what makes a T?? turbo.?

[raj]

just wondering if someone could explain what makes a t2 turbo a t2 turbo? and when is a turbo called a full t25? and when does it become a t25/t28 hybrid? and the same with full t28?

also what is the size of the std t2 turbo on the gtt.? comp/ex.?

are all t25's/t28's the same size? or do they have different comp/ex sizes.? if so can someone give some sizes?

sorry if the questions sound daft

[Scoff]

Think of T2, T25 and T3 being different families, that differ in size and construction, with each family having a lot of members, or sub-sizes.

Each family has a range of different sized compressor wheels, turbine wheels and A/R housings, but each family, regardless of it's wheels and housing have the same core and shaft dimensions as any other turbo in its family (T2, T25, T3).

In other words you can take any T2 component and fit it to any other T2 turbo. T25 components will bolt into any other T25, and so on. But, you can't bolt T2 bits onto a T25 core, or T25 bits onto a T3 core, without machining stuff up to make it work.

T28 is a hybrid, it uses bits from T3 and T25 families. Namely T3 compressor bolted to a T25 core and T25 turbine. Not all T28's are the same, as above, there are lots of different sized T3 wheels that could be used, and different sized T25 turbines. Most of the better GTT units are 60trim T3 in 0.42ar, with T25 0.49ar turbine.

[raj]

thanks for that scoff that explains it

also, do you happen to know the size of a std gtt t2 unit?

[THE MASTER]

scoff your post makes perfick sence to me

[raj]

so, anyone? whats the size of a std t2 unit fitted to the 5.? ex?/comp?

id also like to know what size t25 is most commonly used on the 5s aswell as the t28.?

also is it the compressor side that is always bigger than the turbine side?
is it the smaller the turbine wheel,the less lag there is.?

[raj]

so, anyone? whats the size of a std t2 unit fitted to the 5.? ex?/comp?

id also like to know what size t25 is most commonly used on the 5s aswell as the t28.?

also is it the compressor side that is always bigger than the turbine side?
is it the smaller the turbine wheel,the less lag there is.?

would i be correct in thinking a turbo with a comp/0.48 ex/0.64 be a t25? how would this unit perform with a std cam?

[bye_all_c_ya]

mine was a garrett m27 ar 0.48 front and 0.47 rear ? what does that mean and is a larger rear better or small better ?

[raj]

i dont think many folk are clued up when it comes to turbo tech questions

wheres adam L when you need him!

[Andrew Cooke]

fundamentally the difference is the OD of the wheels

T2 ~48mm
T25 ~52-54mm
T3 ~60mm

so measure your wheels and know the answer, but then if you read this:

http://www.turbobygarrett.com/turbob...o_tech101.html
http://www.turbobygarrett.com/turbob...o_tech102.html
http://www.turbobygarrett.com/turbob...o_tech103.html

you'll understand the basics

[bye_all_c_ya]

so would garrett m27 with ar 0.48 front and ar 0.47 rear be a t2? or a t25 as ive always thought it was a t25?

[raj]

is there any size difference between the t25's fitted to 200sx turbos and the t25's that are fitted to saabs?

the reason i ask is that im just wondering if you can swap the turbine housing over from one another? as the 200sx one seem abit easier to fit compared to the saabs.

[raj]

also,

i think im going to rebuild one of my spare t2 turbos, could someone give me a clue on which rebuild kit i would need? what i mean is there are 2 types available i think! 1 being a dynamic seal? and the other being a carbon seal? id also like to throw a 360bearing in the mix too. pls advise

[bye_all_c_ya]

when you strip the turbo you will have a solid plate ( dynamic )
or a plate with carbon on it you will now when you see it

go to the bottom of this page
http://cgi.ebay.co.uk/Garrett-T2-T25...A1%7C294%3A200

[Scoff]

also,

i think im going to rebuild one of my spare t2 turbos, could someone give me a clue on which rebuild kit i would need? what i mean is there are 2 types available i think! 1 being a dynamic seal? and the other being a carbon seal? id also like to throw a 360bearing in the mix too. pls advise

If it smokes currently, don't bother trying to rebuild it, leave it to the pro's! smoking can be because things are scored from contamination, something a rebuild kit won't solve. Been there, got the T shirt!!

[raj]

If it smokes currently, don't bother trying to rebuild it, leave it to the pro's! smoking can be because things are scored from contamination, something a rebuild kit won't solve. Been there, got the T shirt!!

thanks for the heads up on that

the t2 unit i want to rebuild,if i remember right did not smoke, the problem with it was it was leaking oil. i cannot exactly remember from which area but oil dripping from the turbine to downpipe join rings a bell.!

at the end of the day, when i strip the unit down and find any scoring i'll know not to even bother rebuilding it

[Adam L]

All the above info is pretty well described, I can't add much to it. The Garrett website actually gives out all the info you need to know about turbochargers, which Andy posted above.

The biggest problem with taking apart a turbo is you really need to know what you're looking for. The wear can be so fine that if you've not done it before the chance is you may overlook it. For instance, if the thrust bearing has visible wear on it you may think a new one will solve your problem. It's not the case. The thrust bearing, collar, collar ring, ali backplate will all need replacing and the ring land on the turbine side of the shaft will need machining for an oversized ring.

The other thing i've seen before is when people say there turbo's are OK and send them in for a rebuild, even when they've taken them apart is the bearing surfaces are severely scored, so badly infact that the wheels have come in contact with the outer housing making them scrap. Shafts are re-grindable though, but the most that's allowed is 10thou from the standard bearing size, and bearing houses are allowed to be honed for oversized bearing, but again, the same tolerance is allowed.

[Scoff]

Good info adam, I wouldn't pretend to have known any of that

I always cringe a bit when I see people trying to diy rebuild a smoker or hugely worn thing, I know it rarely works out. As a general rule the only time I've had success rebuilding them myself is when the unit isn't scored from contamination and/or the wear isn't so bad to have buggerd other stuff up, IE the turbo is still usable but has a little bit of play, etc.

[tiff_lee]

Good info adam, I wouldn't pretend to have known any of that

I always cringe a bit when I see people trying to diy rebuild a smoker or hugely worn thing, I know it rarely works out. As a general rule the only time I've had success rebuilding them myself is when the unit isn't scored from contamination and/or the wear isn't so bad to have buggerd other stuff up, IE the turbo is still usable but has a little bit of play, etc.

So would it be fair to say rebuild kits are really only effective as preventative maintenance before a turbo starts to show significant signs of wear rather than being able to 'rebuild' a completely knackered turbo?

[Scoff]

tiff, yeah, thats fair to say, in my experience atleast.

[raj]

So would it be fair to say rebuild kits are really only effective as preventative maintenance before a turbo starts to show significant signs of wear rather than being able to 'rebuild' a completely knackered turbo?

in a way yes.

but the thing is,usually by the time you "notice" a problem with a turbo unit its more than likely too late anyway.

im now thinking these rebuild kits are abit of hit n' miss.! are they worth it? probably not. however i will strip my unit down and checking for wear before purchasing a kit.

[raj]

on the off chance, does anyone know if the rover t25 turbo unit has a dynamic or carbon seal.? im thinking carbon seal due to them being pretty old units?