7 MPG big issue what am I doing wrong?

[bigdodge]

Gotcha! So 89 will ignite at the right time v 87 igniting prematurely?

That's the science anyway. There will be plenty that say 87 runs just fine and maybe it does. Something along the way while engineers were testing this platform decided 89 was a safer alternative. so all the keyboard warriors in the world won't convince me otherwise. engineers actually use testing data to come to a conclusion not "well I've been doing it this long and nothin blew up" or depend on their calibrated butt cheeks for testing.

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[2003F350]

That's the science anyway. There will be plenty that say 87 runs just fine and maybe it does. Something along the way while engineers were testing this platform decided 89 was a safer alternative. so all the keyboard warriors in the world won't convince me otherwise. engineers actually use testing data to come to a conclusion not "well I've been doing it this long and nothin blew up" or depend on their calibrated butt cheeks for testing.

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You're absolutely correct. 89 is a safer alternative, particularly when the MDS kicks on. In my PW, though, that is actually pretty rare, and usually only while coasting down a hill.

 

[olyelr]

That's the science anyway. There will be plenty that say 87 runs just fine and maybe it does. Something along the way while engineers were testing this platform decided 89 was a safer alternative. so all the keyboard warriors in the world won't convince me otherwise. engineers actually use testing data to come to a conclusion not "well I've been doing it this long and nothin blew up" or depend on their calibrated butt cheeks for testing.

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True. And you can bet your ass they would not recommend a more expensive gas if they didn't feel it was needed or beneficial.

But I will still continue using 87 I think LOL

 

[62Blazer]

That's the science anyway. There will be plenty that say 87 runs just fine and maybe it does. Something along the way while engineers were testing this platform decided 89 was a safer alternative. so all the keyboard warriors in the world won't convince me otherwise. engineers actually use testing data to come to a conclusion not "well I've been doing it this long and nothin blew up" or depend on their calibrated butt cheeks for testing.

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Regarding 87 and 89 fuel igniting at different times there is a little more to it than what some of these posts seem to insinuating. On a gasoline engine the air fuel mixture will ignite when the spark plug fires. Not like 87 will ignite before the spark plug fires, and 89 ignites after the plug fires (assuming you are not getting into a pre-detontation/knock/pinging situation which indicates other problems....this is a whole different story). For the comment about 89 octane being "safer", where exactly does it state it is "safer" in any official documentation? The owner's manual states 89 is "recommend" but 87 is "acceptable". I think people are making assumptions this is entirely because of the MDS system.

 

[bigdodge]

That's why I said "that's a very basic explanation". If there was no possibility of pre ignition then they wouldn't recommend 89 octane. That's the only point of higher octane.

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[Grand Mesa]

Mid-grade octane level varies by state and by the location's elevation or what's available from the refinery. 89 octane isn't available for over 500 miles in any direction that I know of around here. I first start seeing the 89 Octane mid-grade gasoline at the pumps some 870 miles west in the Reno, Nevada area. At Reno's high elevation my PW still gets filled with the Regular 87 Octane gas since at its 4,500 feet altitude that would be my state's mid-grade gasoline.

https://en.wikipedia.org/wiki/U.S._State_Fuel_Octane_Standards

 

[Trailmaker]

Mid-grade octane level varies by state and by the location's elevation or what's available from the refinery. 89 octane isn't available for over 500 miles in any direction that I know of around here. I first start seeing the 89 Octane mid-grade gasoline at the pumps some 870 miles west in the Reno, Nevada area. At Reno's high elevation my PW still gets filled with the Regular 87 Octane gas since at its 4,500 feet altitude that would be my state's mid-grade gasoline.

https://en.wikipedia.org/wiki/U.S._State_Fuel_Octane_Standards

True but you have 85 as regular right? And premium is 91. I ran 91 in 66 mustang on the 1/4 mi when I lived up there. The colder dense air at night in the spring time, made me adjust my Holley carb some and shaved 0.5 second off my time. There at the mile high track even though the altitude caused me to lose ~15% hp

 

[Grand Mesa]

Yes, it's 85 octane regular here.

