Turbos which keep spinning long after the car stops

[GTRgeoff]

Shouldn't be. The stickiness (stiction) would be from the seals. The bearings would be a little loose for thermal expansion and oil space.

[wilch]

Not a great idea but these are more for longevity rather than response. The bearings add weight to the rotating parts. A good plain bearing should have no contact as it floats in the viscous oil pulled around the journal. It will not last as long though, but well cared for will give a good life.

Interesting.

So a plain bearing turbo would be more responsive than a ball bearing turbo of the exact same size?

I'm curious to know as I have the opportunity to buy a brand new steel wheel'd plain bearing turbo or get a GCG hiflow. The new plain bearing is significantly cheaper though.

[B-Man]

I can't work out something ....

is it:

Turbos which keep spinning

OR

Turbos that keep spinning

I guess it depends on whether your car is a twin turbo or a single turbo

[GTRgeoff]

Well the bearing will add extra mass that resists acceleration, either positive or negative. This in in the form of the rollers/balls (depending on construction) and the inner race over the shaft. I have seen needle rollers in a different low speed application that run on the shaft itself.

Plain bearing application is well advanced, and the shaft basically runs on hydrodynamic oil pressure without contacting metal. The bearing metal is there as a soft surface for when the parts touch, which it will eventually from time to time as the bearing ages.

It's a choice of longevity, but plains last years and many miles when well cared for.

[discopotato03]

Cubes , SB8006A CHRA ? . I dug through all the good and not so good GT30 CHRA no's eg 700177-10,11,12,13,14,15,18 and the best 700382-12 . What does that number you gave show or what listing is it from . I've been trying to remember the name of the turbo dealer in north QLD as his site used to have some early Garrett parts lists .

Cheers A

[discopotato03]

Sorry that last one (GT30R) should have read CHRA no 700177-7 , for turbo assembly no 700382-12 . There are at least 14 GT30 turbine based cartridges I know of and have the part numbers for 11 0f them . Compressors range from GT35 to GT37 to T04S to GT40 .

Cheers A .

[Cubes]

Sorry.. I grabbed that number from Ray Hall. His listings appear to be different to that of Garrett them selves. ?!?

The real part number for the chra is 700177-0014 according to Ray Hall.

I don't understand to be honest as Garrett don't list a GT30R that runs a 64trim comp wheel?!?

Comp: 64trim GT40 comp wheel 2.41(61.21mm)/3.22(81.78mm).

Turbine: 84trim 2.16(54.86mm)/2.36(59.94mm).

I really need to do a bit of reading to understand the trim etc..

[browny]

One good argument i've seen regarding response, is that the bearing design doesn't matter much, but the blade design does.

IMO its incorrect to attribute the better response of modern turbos solely to the use of ball bearings, because the blade designs are years apart in terms of development.

[wilch]

Well the bearing will add extra mass that resists acceleration, either positive or negative. This in in the form of the rollers/balls (depending on construction) and the inner race over the shaft. I have seen needle rollers in a different low speed application that run on the shaft itself.

Plain bearing application is well advanced, and the shaft basically runs on hydrodynamic oil pressure without contacting metal. The bearing metal is there as a soft surface for when the parts touch, which it will eventually from time to time as the bearing ages.

It's a choice of longevity, but plains last years and many miles when well cared for.

Cheers thanks for that GTRgeoff. You may have just saved me $1000

[discopotato03]

Cubes the 700177-14 cartridge should have a 56 trim GT40 compressor on it . Most people call them a GT3040R . HKS did a similar thing but with a 50 trim GT40 compressor wheel .

Turbo bearing systems . The annular contact ball bearings have very little contact area with the inner and outer races . The reason they have small oil restrictors is that high speed ball race bearings suffer drag losses if too much oil is present . Clearence on ball race bearings can be much closer than bush bearings in high speed applications meaning less "orbiting" of the shaft . This allows less clearence between the wheels and housings raising the efficiency of the compressor and energy recovery of the turbine - less slip losses .

What happens with floating bushes in turbos is a large contact area between the turbine shaft and the oil cushon . The large contact area initially gives a drag or oil shear effect that slows the acceleration of the rotating assembly from low speeds - lag . The collar and plate thrust bearing also has the large contact area drag problem . If there is a carbon compressor end seal (mechanical face seal) its more drag again .

The reason turbos with very low drag bearing systems contine to revolve when the engines shut down is because the mass of the rotating assembly has little resistance to revolving for a short time . The lubricating oil is hot and thin as well .

Cost aside I can't think of any good reason to use a bush bearing turbo if a ball bearing alternative is available .

Lastly would you believe me if I said Garretts GTBB turbos have a lower part count than the bush bearing ones ? Believe it .

[GTRgeoff]

That all makes sense to me so I won't dispute it except one bit.

As far as the BB part count goes, I assume each bearing cartridge is a single part, where if you said moving parts it would be different.

[INASNT]

Well the bearing will add extra mass that resists acceleration, either positive or negative. This in in the form of the rollers/balls (depending on construction) and the inner race over the shaft. I have seen needle rollers in a different low speed application that run on the shaft itself.

Plain bearing application is well advanced, and the shaft basically runs on hydrodynamic oil pressure without contacting metal. The bearing metal is there as a soft surface for when the parts touch, which it will eventually from time to time as the bearing ages.

It's a choice of longevity, but plains last years and many miles when well cared for.

White bearing metal is very expensive to replace also when it wears out

[mokompri]

spinning it with your hand would be alot slower than it spins when being pushed by exaust gas. Also doing it once or twice with your fingers wouldnt matter, but doing it everytime you turn your car off, can't be good for it?

yeah thats exactly what i was saying, having exhaust gasses pushing it means there is load behind the turbine wheels, but in this instance the car is off and it keeps spinning because the inertia of the rotating parts is enough to overcome the friction of the bearings. of course the friction will slowly turn the inertia into heat and transfer the energy to the oil and bearings over the period that it keeps spinning after the car is off, once that energy is expended it will stop spinning as its converted all its energy into heat.

now if there was enough energy it can be argued that it will cause damage as there is no longer a proper oil supply, but its not really its a very negligible amount of energy when the engine is off.

[carl h]

my gt30r will spin for a minute after shutdown.

course it is a dual steel BB unit so its to be expected.