Is it possible for a machine shop to modify a stock twin turbo to use ball bearings instead of the stock bearing??

 

anything is possible with enough $$$, but I have never heard of anybody converting a turbo from oil suspended bushing to ball bearing. Why would you want to do that?
M2 makes a replacement ball bearing set, I dont know if you can maintain the sequential operation though.

Not to make this a ball bearing vs. bushing thread but there really isnt much of an advantage in ball bearing. I was looking into the subject a couple months ago and it seems the only people that say ball bearing are oh so much better are average joes that just heard it somewhere. Every web page I found that looked remotely professional said spooling is more a function of not getting a turbo that is too big. Ball bearing will spool about the same rate. The only thing I could find that really made one better than the other is that an oil suspended bushing has a much longer life.

 

As far as I know, M2 is no longer doing this modification (as it's not listed on their site). It was a sequential setup though and spooled faster than the stock setup. Artguy had a dyno showing his M2's while back.

However, I doubt M2 was doing the work themselves, rather sending them out for the modification. It would be interesting to find out if that's the case as the modification could still be around for those that want it by using the original source.

 

I do not claim to be an expert but Brian at M2 showed me a set of the BB turbos before he made them public. All you had to do was gently blow and the turbines would start moving. Now on the stock twins its a whole different story. No matter how hard I tried to blow to make the turbines spin they did not budge one bit. The fact that you need less gas pressure to spin the turbines on the BB set has to mean something no? And I believe the ONLY reason why M2 was discouraging people from buying their BB set was because many people thought they could simply slap them on and get 400rhp right away, which is simply not true. They were not taking into account fuel, ignition, ecu, bolt-ons and etc.

 

Just because you weren't able to find anything searching on the web doesn't mean that there is no appreciable performance difference between ball bearings vs. bushings. And it's easy to make a web page look "professional", but still populate it with hearsay and conjecture.

Ball bearings have far less internal drag than oil-film bushings. They're actually the ideal bearing setup for a turbo. It's the reason you see them used in so many low-load/high rpm applications where the absolute minimum internal drag is desired. Oil-film bushings actually suffer from drag induced by the oil film itself, due to the surface tension properties of oil. The reason you see oil-film bushings used so much with engines today instead of ball bearings is cost, their load-bearing capacity, and--as you "found on the web"-- longer overall service life.

 

That's because you didn't have any oil pressure to make the oil suspended bushing effective.

 

BB also have alot more mass to spin up because of that bearing. Generally a similarly sized BB will not perform as will at the top end because of this.
In my searching I could find nothing about why BB is better other than "I heard form somebody" while I did find alot of sites from professional racers including RX7.com stating they use the oil suspended bushing because it does spool up just as fast. The difference is they use the same turbo for the whole season instead of having to rebuild every couple races.

I didnt mean the page looked like it was made by a professional web page builder or not, I am smart enough to realize that any idiot can have a good looking web page.

 

Agreed. I've heard they also make cool sounds after you shut off the car because it takes awhile for them to spin down to a complete stop.

 

why would you need ball bearing for stock sequential twins??? they spool really fast already and i dont see an advantage... now if you want to run them non-sequential, thats a different story!

 

Q: Why do Turbonetics ceramic ball-bearing turbos only use one ball bearing?

A: Turbonetics created the ceramic ball bearing turbocharger for durability. By utilizing a single, ceramic, angular-contact ball bearing on the compressor side instead of the more common bronze piece, the ball bearing can absorb the thrust loading that all too often can lead to turbo failure in high performance gas applications. The Turbonetics ceramic ball bearing turbo can withstand up to 50 times the thrust load capacity, compared to a conventional floating bearing unit.

*Dual ball bearing turbos can only withstand 2-3 times more thrust loading than standard turbos.

Q: Do the ceramic ball-bearing turbos "spool up" faster than a normal turbo?

A: YES! The ceramic ball-bearing design reduces the frictional loss that occurs with a conventional floating bearing-and-thrust system turbo. The ceramic ball-bearing design allows the turbo to accelerate much quicker, thus decreasing spool-up time. In most cases we have found our ceramic ball-bearing designs require 50 percent less energy to drive the turbo.

http://www.turboneticsinc.com/faq.html#2

You just got done saying you couldn't find any justification for ball bearings but hearsay, and you throw this out as fact? There are thousands people running ball bearing turbos on the street on a daily basis without having to rebuild with any sort of frequency that I've ever heard of.

 

Of course this depends on the specific turbo design, but the overall mass gain from the ball bearing "cartridge" is totally negated by the decrease in drag, especially at high rpm.

