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I think that, the problem with twin turbo upgrades, at least SEQUENTIAL ones, is that everyone has focused on bigger, higher flowing turbos, when the bottleneck is the manifold.
That's why "upgrade" twin turbos never really make much (if any) more peak HP that a really good set of OE 93-95's. In fact, the efini '99's are slightly smaller. It's obvious Mazda chose them for "same" peak power, better spool up, because they likely know that no more peak power was to be made through the log.
I think that's why the M2's were ultimately GT25's, instead of the essentially GT28's that BNR uses. Have BNRs ever consistently made much more power than anything else sequentially? I've not seen that... yet consistently you'll see people say "don't get '99's they aren't an upgrade, get BNRs, they're bigger".
Not looking to start an arguement, just food for though. I don't think it would matter if you bolted twin GT42's onto the stock log, you'd probably make 365-385 peak HP depending on the rest of the system.
What we really need is a proper high-flowing stainless manifold with actuators to run a TT system. Then your GT28's would do something for you.
In terms of the rest of it, the only real other fault were the plastic solonoids and crummy factory computer—both solved with the PFC and saxyman's upgrade solonoids.
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