Now if the thought was not already in your head, it should have been. Where am I going to find a turbo with that bolt pattern on the exhaust housing? Well, on a 280ZX Turbo or 300ZX turbo. I believe a few other cars used them too, but none of them with any stock turbochargers larger than the T3. You (essentially) have two options here:
1. Use a turbo with a 4 or 5 bolt exhaust/turbine housing, buy a flange and make a custom downpipe with an O2 sensor bung in it. Also, install an external waste-gate.
2. Swap the stock Nissan T3 exhaust/turbine housing onto the new turbo and use the stock O2 elbow and downpipe configuration.
Without a doubt, option 1 is better in terms of maximum power potential; however it is also more expensive and much more labor intensive. I went with option number two, take a look at the stock T3 compared to the T3/T04E I bought on ebay (yup, I'm THAT cheap).
T3/T04E w/ stage 3, 57 trim, .50 a/r comp .63 a/r exhaust, $399 and it was DOA!!! Read on for more information!
Notice this unit I purchased does not have a water cooled center section, this is common in "aftermarket" hybrid turbourboshargers because the water cooled T3 center sections are slightly more expensive. In addition, many people making custom turbo setups do not wish to incorporate water lines. Also note that the stock T3 exhaust housing actually has a BIGGER waste-gate port than the Turbonetics stage 3 unit. This turbo also has a stage 3 exhaust turbine wheel. This is substantially larger than the stock (or stage 1) part, and you will need to find a place to have the exhaust stock housing bored out for the larger wheel. You can sell the stage 3 housing that came with the turbo since you won't be needing it; they usually go for $80-120 on Ebay (yet they are almost $200 new from Turbonetics). If you can't find anyone locally to bore the stock exhaust housing, you can send it to Turbonetics, Inc and have them do it for you. Don't expect them to be quick about it; from the day I sent mine in it was well over 3 weeks before I got it back. The charge for this process is $100, with UPS shipping both ways my total came to just over $128 for me.
Stock Nissan housing bored for stage 3 wheel vs. Turbonetics stage 3 housing:
Stock exhaust housing and turbine wheel vs stage 3:
I also took the time to enlarge the waste-gate port. Notice that (oddly enough) in the picture three above; the stock Nissan waste-gate port is already bigger than the port on the Turbonetics "stage 3" exhaust housing. I find this odd, to say the least. I ported out the stock housing's hole to ~3MM smaller than the flapper that fits over it, then carefully smoothed all the metal around the hole entrance for good airflow. The problem with internal T3 waste-gates tends to be boost creep, the amount of air coming through the housing cannot be adequately diverted by the waste-gate and the turbine "over-spins" causing excess boost in the top end. Porting and smoothing the hole slightly should at least help to eliminate over-boosting situations.
The exhaust elbow will also have to be ported larger, this should be done with a die grinder on account of the cast iron being so hard. I did not have a die grinder at the time, so I used a dremel with two #8193 Grinding Stones. The work took over 2 hours to complete, so I would suggest finding a die grinder. While I was at it I removed the ring on the inside where the stock downpipe slides in, since I have a Certified Muffler aftermarket downpipe that does not need that ring to be there. I'm sure it flows slightly better with this part removed and the metal around it smoothed out.
Exhaust elbow:
Turbo side:
Downpipe side:
View through exhaust housing into elbow:
Now the turbo is to be assembled. This is pretty straight forward; but I would suggest using a very small amount of anti-seize lubricant on the bolts (and two nuts) between the exhaust housing and elbow.
The newly assembled turbocharger assembly:
This turbo is complete garbage! DO NOT even think about buying one of these on ebay, you could end up getting screwed like I did. They are all over the place with cheapass names like XS-Power, superpower, etc etc. Usually selling between $350 and $450 and featuring auctions that contain no real information about the product, these turbos are cheap knockoffs of the actual thing. The supposed "stage 3 turbine" they included with it was the right bore size, but was absolutely not a REAL garrett stage 3 turbine. The seat for the compressor wheel was machined incorrectly, causing this brand new turbo to hammer the compressor wheel into the housing, sending shards of aluminum into my intercooler piping. I ended up with a wrecked turbo and a bunch of pipes to clean out, but considering what happened I was actually lucky. The seller refused to answer my e-mails and it was just out of the time period that PayPal can take action. DO NOT BUY ONE OF THESE TURBOS; YOU HAVE BEEN WARNED!
After my jets cooled, I sent an old stock T3 turbo off as a core to be rebuilt and upgraded. Joel at AZ Turbo and Tractor Supply did the job for me at a very fair price. They specialize in trucks and farm equipment turbos, but can do just about anything turbo related, and well. He rebuilt the stock T3 center section, used a garrett stage 3 turbine and t04S (AKA 60-1) compressor:
The eBay turbo's "stage 3" turbine wheel (left) vs a Garrett turbine wheel (right):
Now a waste-gate actuator is needed. You can find a way to mount and use the stock actuator, but keep in mind it will not be as good at controlling higher-boost as one with a bigger diaphragm and stronger spring (or so I hear). I used my stock actuator because I was unable to find an inexpensive and appropriate unit. I simply used a piece of angle steel and drilled some holes in it to mount to both the compressor housing and the stock actuator. Then I added a couple small throttle return springs to assist the actuator in controlling higher boost pressures. The stock actuator is now able to hold 20+PSI very stable with the help of an electronic boost controller. As far as where the boost signal line comes from; it's up to you. Most people take boost signal directly off the compressor housing, but this can sometimes give you inaccurate readings due to the pressure drop through the intercooler (if you have one). I took my reading off the intake plenum (hooked in by the fuel pressure regulator), to read how much boost the engine itself is actually getting.
The turbocharger assembly, once assembled, needs to be "clocked" for your engine. Clocking is simply rotating the housings and center section until they are the right orientation for your engine. This is MUCH easier to do with the engine out of the car, changing the turbo is a cake-walk with the engine out.
Oh no, you are not completely done yet. Chances are your turbo has a 3" inlet as opposed to the stock T3's 2". Well this won't work with the stock S-pipe, will it? Yes, it can actually. You can creatively get the S pipe to fit over the 3" inlet, but keep in mind that part is a major intake restriction and is going to be more of one now that you will be pulling much more air through it. One solution is the Cobra Head and a tight 90 degree, 3" exhaust bend (or silicone bend, whatever; as long as it is 3"). Then you'll have to get a little creative mounting the airflow meter, but that's easy.
Another Solution is the "Ken In AZ" style intake/engine mount, which I copied with great success.
Ken's setup:
My setup (4" inlet required a 4"-3" reducer):
And there you have it. Total costs associated with upgrading the turbo: