anyone using or can tell me about the comp cams XR276HR.

 

And the cam specs are what? And what car are you putting it in? And what do you want out of it. I could tell you a lot about the 276's as there are more than 1.

 

.50 duration-224 230
lift-502 510
110 duration

 

Yeh, it has too much overlap for a nearly stock TPI, b/c of the duration plus the 110* LSA.
Don't buy into the "bigger is better", and surely don't buy a cam only b/c youy want a lopey sounding idle.
I have some test results of some COMP's cams 252, 268, 280, 292 and the results point out that in a mildly modified 350, 355 the 268 was superior accelerating, idling, pulling past the redline! The 252 was suprisingly strong!
**In the real world ask for and compare by the "average" torque and Horspower numbers since our cars are "street" driven in the 1500-5800 rpm range.**
Results"Petterson's")
252*=347.9HP@5000/398.2lbft (350lbft+,2600-5100rpms)
268*=380.2HP@5400/401.6lbft (350lbft+,2700-5600rpms)
280*=404.7HP@5700/403.8lbft(350lbft+,2900-5900rpms)
292*=430.5HP@"6700"/399.5lbft(350lbft+3200-6300rpms)but this cam has a very chopy idle @900rpm would require at least a 3000stall, and 3.70+gears and 9.5:1+compression minimum.
I'd strongly recommend the XR264 to get the best all-around performance.
Also our stock heads will NOT "safely"accomodate lifts more than .420" Intake .440 Exhaust. They require machining of the valve guide bosses to give adequate "retainer-to-seal" clearance. And you need at least .010" between each of the valve springs 6 coils at max lift which equals .050". So take the installed height of the spring and subtract the compressed(solid) height and subtract another .050" for safety and you have the max lift for a given spring. Measure the retainer to guide-seal distance along the valvestem w/o the spring installed. Subtract the .050" safe clearance for it also and you have the max lift the head can support w/o machining.
My #14101083 heads needs machined for the ZZ4 cam I'm installing in my short block now. And these are 285/300HP iron service heads with 1.94/1.5 valves and 64cc chambers. And the "Orange" springs I bought will be taxed to the max with this cam, so they'll end up in my "Suburban", as durability demands more spring.