Volvo used very aggressive spark advance coupled with knock sensors (usually 2) and high compression on all of its NA engines. As soon as you feed the engine hot air it retards timing and you lose both power and FE. A 1992 the white block engine with a stock 10.7:1 CR is perfectly content running on 87 octane (volvo recommends 91) so long as you feed it cold outside air. As soon as the thermostatic intake heater fails in the HOT position drawing air from near the exhaust manifold (usually does after 10 years) both FE and power take a dive. Most owners and mechanics are unaware of this little component. In California this little part causes a lot of volvos to fail Smog Check because of high NoX. CAI is king.
Here is the stock thermostatatically controled intake from a Volvo. The intake is designed to maintain a
MINIMUM 70f for the incoming air. When the intake temp is above 70f, the airflap moves to the CAI only side breathing cool air from in front of the radiator. When the temp is below 70f it mixes in more air from the HAI side which is hooked up to a tube off the exhaust manifold heat shield. The colder the air, the more hot air it breaths. When the thermostat fails (its a cheap $5 part) the flap ALWAYS sits in the hot air side (as pictured) no matter what the intake temperature. The intake temp can reach close to 200f which can eventually damage the mass air flow sensor.
