ORIGINAL: speedracerntrixie
The thing about gassers is that they will continue to run when overheating. The biggest tell tale sign would be sagging at high throttle settings. Truth is that you can run at close to 300 degrees and really not know it. You can always read the plug color but usually if you have run it hot long enough to do that it may already have some damage. Having muffler bolts constantly coming loose is a sign of overheating. If your worried about the install make sure you are directing air through the fins. Its always easier to pull air rather then push it so your exit area need to be at least twice the intake area. Don't wait until you have an issue, plan ahead so you don't have an issue. I'm currently rebuilding a 40% Extra that is a good example. notice I have 2 exits, one at the bottom of the cowl and one just behind the canisters.
What I've been doing is adding a hood or dam in front of the exit holes to act as exhaust louvers. Outside Air deflects away from the hole and creates a negative pressure condition which in turn creates the "pull" air flow inside the cowl or fuse Shawn is talking about..
In addition for best results, the inlet side needs to have some sort of ducting (I have used depron, 1/32" balsa sheet, even cardboard) to guide incoming air directly over the fins. I pay attention to avoid large gaps between airframe or cowl and the engine crankcase. These large holes can reduce airflow through the fins because air will flow through this path of less resistance first. I also close off cheek holes unless there is a cylinder inside the cheek.
Good cooling is effected by both proper treatment of the incoming air (ducting) and proper treatment of the exiting air. BTW.....my exiting area is seldom if ever greater than 100% the entry area; the hooding and louvering of the exit holes is that effective