those Evo turbos are actually pretty good stuff ..
the new model Evo X have 47mm / 68mm compressor wheel and the same 49,1mm / 56mm turbine wheel, as the older ones, and making around +100hp more atwhp, when tuned.
its not all about the wheel size, or that its having only 295hp ( evo x ) standard.
another one : evo 6.5 TME = those oldes evos have a little bigger compressor wheel ( 48,2mm ) and those are also making around 400hp flywheel, around 1.5bar boost. same power cabable also evo 8, 9 , ( just use the 10.5 housing )
evo X have 12 housing )
even with the "very old" evo 3 16g turbo could go there ( but with big exhaust pressure )
evo X spools 20psi at 3000rpm and make +400hp, sounds good ?
best turbo from X is the one with titanium turbine wheel.
also you can find that turbine wheel with older models, but I´m not gonna lists all those here, it reads on the turbo model name as A ( TDo5HRA example )
if I was gonna chance my turbo now, evo X could be my choice...
still I want to talk about wheel size
lets take the "new" holset turbo here ...
model : HE221W with billet compressor wheel..
compressor wheel : 43mm
turbine wheel : 45mm
with those specs, you could think, that ok.. its very small turbo, right ?
and its not making any real power on our cars ..
well, the wheel is not all about the size .
here is results with opel 2.0 16v engine using this turbo and 98e octane fuel:
575nm 4760rpm
peakpower 312kW 5700 / 0.93bar.
400nm 3000rpm.
results can be found here :
http://www.turbotec.com/kilpaautot/bmwrox.htmltheres older results and new ones, turbo spools good too,
1bar at 2750rpm.
and theres couple fotos of the turbo also.
if thinking something very fast spooling turbo, then I would take perhaps Evo X turbo, and if its possible, using there billet middle section with those 200% lighter balls, than normal ball bearing turbo has... now that could be the real superspool
text can be found for those, here:
http://www.billetturbochargers.com/About_Billet.ewsmaybe theres even more better spooling turbos, that are making more power with smaller wheels, but I just wanted to say, that its not just were the turbo have been standard, or whats the wheel size.