TTI vs Dougs

gabe380 said
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 discount through Advance, 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.

The impact on underhood temperatures breakdown like this:
Radiated heat doesn't directly transfer to the air. It tranfers to the first solid object. The darker it is, the more it will transfer.
Insulating the headers with a thicker coating will reduce the amount of heat conducted to the surface, and from there transfered to the air (convection) and radiated. Zirconium dioxide is one of the few coatings that will do that. Its a commercial process, although in the US Swaintech specifically markets it for headers (they call it white lightning or such). It will bring the overall heat conduction through the tubing about the same as if they were made of stainless steel.

If that sounds like overkill for modest gains, a decent polymer coating will certainly not hurt, and probably will help reduce the heat transfer - especially the radiated heat transfer (if its not black). The inorganic components in the coating can make a big difference in the coatings properties. So it is probable that ones with higher insulating materials in them may have less conduction than ones that have something like aluminum in them. But the point that a .003 film is going to have little effect on overall conduction through the tube is correct. The main things you'll be reducing is the heat transfer off the surface.