My 1968 high compression Ford V8 per the Mercury Cougar owner's manual stated to use premium gasoline with a minimum of 100 octane. Those were the days of a factory installed Engine Code W NASCAR engine within a family car.

 

[dhay13]

A higher compression engine will create more heat and cal lead to detonation/pre-ignition. This can be disastrous to an engine. Higher octane will resist that pre-ignition. In older cars this was potentially much more dangerous but newer cars have sensors in place to retard timing if it senses any detonation. While this can help protect the engine it will also reduce power output, hence why if your engine 'needs' higher octane than it can improve performance. I don't know near as much with the electronically controlled engines as the older carb'd engines but performance camshafts can bleed off compression with lots of overlap so you can get away with a little higher compression. Aluminum heads help dissipate heat better too so will help tolerate higher compression. I had a 11:1 327 small block chevy that ran fine on 93 octane. Back then anything over 10:1 was considered pretty high. The camshaft had high overlap so bled alot of compression. In todays engines my understanding is with VVT this same bleed-off can be accomplished but I have never built any engines like this so somebody else will have to correct me if I'm wrong. The only engine I ever built that required race fuel was a 12.5:1 454. My 11:1 327 and 10.7:1 393 both ran on pump gas and IIRC I was running about 36-38* of total timing. The 393 dyno'd at 552HP on pump gas.

So yes, there are benefits to running higher octane fuel (if your engine needs it) but if your engine doesn't need it then you are wasting money.

 

[Trailmaker]

A higher compression engine will create more heat and cal lead to detonation/pre-ignition. This can be disastrous to an engine. Higher octane will resist that pre-ignition. In older cars this was potentially much more dangerous but newer cars have sensors in place to retard timing if it senses any detonation. While this can help protect the engine it will also reduce power output, hence why if your engine 'needs' higher octane than it can improve performance. I don't know near as much with the electronically controlled engines as the older carb'd engines but performance camshafts can bleed off compression with lots of overlap so you can get away with a little higher compression. Aluminum heads help dissipate heat better too so will help tolerate higher compression. I had a 11:1 327 small block chevy that ran fine on 93 octane. Back then anything over 10:1 was considered pretty high. The camshaft had high overlap so bled alot of compression. In todays engines my understanding is with VVT this same bleed-off can be accomplished but I have never built any engines like this so somebody else will have to correct me if I'm wrong. The only engine I ever built that required race fuel was a 12.5:1 454. My 11:1 327 and 10.7:1 393 both ran on pump gas and IIRC I was running about 36-38* of total timing. The 393 dyno'd at 552HP on pump gas.

So yes, there are benefits to running higher octane fuel (if your engine needs it) but if your engine doesn't need it then you are wasting money.

cool I can get nerdy with you on this and add a little more. The SRT is a 6.4 as well but require premium instead of mid grade. And pump out ~50 more horses.
Valves are the same size between both motors (2.138/1.654). Compression is lower by about 1 point, 10.9:1(SRT) vs. 10:1 on the Ram. Apache head design is basically the same for both motors except for material (356 Aluminum on the HD) and redesigned cooling jackets. Tech Authority lists the cam lift and duration for the HD motor, but at a glance it seems unlikely to be 100% accurate. Especially considering they appear to mimic the SRT cam specs. Yes, the truck 6.4 has different heads, cam & intake manifold

Throttle body however is the same on the 5.7, 6.1 & 6.4

 

[bigdodge]

There 6.4 in the truck is based off the 6.2. Not the same 6.4 as the Challenger. There is an interview out there somewhere with the lead engineer that discuses this.

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[Tony1945]

I'm still not sure how so many of you guys can't break 12mpg in your Wagons. I routinely pull off 14-15+, but then, I rarely go over 65mph. My drive to work is 30 miles of 55 mph or less, and even on the expressway I set the cruise at 70 and call it good - because my mileage drops to about 13.

