header wrap, or cermaic coating?

[rhock99@epix.net (Ryan H)]

Scott, a heat soaked manifold won't make much of a difference... it's where the air is drawn from that makes the biggest difference.  Air going through the intake manifold is traveling at around 5 ft. per second at WOT, not nearly enough time for the manifold to affect it any.  Idle may be a different story, though.  We did an experiment like this once with a NA 2nd gen. RX-7 and some thermocouples (is that what they're called?), and I don't remember numbers, but the difference (heat soaked vs. ice cooled) was negligable.
> 
> From: "Scott F. Williams" <sfwilliams@comcast.net>
> Date: 2003/04/07 Mon PM 06:34:47 EDT
> To: scirocco-l@scirocco.org
> Subject: RE: header wrap, or cermaic coating?
> 
> Ryan H. wrote:
> > I'm not sure there would be many advantages with either, other
> > than keeping some of the heat out of the engine bay...
> 
> That's an advantage that pays dividends on several levels. First of all, it
> keep the heat in the exhaust. This maintains the exhaust gas velocity which
> means greater flow/horsepower. Secondly, it keeps the heat out of the engine
> bay like you said. That means that the intake manifold won't be heat soaked
> as readily. The intake charge will be denser which, again, contributes to
> generating more power.
> 
> The question is, how much power will be gained for these reasons? And, will
> the gains be worth the investment? On a carbed (non-crossflow) 8v, I'd
> definitely think so. On a turbo'd anything, I'd also consider it a
> no-brainer. A header also radiates more heat than a cast iron manifold. So,
> perhaps any engine with such an exhaust would benefit? What I do know is
> that you lose about 1hp for every 10degF increase in underhood temperature.
> --
> Scott F. Williams
> NJ Scirocco nut
> '99 Subaru Impreza 2.5 RS
> Mazda 323 GTX turbo "assaulted" vehicle
> Golf GTI 16v "rollycar"
> ClubVAC: "Roads found. Drivers wanted."
> 
> 
> 
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