The Stillen kit in a sense is more reliable because it produces less torque compared to GTM's kit but if you want CARB legality then Stillen is the only option for now. GTM has applied for CARB on their GTX turbo kit and are claiming that they will eventually try to get CARB for their Stage 0 SC kit but CARB is tough to get.
The Stillen kit is not as efficient as the current GTM's SC kit. When GTM's SC kit initially came out it produced only about 410 whp on 91 OCT and 8spi but they have modified it through out the years to produce more power.
SC setups are pretty reliable if installed properly, just need to check the belts and tensioners once in a while. Have not heard of any tensioner assembly issues, this is where headaches could occur with belt slippage and belts walking off the pulleys and tearing things apart.
So Stillen if you want CARB but will sacrifice total power potential (420-440whp average with kit; extreme modification to kit up to 480whp, see Motionlab threads) versus GTM that does not have CARB but proven to produce 500+whp power or as much psi as your block can handle or dare. And with the coming of ECUtek and UPrev VVEL tuning we'll see how much we can get from these SC kits.
My opinion is that Stillen produced a CARB approved kit and just said OK, we're done, whereas GTM continued to tinker with their kit to be more efficient and powerful.
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