FUCK I hate the new FEOA boards....they keep loosing everything I write and everytime I type something new it gives me a "I need to wait 30 seconds" So now I have to retype 15 mins of writing again.
Okay, let me restate the quote:
I said, I had a roommate that had a 99 Civic EX (D16Y8) = 1.6L VTEC. He had a T3/T4 hybrid and because he was only a 1.6L it didn´t really spool till his VTEC kicked in.
Okay, now I need to remember how I said what the last time I posted.
Okay the T3 is a meaurement size, not a specific turbo. Many companies ripped off this sizing method from Garrett. And they actually make different ´sizes´ of T3´s. The housing is the same size but the A/R ratios are different. The tighter an A/R ratio the faster you can spool, however it will limit the amount of boost you can produce.
The VJ20 is technically an RHB5 VJ20. The RHB5 family is the most popular family of turbo´s for IHI (Warner-Ishi). RHB5´s have been used in everything from Scooby´s to Isuzu Impulses. The VJ20 part is the specific turbo, like a sub-measurement of the T3. The VJ20 is a 52mm compressor housing and I´ve heard they can produce up to 20psi on a spike, but I´m guessing they wont hold much over 17psi. That might be hoping for a little much too.
Anyhow, IHI´s are known for spooling quickly because their A/R ratios are really tight. I believe the VJ20 is almost equal to a T3 with a .40 A/R ratio (smaller T3).
However if you compare across the board...even though the VJ20 is slightly bigger then a 14G in a DSM (14G is pretty close in size to a T28 which is technically smaller then a VJ20) I believe the 14G will actually produce up to 22psi on a spike. This is all because of the slight differences in the design of the turbos.
Here´s where I´ll try to answer you question specifically: Because the VJ20 is made by IHI their flanges on the turbos are radically different from the T3´s made by other companies. If you have a VJ20 you can use the manifold from the 323GTX if you get a T3 the size of the turbo will be close, however you´ll have to have an exhaust manifold made with a custom flange for that turbo.
On another informational note: the 323GTR used an RHB5 VJ23 turbo. The VJ23 is 60mm (8mm larger then the VJ20) and has a ballbearing cartridge, so it produces close to 2BAR of boost and can hold the peak boost through out your rev range. :-]