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  #31  
Old 04-28-2010, 06:46 AM
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Originally Posted by Buffman View Post
IIRC isn't that bad on the Evap system? I always stop when it clicks and I always 9 out of 10 times use the same pump

That is what they say. Never had any problems for years. I get better mileage this way though.
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  #32  
Old 04-28-2010, 10:48 AM
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Originally Posted by wytltng View Post
X2.
I am not modded at all. I get better fuel economy out of it. I did tests with a tank fulls of different brands & octane & shell came out on top. Especially on highway. I did tests with my 94 RMS w/195k on it. With Shell 93 on highway I was pulling down 28 mpg with average speed of 75 mph. My 96 454 C3500 likes it better than any other brand & octane. It seems to run better & & pulls better with it.

Even though the computer controls timing by pulling & adding timiing out on knock, the higher the octane the less knock you should be getting & the timing will stay in.

Higher octane burns more hotter than lower octane. It also burns more completly.
I agree...my gasoline stays way supreme!!!

As the saying goes "you are what you eat"!
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  #33  
Old 04-28-2010, 01:59 PM
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I agree...my gasoline stays way supreme!!!

As the saying goes "you are what you eat"!
Umm, take that analogy to the proper extent then. Professional athletes have a totally different food requirement then normal healthy lifestyles do. That's the same for your car and the octane level. If it is tuned for higher octane then it needs it. Otherwise it doesn't, and it does NOT benefit from it.
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  #34  
Old 04-28-2010, 07:31 PM
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Umm, take that analogy to the proper extent then. Professional athletes have a totally different food requirement then normal healthy lifestyles do. That's the same for your car and the octane level. If it is tuned for higher octane then it needs it. Otherwise it doesn't, and it does NOT benefit from it.
Then how do you explain more mileage per gallon & better engine performance using 93 than 87? Vehicle in question is 1996 GMC C3500, crew cab dually with 454 towing a 23 ft trailer with a b-body on it?
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  #35  
Old 04-28-2010, 08:11 PM
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Then how do you explain more mileage per gallon & better engine performance using 93 than 87? Vehicle in question is 1996 GMC C3500, crew cab dually with 454 towing a 23 ft trailer with a b-body on it?

On a vehicle w/ a knock sensor and a PCM capable of advancing ignition timing to pre detonation levels, that could account for better milage w. 93 over 87.

Not because there is more ENERGY in the 93, becaust it's hicghe OCTANE allows more advanced timing W/O detonation.

In 2003 I bought my 2001 Corvette in OKC, OK. Driving it the 1800 miles home, I monitored its MPG, on the onboard computer. FIRST tank of California GASOLINE, I LOST 4 MPG!
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Old 04-28-2010, 08:34 PM
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On a vehicle w/ a knock sensor and a PCM capable of advancing ignition timing to pre detonation levels, that could account for better milage w. 93 over 87.

Not because there is more ENERGY in the 93, becaust it's hicghe OCTANE allows more advanced timing W/O detonation.
However, this is not how the PCM controls spark advance. It is preset with tables, which have been developed specifically for the vehicle, drivetrain and fuel. There should be no detonation (and therefore, no timing pulled by the PCM) under normal operating conditions. My theory is that a B-body experiencing better fuel economy using mid-grade or premium has some other problem, like carbon build up or being due for a tune up.

Also, as some have mentioned, certain companies do not add ethanol to their fuel. Our cars were built before the ethanol craze and seem to be very sensitive to it. I know my old '95 lost 1 - 2 MPG's when MO started mandating E10 fuel statewide. This could account for the difference in some situations.
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  #37  
Old 04-28-2010, 11:32 PM
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Originally Posted by cletus284 View Post
However, this is not how the PCM controls spark advance. It is preset with tables, which have been developed specifically for the vehicle, drivetrain and fuel. There should be no detonation (and therefore, no timing pulled by the PCM) under normal operating conditions. My theory is that a B-body experiencing better fuel economy using mid-grade or premium has some other problem, like carbon build up or being due for a tune up.

Also, as some have mentioned, certain companies do not add ethanol to their fuel. Our cars were built before the ethanol craze and seem to be very sensitive to it. I know my old '95 lost 1 - 2 MPG's when MO started mandating E10 fuel statewide. This could account for the difference in some situations.
Above I was not specifically refering to 94-96 B bodies, just vehicles that adjust timing, when detonation occurs.
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  #38  
Old 04-29-2010, 04:51 AM
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I use regular. There may be a small performance gain with premium but not enough for me to justify the extra cost.
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  #39  
Old 04-29-2010, 05:17 AM
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Originally Posted by LT1WGN View Post
I use regular. There may be a small performance gain with premium but not enough for me to justify the extra cost.
This is true on stock motors & some slight mods like air intake & exhaust.

My testing & calculations have all been done on 91-96 vehicles. I have nothing newer than a 96.
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  #40  
Old 04-29-2010, 06:21 AM
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Originally Posted by Mikeceli View Post
Above I was not specifically refering to 94-96 B bodies, just vehicles that adjust timing, when detonation occurs.
To the best of my knowledge, all GM cars handle spark advance through tables. I also assume most will be this way. FWIW, many Ford cars with the 4.6 didn't even have knock sensors well into the '90's, they tuned them so conservatively.
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