Some say that changing the intake system will cause the car to run lean (more air/less fuel) and will damage the car. However as long as attention is paid to the spark plugs and the remaining parts (such as ECU) are stock, this is very unlikely to be a problem. It is true that increasing the amount of air will make the mixture leaner but with the stock ECU, the mixture has a tendency to be slightly rich (more fuel/less air) so the increase in air can often bring the mixture closer to ideal conditions. At HKS, all intake and muffler systems are designed to work with the stock ECU and so there should be no concerns about safety when using HKS products.

Boost is raised by an EVC but the stock ECU may detect an error when it sees more boost than its set for and cut the fuel to save the engine. In order to prevent this, an FCD can send a lower level signal to the ECU and make the ECU believe that the boost has not risen above a certain level. However in practice, it is necessary to increase the fuel amounts to balance the increase in intake air. In order words, it would be better to use a device which can function both as an FCD as well as something which can control fuelling such as an F-CON iS. It is also necessary to do similarly when changing the intercooler.

Changing the turbo can lead to massive power increases and so it generally becomes necessary to change the fuel pump which delivers the fuel from the tank and also the injectors to one of higher volume capacity. Some vehicles may require fuel parts upgrades even with just "boost up" tuning and this can be monitored through fuel pressure gauges and also monitor functions though F-CON which allows users to check how much of the injector capacity is being used. Depending on the type of turbo being used and the target power output, it may become necessary to replace and strengthen some engine parts also.