david,
I spoke to a tech rep from ThermoTech, the guys who make one of the
brands of header wrap, a few years ago regarding temp vs. flow rate. I
was again researching an article for our club's newsletter, before
actually wrapping my Monza header. According to him, hotter gasses are
"thinner" and able to flow faster and more easily. The faster the gasses
flow, the better the scavaging effect during exhaust. So, in addition to
keeping the heat out of the engine bay, and away from the carbs, there's
a performance benefit.
Hope that helps,
Charlie B.
Spitfire Pilot
>
> I've seen several TRs with a heat shield as you describe and the
> >owners said they worked fine. I decided on the header wrap because it
> >keeps the heat in the header tubes which keeps exhaust gas velocity
> >high, theoretically increasing flow. It also gets the heat out of
> >engine compartment completely, rather than simply redirecting it. The
> >disadvantages include faster deteriation of the header due to more heat
> >and the wrap's potential to hold moisture, and possibly hotter feet for
> >my passenger.
>
> With no malice towards the orginal author, I a not sure about having high
> temperature increasing the gas velocity. Isn't it true that for the same
> mass flow rate highter temperature will CAUSE higer velocites due to the
> greater VOLUME flowing through the exhaust. With the greater volume you
> will have more back pressure. Less back pressure is what you really want.
> The use of heat wrap is most likely for the protection of other equipment
> mounted near the exhaust?
>
> Flame suit on, Flame away
>
> Dave Simpson
> 61TR3B
> 76 Spitfire, now reassmebling after new paint, lots of FUN!!
> can't wait to drive it now!!
|