It makes sense that any type of coating/barrier that keeps heat in the pipe, will lead to better performance. Theoretically, if the tube stays cooler, there will be more of a "draw" which will lead to more power. That said, it's only a 318 with a stock 340 cam and stock 318 heads, so I wouldn't expect the "thermal barrier" option from TTi to result in a noticeable difference in power. I was more interested in the lower underhood temp, and keeping a little more heat away from pumps/wires/reservoirs/etc under the hood.
It seems like everyone generally rates both Doug's and TTI very favorably, and very comparable to each other, with an ever-so-slight edge to the TTI's . I was prepared to shell out the $$ on the TTI's, but with the 20% off deal through Auto Zone, the ceramic Doug's really are only $560 right now, compared to $954 (incl shipping) for TTi. That's hard to pass-up on its own, but when you add-in the fact that TTI says there's a 4-6wk lead time for the 273/318 headers, I think I'm going to go with the Doug's.
