[AcesHigh]

You will always gain some horsepower if you tune an AFC correctly on a Prelude; the car was tuned conversatively for emissions and reliability.

The SAFC and VAFC are blackboxes that alters the signal to and from your ECU to make your engine components run more efficiently. However, the two AFC's have severe limitations and are only good with lower to mid level modifications. Interupting ECU signals sometimes create a snowball effect and can cause a whole load of problems.

With that said, the VAFC/SAFC are still two very good piggybacks that will help you squeeze out that extra amount of power. Even a stock Prelude can net around 5whp. Another plus is that they are incredibly easy to tune, about an hour at a dynonameter and you'll be set to go. They are also easy to install, and greatly help novices learn about automotive tuning.

If you are feeling brave, you can also check out the Hondata s200. It provides datalogging capabilities and nearly complete control over your car. It is more difficult to tune than an AFC. The most difficult to tune (but the one that provides the most control) is the AEM EMS, which does away with your ECU altogether and works on its on in place of the ECU as a standalone. It's more difficult to tune than Hondata because there are more variables you can change, much like Hondata is more difficult to tune than an AFC because it has more variables you can play with.

And the DC-S header won't do you much good.