[wickedchargerrt]

Just for your guys knowledge i did a experiment with my car hopefully to save you guys money in the future. In three weeks time (7 days on each) i did several types of fuel. In this three weeks i had the exact same schedule. This is primarily 80% city and 20% highway. Tire pressures were checked daily at 7 a.m.
40 psi all the way around. Temp average over stretch was 88 degrees but stayed around there for most of the three weeks.


91 octane $ 2.95 a gallon 19.5 mpg
89 octane (10% ethanol mix) $ 2.74 a gallon 18.4 mpg
89 octane 100% gasohol $2.85 a gallon 19.2 mpg

My major thing i do is save people on gas mileage at both of my self contracting jobs (auto tech). This is what i've been known for helping people with in my area. I have posted on other threads some gas saving techniques. I know what factors play an important role in gas mileage so pleas no people saying "well this is a factor and this is a factor" . Let me tell you i went through almost identical scenarios with each fuel, same trips , same time of day , close to same temps, air pressure checked, pulled out almost every drop of fuel i could before getting gas, everything i know of in 11years of doing this. I hope this is helpful to any 5.7 guys.

If mods are a factor for you i have afe stage 2, blycream , and 180 tstat, so lets just say i'm stock.

 

[08MagRacer]

you didnt do a test on the 87?

 

[SupremeG]

From what I understand, using 87 octane on a 5.7, although cheaper, causes it to pull timing. Which results in slightly lower MPG, and in the long run, your actually re-fueling more quickly then you would with 89 thus negating the use of the 87 over the 89.

 

[Slow4Dr]

Now if I could actually find 89 octane without the ethanol I'd be in business. Either way good research and thanks for the results.

 

[GLHS837]

40psi? Isnt that a bit high? Is the R/T supposed to be 40?

 

[NECharger]

40psi? Isnt that a bit high? Is the R/T supposed to be 40?

Yeah, I think it's supposed to be 32psi.

you didnt do a test on the 87?

If you want to save money, use 87. I never noticed a difference in performance or gas mileage compared to 89.

 

[SupremeG]

I could of sworn that we're supposed to run 32 psi.

 

[tramp]

very interesting
they said that running 91 might hurt your milage
guess they were wrong

 

[wickedchargerrt]

psi: 32 is recommended from factory as a average median between gas mileage and ride comfort. The tires and your driving style change what the psi should be. Max on most tires is 44 psi cold. If you can run 40 you will get an increase in gas mileage but some people dont like it as it stiffens up the ride. In a neon you will feel this, in a charger, not so much. I get about 38 mpg in my neon with 40 psi and only about 34 with 32 psi. Now that is extreeme and not the case with the charger. But my average nears the mid 18's with only 35 in them. I dont run 32 asthe sidewall drags a bit on the michelin 18's at 32. I'm a major tire guy and thats one thing i hope my knowledge is good on.

I didnt run 87 octane as it recommends 89 in the manual and thats what i giver her. Almost any "r/t " and above since the mid 90's has specified 89 or 91 including neon r/t's , viper r/t's, charger r/t's, dakota r/t's, and um, um , thats all i remember.

 

[wickedchargerrt]

oh and forget that tire analysis for suv's. Then you get into stability issues and for someone that worked for ford and firestone both i dont want to talk about suv's and tire stability.

 

[tvieno]

Here's some more numbers (using the OP's stats). I drive about 124mi day (62 mi one way). Based on my 620 mi/week, I would spend $93.79 for 91 oct, $92.33 for 89oct (10%), and 92.03 for the 89oct (100% gasohol). In my case, gasohol is not an option. But you can see that I would only spend on average about $1.47 more a week for 91. About the price of a 20oz soda.

In my commute, I drive about 85% interstate, 15% city and usually set my cruise at about 70. I have noticed that at 70, I'll average about 20-21mpg, if I slow it to 68 - about 22-23mpg, and if I really slow it and plant myself in the right lane and set it to 65 - 23-25mpg. I also have found that the time it takes me to get to work at 70 and at 65 is only about 4-5 minutes difference in time.

Don't get me wrong, I don't regret getting this car with 8 cyl one bit. When you are talking about $75/wk in gas versus $92/wk, sometimes the wallet speak louder.

