Back on point, I've found the XRs Only folks and others (e.g. Baja Designs) who use "derivative" technology to be the most informed about what works and don't. They also provide a valuable "feedback" loop to the designers, who aren't the ones most often fixing what didn't cut it in design.
What about companies who engineer, design, manufacture and test the product? What about companies who do all these things to many different products, then just choose the best to sell?
I agree there are many companies who spend years testing products much harder than some original manufacturers, and have better ideas about what works and what doesn't. But that doesn't preclude manufacturers from also doing testing which is just as good.
Regarding the Camshaft debate. After dealing with the RFVC engines since 1984, here is what the cam grinding companies, and other manufacturers have determined.
Due to the rocker/sub-rocker design that the RFVC head uses, an increase in lift from a "performance" camshaft results in a big increase of pressure on the camshaft & rockers.
Increasing camshaft LIFT will cause increased pressure on rocker and camshaft lobes.
Increasing camshaft DURATION will not cause increased pressure on rocker/camshaft.
The HRC camshaft increases duration without greatly increasing lift. This is how they are able to run a "performance" camshaft without using hardfaced rockers.
If the XR's Only camshaft is not hardfaced, then it is either Billet (made from a new core), or a re-grind.
A re-grind removes material from the base circle of the camshaft making the rockers drop down further towards the centerline of the camshaft. This allows a company to make an inexpensive grind that can increase lift and duration without actually having to add material onto the camshaft.
If XR's Only does not require a core exchange, then it's a Billet cam. If they do require a core exchange, it's a re-grind. Either way, since it does not require hardfaced rockers, it has an increase in duration, and not much of an increase in lift. I assume the cam will run with stock springs also?
Most aftermarket engine builders have found, after years of testing, that with the RFVC engine it is best to use hardfaced rockers with ANY change in lift or duration. It's cheap insurance against cam/rocker failure.
Also, there's a reason most aftermarket cams for the 400 increase the lift. Because the engine responds really well to it! Just an increase in duration does help, but not very much (gives more top end, but doesn't do much for midrange and throttle response stays about the same).
If you'd like more information about camshafts, check with the two cam grinders in the US who build aftermarket cams for the ATV and Motorcycle industry. Megacycle (415-472-3195) and Web Cam (909-369-5144)
These two companies grind about 99% of all aftermarket cams made for 4stroke singles. Both companies have been around a long time, and they both can explain the causes for cam and rocker failure better than I can.
These are the companies who supply Powroll, White Brothers, XR's Only, Thumper, and everyone else with their camshafts. Some companies (like White Brothers) just purchase the "house grind", other companies make up their own design and have megacycle or web do the grinding.
BTW, we have seen other kits sold by performance companies which made the stock liner "really thin" also (a 78mm piston kit for the XR250).
When you looked at the liner, you could actually see 'ghosting' where the piston left a mark on the bottom of the liner. The sleeve was essentially collapsing in on the piston during use.
The aftermarket company in question attributed the problem (seen in more than one instance) to improper installation, fuel wash, and/or ring failure.