I see Tom Telesco a few times a year at the Buick gatherings around here, so I speak to him often.
He and a (now deceased) friend of his started development on the roller rockers nearly 10 years ago. At one point TA Performance got involved with the project. Things weren't progressing, so Tom T and TA eventually brought two different versions to market.
Toms roller rockers use the stock shafts, stands, spring spacers, and even stock pushrods. They are made to work with all stock valve covers, even the cast alum VC.
Cost in in the $900 range.
The TA Performance version uses needle bearings on the rockers. They are sold as a complete setup with rocker shafts, stands and alum tube spacers (instead of springs). they are designed to be oiled thru the pushrods, so different lifters and pushrods need to be used. They will not fit under the stock cast alum valve covers, and one source told me they may interfere with the stock steel vc's as well.
Cost is higher, over $1k for the rockers, required lifters/pushrods add to that.
I installed a set of Toms rockers on my recent build, but not have not fired it up yet.
I did measure some profiles of a few cams using a dial indicator and degree wheel, and then plot the data on graph paper.
In general, the extra ratio of the rockers will add about 0.050" lift to any cam. They will not change the opening/closing 'seat' times of the cam, so drivability will not be decreased. They will add a bit of valve lift at low low lift.....I've found they will decrease valve-piston clearance about 0.020", which shouldn't be a problem unless you have weak valve springs or a lot of slack in the timing chain.
Valve-piston clearance is tightest during valve overlap....when the exhaust is closing, and the intake is opening. Basically from 10* BTDC to 10* ATDC.
What the extra ratio of the rockers WILL do is increase the overall amount of lift of any cam profile and increase the overall EFFECTIVE duration of the cam lobe, or increase the 'area under the curve' so to speak. On paper it looks pretty impressive!
In effect, adding the roller rockers to a stock cam will give you the performance of a mild performance cam. Adding rollers to a performance cam will turn it into a monster cam but without hurting the drivability!
Are they worth the cost? well, for a 10-40(?) hp increase they are expensive. But as all of you know, it's hard to get extra hp out of a Nail. For a top-performing Nail, I'd say they are a 'must-do'.
