It's got a Garrett GT28-76 on it.
I haven't looked at the compressor maps for that turbo since it was put on about 12 months ago. From memory though, that's about as much as it will make. Seeing as the turbo is rated at 440hp and IF the engine made 100% volumetric efficiency(4A = 100ci = 100hp) it should make 540-550hp MAX.
The engine itself isn't anything super special either. STD GZE block and bigport head, custom forged pistons, spool conrods, cometic MLS head gasket, arp head and main studs and stupidly huge cams(only specs I was able to get was the 312deg duration). I was fairly reluctant to fit the cams, but that's what the owner had and wanted fitted, they do seem to work quite well though.
We have been thinking it might be the most powerful 98 premium fuel 4A in AUS. But not too sure.