It may seem a bit odd to you, but if one looks at it from a business point-of-view, there just isn't a significant amount of people who would buy the products to ramp-up the performance of a 328's normally aspirated engine when its counterpart already exist in the version of a 335. Folks buying a 335 are far more into performance than 328 buyers.... or, they would be buying 328's. And, again, unless someone has a LOT of cash to throw away on a hobby (hopping up an engine), why re-invent the wheel? If I was looking at performance, why would I buy a base model with the idea of making a hot ride, when the hot ride already exists (and again, most likely at a lower cost, and far better engineered than what 99.9999999999% of engine builders could create)? And, with a 4 year warranty? No customers- = no products. Makes perfect sense to me.