...if this has been beat to death I apologize for asking.
At what point, power level, does it pay to get away from journal bearings? Have read claims that ball bearinged (is that a word) spool faster. While I understand the theory, sort of, I do question the truthfulness of it. Assuming a properly sized turbo & properly sized/positioned waste gate will replacing a journal bearing turbo with one spinning on ball bearings really be that noticeable?

 

It's noticeable, but Imo they're not worth it for the average Street/strip setup. On an application where you want to maximize the boost curve, run very high boost numbers, or where oiling is an issue is where they shine.

 

I replaced a PT76GTS with a PT7675 CEA ball bearing and gained about 700 rpm spool on my 347. I love mine on the street but they are big dollars.

 

I lean towards saying it starts to become a benefit for someone running high boost. Like 30 plus. I say this because Ive been around some 6 second drag car guys that talked about how much faster boost came on for them. Whole different level from just your average street/strip car though.

 

Better/faster spool with bb over jb is another great misnomer in the turbo community imho and usually a seat of the pants placebo effect. There is also some misconception as to what spool is. The time it takes to start making boost at the manifold, that is really transient response which is generally measured by what rpm you start registering boost at and can be called the boost threshold, then you will have an rpm you achieve desired max boost at, often called full spool. Spool really being time from initial boost to get to desired boost at wot. Most though consider it when boost starts being made, ie my turbo spools up at 3000rpm and full boost 45000rpm.

Many factors to look at but in general no there will be no night and day spool difference especially if the turbo is already spec'd nicely for the engine size. You could expect at most a 100-200 rpm difference tops in boost threshold, but spool itself on a v6-v8 4 to 6 liters from my experience, ie barely noticeable to no measurable difference going from jb to bb with all other factors equal.

Resistance of the bearings difference is minimal, a couple percent for 360 journal vs angular contact bearings, so all else being the same not much difference in the ability of the mass of the shaft and wheels to accelerate with the same turbine drive pressure.

That said a bb setup is generally mechanically superior to jb in every way. Requires less oil volume and pressure to lube and cool. Less surface area contact so this reduction in friction generates less heat in the bearings which means its more mechanically efficient for optimal acceleration. This also leads to increased stability, as the ball bearings are less likely to deform at higher temps and shaft speeds. A ceramic ball being the best over a steel ball, but steel ball still superior to a 360 journal. To sum it up this leads to bb generally having a longer service life and able to withstand more abuse. It will handle things like surge, stall, shifts, 2-step launches and high pressure ratio/shaft rpm better.

So the real question boils down to if the increased cost is worth it to you for your setup and goals for the car.

Spot on.

This measured gain came almost completely from the cea wheel design over the gts wheel. The wheel has less mass, extended inducer tip and wider vanes with a smaller hub which allows it to move more air at the same pressure ratio/shaft rpm. This leads to faster transient response and spool time. I had similar results on my 4.6 I went from a pts cast wheel 67 to a cea billet wheel 67 both journal at transient response was almost instant and max boost (12psi) came in 900-1000rpm faster.

Engine size plays a role in this as well obviously, a 2.0 liter 4 cylinder that revs to 10k rpms will see a much more noticeable gain with a billet wheel and more efficient bearing compared to same kind of upgrade on a 5 liter v8 that revs to 5500rpms for example. The larger motor has more exhaust volume and turbine drive pressure.

Exactly. When running a mild setup at say 10psi that takes 2 seconds to get from zero to 10psi with a turbo thats only running 50k shaft rpm there is less time to see significantly faster rotor acceleration over. Flip that to 30psi plus setup running a turbo at 150k shaft rpm that needs to quickly make boost at the line before launching and that more efficient rotor acceleration will definitely be more noticeable.