Non-ethanol discussion
#21
Join Date: Jan 2010
Location: San Pedro, California
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Thanks for the post. One minor point: the 5.7 Hemi in Ram trucks are actually designed to run on 89 octane. As with most systems of this type, when using 87 octane the ignition timing is retarded accordingly. Whether the engine controls will provide a more advanced timing for octanes greater than 89 is possible, but not known at this time.
Best regards,
Dusty
2010 Ram Big Horn 1500 Quad Cab 2WD, 5.7 Hemi, 545RFE, 3.92 LSD, factory dual exhaust, 20” wheels. Now at: 101,000 miles.
Best regards,
Dusty
2010 Ram Big Horn 1500 Quad Cab 2WD, 5.7 Hemi, 545RFE, 3.92 LSD, factory dual exhaust, 20” wheels. Now at: 101,000 miles.
Another thing is that when one puts 87 in the tank, the hemi does not automatically know this and selects a different timing pattern. The timing for 87 and 89 starts out the same. What happens is that timing is retarded at the first sign of pre-detonation, regardless of octane in the tank. Because pre-detonations can be caused by many factors (air density, cylinder head temperatures, engine load, air temperature), under benign conditions, the timing for both octanes will be the same. Since most of the time we do not drive in conditions that merit ignition retardation (towing on a hot day or pulling a trailer up an incline), we will not notice a difference.
I run 89 when I think I'm going to need all of the hemi power.
#22
The timing for 87 and 89 starts out the same. What happens is that timing is retarded at the first sign of pre-detonation, regardless of octane in the tank. Because pre-detonations can be caused by many factors (air density, cylinder head temperatures, engine load, air temperature), under benign conditions, the timing for both octanes will be the same. Since most of the time we do not drive in conditions that merit ignition retardation (towing on a hot day or pulling a trailer up an incline), we will not notice a difference.
Best regards,
Dusty
2010 Ram Big Horn 1500 Quad Cab 2WD, 5.7 Hemi, 545RFE, 3.92 LSD, factory dual exhaust, 20” wheels. Now at: 101,000 miles.
#23
Join Date: Jan 2010
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A tuner can open up the timing advance to take advantage of the higher octane than 89. The stock tuning will limit the timing advance of the engine to what Chrysler engineers consider safe per their recommended 89.
The only time I would think that running higher than 89 would provide any benefit, is when the hemi is so hot and under load that it pre-detonates even with 89, then the 91 would help some. This would be a very rare occasion and probably not worth the extra $$$.
The only time I would think that running higher than 89 would provide any benefit, is when the hemi is so hot and under load that it pre-detonates even with 89, then the 91 would help some. This would be a very rare occasion and probably not worth the extra $$$.