Turbo Design Preferences: Journal Bearings vs. Ball Bearings | Single Scroll vs. Twin-scroll

[B C]

Is a ball-bearing turbo worth the added cost? or Is a quality name brand journal bearing single scroll turbo good enough?
Is a split pulse/twin scroll turbo a "must-have" feature even though it requires two wastegates?

 

https://turbobygarrett.com/turbobygarrett/journal_bearings_vs_ball_bearings

 

"Turbo Response – When driving a vehicle with the cartridge ball bearing turbocharger, you will find exceptionally crisp and strong throttle response. Garrett Ball Bearing turbochargers spool up 15% faster than traditional journal bearings. This produces an improved response that can be converted to quicker 0-60 mph speed. In fact, some professional drivers of Garrett ball-bearing turbocharged engines report that they feel like they are driving a big, normally aspirated engine.

Tests run on CART turbos have shown that ball-bearings have up to half of the power consumption of traditional bearings. The result is faster time to boost which translates into better drivability and acceleration.

On-engine performance is also better in the steady-state for the Garrett Cartridge Ball Bearing" 

 

 

 

 

[B C]

The two cars I have been in with ball bearing AND split pulse turbos were both had the least lag out of any turbo car I have been in/driven. One of them was an RX7 with a big turbo.

Seeing the difference in how easily a journal bearing spins vs a ball bearing isnt quite fair  when you are doing a bench comparison since you arent running hot oil through the journal bearing. I do believe that on a lower boost application you can strike the right balance between size and response but on a larger high hp setup with larger turbo and more inertia I think ball bearing would be critical for response. 

My current feelings are that split pulse are more beneficial for a 4cyl than a 6 cyl, but are still beneficial, but not worth having 2 expensive wastegates on a lower boost car like my E30. So with that I vote single scroll. As for bearings I am more conflicted. 

[The Full Banana]

Relevant content from an engineer at Garrett (fun fact: he also happens to have been on the project for designing the turbo i'm running--gtx3067r)

Quote

Ball bearing turbos are pricier than journal bearing equivalents, but depending on your goals and how you'll use it, the ball bearing can offer some real quantifiable advantages. There's no separate thrust bearing to worry about, which is a common failure point when running very high boost or backpressure. Ball bearing turbos can handle surge without much problem for the same reason - no thrust bearing. 

Spool-up can be as much as ~25% quicker depending on what it's being compared to. Transient response is quicker too (which doesn't show up on a dyno sheet); when you are transitioning from cruising to full power, mat the throttle and the turbo will "catch up" quicker than a comparable journal bearing unit.

If they are not overheated and run with water lines hooked up, ball bearing turbos can outlast journal bearing turbos, even when beat on pretty hard.

 

[B C]

Slightly unrelated, but, a guy on r3v with a twin turbo setup has water cooled bearing sections. He has the coolant return heading back to the drivers side of cylinder 6 which is normally a line for the throttle body heater. He has cracked 3 heads IIRC and has concluded that the cause wasnt due to the engine running too hot or head machining/mounting/defects, but that the hot coolant exiting the turbos and running back to hot cylinder 6 was creating a real hot zone.  
Again, not totally related, but an oil cooled journal bearing turbo prevents me from having to come up with a coolant line solution  

Thanks for that info you posted Tom. Looking forward to a ride in your car which may seal the deal on whether I spend the extra cash on a BB unit or just get a downsized journal bearing unit.

[Earl]

Would it be wrong to run the coolant return into the "hot side" of the radiator instead of into any point of the motor? To me that would make sense for a return as it is the hotest point of the cooling system (I would think)

[B C]

That would make the most sense, most M20 guys utilize the throttle body/PCV heater lines out of convenience. Big difference in application between actually losing a little bit of heat to the throttle body and incoming air in its stock configuration as a throttle body/PCV heater vs adding an immense amount of heat to it before heading to the back of the engine

 

[Earl]

They must not like to mess with bungs

[The Full Banana]

1 hour ago, Snap said:

Slightly unrelated, but, a guy on r3v with a twin turbo setup has water cooled bearing sections. He has the coolant return heading back to the drivers side of cylinder 6 which is normally a line for the throttle body heater. He has cracked 3 heads IIRC and has concluded that the cause wasnt due to the engine running too hot or head machining/mounting/defects, but that the hot coolant exiting the turbos and running back to hot cylinder 6 was creating a real hot zone.  
Again, not totally related, but an oil cooled journal bearing turbo prevents me from having to come up with a coolant line solution  

Thanks for that info you posted Tom. Looking forward to a ride in your car which may seal the deal on whether I spend the extra cash on a BB unit or just get a downsized journal bearing unit.

Interesting. Definitely not a problem on any Volvo engines I've tinkered with--but then again, they are designed for use with watercooled turbochargers. 

Like Earl said, definitely sounds like it could be remedied by circulating the coolant back in somewhere else... and if still a problem, then that would be more up to the radiator to handle. 

 

also, WHERE IS YOUR M20 GOD NOW, BRIAN?

[The Full Banana]

Back on topic, a big consideration for me personally is the application of the vehicle.

For a daily driver that sees a lot of miles, I would probably opt for a journal bearing turbo that is simple and cheap for me personally to rebuild. In that case, I don't need to squeeze out every bit of efficiency, and I'd rather have the lower up-front and maintenance cost. However, for a weekend/special use car (like my 242) that doesn't see quite so many miles and where optimal performance is critiqued every time I drive it, ball bearing is the way to go. Sometimes I just want to have my cake and eat it too, even if it's expensive. 

Both are good options. Twin scroll typically doesn't add much if any cost (at least with the turbos I've looked at) so it's kind of a no-brainer to me, if your platform can support it (*cough* odd cylinder count).  

[Rowleym]

One thing is for sure, twin scroll is more easily justifiable with a 4 cyl engines. Evo engines for example, with lower power output, lets say sub 500whp, twin scroll will show little to no benefit. But you also have to understand these engines run very high drive pressures in comparison to ours. If you were going big boy turbo in this application, and want nothing more than straight line performance, single scroll is also the way to go. Twin scroll benefits largely in a street application that also wants big power, say 600+ minimum. The big borg turbo's really shine here. Its awesome to be able to say you have an 800hp 4 cyl and a very usable power band. Twin scroll also works great for people who need lower drive pressure but still want to make good power and usable powerband. AKA pump gas power. 

As far as journal vs ball bearing, I would always choose BB if I could, but thats not always needed, and of course most times Im not willing to spend the money. Ball bearing works awesome if you need fast response with a larger turbo, such as a low pressure street turbo. It also helps a lot with transient response. But of course we ask how much? Well, if youre in the sub 500whp level, its not as noticeable. When you are using larger turbos for the setup, it only helps. For me, I will always use journal bearing twin scroll turbos in the sub 600whp range, And only will I use BB if the application NEEDS it. Lets say a street strip car that doesn't want to swap turbos between events. They say BB is better at high boost levels... well look at borgs. You don't need BB to run high boost, but it is a band aid most definitely.