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Greg
Dodge Dakota
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5/06/2003
00:06:02
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 Subject: Gasoline octane & mileage
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Just curious to know what everyone is using for fuel (87,89,90 gasahol,91 or 93 octane premium) & the kind of mileage you get from your brand. I'm running an '03 4x4 CC AWD with the 4.7 V8 & 5spd auto. I've been trying different fuel grades just to see if there'e any difference & I'd like to know other people's numbers for comparison.
Thanks,
Greg
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gasman
Dodge Dakota
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5/06/2003
07:00:31
|  RE: Gasoline octane & mileage
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http://theserviceadvisor.com/octane.htm
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donny
Dodge Dakota
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5/06/2003
07:22:52
|  RE: Gasoline octane & mileage
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I have a 99 rc with 3.9, manual trans, light mods. I get 20 to 24 mpg using 93 octane; this is the same miles per dollar as I get using regular and the truck runs better.
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HotRodSRJ
Dodge Dakota
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5/06/2003
11:01:52
| RE: Gasoline octane & mileage
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Octane is an often misunderstood science in our plethora of automotive subjects.
Octane is strictly a yardstick of anti-knock capability of the fuel, but moreover exihibits certain burning rates under controlled circumstances. Higher octane fuels actually burn slower than lower octane fuels. This is due to the addition of aromatics to the fuel concoction like xylene and toluene, both of which are octane enhancing agents/additives.
The most common myth about octane is that more is better! Or, if it runs good as designed for on 87 it will run better on 89 and best on 93! WRONG, in fact is often worst. YOu can actually diminish power and milage with higher than designed for octane fuels.
The reason you should stick to what your OEM recommendations are besides that they have thrown millions of dollars of R&D at this, is that the total engine specification including dynamic compression ratios, cam timing, ignition/map timing, combustion chamber design, etc are all intregal to the octane requirement issue. My 2001 Dakota 4.7 gets about 10 hp more on 87 than on 93. I proved that on the chassis dyno! The reason is that the engine is designed to burn or combust at certain rates to optimize the peak combustion pressure to produce the designed peak power. By reducing or conversely upgrading the octane levels you can be adjusting the combustion wave front travel/burn rate in the cylinder to the extent of degrading the power production.
My recommendation is stick to the book recommendations unless you have modified something to require a change. If you feel 93 burns better than a designed for 87 engine, it's your imagination. Save your hard earned $$$ and go with the OEM recommendation.
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kotagtx
Dodge Dakota
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5/06/2003
20:21:28
| RE: Gasoline octane & mileage
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Currently using 87 in '00 QC, MP computer, bumped timing, M1, 4bl, Hooker,3.92,RR,MSD, etc. Hard to
believe but no pinging. There may be detonation sensors in the late models. I can't remember to ask the dealer.
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kotagtx
Dodge Dakota
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5/06/2003
20:22:43
| RE: Gasoline octane & mileage
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Currently using 87 in '00 QC, MP computer, bumped timing, M1, 4bl, Hooker,3.92,RR,MSD, etc. Hard to
believe but no pinging. There may be detonation sensors in the late models. I can't remember to ask the dealer. highway 16-18 in warm weather.
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01Motorsport
Dodge Dakota
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5/07/2003
09:37:40
| RE: Gasoline octane & mileage
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When running all 87 octane once early in the life of my '01 RC 4.7 5-spd, the engine was pinging slightly up a steep mile-long hill. Since then, I've run either a 50-50 mix of 87-93, or 60-40 of 87-93. I end up with a 90 octane on the 50-50 mix for the cost of 89 at the pump. I think I could trim back on 93 usage, but it's just easier to alternate 10-12 gallons of 87-93 in my daily routine. Here's a thought: when gas is close to $1.00 a gallon, the $.20 difference between 87 and 93 is significant. At $2.00/gal., the difference is 10 percent, so the economic argument fo 87 is less. Remember, as engines get older (100-200K mi.), they need more octane to avoid spark knock.
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01Motorsport
Dodge Dakota
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5/07/2003
09:43:09
| RE: Gasoline octane & mileage
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By the way, my '01 has a custom aluminum air intake and Flowmaster 70 catback 2 1/2" duals.
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HotRodSRJ
Dodge Dakota
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5/07/2003
19:57:19
| RE: Gasoline octane & mileage
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Today's engines are not as prone to needing more octane at an older age but there CAN be a need for more octane down the road, yes. This is because the older engines would build a sheet of carbon and other combustion by-products across the piston and chamber that took up space and therefore raising the compression ratio a tad!
The fuel management systems of today are much better at aleviating this condition. And some engines have knock sensors that retard spark when needed. But, in general, older engines might need at smiggin more octane in some cases.
On the octane front, if you want to make an elixer of octane booster just go and buy a gallon of toluene from any paint store. Usually this stuff can be around $2 a gallon and has a RON of 114! A couple of pints can make a very inexpensive way to raise octane appreciably.
For more on octane visit http://www.inccn.net/jsoctane.htm
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Adam12
Dodge Dakota
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5/07/2003
20:28:49
| RE: Gasoline octane & mileage
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I was reading what was on the website that gasman posted. I read about the rotten egg smell. I have used 93 octane in my 4.7 pretty much since I got it,(has 30,000 now) I changed to 87 octane about 2 weeks ago and now everytime I go WOT and stop back to idle, there is a really bad rotten egg smell. The website said that this would happen while I was on 93 octane, but it was completely opposite. Does anyone know why this would be? Could I have messed something up on my truck because of using 93 octane for so long?
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Flat4VW
Dodge Dakota
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5/07/2003
21:55:32
| RE: Gasoline octane & mileage
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Bone Stock 1999 Sport CC 4x4 5.2 5 speed with 3.92's and 31" tires, always use 87 gas. usually get 14-15 mpg in town if i granny it and 17 on the highway (80mph, 2500 rpms) 64,000 miles on the truck.
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