Re: cabin heater scat tube size
Posted: Tue Aug 09, 2022 1:21 am
Without addressing the legality of this modification… I’d like to comment on what may not be particularly “obvious” …
If additional heat into the cabin is desired…. simply increasing the tube or “scat” size at the entrance to the cabin may not make any improvement at all. In fact, it might DECREASE effectiveness.
How? In order for the air to be heated it must pass over a heat-source. In this case…it is the exhaust muffler surfaces. The amount of heat absorbed to be conducted into the cabin will depend upon HOW MUCH TIME is spent by the moving air at the source of heat. If the air is “speeded up” in its’ passage-of-exposure to the heat source… that air will have LESS time to absorb the heat which will be carried to the cabin. In other words, the cabin air input may be at a lesser temperature than prior to the modification.
If the exit of the heat-source is increased in size…such as increasing the 2” scat to 3” scat… then the back-pressure of the air inside the heat source (the inside of the muffler “shroud”…. will likely be reduced and will speed up the air flow into the cabin…. resulting in more air perhaps…but at a lower temperature than previous.
What I am attempting to illustrate is that an increase of the scat between the muffler and the firewall may actually REDUCE the calories introduced to the cabin. It may actually prove MORE efficient to increase the size of the scat INTO the muffler-shroud.
Hope this helps complicate matters.
If additional heat into the cabin is desired…. simply increasing the tube or “scat” size at the entrance to the cabin may not make any improvement at all. In fact, it might DECREASE effectiveness.
How? In order for the air to be heated it must pass over a heat-source. In this case…it is the exhaust muffler surfaces. The amount of heat absorbed to be conducted into the cabin will depend upon HOW MUCH TIME is spent by the moving air at the source of heat. If the air is “speeded up” in its’ passage-of-exposure to the heat source… that air will have LESS time to absorb the heat which will be carried to the cabin. In other words, the cabin air input may be at a lesser temperature than prior to the modification.
If the exit of the heat-source is increased in size…such as increasing the 2” scat to 3” scat… then the back-pressure of the air inside the heat source (the inside of the muffler “shroud”…. will likely be reduced and will speed up the air flow into the cabin…. resulting in more air perhaps…but at a lower temperature than previous.
What I am attempting to illustrate is that an increase of the scat between the muffler and the firewall may actually REDUCE the calories introduced to the cabin. It may actually prove MORE efficient to increase the size of the scat INTO the muffler-shroud.
Hope this helps complicate matters.