Bruce, according to Todd of Protomotive, a GT2 EVO cam works great on everything they've put it in so far. Only the idle is mildly annoying (tunable via the Motec I guess), but it makes more torque and power than anything else they've run on the street. Otherwise, a 20/21 is like going from a 3.2 to a 964, but up from there, almost .500" lift a little more duration, really steep ramps for more top end, but it needs really good valve springs.
HP increase is between 15-20HP, BUT boost response and torque increase is the main reason to go for them. Apparently peak torque comes in much earlier
Hope this extra info helps
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Merv
'89 911 Turbo Cab
Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition
