Ball Bearing VS Journal Bearing and size!

[suprastroker88]

I am in the process of buying my buddy's supra. The current turbo is a bit on the large side for me since I want a bit faster spool and I'm use to my sp61gt dbb turbo. You can check out the build on "thedave925" profile. He currently has a fully built motor with an old school Turbo Concepts t70 bolt-on turbo. I'm looking at getting something more in the 64-67mm range, but my question is, at which point should I go to a ball bearing turbo over a journal bearing turbo? What are the benefits of both and the downfalls (besides ball bearing costing more to rebuild)? And should I go to t4 or stick with a bolt-on? I will be doing some time attack and also some drag racing in the car next year so I need to find a turbo to suite these needs. I am looking to make between 500-550hp at around 18psi on 91 california pump gas daily and over 600 on race gas. What size turbos should I be looking at for this power range with quicker spool? And should I be going ball bearing or just using journal bearing? And I am not interested in a qsv. Any and all opinions are welcome

 

[toyotanos]

*This is strictly from my own experience, and may not be completely accurate*

If you were starting from scratch, I would go T-4 without hesitation. On my billet P-trim 67mm, going from a .83 CT to a .81 T4 I gained ~1000rpm of spool with the exact same turbo and similar downpipes (was using a divorced ebay, went to 3" and an external WG) Well worth the money IMO.

My turbo has always been BB, but that was more personal and at the advice of the guy who sold the turbo (He has still never seen a failed TBB Comp Turbo center section so far) So reliability was a big selling point. Not sure if it helps spool or not, but that wasn't the main point for me.

With the stock mani and a LIPP BOSS Sr. .83a/r CT housing, my 64mm turbo was at full boost around 4300rpm.
same setup with the 67mm billet wheel it shifted to ~5000+rpm
Going T-4 with the 67 its now back to around 4200rpm

 

[suprastroker88]

would it make the spool faster with a .70 ar instead of a .81? I dont really understand the AR stuff

 

[toyotanos]

It would help the spool, but it would hurt the top end. Think of A/R as a firehose nozzle. Small A/R means a tight, powerful stream, but it becomes more of a bottleneck when flow increases. Big A/R is an open firehose. Not such a strong stream at lower flows, but it has the capacity to flow a higher volume efficiently.

What that means in the real world (all things similar)
Small A/R turbos spool faster and have more midrange, but choke up top (like a CT-26 with its .58A/R it usually chokes around ~5000) They usually are nice fat powerbands that taper up top.
Big A/R turbos spool later, but they don't choke and make bigger peak numbers. The higher the number, the more narrow powerband is, becoming more focused in the upper RPMs.


The thing is, A/R is only one of many tuning variables you have control over when picking a turbo out. Compressor size vs turbine size vs compressor cover vs exhaust housing A/R vs etc. Best option would be to go to a tuning shop that has experience in I-6 turbocharger selection and give them your *realistic* expectations and budget.

 

[suprastroker88]

ok thanks. now how about the ball bearing and journal bearing situation?

 

[hvyman]

Ball bearing spool faster. But there more expensive. If you get something with a billet wheel it will spool faster as well. It's why holsets spool so fast for there large size.

I'm getting a 62mm with billet wheel journal. If I have more cash which I won't I'd get ball bearing. But it's what ev. Still need wastegate too and someother things.

 

[suprastroker88]

so a billet ball bearing would spool the fastest out of all.... correct?

 

[dubsupra209]

the bigger the ar the more turbo lag... ***fixed***

 

[hvyman]

A/r is b0th on compressor and turbine side.

Yes billet ball bearing would spool the fastest.

 

[suprastroker88]

is Precision the only company to make billet ball bearing turbos?

 

[hvyman]

No. Comp turbo and turbonetics do as well. Borg Warner too. Maybe Garrett.

 

[toyotanos]

garrett does- the GTX series of wheels are billet.

 

[IJ.]

"Billet" wheels don't actually spool faster, they have more fin area due to the slimmer/smaller hub so move more air so "lag" feels like it's reduced

Might be a different matter if it were a Turbine wheel we were discussing.

PMoI on the Billet wheel might be lower but I'm guessing the more dense grain structure of the billet Al will offset the thicker Cast wheel.

 

[suprastroker88]

ok so what would be my best choice for what im trying to do?

 

[hvyman]

Just make sure you have the proper size turbo and the right a/r on the exhaust side and any turbo will do.

Like a 57mm with a .63 or .68 a/r. Just wont have good top end and will max out at like 400-450.

 

[suprastroker88]

yea that's too small for me. i had an sp61gt dbb on my previous supra that I built and i loved it and I was still on pretty much a stock motor besides injectors and lexus afm and exhaust. This new one is BUILT so I figure that sp61gt might be a bit small for what im going for. Am I right or wrong? I was thinking a 64 or 67mm might be where I should be looking at for the power and spool I want. Please correct me if I'm wrong.

And would going to t4 make spool faster or just more top-end?

 

[hvyman]

t4 have better flow than a cast manifold. 67mm is pretty big if this is for a 1jz.

also if you dont really have anything good to tune with like a maft pro at the least your not going to see all the potential that the turbo has to offer. Can always get a different housing for the sp61 and give it some more boost.

What engine is this for? A 61 on a 2.5 is a lot different than a 61 on a 3l.

 

[suprastroker88]

check out the motor on thedave925's build thread. I'm buying his car. Its a fully built 7m with 272s. I'm going to put dual walbros and 750s in it. It already has a maft-pro in it

 

[Nick M]

Small A/R turbos spool faster and have more midrange, but choke up top (like a CT-26 with its .58A/R it usually chokes around ~5000)

It seems like the CT26 is a .44 A/R My Boss Jr is .58, and it pulls positive to 6000 rpm.

Just make sure you have the proper size turbo and the right a/r on the exhaust side and any turbo will do.

Like a 57mm with a .63 or .68 a/r. Just wont have good top end and will max out at like 400-450.

You make that sound like it isn't enough on a street car.

 

[toyotanos]

The Boss Jr. Also has a larger turbine which helps flow up top a lot. iirc it was designed to be as close to the CT as possible (being that it was designed as a 57 trim/60-1 repacement unit)