Take this how you like, but there is a good reason for a spacer, beyond the heat-soak issue. Adding a spacer will add perceived plenum volume to the intake manifold. By "perceived," I mean that the carb and the engine will both "see" more intake plenum volume, and the engine will gain top-end power and additional rpm by its inclusion. The use of a 4-hole spacer will also trick the carb into thinking that the plenum is smaller, at idle and part-throttle cruise. This is due to the increased vacuum signal present at the carb venturi, because of the additional length under the carb, before you get to the actual plenum. A 1/2" spacer is ideal; if the engine wants more spacer, you should have used a bigger intake manifold. Using a phenolic resin or wood spacer is the best for blocking heat transfer from the intake to the carb. Many tests have been conducted on the use of spacers to increase performance, and the usual conclusion is that the open spacers increase plenum volume, resulting in better top-end performance; 4-hole spacers increase torque production by increaing vacuum signal and thus improving throttle response and carb response. My own experimentation has proven that the 4-hole spacer does also increase perceived plenum volume, thus improving top-end without the softer low-end performance of the open style. If you are using a big intake manifold, and your throttle response and low-rpm performance are suffering, try a 4-hole spacer under the carb to get the snap back. Again, if you seem to do better with a taller spacer, it is likely that you didn't have enough plenum to begin with. There are some cool "hybrid" spacers out there, which start with 4 holes, then open up as they come to the top of the intake. I have not tried one of these, but the theory behind them is sound, and I bet that they are better still than the 4-hole spacer by itself.
