Originally Posted by gsxr

The old prechambers were vertical, the newer (~1990-up) are inclined/angled. The purpose was mostly for emissions reduction, though. And once the crack gets bad enough to where you get the "high cold pressure" symptom - which is usually the first & earliest symptom - you WILL see higher operating temps than normal. Trust me, I've seen this myself on my car, and also a co-worker's. It's not so much an overheating thing, but you can see rapid (and large) temperature swings that would othewise not occur with a good head. And under heavy load you can get overheating, particularly in high ambient temps.