i had one done(custom) at my local shop, they built me custom intake, headers, and exhaust system. the price was great, i had very good power gains, it is just that the quality wasn't in it, and there was no warranty. i enjoyed it for a little over a year but i am now going to redo my car with comptech, mugen, or toda parts only, yes it will be expensive but as i am learning and many others will tell you it is better to spend the money the first time and do it right, so yes id go aftermarket with a reputable company who can back their product, that is why they charge the little extra money they do, so they can support research and development, which eventually leads to a better prodcuct for you