 

[SafetyLighting]

Damn, this whole time, I've been using 87. Thanks for the tips.

 

[wickedchargerrt]

Here's some more numbers (using the OP's stats). I drive about 124mi day (62 mi one way). Based on my 620 mi/week, I would spend $93.79 for 91 oct, $92.33 for 89oct (10%), and 92.03 for the 89oct (100% gasohol). In my case, gasohol is not an option. But you can see that I would only spend on average about $1.47 more a week for 91. About the price of a 20oz soda.

In my commute, I drive about 85% interstate, 15% city and usually set my cruise at about 70. I have noticed that at 70, I'll average about 20-21mpg, if I slow it to 68 - about 22-23mpg, and if I really slow it and plant myself in the right lane and set it to 65 - 23-25mpg. I also have found that the time it takes me to get to work at 70 and at 65 is only about 4-5 minutes difference in time.

Don't get me wrong, I don't regret getting this car with 8 cyl one bit. When you are talking about $75/wk in gas versus $92/wk, sometimes the wallet speak louder.

yea lots of guys post that they get better mileage at 80+ which i have a few times but head wind and angle (uphill or downhill) of trip has tons to do with it.
If you put your evic in diag mode and try to keep throttle below 15% and use cruise as much as possible on highway thats the way to go. Also dont fly onto the interstate, unfortuanately its not economical

 

[Crunchyriff]

psi: 32 is recommended from factory as a average median between gas mileage and ride comfort. The tires and your driving style change what the psi should be. Max on most tires is 44 psi cold. If you can run 40 you will get an increase in gas mileage but some people dont like it as it stiffens up the ride. In a neon you will feel this, in a charger, not so much. I get about 38 mpg in my neon with 40 psi and only about 34 with 32 psi. Now that is extreeme and not the case with the charger. But my average nears the mid 18's with only 35 in them. I dont run 32 asthe sidewall drags a bit on the michelin 18's at 32. I'm a major tire guy and thats one thing i hope my knowledge is good on.

I didnt run 87 octane as it recommends 89 in the manual and thats what i giver her. Almost any "r/t " and above since the mid 90's has specified 89 or 91 including neon r/t's , viper r/t's, charger r/t's, dakota r/t's, and um, um , thats all i remember.

there is more to it than that regarding tire pressure for "ride comfort". There is gross vehicle weight depending on payload... has a bearing on what PSI you run in your tires. If you run them too low, premature wear on the outside of the tread and sluggish handling (along with lower mileage will occur) and you run an overheating risk ; and too much PSI will certainly help your mileage...but cost you the center portion of your tread wearing faster than the outsides. It will also cost you some traction in not enough rubber being planted squarely on the ground. The brunt of the weight of the vehicle will be focused on the center of the tread.

Rule of thumb:
outer treadwear greater than at the center- too little PSI
center of tread worn more than the outside: too much PSI

The PSI sticker in the driver's doorjamb was put there as a guide to have correct PSI for treadwear for a given size of tire on that vehicle. i have found them to usually be pretty accurate.

 

[TripleTransAm]

From what I understand, using 87 octane on a 5.7, although cheaper, causes it to pull timing. Which results in slightly lower MPG, and in the long run, your actually re-fueling more quickly then you would with 89 thus negating the use of the 87 over the 89.

This should only happen if you keep your foot on the throttle fairly heavy. It's all about cylinder pressures and temperatures... if you're not hard on the throttle all that often, 87 is fine (as indicated in the manual).

Of course, there are plenty of local variables too... the quality of the local fuel, the additives used to get the octane increase... there is no one true answer as to whether 87 is more fuel efficient than 89, it all depends on local factors. Even between brands... heck, even between stations of the same brand! Back where I used to live, there was an Esso that had me thinking my engines were all about to fail on me (bad mileage, pinging, etc.) and meanwhile another Esso downtown gave me the best mileage numbers on all my cars (and my best times in all my cars were run on that fuel).

With my now-local station (a "good" one), I've pretty much used 87 exclusively with the occasional 89 and I can definitely say that 87 is the more fuel efficient of the two, in my environment and types of driving. I think I've heard a momentary audible ping maybe twice or three times over my entire ownership of this car, and I never hesitate to honk on it whenever I feel like it (high RPM, auto-stick, etc.). I do a lot of highway too... I rarely need to stay at WOT for very long periods of time.

