<<I just replaced the exhaust system on my Super ES.  The new system is
larger both in primary and collector sizes.  Seems to work just fine.

When installing it, I made sure to locate the EGT probes in the same
location as on the earlier models (within a 32nd or so, anyway).

Question:  Why are my EGTs now averaging 100 degrees cooler than before?..
Don't see any of this as a problem just want to know what happened.

Jim Scales
Angels Playmate N98AF
Lancair Super ES >>

I'll take a guess.  Without knowing the orientation of the probes I'll bet
the flow patterns are different than before.  Much of the heat transferred
to the probe occurs during the "blow-down" period.  This is just after the
exhaust valve opens and takes maybe 20 degrees of crank rotation.  At the
beginning the pressure in the cylinder is probably 100 to 150 psi so the
velocity is very high.  This jet of exhaust will typically attach itself to
one side of the exhaust pipe, concentrating the flow.  If the probe is in
the way it will pick up a lot of heat, otherwise not.  I've seen
installations where the probes were carefully placed an equal distance from
the cylinder, but because of clearance reasons were placed at various angles
around the pipes, creating a difference in the reading.  If the header pipes
are larger this concentration of flow will be more pronounced.

Why would it burn more fuel?  The scavenging effect of an exhaust system
depends on the length of the pipe and many other factors, with smaller pipes
producing a more pronounced "tuning" effect.  The thing that matters is the
pressure at the valve during the overlap period when both intake and exhaust
valves are open.  It's possible that the new system, because of a different
tuning or just because the overall back pressure is less, produces a lower
pressure at this time in the cycle.  This pulls more exhaust out and hence
more intake charge into the cylinder.  If you're lucky little or none will
short circuit and go out the exhaust.  Therefore, higher volumetric
efficiency, more intake air and fuel flow producing more power.  Since some
is certain to short circuit, you are probably getting something like half
the benefit - for every 2% more fuel burned maybe 1% or so more power.

Gary Casey
ES, still in my garage