So im finally back on my engine build, 4jb1t, original plan was to switch over to a garrett turbo but wasnt going to be 100% happy with it, so started researching other IHI turbos.
The biggest complaint ive seen is boost dropping off after 3,000rpm and this is why. The stock turbo has a 35mm x 47mm compressor wheel (intake wheel), after 3,000 rpms it goes into what is known as choke. This is a condition in which the engine needs more air than what the wheel can produce. All the other 2.8’s ive built turbos for have atleast a 39mm x 56mm wheel, and that begins to choke also, but not as bad. The best i have found to work is a 41.5 x 56 wheel. I know one person on here has swapped the wheel and housing from another turbo, but being honest, the exhaust wheel is too small for any performance as well.
So i went on a hunt and found an IHI rhf5 vf38 off a subaru legacy gt. Features ball bearings, titanium exhaust wheel/shaft, and twin scroll housing. The inlet flange is for the subie so it will take some fab work to get it down to a t25 pattern i already have on my manifold. Found a 42mm wheel of an isuzu rhf55 turbo that i will use for the induction part. Ill keep this updated as i build, but from my turbo building experience, this should be exactly what these 2.8’s need, with room for more power.