In the stock setup for our Stovebolt’s, the exhaust is
diverted so it flows directly up against the floor of
the intake manifold for the first few minutes and
then as the butterfly opens the majority of the
exhaust (95%) flows straight out the exhaust pipe
unless more heat is called for. In which case the
thermostatic bi-metal spring, if properly adjusted,
partially closes the butterfly diverting more heat to
the intake.
When we get rid of the stock exhaust manifold in favor
of a cast iron header or any header as far as that
goes the only options are to run a pipe over to
a ‘dead end’ plate or run coolant thru a heat
exchanger plate.
The first one, the pipe, has always seemed to me, to
be nothing much more than a decoration since it is,
just as I posted, a ‘dead end’, with none of the
exhaust gas flowing across the bottom of the intake.
The tube simply serves as a small path to transfer
heat by conduction. This does very little for a fast
pre-heat after initial startup nor does it seem
adequate to maintain heat once the engine is up to
operating temperature. The original design was meant
to heat the floor of the intake fast so that fuel
vapor rather than raw fuel enters the engine and to
maintain adequate heat to the floor of the intake.
The second attempt, which is circulating coolant under
the intake has its flaws also. Coolant is regulated
at 160° to 180° as it exits the engine but by the time
it would reach the bottom of the intake it would be
considerably less because the hoses act as heat
exchangers also. And, as has been discussed before, it
would take 10minutes or more for the coolant to reach
temperature, which would not satisfy the design
criteria for rapidly heating the intake floor.
Considering these facts it would seem that splitting
the original exhaust manifold even though it isn’t as
efficient or as pretty, might be a better choice after
all.
So….are we wasting our time and money by installing
these inefficient methods of heating the intake when
we install aftermarket headers, or would we be better
off just running without a method of raising the heat
to the intake??
Denny Graham
Sandwich, IL
