As with many modifications, there are advantages and disadvantages. Sometimes buying one mod requires buying additional mods to obtain the full benefits. Air intake filter mods fall into that category. Here are some facts related to them:
1. Since engine heat soak (rise in temp after you shut your hot engine off and leave it off for a period of time) allows ingestion of hot( > 100 degr F) air, which causes your knock sensor to retard timing and reduce horsepower, a true cold air intake makes sense. It does allow a small amount of heat soak to present itself at startup but the higher than ambient temps quickly drop.
2. The added benefit of CAIs is that intake air flow increases. However, to increase it further, a lower restriction cat-back exhaust can be added. Those exhaust systems are commonly stainless steel and lighter than OEM systems. Expect $800+ for a good quality system.
3. The added power ( and elimination of power drop from heat soak) from a CAI and exhaust system is more evident at higher engine speeds and throttle positions.
4. True CAIs position the cone shape air filter directly in the path of frontal air flow, which subjects the filter media to rain and small pebbles that get by the grill. Having a "sock" over the filter helps but really, it's not a good idea to drive around at high speeds in a rainstorm that leaves deep puddles. This is why I leave the MX5 at home during such weather conditions.
5. You can monitor your intake air temperature with a Scangauge 2 plugged into your OBD II port which is close to your left knee. Keeping intake temps below 100F is always a good thing for reasons mentioned above.
