This was originally posted by ARRO the rest of this thread can be found here (http://www.club-s12.org/forum/viewtopic.php?t=2027)
OOOOOOOOOOOOOOOK
Lemme break it down for everyone.
Turbos that will bolt directly on to your stock manifold and piping:
Garrett T2 (also known as AiResearch M10) - Stock turbo is a T2. Once you go above 10psi you are starting to get too hot. Some guys have pushed it to 15psi but I bet it's barbequing.
Garrett T25 - T25 is a direct bolt-on EXCEPT for a T25 taken off of a 2G DSM (Eclipse and Talon turbo), because the DSM uses a custom Mitsubishi exhaust housing with the wrong flange. Our manifold uses a standard Garrett T2-style flange, so any other car's T25 with a standard flange will fit. Some Z31 300ZX's have T25's (I think 86-88?), some of them have T3. The Z31's with the T25's will bolt right on without any changes. T25 can take you to 15 psi before it starts to get too hot, so I'd say it gives you about 5 psi more potential over your stock T2.
Garrett T28 - T28 is larger than T25, much larger. T28 is only available on some Skylines and I think maybe some JDM S15 Silvias (not sure though), but the way most people get one is from a turbo build vendor who takes a T2 or T25 core and rebuilds it into T28 specs. Should flow for about 20 psi before too hot, 5 more above T25 and 10 above T2. Should also be able to use standard T2-style exhaust housing as far as manifold flange goes, but will posess a larger turbine wheel.
Forced Performance FP-Big28 - The FP-Big28 flows more than the T28. Forced Performance has secret specs for their compressor wheel and turbine wheel, which they tell us are both larger and more efficient than the standard T28 internals. They say it won't have any more noticable lag than a standard T28, but will definitely outflow it. Expect around 25psi worth of efficiency, which is 15psi more than the stock T2's efficiency (more than double). To make this they take a stock T2 or T25 core and rebuild/rework it for around $750. In the world of turbochargers, this is an extremely good price, both because it is a 100% bolt-on solution requiring no physical modifications to install, and for the claimed results. Forced Performance says they have the performance data to back it up. They have been building some crazy high-potential turbochargers for some time, and are a major force in DSM and other turbocar communities.
Turbos that will NOT bolt directly on and require modification:
Garrett/AiResearch T3 - Alot of people like these for a number of reasons. T3 can flow good amounts of air, has a large variety of compressors and turbines and housings both exhaust and compressor side. You can even get them built with heavy duty shafts which are stronger and thicker than stock T3 shafts. 360-degree thrust bearings are available. durability and reliability are one of the best you can get. A wide variety of accesories like bare flanges for custom weld jobs and a plethora of oil and water fitting options make these very desirable turbochargers. It also helps that these are probably the most available turbochargers you can find, as they are used on a wide variety of cars. They WILL however not be bolt-on for a turbo S12. You can either have a custom tubular manifold made with a standard Garrett T3 flange, or you can weld on a T3 flange over the T2 flange of the stock exhaust manfold. This is quicker and easiest, and also will give the turbo's larger compressor housing a quarter of an inch or so extra clearance underneath the exhaust runners. T3 swingvalve assemblies are available that let you weld on tubular downpipes to house your O2 sensor and route directly to where your stock downpipe starts. Water and oil lines will have to be custom, but you can use AN-style fittings as they are also widely available for T3 fitting sizes. There are even braidd line kits available for T3 turbochargers.
Switzer turbochargers - I am told that there are some smaller Switzer turbochargers that are comparable to T3 turbo size that have been successfully used on CA18ET engines in Europe. However, I have no information on these turbochargers at this time. I recommend T3 instead as there is much more part and technical support for the Garrett turbochargers.
Turbos that are WAY too big for CA18ET and CA20ET (hybrid) engines:
T3/T4 Hyrbid - The T3/T4 is way to big on the compressor side. All levels of T4 compressor wheel trim are too big. T4 is for people looking to go past 25psi while maintaining cold, dense air charge. I do not see a CA18ET or CA20ET hybrid engine handling upwards of 30psi. Sure, a T4 compressor can be held at 20 psi, but it's no more efficient there than a T3 or an FP-Big-28. So instead it becomes a collosal waste of money, since these usually run $1,000 USD or more depending on configuration. It will also have alot of lag. DON'T WASTE YOUR MONEY!
Full T4 - Full T4 is for 18-wheelers... for diesel rigs pulling trailers with their fifth wheel. OR for hard-core drag race engines, built from the ground up, with redesigned engine blocks, lots of custom internal parts (some you could also order, some you cannot so easilly obtain no mater what). Not for our cars. Our cars will never be drag queens. Our cars are more road course imspired, as was popular with 80's Japanese and European sport vehicle manufacturers. Besides, T3 or FP-Big28 will be able to yield excellent dragstrip times on their own in our cars.
Hope this info helps.
Of course, with any turbocharged engine, the more air and boost you flow, the higher the fuel requirements, so any resonable improvement in turbo will likely require you to upgrade your fuel system in some fashion.
I decided to post it here becuase we seem to be getting alot of turbo questions lately If we could sticky this like it was in the other forum it would be nice
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