just did my h/c swap last week, running tr6's and the car is running great. Like stated a good rule of thumb is a 100 horse over stock go a step colder

 

If I'm not mistaken, if your plug is too hot you see some speckling or blistering on the porcelan. It's difficult to see if you don't know what you're looking for.

 

How to tell if too hot:

http://www.dansmc.com/Spark_Plugs/Sp...s_catalog.html

 

If you have TR55, could you just gap it to 0.045-0.050 and effectively have a TR6? Is there more to it than the gap?

 

More to it than the gap.

You can buy TR5's; they come gapped at .039 but are the same heat range as a TR55. The difference is merely gap, a TR55 is gapped at .055. The manufacturer doesn't recommend moving a gap more than +/- 10, thus why the TR5 exists.

 

TR55..thats what the pros like ECS uses.