Spool up: BB v plain bearing

[NXTIME]

I realise that I may be opening a can of worms here, but I have found different stories regarding the perceived improved spool up that a BB turbo provides over a plain bearing.

How much is the actual difference in this much-toted benefit of BB turbos? Obviously it would have to be a comparison between two similar, if not the same, sized turbos, with one being BB and the other plain bearing (all other things being equal).

I am mainly concerned with larger turbos, such as GT30 and up, but feel free to give any real world comparisions from your experience and knowledge :)

[badbiki]

spool time, turbine rpm increase (more boost for same size dimension wise wheels)..

a "320hp" gt25 will have the same spool time as a t25 off the ca18 basicaly.. bigger unit with same spool time due to BB =)

gt30's start at a rating of 480hp... they WILL be laggy in comparison to the t25 or gt25 =) like 1,000rpm+ difference.. expect full boost by 4K =) thats what i'm hoping anyway.. as thats what i'm going =P

[6BOOST]

Despite what anyone says, there is very little difference in spool time due to the ball bearings, maybe 2-300rpm at an absolute max, the only reason ball bearing turbos have been tunted as being able to spool quicker is often misunderstood as the bearins, not the actual wheel designs. Think about it, ball bearing turbo's, at least in the main streem are all relatively new in design, most 10-12yrs, where as plain bearing turbo's wheel designs were mostlt designed about 25-30 yrs ago.

The next benifit, is part the reason they can have smaller wheels is the fact that ball bearing turbos can tolerate higher load and higher shaft speed, and can turn at MUCH higher rpm than an old design plain bearing turbo, giving higherf olw rates from the given comp wheel/exhaust wheel, the other reason is teh fact that with fluid dynamics and computer modeling, they can completely build and test a comp wheel on computer, without ever having to actually make it.

6BOOST:)

[CnC]

If what you say is correct and they were designed 10-12 years ago im not sure their computer modelling abilities would be anywhere near as good as they are now.

I would suggest that If they redesigned them today they would probably be even better still considering all the advances in technology of late.

I cant wait to see a really well designed turbo coupled with the new electric assist technologies.. should be very interesting :)

[6BOOST]

For sure, I stated 10-12 years, as some ball bearing turbos have been around for that long, IE R33 skyline maybe even R32?? etc, and I though I would cover all bases and save someone bringing it up. Even newer is the garrett range, which have been the last 6 years or so, and some in the last 2-3 years, such as the 800hp ball bearing;) I have not heard of electric assist, please point me in the right direction to finding some info:D

6BOOST:)

[Warpspeed]

Spot on 6BOOST.

The modern turbos are the product of recent developments in computer CAD/CAM simulation. The wheel design, blade shape, and inertia reduction, is light years ahead of the thirty year old clunkers.

Another thing is that the exhaust turbines are generally better matched for speed and energy to the compressors these days. Todays compressors also have a wider flow range, and higher peak efficiency as well.

It is a whole lot of things, not just a few steel balls.

[timmeh]

im an aircraft engineer, and i work on what are essentially, HUGE turbos :P, a gas turbine engine. you can definately see the different build philosphies between the new engines, and old engines, the fan blades are different shapes and the blade tip clearances are much more refined...

wait till u see a GE90 up close, and the fan blades(1st stage compressor) are 1.5m long each.. 110,000lbs of thrust there

[Warpspeed]

Fascinating stuff timmeh. Are any of the modern commercial gas turbines using hollow air cooled exhaust turbine blades these days ?

I know the high pressure ratio military jets were using these about ten years ago. I was involved in the design of a high power industrial laser drill used to drill the tiny holes in the blades.

[timmeh]

yeah all of the turbine blades(and turbine stator vanes) have cooling holes through them, they need them, they keep a lower temp boundary layer of air over the blade even though it is operating at a temperature higher the the burning point of what theyre made out of (titanium alloys usually), coz as we all know, the higher the temp, the more power you can extract out of it.

[Warpspeed]

I thought by now the military technology might have filtered through to the commercial stuff. I remember looking down some of those holes with a microscope, and thinking that not a whole lot of air is going to flow down a one hundred micron diameter hole, but it does.

We used to blast those holes with a two megawatt peak pulse laser, I designed the power supply for the infrared laser.

[QIK78U]

Well, Im not to fussed over the high prices that you have to pay for a BB turbo, I have a "OLD SCHOOL" T04b on my rotor and it takes stuff all to spool up and even after the car has been switched off it keeps on going , going, going ........

It was built buy someone that knows what they are doing when setting a turbo up for a car....

I have also heard cost wise getting a BB turbo re-built is enough to make you cry...