Also, no one has proven that the Hemi uses an adaptive spark timing (where it will switch to a less-aggressive spark table when it detects too many retard events, as on my LS1). Therefore it's likely that the spark retard is only going to happen momentarily, and the regular spark curves will be back in action within moments of the event.

In today's lawsuit-crazy society, DCX wouldn't have mentioned in writing that 87 octane was fine if there was any risk of danger, by the way. If you want your engine to always deliver 100% of what it can at all times, you're better off at 89, that's for sure... but then fuel economy shouldn't really be a priority, right?

 

[TripleTransAm]

By the way, for what it's worth I've noticed I get the best fuel mileage results from running the factory recommended pressures, on all my cars. Don't ask me for a logical explanation... it could be something as silly as the tires being engineered to deform a certain way during normal driving at normal pressures... who knows.

 

[wickedchargerrt]

there is more to it than that regarding tire pressure for "ride comfort". There is gross vehicle weight depending on payload... has a bearing on what PSI you run in your tires. If you run them too low, premature wear on the outside of the tread and sluggish handling (along with lower mileage will occur) and you run an overheating risk ; and too much PSI will certainly help your mileage...but cost you the center portion of your tread wearing faster than the outsides. It will also cost you some traction in not enough rubber being planted squarely on the ground. The brunt of the weight of the vehicle will be focused on the center of the tread.

Rule of thumb:
outer treadwear greater than at the center- too little PSI
center of tread worn more than the outside: too much PSI

The PSI sticker in the driver's doorjamb was put there as a guide to have correct PSI for treadwear for a given size of tire on that vehicle. i have found them to usually be pretty accurate.

Yes keeping an eye out for tire wear is common sense. Let me tell you from 10 years of doing alignments and 2 years of doing them on chargers, 90% of the time outer edge wear is the cause of ruined tires. I have never once seen one of my customers ( who are all at 40 psi) have center tread wear at any higher rate than the sides. Most people are lazy and dont check pressures every week too so that also plays a factor

 

[hendge]

How often do you recommend checking psi?

 

[wickedchargerrt]

By the way, for what it's worth I've noticed I get the best fuel mileage results from running the factory recommended pressures, on all my cars. Don't ask me for a logical explanation... it could be something as silly as the tires being engineered to deform a certain way during normal driving at normal pressures... who knows.

I have seen this to be true on some vehicles, especially trucks, vans and suv's. Company's keep the psi low on those vehicles for stability reasons, lest i mention the firestone /explorer thing again where ford went back in 01 and issued a recall on door jamb stickers to adjust tire pressure from 32 front back to 26.

Most people use the excuse of they do what the tire needs. Thats booty. THe new f150 came out with michelins, continentals, generals , and goodyears. Those tires came on several different models but were all on 1500 2wd's. All of them had the same pressure on the door jamb. This has been like this with several fords/dodges over the years. Those are the only dealers i worked at so chevy's i cant help you with.

Anyway this is not a tire pressure debate,everyone is free to run what they want. I run 40 psi on the street in mine, I have done alignments for 10 years and worked for firestone, ford and chrysler dealers. I have experience to back up findings. The thread was meant only to save people money on gas or to give them an example to use if they were wondering. All things aside gas prices are only going to go down if we reduce the demand. So do what you want and believe with tire pressures, dont matter to me. :grin:

 

[went_postal]

yea lots of guys post that they get better mileage at 80+ which i have a few times but head wind and angle (uphill or downhill) of trip has tons to do with it.
If you put your evic in diag mode and try to keep throttle below 15% and use cruise as much as possible on highway thats the way to go. Also dont fly onto the interstate, unfortuanately its not economical

I am down with everything you said... EXCEPT about the cruise control. I found that my gas mileage blew chunks when using cruise. The terrain around here changes so much that the cruise will simply stomp on the gas to go uphill and turn the MDS off. If you operate the throttle manually you can control hard hard of an acceleration you will get and I have noticed mine stay in "FUEL SAVER MODE" more that way. just my $0.02