Can you explain this? I don't see the correlation...

With all due respect to RX7.com, a very specific application (dragracing) from one very specific website is not the end-all for turbo knowledge.

My statement was not meant to demean you personally, it was only because your post inferred that if you can't find it on the web, then it either must not be true or not exist...

 

They do, especially on all of the turbo-ed bikes I've ridden where the turbo unit itself isn't hidden inside an engine compartment...

 

ball bearing conversion for oem turbos?????

you are re-arranging deck chairs on the Titanic.

yes, they might spool faster. yes, there may be less drag

BUT

the turbos are poorly sized for additional power. at 15 psi they are running 150,000+ rpm and cavitating/superheating the charge air. sure you can major mod the ports and support systems and temporarily make 400 hp but it won't be pretty and it won't last.

in addition to the turbos being poorly sized the manifold ( 22 pounds of cast iron) bolted to the block does it's significant part as to frying the engine.

cast iron retains lots more heat than stainless steel which retains 33% more heat than mild steel. the rotary creates approximately 500 degrees more exhaust heat than a comparable piston engine. somewhere around 1600 degrees.

the manifold can't take the heat:

i'll bet there aren't any remaining oem cast iron manifolds existing that don't have large heat cracks.

the engine can't take the heat:

i believe that more than half of the rotary engine failures are substantially related to the baking effect of the 22 pound cast iron manifold.

engine builders have to love it.

so you heat the 22 pounds of cast iron bolted to an aluminum/mild steel block to a very high temperature and then you turn off your motor. the 22 pounds bakes the block for an hour or more. the mild steel and aluminum block receives the heat.

instead of screwing around w an engine killing turbo system junk it or use it for a boat anchor. bolt on 6 pounds of stainless steel (flangeplates from a single turbo) and spend the additional time and money you will save from not melting your motor at the track.

howard coleman

 

I know I am no turbo expert, I am just stating things I remember finding in a few searches.
The comment about turbo life was not based on just rx7.com. I found similar statements on many web sites belonging to serious racers. rx7.com was the only name I specifically remember. I do remember asking a few years back on the rx7club about the expected life of the M2 turbos and was told it was much shorter than the stockers because of the ball bearing design. It isnt like I am saying in a street application you will have to rebuild it weekly I am just saying you may not get the 100k+ out of a bearing that you will from the bushing. The thing about high end not being as good I admit I have only heard a few times but at least once was from a friend who rebuilds turbos for a living.

The way I understand it is ceramic ball bearings are a relatively new thing that seem to have resolved any shortcomings of the conventional ball bearing turbos. This thread looked to be more about a conventional dual ball bearing vs bushing any ways so I didnt even consider ceramic.

I am done here before I look like any more of a tool for trying to talk about something I dont know much about

 

You can say that again. When we converted my car to non-sequential at about 3,700 miles on the odometer, I already had light cracking evident on the exhaust manifold and wastegate orifice. We eliminated both with porting, but I suspect that when my turbos came off the last engine at ~13,000 miles and were sold to Stephen (SPOAutos) that there was already light cracking present again.

 

Wasn't there some downsides to the ceramic bearings t'netics use?

 

Cost.

 

From a performance point of view is what i meant.

 

I must be one of the lucky ones. I bought a set of Twins not too long ago that reportedly only had 42K miles on them. The Manifold (and Turbos) are in pristine condition. The complete assembly, including the WG/PC Actuators look brand new. Then again, they were pulled from an Auto

 

No offense, but this was the reason I even entered this thread...

 

Turbonetics spin. I would accept 50% less bearing drag torque, which is trivial vs exh driven torque required to quickly accelerate the turbo's inertia, and the torque required to start supplying compressed air at high flow rates, which is part of spool up as I see it.

 

My stock exhaust manifold cracked at 90K and was replaced under the extended factory warranty along with the engine. I now have another 50K on the current engine and stock twins and have done about 40 hours of track time (about 20 track days approx 2 hours track time each). So far no cracks or blown coolant seals. I'm sure it will happen eventually. I use synthetic motor oil... maybe that helps.

Going Single Turbo is tempting but I do still drive the car on the street and there is no way I can pass CA smog with a single turbo.

-John

 

all this talk about the cast iron manifold beingbad gives me an idea.Why not just get a stainless steel manifold made to work with the existing twins? Does the manifold have the wastegate built into it?

 

$$$$$$$ A S/S Manifold that would house the Twins??????
It would probably cost less to convert to Single!

 

Did you not read Howard Colemans post?