The terra's have a roller tip that reduces friction; this is why the produce more power ove rthe stock rocker that has no roller tip.

JMX claims they only pick up 3 or 4 HP ...not sure where he gets this from, however..

I think the main advantages are strength and quietness...

Hey Big SS,
I don't know if Mark will echo the exact sediments, but in my opinion as I mentioned above, "A proportional duration to .550 lift", ie 224 cam + which would have a direct reflection on what spring rate must be used to run these cam size mentioned and are usually shifted at 6,200 and higher. Not only that, it's just good insurance IMHO. Recently, I installed a set of brand new stock rockers on a 230 cam car, quiet at first, then they began clattering within 1,500 miles if thats anything to go by? I give them my seal of approval and all our new builds will either come with them or be suggested, but we have made due over the years with the stock pieces too but with issues.

The reason for the explanation in my frst post is that they are not exactly "plug N play" you really have to check your valve train geometry well if your extensively modded. For example, I tried to install them on EZSS's car, and we had no preload at all, so at this point, there would be a coulpe different things that could be done, longer pushrods, re-adjust lash cap thickness to ballance out the "strike" area on the valve tip, starting at -0- lash is a tough one though because there is no real reference point besided subtracting out what the stock rocker preload was at so it's kinda hit or miss till the correct geometry and pre-load is acheived.

Joe.