My 4.1 (.040" over) Stage I engine has GN1 heads, Erson 214/214 cam flat tappet, V2 intercooler, and 84# injectors. I've tried 3 different turbo's over the past 1 1/2 years. A PT51, TE62, and PT70-1 (old style 68mm).
PT51, power done at 5000-5100rpm, 1/4 mph 115, no more power after 22psi...