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The 4A91 is part of Mitsubishi’s new endeavor of all-alloy inline four cylinder engines, developed in house and built by the ex-DaimlerChrysler MDC Power plant in Germany.
First seen on the 2004 Mitsubishi Colt, the 4A91 is the four potter in the family to utilize a high-pressure die-cast aluminum block.
Effectively replacing the workhorse 4G series of engines, and in particular, the 4G15 in this application, both the 4A’s cylinder block and head are made with aluminium, and feature four valves per cylinder, double overhead camshafts, and MIVEC continuous variable valve timing for the intake.
The 4A91's DOHC works with a single roller chain of 8.0mm in pitch and 12.5mm in width, different from the 4G15's timing belt setup. The camshafts manipulate the bucket-type tappets, with the intake cam fitted with continuously variable cam-phasing.
This changes the timing profile of up to 50 degrees. The new angle of the valves on the 4A91 is at a narrower 34 degrees, as compared to the 4G15's 45.
The total 1499cc displacement (75.0mm bore and 84.8mm stroke) has a compression ratio of 10.0:1, and produces 109ps@6000rpm, while torque figures are 145Nm@4000 rpm.