Z1 is a good tuning shop, that's part of what makes this all up in the air. The results with proper tuning have been mixed depending on the car, the mods, who did the tuning, etc. The only definite thing seems to be that you'll get some good midrange gains on a factory tune.
The whole thing is kind of frustrating to understand. If longer intake runners produce more midrange torque (which makes general sense), they should continue to do so with proper tuning as well. Based on my dyno runs with the M370 on+off the car over two days, the M370 does seem to also lean out the engine slightly though, so that's something to be accounted for one way or the other.
It's possible that either the tune needs to be adjusted to keep things sufficiently rich in order to realize tuned gains with the M370, or the M370's un-tuned gains are all from just running leaner rather than "true" gains in breathing configuration.
Results like the ones from Mike (tuned at Z1) would seem to indicate the latter. But then again my stupid canned uprev tune basically did nothing but lean out the engine, and I saw basically zero gain from that on the stock manifold (and a very slight loss w/ the M370), so it doesn't seem like our cars respond well to being leaned out in the first place.
Personally, my jury's out on this until I get it tuned on my car (still waiting for LTHs to come in first).
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