Burnout, you got to look at the configuration of the fuel system. It may be true that installing a spacer to the types of fuel systems you're talking about may have shown some increases in power but, the systems you're talking about are injecting fuel closer toward the throttle body. Like all carburetors, fuel tends to atomize better given more time. That's why spacers have proven benefits. But modern fuel injection directs fuel directly on a hot intake valve. This has 2 adverse effects, one being a cooler valve and the other being a very precisely atomized measure of fuel.
Cold air Intakes are different from what you're talking about too. CAIs' in principle tries to draw air from a cooler area resulting in a denser air charge. Denser air results in an increase in power.
