iHaveGas
FRF Addict
The real answer really depends on alot of variables. The two biggest factors being how far your tuner went and your elevation. If your at 8,000' el. you could run 87. When tuning on a dyno you set a load on the engine at a given RPM/TPS. Then advance the ignition timing until max numbers are reached. At this point you can keep advancing ignition timing alot before detonation. Where a tuner stops advancing is all in there own way of doing things.
Here comes the tricky part. All ECU's have factory set parameters that can't (usually) be changed. These parameters are to allow for adjustments from sensor input do to current conditions. So your tuner built your map in a climate controlled dyno room. 68 degrees at sea level. You then go to Death Valley below sea level in 120 degree temps. Your ECU reads the input from Ambient air temp and pressure sensors then compares this to Manifold Air Pressure. Maybe even get an input from a knock sensor. It realizes it needs to back off the timing and change the fuel. If your running 87 it might need to back off the timing farther than the preset values will allow it do to the tuners map having them advanced so far.
This is a generic explanation. Fords ECU might run differently but you get the general idea.
Your friend is going off the fact that the knock sensor(s) will retard the timing enough for 87. Fact is probably not a good word to use. It is fact that it will retard the timing. But is it fact that it will retard it enough? Only your pistons and rods will know. As Ford quotes you can run 87 but 93 was used for the 411HP rating on the stock mapping.
Not a good word to use but you use it 2 more times after you said it.