Long story short, if you want more mileage in these things, slow down. You're driving a brick, it's going to get the mileage of a brick.

Got 18.9 hand figured running 75/80 on a 380 mile round trip
The panel said 19.7 and that’s as close as its ever been
BTW the gas gauge is set for 26 gallons when is the 32 take a little convencing

 

[Grand Mesa]

Got 18.9 hand figured running 75/80 on a 380 mile round trip
The panel said 19.7 and that’s as close as its ever been
BTW the gas gauge is set for 26 gallons when is the 32 take a little convencing

You should round the panel's 19.7 MPG to 20 and then send a thank you letter to FCA. With our Power Wagon's 6.4L it seldom requires hand figuring, but only a couple of toes to calculate the MPG.

 

[Trailmaker]

There 6.4 in the truck is based off the 6.2. Not the same 6.4 as the Challenger. There is an interview out there somewhere with the lead engineer that discuses this.

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Correct. I was using the same displacement, as a reference to Compression example of two similar engines, to echo dhay13

 

[62Blazer]

A higher compression engine will create more heat and cal lead to detonation/pre-ignition. This can be disastrous to an engine. Higher octane will resist that pre-ignition. In older cars this was potentially much more dangerous but newer cars have sensors in place to retard timing if it senses any detonation. While this can help protect the engine it will also reduce power output, hence why if your engine 'needs' higher octane than it can improve performance. I don't know near as much with the electronically controlled engines as the older carb'd engines but performance camshafts can bleed off compression with lots of overlap so you can get away with a little higher compression. Aluminum heads help dissipate heat better too so will help tolerate higher compression. I had a 11:1 327 small block chevy that ran fine on 93 octane. Back then anything over 10:1 was considered pretty high. The camshaft had high overlap so bled alot of compression. In todays engines my understanding is with VVT this same bleed-off can be accomplished but I have never built any engines like this so somebody else will have to correct me if I'm wrong. The only engine I ever built that required race fuel was a 12.5:1 454. My 11:1 327 and 10.7:1 393 both ran on pump gas and IIRC I was running about 36-38* of total timing. The 393 dyno'd at 552HP on pump gas.

So yes, there are benefits to running higher octane fuel (if your engine needs it) but if your engine doesn't need it then you are wasting money.

This is one of the better explanations I have seen on this post regarding octane levels. Yes, increased compression will cause more heat and can cause pre-detonation which can be countered with higher octane fuel. The biggest take away is that generally by increasing compression you can increase power, and that increased compression requires higher octane fuel....but that is only if the engine is designed/calibrated/tuned to require it. If the compression and ignition systems are designed to run on 87 octane than running higher octane does absolutely nothing. Basically if the engine is tuned to run on 87 octane it doesn't magically adjust compression and timing if you put 89 or higher octane fuel in it. I would speculate the entire "89 recommend, 87 acceptable" could be based on tuning the engine for optimal performance on 89 octane but if the sensors detect any pre-detonation (knock) it backs the timing off slightly which would lead to ever so slightly less performance. Now let's put that in perspective as the difference between 87 and 89 octane fuel is very small (just over 2% difference) so not like there would be some huge difference in performance. I'm not a fuel expert but would guess the variation between brands and loads of 87 and 89 octane fuel means there is some overlap.....meaning some fuel advertised as 87 has as high, or higher, true octane when compared to some of the advertised 89 octane fuel. Again, this is speculation but from work experience this would not surprise me at all. The best analogy would be if you have a candle burning and you dump a 16 oz. glass of water (i.e. 87 octane) on it which puts the flame completely out. You relight the candle and then dump a 18 oz. glass of water (i.e. 89 octane)...and of course the flame goes completely out. Now you jump on the internet and tell everybody that the 18 oz. glass of water is obviously better. Well, is 18 oz. of water really better than only 16 oz. of water in this case? Now the scenario may be that every once in awhile 16 oz. doesn't completely put out the flame and you need that extra 2 oz.

