Turbos

Whilst theres few GTT owners on here this article will be worth a read to those that are not to familiar with the whole turbo thing.

Its also a handy guide for those that want to obtain turbos for their 16V turbo projects.

I will assume you all know what a turbo does and what it looks like, but heres a pic of what it looks like on a GTT manifold anyway





There will be a time when you want a 2nd hand turbo either because the price is great, you want one as a spare, yours has gone pop or simply its bigger and you can't afford to buy a new one.

First thing you do is feel for float on the shaft, using your finger on the shaft the blades should not touch the housing, if it does then its not fit for use. The compressor side is where you feel for this as its normally easier to access.



then look at the blades, as you can see this one has ragged edges, not perfect but not enough to warrent it to be scrapped!

Then inspect the compressor housing for cracks, these rarely crack but it can happen



Next thing is take the exhaust elbow off if its not already removed.

Then remove the clip on the wastegate so you can move the penny valve. The penny valve should rotate with ease, if it does't ask for some wd-40 and try and work it back and forth, if it frees up great if it doesn't then its not worth having apart from spares!

With the elbow off this is what you get



see the crack?



after a quick clean with the wire brush in the drill



thats a decent sized crack, its not terminal, it stills boosts fine but its not going to last another 100k by any chance!

But you can replace the exhaust housing, as you will see later.

If you look closely you can see theres a slightly dented fin on the impellar. Again in this case its not bad enough to warrent the bin, any worse it would.

Do NOT try and straighen bent fins the fatigue then break off, this can kill the turbo, also if its the compressor wheel then it will go into the engine.

See how the head on the shaft has been ground to a funny shape? thats how the assembly is balanced.

Exhaust elbow now, this is normally easy to get another good one of, so if its busted its no issue if the turbo itself is fine.

Heres some pictures of the GTT cast iron elbow, you can see it turns through a pretty tight angle, this is not good for power but its compact enough for its application, the high flow elbows are opened out to make the gasses turn easier



this pic shows the elbow is not a perfect match to the turbo housing, you can grind it back so it is which will give slight gains. See the hole in the middle? thats where cracks can grow, thats a back pressure feed pipe.



where the downpipe mates to, this conical section can wear and blowing is common due to pitting like this one.



The exhaust housing can be removed, its held on in this garret T2's case by 5 13mm bolts. Which actually pass through these split washers



this is the turbo with the exhaust housing removed.



pipes on the left oil feed pipe (very important) on the right oil drain again very important, of you look in the drain the shaft should be shiny.

Top and bottom are the water feed and return pipes

The exhaust housing itself



a slight clean and different angle, theres that crack we saw earlier



see how far its spread?

this is looking up the turbo entry and thats the wastegate hole, you can see the crack that again we saw earlier



this turbo may not be in as new condition but its good enough to be used, a rebuild kit and new exh housing would make it pretty much perfect for another long term of serivce.

Any turbos with damaged cores or impellars should be aavoided, as should damaged exh housings unless you have a good one spare and the rest of the turbo is in top condition.

In this last pic showing the exh manifold exit and the turbo entry, they should be either exactly the same size or the turb entry larger to prevent reversion. This case the turbo entry is actually a slight bit SMALLER so it needs opened out.