Join Date: Jun 2005
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Why the HY turbo was used on 2001 autos.....
A truck with an automatic transmission has to meet soot emissions standards when torque converter slip allows the engine accelerate quickly. This does not usually happen with a manual transmission because for the engine speed to increase, the truck must accelerate - and that takes time. The HY-35 builds boost a little more quickly than the HX-35 does when the engine load is light, so from an emissions standpoint the HY-35 is better suited to stop-and-go driving with an automatic transmission.
FWIW: The HY-35 and HX-35 are functionally equivalent under most engine loads, and the wastegates on both turbos are set for the same boost level. The HY-35 does not breathe as well as the HX-35 at higher speeds under a heavy load. The choke point of the HX35 is around 35psi; the HY35 chokes at about 29psi.