Mitsubishi 6G72 DOHC Timing Events

by Jeff Lucius
Cylinder numbering and arrangement
The 6G72 is a DOHC 24-valve 60 V6 gasoline engine that displaces 2.972 liters. The cylinders are arranged and numbered as shown below.
Mitsubishi 6G72 cylinder numbers

Ignition Timing
The firing order is 1-2-3-4-5-6, with each numerically-successive cylinder reaching top dead center (TDC) 120 crankshaft degrees after the previous one. Paired cylinders have pistons at the same relative position, such as both at TDC, but they are 360 out of phase, such as one is in the exhaust stroke and the other is in the compression stroke. Paired cylinders are 1-4, 2-5, and 3-6. Spark plugs are fired simultaneously in paired cylinders, during the compression stroke for one cylinder and during the exhaust stroke for the other cylinder. The spark during the exhaust stroke is wasted because the basically inert exhaust gas cannot combust.
Mitsubishi 6G72 ignition events

Sequential Fuel Injection Timing
It is not clear from the available references (listed below) exactly when the fuel injection activation signal begins. The pattern Mitsubishi uses in other engines is to use the either the begining or the end of the crank angle sensor (CAS) signal of one cylinder to activate the injector of another cylinder. The CAS signal is 50 "long" and starts at 5 before top dead center (BTDC) and ends at 45 after top dead center (ATDC) at the start of the combustion stroke. For the 6G72 this means that the start of the CAS signal for cylinder No. 1 probably activates the injector for cylinder No. 5 during the exhaust stroke (see the figure below); and cylinder No. 2 activates cylinder No. 6, and so on. On the other hand, it is possible that the end of the CAS signal for cylinder No. 1 activates the injector for cylinder No. 5 later in the exhaust stroke or even for cylinder No. 6 very late in the combustion stroke. It is unlikely that the cylinder No. 1 CAS would activate cylinders Nos. 1, 2, 3, or 4 because activation would start too late during the intake or compression stroke. If the three possible options are considered, then injector activation starts sometime between 18 before bottom dead center (BBDC) in the combustion stroke to 78 BTDC in the exhaust stroke.

Mitsubishi 6G72 sequential injection

Valve Timing
The intake valves on the non-turbo and turbo engines open at 16 BTDC and close 55 ABDC (after bottom dead center), which is a duration of 251. The exhaust valves for the turbo engine start to open at 50 BBDC and are closed at 17 ATDC, a duration of 247. For the non-turbo engine, the duration is 243 with the exhaust valves opening 48 BBDC and closing at 15ATDC. Overlap for turbo engines is 33 and it is 31 for non-turbo engines.
Mitsubishi 6G72 valve timing

Summary
The figure below summarizes all timing events (valves, ignition, and injection) for one cylinder.
Mitsubishi 6G72 Timing Events

References
Chrysler Corporation, 1988, 1990 Laser Technical Information Manual: Part number 81-699-9002, various pagination.
Chrysler Corporation, 1990, 1991 Stealth Technical Information Manual: Part number 81-699-0114, various pagination. Available on-line at 2-stim.htm.
Mitsubishi Motors Corporation, 1999, 1992 - 1996 3000GT Service Manual, Vol. 1, Body and Chassis: Pub No. MSSP-001B-96 (1/2), various pagination.
Mitsubishi Motors Corporation, 1998, 1999 3000GT Service Manual, Vol. 1 & 2: Pub No. MSSP-001B-99 (1/2), various pagination.


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Page last updated September 27, 2005.