'Oil cooled' turbos

[thechuckster]

As Norbie's said elsewhere - the materials used in the turbine wheels and housing are much the same for petrol and diesel. It's the selection of housings and wheels that's wildly different (excluding high HP rotaries).

Also, important point - the oil serves as a lubricant for the turbo bearing, it doesn't have a key role in cooling - the flow is so low (Bell suggests 0.5 gal/min under maximum load) thru the bearing housing it's effect on cooling is incidental compared to radiation and convection thru materials attached to the housing.

As wilbo suggests, the water cooling is partly in response to poor owner-maintenance however it doesn't extend oil life, just the bearing's working life.

I've found my photocopies of various pages of Bell's book. pg41 in my edition has a comparison of average oil temps (inside the housing) from water-cooled and non-water-cooled housing:



PDF of entire chart (PDF 781 kB)

It does suggest that a water-cooled housing will keep the oil temps below the level coking would occur. However, it may not take acount of the hot surface of the turbine shaft which is most likely above those temps - so there still a risk of oil-coking with water-cooled housings.

cheers,
Charles

[30psi 4agte]

From memory in one of my HPI vids there is an interview with someone from HKS or TRUST and they are talking about oil only turbos.

Ill look into it further. But it would only be a select few that are.

[The Real Roadrunner]

the thumper series aren't TAs and i believe that they have actually designed them to suit petrol engines but im not 100% sure , i can pull one apart and measure if you want .
what size the 1300hp or 2000hp.

[MR 1JZ]

Trust T78-33D is oil only

[wilbo666]

the oil serves as a lubricant for the turbo bearing, it doesn't have a key role in cooling

Sorry Charles, I think this is rubbish! The oil plays a very significant part, much more significant that the water!

Cheers
Wilbo

[mic*]

Im with chuck.

The oil is a lube moreso. Thats all the bearing needs - lubrication. The oil just needs to be oily, not carbon-y.

Coking occurs when the oil is too hot entering the turbo, or when the flow rate thru the turbo is too low. Neither really have that much to do with the turbo design, more the design of oil lines, coolers, sumps etc & shutdown procedure.

I didnt honestly realise that roller types required so little oil. It makes perfect sense that they would all have a water jacket to keep the core cool enough so that the oil will not pick up enough heat to coke, since it has much more opportunity to do so.

Has anyone got info which compares the volume of oil space within various turbo's & bearing types?

[assassin10000]

This almost deserves a -ve rep

Really?

Talking with serious engine guys the oil both lubricates & cools the bearings, pistons, journals, and lower end parts. Why else would oil squirters have even been invented? They cool the piston & piston skirts, but also provide extra lubrication. But from what I remember they were there for the cooling effect, not the additional lubrication. And just like coolant it has a happy temp range that is ideal for it, which is about 20-30 degrees F lower than coolant.

In any case, this seems to be quite the back and forth discussion.

The only reason that water cooling was added was for additional cooling, an oil lubricated & cooled turbo is just fine. It just requires a little more cool down time and proper maintenence.

The only time I've heard of ANY 'coking' or 'cooking' of the oil in the bearings is when people shut the keys off and the turbine stops recieving oil, AFTER an extended drive or hard/race use. The turbo would still be super hot and since the oil flow stops, its allowing the excessive heat to transfer to the oil and cook it in the bearings.

If you keep your oil temps at a happy 150-160 degrees F going in, you should not have any 'coking' problems. If your temps go above the 180-190 range under 'race' or any other conditions it's time to invest in an oil cooler, or a larger one if you have one already equipped.

Even the roller/ball bearing type turbo's need the oil to both lubricate and cool. If the oil didn't have a cooling effect the bearings would build up so much heat that it would cook what little oil they see as soon as it hit the bearings.

My .02c

Andrew

[Endless]

Also, important point - the oil serves as a lubricant for the turbo bearing, it doesn't have a key role in cooling

Well if the oil doesn't cool the turbo bearings in an oil only cooled turbo... what does?

[Billzilla]

Well if the oil doesn't cool the turbo bearings in an oil only cooled turbo... what does?

How about someone with an IR gun measure the heat of the oil pipes into & out of the turbo, so we can see the temperature rise?
Betcha it's a fair amount, thus taking a useful amount of heat out of the turbo.

[EldarO]

As a very big generalisation, water cooled turbo's are great for factory / mild street cars coz they allow much of the residual heat in the turbo to be dissapated into the coolant rather than the oil (water conducts heat well, oil poorly) when proper shut down procedure is not always adhered to by daily drivers.

you must be speaking comparatively?

if not.

what?

Elmo.

[nick.parker]

Why else would oil squirters have even been invented?

Well what else can be done to cool the piston? Spray water ? I would say the ONLY option to remove some heat is to spray some oil at it, I dont think that proves anything about the ability of oil to conduct significant heat.

[MWP]

Really?
Talking with serious engine guys the oil both lubricates & cools the bearings, pistons, journals, and lower end parts. Why else would oil squirters have even been invented?

Oil squirters are there to cool the pistons, yes, but thats only because you cant get coolant into/onto a piston to do that job can you?

[edit]
Ooops, as said above

[BeRad]

Nothing like a heated discussion on a sunday morning

[Billzilla]

FWIW If you have a really god dry-sump system and it has a big cooler, you can run the engine out of water and it'll still keep going for quite a while and survive. Seen it a few times in various motorsport events.
A wet-sump engine will die very quickly.

[Merudo]

Is that because a wet-sump engine doesn't give the oil a good enough chance to cool down enough, as it's still right there, being constantly soaked with heat?