1INSANEGTO

iTrader: (13)

Cool tech I found

There is always a discussion in regards to ball-bearing vs. non-ball bearing turbochargers and the performance and reliability aspects of one to another. This question was presented to Rob Smith master-tuner and owner of RPS Automotive in California.

QUESTION TO ROB SMITH: "Rob, everyone is asking about ball-bearing turbo's and do they spool quicker than non-ball bearing turbo's. Should I pay the extra $425 which is the difference between a non-ball bearing RPS turbo kit and a ball-bearing unit?"

ANSWER: "All right! This question has been asked many times and I have yet to answer, so here goes. The main factor that determine when a turbo will start to spool hard is the A/R of the exhaust housing. On a side note, the wieght of the exhuast wheel is a factor, i.e. a ceramic wheel. Unfortunately ceramic wheels are very, very expensive and are not readily available in the sizes we need.

Everyone needs to remember that a turbo is basically just like a kid's pin wheel that you can hold out a car window and make spin. If you increase the velocity of the car (i.e. the exhaust going into the turbo) the wheel will spin faster. If you put your hand behind the pinwheel, the wheel will slow down because air cannot flow though it. Let's talk about a Supra engine running at 3,000 RPM, full throttle. The engine will produce a constant amount of exhaust gases as long as the RPM is held constant. So the only way to spin our "pinwheel" faster is to increase the velocity of the air. The only way to increase the velocity of the air is to use a smaller A/R ratio. The problem with too small of an A/R ratio is that it will choke off air flow at higher Rpm's. This is why matching the turbocharger's size, CFM, exhaust back pressure vs. intake pressure, and A/R ratios is so important.

The ball bearing option was developed to improve the reliability of high output turbos. When high boost is used, there are great stresses on the center housing bearings to keep everything in place. The ball bearing option is a great way to handle these added stresses and improve reliability.

As a side effect of using the ball bearing option, drag cars saw immediate improvements in et's. The reason for this is the ball bearing improved the rate of acceleration of the exhaust wheel, thus boost. Remember, the A/R ratio determines when the boost will start, a freeing spinning wheel (less friction with the ball bearing) will make the boost rise at a faster rate.

It's that simple. The A/R ratio determines when, the friction in the bearings affects how fast."

Tiger2o69

iTrader: (16)

I read this somewhere.. Considering low boost setups looks like it wouldnt help much.. Probably would with those 15+ psi guys.

99Z28LS1

iTrader: (4)

this should be a sticky

Boo"SS"t

iTrader: (2)

This is really a great information. Thanks for posting it!

Ryan K

iTrader: (11)

Another interesting point is that Ball bearing turbo's need less oil.

Ryan K.

DrTurbo

iTrader: (3)

I don't see anything new in this reply. This is stuff that has been said for many years now. He doesn't mention pitch, and blade count, also why a GT4274R and a GT4274 with both the same A/R spool at a different rpm. The "when" was skewed by the BB.

NassyVette

iTrader: (22)

How much sooner will a T76 BB spool than a regular T76 assuming they're both on the same 346 ls1 setup? Any idea? And what about the durability issue. Is a BB turbo really more reliable or durable than a standard unit?

JZ 97 SS 1500

iTrader: (2)

Durability will depend on maintence. Change your oil frequently and the journal unit is every bit as reliable. Also the journal can easily be rebuilt. The DBB's from Garrett are not. They use a cage system and will not sell just the individual parts outright. They can be sourced and something custom can be done, but not worth it. Easier to buy a CHRA and be done with it. As for spool up.....200-400rpms difference tops. Also alot will have to do with tuning, overlap, compression....yadda...yadda.

Grr

iTrader: (2)

IMO, spend the 425$ you saved to get the some thermal coating done and you will outspool the BB turbo, all the while having a cooler and better looking engine bay. BB is pretty much a rip off if you ask me, and the fact that many BB turbos must be water cooled as well. The rotary guys wont use BB turbos cause they just cant handle it.
Gary

1INSANEGTO

iTrader: (13)

Main reason I found this info is because a guy called me and had no interest in my T76. He said he wanted BB and I asked why? He could not give me a answer so I guess he saw BB was good on a vtech board

JZ 97 SS 1500

iTrader: (2)

To many folks rely on the internet, and what any yahoo says. Best thing to do is talk to the engineering facilities that work on the different units. They will give you a better response on what works and doesn't

fitz98ta

iTrader: (29)

or they can just come talk to you

chuntington101

i know the import guys dont like to run anything but BB turbo units now. its really taken off a storm and has proven great in lots of race cars (both autocross/sprint and drag). also think alot of the rally teams over here like to use them cos they need everything they can get to make the cars faster!

guesse its what you want form you car and what you have to work with. im sure the guys that sell turbos are the best to talk to as they know whats about.

thanks Chris.

obZidian

iTrader: (2)

im assuming the import guys you are talking about are the guess pushing 2bar's or boost or more. For example, 900rwhp EVO, great!! but that was at an est. 42psi plus c16.

"The ball bearing option was developed to improve the reliability of high output turbos. When high boost is used, there are great stresses on the center housing bearings to keep everything in place. The ball bearing option is a great way to handle these added stresses and improve reliability."

BB i have been told will require more atention and if your not running a pure track car, one that you inspect between runs, i believe, a BB turbo won't be necesary.