Low temp thermostat

[G. Scott Ponton]

Tyler wrote
<snip>
>Since we are talking about people who are trying to optimize a
>particular heat pump it would be of interest to everyone to know at just
>what temp that pump gets the best HP given optimal conditions. A blanket
>statement that this temp is 159 or 220 or 190 does an injustice to all.
>It is obvious to all that you have an experts knowledge of what is going
>on here but there are three temperatures that are critical to an engine
>for hp, water, oil and inlet air.  So if an engine can have an under
>hood water temp range that optimizes these one would set chip
>programming to take advantage of this range.  It may be that the LT-5
>motor sees 190 deg oil temp 130 deg inlet temp at 159 deg water temp and
>this is the best balance that can be attained in a C 4 body style.  I
>believe that this is a thought process that should be a part of any
>effort to design a system for a given engine.

    All this is right on the money. The last line in particular says most of
what needed to be said. Lower block temps do have an effect on the
horsepower that is a vaolable in the application that you have specified. I
think that there is a lot of misunderstanding as to the real effect water
temp has on the system. In the end it is all "engine" dependant.
    The actual effect water temp has on the equation is due to thermal
expansion of the block and pistons. A higher oil temp with a lower water
temp speaks volumns as the oil temp is a direct indicator of the temperature
of the pistons and the rest of the rotating assembly. Whereas the water temp
is a reflection of the temp of the block and heads. Inlet air temp is also
important as it obviously indicates the differences in the density of the
air the engine is ingesting.
    I find it hard to believe, under WOT and a reasonable engine speed
(above 4,000), that the temperature of the engine will effect the inlet air
temp by more than a couple of degrees. Air is a great insulater from heat.
The lenth of time that it remains in the intake track during racing
conditions isn't going to be long enough to really effect it's temperature.
    Yes if your air inlet is "underhood" the temperature of the underhood
air becomes the inlet temp.  At this point the temp of the cooling system
has an effect on power production and installing a lower temp thermostat
will have an effect. But if the air inlet is isolated, by either a "ram air"
system or a hood scoop the underhood temps have little or no effect on inlet
temps.
    If you look at auto racing in all of it's forms I think you will find
that in every instance they run their water temps at 200+ F. This includes
Indy, NASCAR and formula 1 as well as most SCCA cars. If it was benifitial
to operate engines at a lower temp I think that these racers would have
figured out how to reduce their water temps by now.
    I drag race a Pontiac. After extensive testing on an engine dyno, a
chassis dyno and at the track I have found that the engine produces the best
power at 200 F, water temp. Through this testing I have found that a change
in the piston skirt clearance of .0005" is enough to effect the temp at
which the engine produces the best power. Through this testing I have found
that if I set tolerances slightly looser, at the piston, and run the engine
at a water temp of 200 F I can produce 30 to 40 more horses and as much as
50 ft/lbs of torque. I also can run the engine with less ignition lead and a
leaner AFR under these conditions while still maintaining the same power
levels. Lastly I have found that the engine is more consistant at the higher
temps.
    Naturally I am speaking about racing here. In a street or OEM
application things are slightly different as the engines are designed and
built to last for a longer period of time. As such the initial tolerances
are "tighter" when the engine is new to allow for wear and tear. If they
were built to optimize their power levels they would need to be rebuild
every couple of thousand miles in order to run optimally.

    just my .02

Scott