I'm running a .81 T4 hotside at the moment. Frank, the thing is the 40r .85 hotside is a twin scroll, so that will aid spool a bit. Also, from what I understand there are some internal differences (other than the twin scroll setup) that make the .85 GT housing different from a regular .81 T4 housing. Since the 40r comes with the hotside, I might as well use it. Ultimately I'd like to break ~600whp. Judging by what I've seen, for that size of compressor/turbine, a .68 housing is going to be pretty restrictive around the 600whp level, and I'd like to accomplish that without running too much boost. A gt40r is similar in size to a T4 T66, so it's not really that large of a turbo for a 3.4l. It would make reaching 600whp much easier and I'd be able to accomplish it at lower boost while still not being that laggy.
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