An intake manifold insulator is basically a piece of plastic that replaces the stock intake manifold gasket. The primary function of this piece is to transfer less heat from the engine head to the intake manifold. This in turn will reduce the intake air's temperature and produce more power. This acts in a similar way to the ever-so-popular cold air intakes. Colder air equals more power. Not only that, but colder air allows you to advance timing without producing knock.
In initial testing on a stock 1996 Tercel, the insulator was found to decrease intake air temperatures by about 21° which yields a 4.2% increase in horsepower. This translates into an increase of 3.3 horsepower on my stock 2nd gen 5E-FE, which was measured with a G-tech pro meter. That equates out to almost 4 horsepower at the flywheel. If you do not see your engine listed below I do not have an insulator for you, but it is possible that one could be developed.
The intake manifold insulators have recently been redesigned to improve performance and reduce cost. These new insulators are currently available.
The throttle body insulator is basically the same as the intake manifold insulator, but at the other end of the intake manifold. In our cars hot engine coolant flows through the throttle body. The insulator helps to block that heat and lower the temperature of the intake manifold so it does not transmit that heat into the intake air.
Testing of this insulator showed a 11°F drop in intake plenum temperature. Using some estimation and referencing the intake manifold insulator testing this would tend to decrease intake air temperature by about 4°F. This decrease in temperature will increase the density of the air by about .85%. This is directly proportional to horsepower gain. Thus a .85% increase in horsepower should be seen. Not much you say? Maybe enough to stop that knock you've been fighting with.
Paired with the intake manifold insulator you should see a very good drop in intake air temperatures and a horsepower increase of at least 5%.
The throttle body insulators have recently been redesigned to improve performance and reduce cost. These new insulators are currently available.