turrbo's with cheap chinese cores (you know the ones on ebay) which can be expected. Most advertise a 0.6 psi pressure drop at 20 psi, its more like 8-9 psi!! A 3'' 90 deg pipe will have more then 0.6 psi pressure drop!

After speaking with a good friend of mine, he mentioned they have been tuning stock turbo's on 17 psi at the intake for a while now without problems! This is surprising and not so surprising:
1) Once the olive or restrictor is removed, some cars will run 1 bar, some a touch under, some a touch over. I have seen some running on 16 psi without an issue for a long time.
2) Your sure to have an old engine/turbo at sometime which will increase the chance of failure, but he hasnt!

He did mention it was also tune related so we have a car booked in for a tune. This is my brothers car which has stock turbos but has -5 turbo's with
R34 exh 0.48 housings, our manifolds (but modified for a tial 44mm gate), prototype dump pipes all ready on stand by. We will see what he does differently to us ;-)

P.s £600?! You would be better off with brand new -7 or -5 BB cartridges for that sort of cash, just machine your housings to suit! We were using GT28R and GT28RS hybrid cartridges before shelf items were easily available from Garrett. We still use the odd Hybrid for certain engine spec's, mainly on engines with a capacity/stroker kit. Just depends on personal preference, if they want more linear power or if they want it to snap onto boost!