Now the other part of the topic is the entire MDS and "safer alternative" thought. I'm not really sure the 89 octane recommendation has anything to do with MDS. Where exactly did this idea come from? Can anybody point me in the direction of a true technical document or official Ram Truck communication stating octane level and MDS is related in anyway, or that higher octane is "safer"? Honestly not trying to be sarcastic with that question as I would like to know if this whole theory comes from anything other than some random poster's speculations or theory at some point in time. Maybe I'm wrong (according to my wife I'm wrong most of the time....).

 

[ALRedneck]

This is one of the better explanations I have seen on this post regarding octane levels. Yes, increased compression will cause more heat and can cause pre-detonation which can be countered with higher octane fuel. The biggest take away is that generally by increasing compression you can increase power, and that increased compression requires higher octane fuel....but that is only if the engine is designed/calibrated/tuned to require it. If the compression and ignition systems are designed to run on 87 octane than running higher octane does absolutely nothing. Basically if the engine is tuned to run on 87 octane it doesn't magically adjust compression and timing if you put 89 or higher octane fuel in it. I would speculate the entire "89 recommend, 87 acceptable" could be based on tuning the engine for optimal performance on 89 octane but if the sensors detect any pre-detonation (knock) it backs the timing off slightly which would lead to ever so slightly less performance. Now let's put that in perspective as the difference between 87 and 89 octane fuel is very small (just over 2% difference) so not like there would be some huge difference in performance. I'm not a fuel expert but would guess the variation between brands and loads of 87 and 89 octane fuel means there is some overlap.....meaning some fuel advertised as 87 has as high, or higher, true octane when compared to some of the advertised 89 octane fuel. Again, this is speculation but from work experience this would not surprise me at all. The best analogy would be if you have a candle burning and you dump a 16 oz. glass of water (i.e. 87 octane) on it which puts the flame completely out. You relight the candle and then dump a 18 oz. glass of water (i.e. 89 octane)...and of course the flame goes completely out. Now you jump on the internet and tell everybody that the 18 oz. glass of water is obviously better. Well, is 18 oz. of water really better than only 16 oz. of water in this case? Now the scenario may be that every once in awhile 16 oz. doesn't completely put out the flame and you need that extra 2 oz.

Now the other part of the topic is the entire MDS and "safer alternative" thought. I'm not really sure the 89 octane recommendation has anything to do with MDS. Where exactly did this idea come from? Can anybody point me in the direction of a true technical document or official Ram Truck communication stating octane level and MDS is related in anyway, or that higher octane is "safer"? Honestly not trying to be sarcastic with that question as I would like to know if this whole theory comes from anything other than some random poster's speculations or theory at some point in time. Maybe I'm wrong (according to my wife I'm wrong most of the time....).

Great explanation. Think the MDS and octane has come from people feeling the MDS runs smoother on 89. I personally can’t tell the difference. Also, my MPG stay the same if I lock the MDS out but I’m on rural roads(speed limit is 45 and I go 45-60 depending on if houses are near by-try to be respectful). I know my Chevy 6.0 would have the computer change timing based on octane level and flex fuel per their manual. Wouldn’t be surprise if Ram has the same but doesn’t advertise it

 

[Grand Mesa]

If a customer purchases 1 gallon of premium gasoline at a pump with a single hose, how much of that 1 gallon purchased is not premium gasoline if the hose was previously used to fill up with regular? Approximately 1/4 to 1/3 gallon per various estimates.

 

[Trailmaker]

Now let's put that in perspective as the difference between 87 and 89 octane fuel is very small (just over 2% difference) so not like there would be some huge difference in performance. I'm not a fuel expert ..).

