My Mitsubishi 4G15P 's carburetor's inlet*manifold is joined with hot water's exit from cylinder head : this design ( esp in cold climate <10°C ) enables * to heat up fast to 40 °C ( ideal temperature for air to receive petrol vapour, per

para 10.2[7] ) but here in e.g. 28°C ambient air, hot water overheats *. I added cooling ( 2 aluminium dishes with water ) to thermostat's cover, significantly reduced *'s heat, got more torque ( as hoped ) + a surprising big drop in exhaust noise. I wonder what made exhaust noise drop : if a drop in air intake temperature cannot cause this drop in noise, then the only possible cause is that distributor ( with transformer coil inside ) & alternator are cooler & so produce more amps & so bigger sparks. Does any1 here know better ?