Community Forums

chrisgolden · 07-27-2015, 02:07 PM

Hi Everyone,

As a " NEWBEE ", I would like Your opinion on the best grade of gas for my 2500 Dodge Ram with the 5.7 Hemi, towing a 5th wheel.

Thank You,
Chris Anderson

BFlinn181 · 07-27-2015, 03:27 PM

What does your owner's manual recommend? I'd go with that octane number. You didn't give a year so I can't look it up for you, but if you don't have a manual I'm sure you can find it on line and download one.

jacwjames · 07-27-2015, 03:33 PM

My brother-in-law has a 1500 Dodge Ram with the 5.7 hemi. He's a performance freak, I believe he said he put a chip in it for more get up and go. He burns nothing but Premium. He told me the additional cost almost pays for itself in better mpg.

He was here ~6 weeks ago and I drove the truck, couldn't really tell if it had more power.

I have a 5.7 Hemi in my Jeep, it does well on regular octane gas but I've never tried premium to see if it makes a difference.

Dutch Star Don · 07-27-2015, 09:35 PM

Modern engines adjust for the fuel you put in them. I would run it on regular around town and before a trip, top off with premium. You'll NEVER see an increase in mileage that pays for the additional cost of premium vs regular gasoline. You MIGHT see .01 -.02 increase in mileage.

lynnmor · 07-28-2015, 03:11 AM

Quote:

Originally Posted by Dutch Star Don

Modern engines adjust for the fuel you put in them. I would run it on regular around town and before a trip, top off with premium. You'll NEVER see an increase in mileage that pays for the additional cost of premium vs regular gasoline. You MIGHT see .01 -.02 increase in mileage.

An engine cannot adjust its compression ratio. The idea that modern engines can adjust for the octane being used is not really true. All that can happen is that the knock sensors and computer will downgrade performance to protect the engine. Use the fuel that the manufacturer specifies in the OWNERS MANUAL.

38Chevy454 · 07-28-2015, 08:38 AM

The computer adjusts the ignition timing and fuel maps to keep the engine out of pre-detonation. Under a high load and with summertime temps, engine is more susceptible to knocking, so using higher octane will help it have better power. whether you get more mpg is debateable, but you should have better pulling up the hills.

dons2346 · 07-28-2015, 09:06 AM

I would run premium and if you can get it, I would go with the non ethanol fuel. You will get better performance and better mileage. Been using the non ethanol while I am in Wisconsin in the Jeep and it runs a whole lot better.

Todd157k · 07-28-2015, 09:20 AM

I have a Bullydog tuner on mine. I run premium when I tow. I end up with better mileage on premium anyway. Not by much, but better.

timetogo · 07-28-2015, 10:37 AM

I believe 89 is recommended.

Cat320 · 07-28-2015, 02:09 PM

I'm with the "do what the manual says" crowd.

Dutch Star Don · 07-28-2015, 09:02 PM

"lynnmor"......Even in your own response you state the engine adjusts by the computer downgrading the performance! Is that not an adjustment. Even goofier is your statement that compression ratios don't change, really....what does that have to do with a computer adjusting for the octane. Maybe the Johnson Rod needs larger bearings????

mel s · 07-28-2015, 09:08 PM

Quote:

Originally Posted by BFlinn181

What does your owner's manual recommend? I'd go with that octane number. You didn't give a year so I can't look it up for you, but if you don't have a manual I'm sure you can find it on line and download one.

lynnmor · 07-29-2015, 02:55 AM

Quote:

Originally Posted by Dutch Star Don

"lynnmor"......Even in your own response you state the engine adjusts by the computer downgrading the performance! Is that not an adjustment. Even goofier is your statement that compression ratios don't change, really....what does that have to do with a computer adjusting for the octane. Maybe the Johnson Rod needs larger bearings????

If you don't know what compression has to do with an engine knocking, then it would be best if didn't give advice on fuel choices.

BFlinn181 · 07-29-2015, 09:02 AM

Quote:

Originally Posted by lynnmor

If you don't know what compression has to do with an engine knocking, then it would be best if didn't give advice on fuel choices.

First rule of the forum: Be courteous.

Knocking can be caused by a number of factors, including compression. Reducing or stopping knocking can be done by using a higher octane fuel, retarding timing, increasing fuel/air mixture or changing compression ratio. Of that list, changing compression is the most difficult, requiring machining or changing parts. In my youth we did it by using a thicker head gasket, but that's certainly not recommended today and was prone to causing leaks.

Retarding timing and adjusting fuel/air mixture is the easiest and most common in computer controlled engines. Dutchstar Don made that point and added that the change in mileage will not be equal to the cost difference between gas octanes. A perfectly proper statement and one in which I agree. lynnmor, you introduced compression ratio and have acted like it's the most important factor in engine octane requirements. It's the most difficult for the non-mechanic owner to do anything about, but the strategy of using lower octane fuel for daily use and adding higher octane fuel for heavy pulling is a perfectly proper strategy.

Over the years I have looked on car lots and noted cars that required premium fuel in order to increase performance. I've never valued speed and peeling tires over power and economic sense, so I walk on past vehicles it. If I want power, I look at diesels.