I’m not gonna completely pick apart your entire message but I may do a little bit at a time let’s just start with octane. It is not measured in percentage as you are speculating. 89 octane is not 89% of the gallon of gas. So 91 is not just 2% more. (1) Octane weighs .02 oz.
Let’s take octane booster for example. “NOS Octane Booster” produced an additional 46 points or 4.6 octane numbers when mixed at a concentration of 60:1. That means you’ll need to add 2.13 ounces of octane boost per gallon of gasoline.

I don’t think this is the place to explain gas. So I digress.

to get some one to quote from Mopar and put all together for you to understand mds, is not very likely. As for me, I not here to argue or to shame anyone. I just like kick it with my peeps that share a similar interest in trucks.

 

[ALRedneck]

Did a little research. Looks like there is no specific chemical that is octane but rather octane is a measurement of the gas ability to resist detonation under compression in comparing iso-octane to heptane. Iso-octane is a rating of 100 and heptane is a rating of 0. So 90 octane gas has the same resistance to detonation under compression as 90 percent iso-octane mixed with 10 percent heptane. Doesn’t mean the gas has these ratios being sold but rather has a mixture of chemicals that have the same equivalence as those ratios. Some chemicals that are alcohols have higher resistance than iso-octane and therefore get ratings higher than 100. Other chemicals can also raise the octane rating such as lead. So octane boost can be a multitude of chemicals that just stabilize the gas under compression. So, Exxon gas may not be the exact chemical composition as Shell gas but their octane rating can be the same based on the lab test. I would be certain our trucks computer can detect “knock” and adjust the timing but probably needs 89 octane to push out all 429 lb of torque. What’s the power at 87 octane in our trucks? Bet Ram knows but isn’t telling. Also bet it’s not enough for me tell! I don’t have that calibrated butt cheek that was mentioned before and obviously had to go look this crap up!

 

[62Blazer]

I’m not gonna completely pick apart your entire message but I may do a little bit at a time let’s just start with octane. It is not measured in percentage as you are speculating. 89 octane is not 89% of the gallon of gas. So 91 is not just 2% more. (1) Octane weighs .02 oz.
Let’s take octane booster for example. “NOS Octane Booster” produced an additional 46 points or 4.6 octane numbers when mixed at a concentration of 60:1. That means you’ll need to add 2.13 ounces of octane boost per gallon of gasoline.

I don’t think this is the place to explain gas. So I digress.

to get some one to quote from Mopar and put all together for you to understand mds, is not very likely. As for me, I not here to argue or to shame anyone. I just like kick it with my peeps that share a similar interest in trucks.

I understand what you are saying but you are on the wrong track. I'm not saying 87 and 89 octane are around 2% different because 89 minus 87 = 2. If you do the math 89 octane is 2.298% higher than 87 octane and the reason I stated it was around 2% difference.

My posts are not intended to be hostile or degrade anybody, but rather to just ask questions and spur some conversation and point out some facts...or lack of facts that are usually the case on these types of posts (again, hope nobody takes this personal). Just seems like some random person will make a random comment that they maybe think one thing is related to another (in this example the entire 89 octane/MDS/"safer" idea) and next thing you know people start saying it's the gospel. In this particular case maybe there is a chance it is all related, but again maybe there is absolutely nothing to do with each other. There is simply a lack of any type of concrete information there is any true relation. This comes from my past work experience as I'm an engineer and spent 15 years in the automotive testing field. Most of my days are spent setting up experiments and trials with multiple variables and then reviewing the data to determine the relationship between them. I'm not an engine design expert by any means, but I have a decent understanding of how auto manufacturers test and verify different conditions (I've personally performed industry standard fuel economy, oil life studies, powertrain durability testings, etc...) and how they write stuff up in the owner's manual. Based on that I will guarantee you that in regards to the comment of "89 recommended, 87 acceptable" stated in the manual, if there was ANY indication in the initial engine development and testing of the 6.4L engine by Ram/Fiat that 87 octane could cause failures, there is absolutely no way they would state that 87 octane is okay to use!

In the end, if people want to use 89, 91, or even 110 octane fuel in their truck that is completely their choice. It's their money and their choice.