Can you run 87 octance with the 91 octane tune?

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kawie95

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I have the 91 octane SCT tune from Henessey, but I figure its similar to 5 star.

Can we run 87 octane with the 91 octane tune? My friend says yes, but he sometimes doesnt know what hes talking about.

I always run 91, but it would be nice to know for sure what can happen. Maybe also with a half tank of 91/87 mixed, or just an empty tank filled with 87 octane, etc.

Thanks!
I searched but didnt see this exact question.
 

keatonskidmore

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Maxx for some reason I'm laughing my ass off at your reply..
OP like maxx said no you can not. Your tuned for high octane so you must use high octane. Although if you're tuned for 87 you can run higher..I think.
 

Maxx2893

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Exactly. You can run higher than you are tuned for, but you can't run lower.
 

tahoeacr

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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.
 
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