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Tech - Which Heads are Which? Identifying 3S DOHC Heads

Identifying 3000GT / Stealth DOHC Heads
Which are Which?

This is an article describing how to quickly identify the heads on a DOHC 3000GT or Stealth and discuss their interchangeability.

Each engine runs the SAME head on both banks, they are just turned 180-degrees from each other so the intake ports are towards the center and the exhaust ports are toward the outside of the engine. Within the same engine, there is no difference between the front/right bank head and the left/rear bank head other than orientation and parts attached.

There are basically 4 different heads on the DOHC 6G72 engine used in the 1991-1999 3000GT and 1991-1996 Stealth:

1991-1992 DOHC Twin Turbo (TT)
1993-1999 DOHC Twin Turbo (TT)
1991-1992 DOHC Non-Turbo (NA)
1993-1999 DOHC Non-Turbo (NA)

1991-1992 heads are referred to as "first gen" heads, while 93-99 heads are referred to as "second gen" heads.

The heads are directly "backward compatible": The 93-99 heads will directly work on the 91-92 engines without any modifications.

The heads are "forward compatible" with light modification: The 91-92 heads will work on 93-99 engines, but you will need the 91-92 CAS (cam/crank angle sensor) and rewire the 93-99 can and crank signal wires to feed from the 91-92 sensor (it actually outputs BOTH signals).

The Twin Turbo and Non-Turbo heads are directly interchangeable. There are intake and exhaust port variations, but they mount to the engine the same, have all the same water/oil galleys, use same valves, accept same cams, etc.

So Which are Which?

To quickly identify the application for a 3000GT/Stealth DOHC head, look at the end of the head such that the intake ports (studs angled up) are on the left and the exhaust ports (studs straight out) are on the right (as pictured below).

The TT and NA heads are easy to tell apart:
The TT heads have a "3-T" marking.
The NA heads have a "3-N" marking.

The 1st Gen and 2nd Gen heads are easy to tell apart:
1st Gen heads have the above markings on the exhaust side
2nd Gen heads have the markings on the intake side
2nd Gen heads have two extra bolt holes (circled below) for mounting the cam angle sensor

ALL PICTURES
<== Intake ports with studs angled up | Exhaust ports with studs angled out ==>

91-92 NA Head with "3-N" on exhaust side of center water port

91-92 TT Head with "3-T" on exhaust side of center water port

93-99 NA Head - "3-N" with 2 bolt holes for Cam Sensor

93-99 TT Head - "3-T" with 2 bolt holes for Cam Sensor