timing and engine/head temps., what's the affect? Options

[toon1]

With the type IV timing set right it's about 7.5 to 8* at idle. Has anyp0ne noticed a difference in temps if the timing is advanced at idle?

Reading the MM on the MS site, it say's, if you retard the timing at idle it will produce lower emissions by creating more heat due to the unburnt fuel left in the system.

If retarding the timing makes things hot,can advancing it make things cooler or more stable, temp wise at idle?

With MS it is possible to advance the timing at idle but still keep a 27* cap at the 3500 mark

Keith

[toon1]

When I had the 2.8L four in the race car we found out several things. As previously noted CHTs went up when timing was advanced and down when retarded. We had the timing set at 28 degrees at 3K and head temps were about 300 degrees at full power but we were over heating the exhausts valves to the point of breakage. We talked to a Union 76 race fuel engineer and he said with their 100 octane unleaded I could probably advance the timing as much as 6 degrees or so. We tried 4 then 6 degrees to a total of 34 and head temps went up to about 450 degrees but the exhaust valve overheating issue stopped and we quit breaking valves. The seat of the pants dyno seemed to bear this out as throttle response was much better. Exhaust A/F stayed the same surprisingly enough at full throttle with the difference in timing.

450* is hot and from what I understand is beyond the failure point for a alum. head. At those temps how did you not drop or damage the valvle seats and how is it that the valves stopped breaking?

Was the 100 octane fuel, more or less octane than before?


Was the car carbs or FI?