coolant system restrictors, and operating temps.

[bruce plecan]

This is in response to some theories about cooling systems that I heard
years ago, and finally had the time, and instrumentation to actually 
measure.  This series of tests was conducted over 2 years, and is in car
testing, numerous times when major component changes were made were the
tests repeated.  
The testing involved the following:
  me driving-about 100 1/4m passes, more than 300 1/8m, with this car.
  Vehicle 84 Firebird, 305 (LG4, ECM controlled carb., then 355 SBC ECM
     Carb, and TBI with ECM 1227747, own chip design, cam 224d @.050, 
     .470" lift)
  All runs were 3 min. average, other than thermostat replacement one
     hour turn around.  Thermostat changes were with straight water.
  Tests done with on-board 600' timing, and 1/4 NHRA sanctioned track.
  All tests done with less than 5 air temp change, and less 1% A.D.
  Thru the mufflers, street tires, radiator fan not allowed to run during
     pass.  Starting line temp. at "stated operating temp".  Some
     temp. creep noted on high temp days, but repeated if excessive creep
     noted.
  Efforts were made to do repeat testing with light car weights, and
     heavy payloads.
  WOT timing was set at 2d less than when the stock EST would trigger
     a knock count according to a OTC Scanner (side note there was no
     loss of performance with this 2d retard that I could measure).
  All fuel for testing was bought at the same station (Sunoco 94 Oct)
  Mileage tests were an loop of 200M..  Yes there were mild climate
      changes.  But, to be declared the best it was repeated.
  Stant Brand thermostats were used, and fixed resistors used for        
    reporting engine temperature to the ECM.  As close as possible the
      radiator fan was manually operated to maintain the tested operating
      temp..  So if I ran a 195d thermostat, I could lie to the ECM about
      the actual temp, and tell it was 160, 180, 190, 210, etc..
   WOT AFR could be changed from ie 12.7:1, to 12.6:1, but to get a 
      repeatable difference, I had to use .3 variance.  So there might be
      some error in that per given atmospheric condition, the AFR was
      always not optimized for that day's testing of coolant temps..  
      But, this testing was repeated so many times while doing other
      testing that I consider the results valid.
   It may be also noted that the TBI ECM did not monitor IAT. 
  The following are notes from the above:
     The track times were always best when the ECM thought the engine
       temperature was 160d F..  
     As test temps approached 210d F., times and speeds were slowest.
     At temps above 230d F they were really slow.
     The higher temps., got better fuel mileage up to 190d F.
     Cooling system restrictors did a better job of maintaining a tunable
       temp. at sustained WOT runs (more than a mile at a time).  On     
       really hot days, the restrictor could be changed, and there would
       be less of a temp., build up, the thermostat opening was too small
       and temps would rise. 
     The best performance got the best mileage, and that was a 180d
       Thermostat with an inline resistor (270 ohm) to the coolant temp
       sensor, so the ECM "saw" an operating temp of 160d F..
     A .5" smaller crank pulley was tried, and there was no measureable
       difference in mileage, or performance.
YOUR RESULTS MIGHT VARY, but this is what works for me and my street car.
Some closing notes, the cyl. heads are AL GM vette heads, total timing 
was "only" 30d., Engine was not CFM, or fuel limited, 9.5:CR. No cat, 3"
exhaust, 3.42 axle gear, the early testing was with aftermarket chips,
and similiar results were accompliced.  While some may say there is some
code about operating temp. corrections, and being ignored at WOT, I have
found that they (if they exist), are less than what can be optimized by
like what I have done here. 
     Hope ya'all might find this a little interesting;  Bruce