failing turbo

Some thoughts on the Garrett T2 series turbochargers and the CA18ET

Facts:
The T2 came on the CA18ET.
The T25 came on the CA18DET and on some VG30ET (300ZX Turbo).
The T25G came on the SR20DET.
These turbos all have the same standard T2-spec manifold mounting flange and O2 housing that connects to the downpipe.

Why a T2 is not good:
The T2 is so small that to make reasonable boost (say, 10 PSI) it has to spin more revolutions than bigger turbos. This means it generates more friction in the air through the compressor wheel. More friction means more heat. Anything more than 7psi on a little T2 is just making heat, because by the time the boosted air gets to the combustion chambers, the crazy heat has re-expanded it. An intercooler would help were it not for the fact that the little T2 can't compensate for a decent-sized intercooler's larger volume. So basically the T2 sucks for anything more than stock.

Why the T25 is a waste of time/money UNLESS YOU WANT TO STAY COMPLETELY STOCK:
The T25 is only marginally larger than the T2. This means it's barely larger. Changing the turbo on a CA18ET is difficult at best, so you'll be doing all that very difficult work and contorting your hands in weird positions just to get a very slightly better turbo that will do maybe 10 psi before making too much heat. There is a better option if you want to tune for some more power on your CA18ET, however the T25 is usually a nice option for those who want to stay completely stock because it is 188% bolt-in, and connects normally to all factory hoses and piping. It offers a bit more heat efficiency so you're getting a bit better of a turbo than stock. If you want more than 10PSI, this is NOT a good option.

Why the T25G is the right choice for most CA18ET engines:
The T25G is a much better revision of the T25. It uses the same exhaust turbine wheel as the T25, but has a notably larger compressor wheel. You can run 12 psi nicely on this, which is 5 psi more than the T2. Depending on what size and core design of intercooler you run, you might be able to get away with more. Some people have pushed 15 psi on a T25G with a medium-sized front mounted intercooler and a WELL tuned fuel system.

FAQ:

Q: What modifications are needed to change to a T25G on a CA18ET?
A: Most T25G's from an SR20DET have flanged output nozzles and inlets. There are companies that sell billet aluminum adapters for both that give you standard ends, allowing you to put your original pipe and intake tube on. The other option is to locate and purchase a standard T25G generic compressor housing that features normal inlet and outlet (non-flanged), although it's probably easier to just run with the adapters. Most people *want* to intercool so really all this is a non-issue for them. Otherwise, the turbocharger should bolt on directly to the CA18ET exhaust manifold, and the O2 housing should bolt to your existing downpipe.

Q: How can I check to see if a T2 series turbocharger is in good working order?
A: Three steps:

Step 1: Wiggle the retaining nut on the compressor wheel. A perfect turbo has NO wiggle, and a decent used one has a VERY little bit of play. If it wiggles a lot, it's bad. Rebuild or replace.

Step 2: If there is a questionable amount of play found in Step 1, try to spin the compressor wheel while pressing the retaining nut to the side; if there is no grinding feel, you are probably okay for stock boost temporarily (file this under "I just want to get the car running for now"). If there is some grinding feel, this is wheel contact with the inside of the inlet on the compressor housing and the turbocharger is bad. Rebuild or replace.

Step 3: Wiggle the shaft end-to-end by pushing/pulling the retaining nuts on the compressor wheel and exhaust turbine wheel. There should be little to no play, same as in Step 1.

Q: Can I use a T28?
A: This is a trick question. T28's came on some S15's and RB20's. The S15's have the same T2-style exhaust flange, although you will need to add a spacer in between your CA18ET manifold in order to allow the much larger compressor housing to clear the #1/2 exhaust manifold runners. You may also need to have a custom or aftermarket O2 housing (the latter of the two is usually easy to find on Ebay) and you may have to modify your downpipe (most exhaust shops can do this for very little money provided you hand them the flanges). You might as well forget stock piping and just intercool to make everything easier. The RB series T28's feature a T3-spec exhaust flange and are NOT compatible with your stock manifold in any way. Also, some T28's feature steel compressor wheels; these can be taken to much higher boost levels. Other T28's feature ceramic wheels and cannot boost beyond 18psi without breaking the compressor wheel. There is information on the internet as to how to determine which wheel it has based on the numbers and letters cast into the compressor housing.

BattleFairy on 09:25:15 AM / 03-Jan-13sorry arro but rb25 comes with a true t3 while the rb20 is the one that came with a bastard t28

i can check if you want.......have the rb25 t3 here

Thanks, information corrected!

Arsenalfc on 08:52:18 AM / 03-Jan-13Very grateful for the information, I have no experience with S12's or turbo charged cars what so ever.  I really like the car, any good ideas where I can purchase a rebuilt T25g turbo?  I've checked ebay but was curious as to where in Central Valley California I could get one.   Thanks again.

First off, you mention you're in the central valley... do us a favor and add your location information in your profile.

I got my turbos from Ebay. Yes, they aren't always on there. But patience will prove worth it. Ebay has the best prices. There's some gamble but it happens. Otherwise you'll have to buy from Craigslist locally to you. Which is not a bad idea either because you can go and see the part directly.

If you get a bad turbo, you can have a company like Turbo City rebuild it for cheap. Or have one of the guys on here do it for you.

If you're new to turbocharging, there are some basic things you will need to know... but for now just don't turn up the boost without first installing gauges, new plugs & wires, and a better fuel pump (Walbro 190).