87 octane vs 89 octane, fuel economy differences

[gimmie11s]

10.2 mpg?! Say what you want about the (mostly nonsensical) extra upfront and maintenance costs of a diesel, but I'd get crazy seeing those MPGs on a daily basis.

Hand Calc'd it was 9.87.

The big tires hurt. I immediately noticed a drop when I went to 35's on mine.

 

[Enve46]

Hand Calc'd it was 9.87.

The big tires hurt. I immediately noticed a drop when I went to 35's on mine.

Yea I lost about 1 mpg with the 37s. Worth it hahaha

 

[MEGA HO]

I lost a few when I went to 35s but I didn't adjust for larger tires and I know speedo and odo are lying and the actual mileage is a bit better but I'm still nowhere near lower tenths

 

[Enve46]

I lost a few when I went to 35s but I didn't adjust for larger tires and I know speedo and odo are lying and the actual mileage is a bit better but I'm still nowhere near lower tenths

You may have not seen but earlier in this thread I explained my commute and it involves really short trips, I don’t care what vehicle I drive it’ll net low mpgs. The worst was my first TRX, at one point was 7.6 mpg I think or maybe 7.8 but damn they’re fun trucks

 

[Riccochet]

No need to waste money on high octane fuels. These are not high compression engines, so they do not require the higher octane.

Lots of factors come into play for the MPG, so saying you got worse by switching to a lower octane is not really accurate.
Sart/stops. Acceleration differences. Different roads. Different temps, different amount of idle time, etc will make a difference.
Now if you did this in a controlled environment with controlled fuels, then the results could be acepted.

I've used the same fuel on the same roads and vary from 11 to 14 MPG. It all depends on throttle, speed and idle time.

Engine masters on YouTube has a video where they tested different octane fuels on the same OEM style motor. No difference in HP/TQ to mention.

To say they are the same throughout the years is not accurate. Tuning can be, and is, different. And compression is not the only factor when it comes to detonation or knock. The 6.4 BGE has variable timing. It can advance timing, to a certain degree, until knock is sensed. You'll get knock sooner with lower octane fuel.

How they changed the tuning over the years is anyone's guess. My 2020 calls for 89, but does say 87 can be used with reduced performance. So, clearly, the tuning will adjust the timing based on what it's sensing for knock.

 

[Firebird]

I have played with a couple more tanks of 87, and now 2 tanks of 89, still worse economy on 87 for me.

 

[AH64ID]

How they changed the tuning over the years is anyone's guess. My 2020 calls for 89, but does say 87 can be used with reduced performance. So, clearly, the tuning will adjust the timing based on what it's sensing for knock.

I highly doubt any tuning was changed since 2020 for fuel, especially since the current online version of the 2020 owners manual doesn't even mentioned 89. The 2019 online manual still mentions 89, but doesn't state anything negative about 87.

My guess is that the bean counters felt the 89 recommendation was hurting sales by recommending more expensive fuels.

 

[Riccochet]

I highly doubt any tuning was changed since 2020 for fuel, especially since the current online version of the 2020 owners manual doesn't even mentioned 89. The 2019 online manual still mentions 89, but doesn't state anything negative about 87.

My guess is that the bean counters felt the 89 recommendation was hurting sales by recommending more expensive fuels.

This is right from the 2020 manual. If you're hearing knocking then the VVT has pulled all the timing it can. Most cases you'll never hear it as it's retarded the timing enough to eliminate it. My guess is they tuned it to run on 87 in following years without much of hit to performance. Only way to know for certain would be to get a 2020 and a 2021 on a dyno.

 

[AH64ID]

This is right from the 2020 manual. If you're hearing knocking then the VVT has pulled all the timing it can. Most cases you'll never hear it as it's retarded the timing enough to eliminate it. My guess is they tuned it to run on 87 in following years without much of hit to performance. Only way to know for certain would be to get a 2020 and a 2021 on a dyno.

View attachment 69074

This is the current digital 2020 manual.



Would be cool to see some dyno charts.

 

[Riddick]

Dynos may not tell the full story, a degree of timing is only going to be a few hp difference which is exactly how much the hp will change from run to run.

You could get the info you want from datalogging a vehicle doing a pull at WOT. You can look at peak commanded timing vs. actual timing. If your tune file is commanding 24 degrees of timing and you are only seeing 21 degrees something is pulling it whether its extremely high IATs or knock from bad or low octane fuel.

 

[Redfour5]

There's a website called Fuelly https://www.fuelly.com/car/ram/2500/2022 If you look at the profiles you might be able to filter it down to octane I'm not sure. Bottom line the average is in the 12/14 range overall... Some people in their profiles will note fuel they use as I remember.

 

[Redfour5]

What about the elephant in the room no one has addressed.

Who buys a 2500/3500 truck for the gas mileage?

I have mine for peace of mind pulling my travel trailer in the 10K range miles every year vs a 1500 which can technically pull the trailer. It is much more relaxing than a 1500. No more white knuckle days or the requirement for some kind of shoulder massage... Oh it's great for hauling appliances home big load transfer station runs also. I just got a Gladiator for a daily driver and if you can imagine, I can stand at the side feet on the ground and touch the bottom of the bed of that. So, even a lot of transfer station duty is now moving to the Gladiator. And its mpg's is so much better at around 18 combined... Oh wait... Oh well, its better...

 

[Gondul]

I have played with a couple more tanks of 87, and now 2 tanks of 89, still worse economy on 87 for me.

I'll hazard a guess your 'better' economy doesn't offset the higher cost of the 89...

 

[Grey]

I only drive in reverse and up hill. So I run 93 so I can achieve negative mpg faster. <Thats a joke, people>

 

[Firebird]

I'll hazard a guess your 'better' economy doesn't offset the higher cost of the 89...

You are probably 100% correct

 

[Enve46]

Fuel economy is low on my worry list that’s for sure but if I can run 89 instead of 93 with no change in performance then it’s a no brainer. So far, in 1.5 tanks I have noticed zero change in how the truck drives and in this last half a tank actually slightly worse fuel economy then my tanks with 93. But I was only at half a tank and went on a trail ride this afternoon so filled it up so take that for what it is.

In my opinion these trucks are severely detuned from the factory so a change in octane probably isn’t going to do a damn thing with a conservative timing table anyway. I still like to geek out on **** like this to keep me entertained

 

[Riccochet]

I have mine for peace of mind pulling my travel trailer in the 10K range miles every year vs a 1500 which can technically pull the trailer. It is much more relaxing than a 1500. No more white knuckle days or the requirement for some kind of shoulder massage... Oh it's great for hauling appliances home big load transfer station runs also. I just got a Gladiator for a daily driver and if you can imagine, I can stand at the side feet on the ground and touch the bottom of the bed of that. So, even a lot of transfer station duty is now moving to the Gladiator. And its mpg's is so much better at around 18 combined... Oh wait... Oh well, its better...

You stalkin my life choices? lol 2500, Gladiator and Wrangler.

 

[Dave01]

Absolutely positively take it to the bank no need whatsoever for 93 octane in these trucks. Completely unnecessary.

I run 87 full time now, when I first had it I was switching between 87 and 89. Saw no difference. I get it that some people will feel better and see better performance/mileage with 89, and I'm not going to argue about it, could be true. It's not going to affect the life and health of the 6.4, but I don't think in terms of other factors there's a definitive answer that is the RIGHT one. And I have definitely run higher octane gas in some vehicles or toys that likely don't need it, so I get it.

 

[Enve46]

Quick update on the last tank of 89. This one has a 35 minute trail ride on it. Dash was quite a bit off on this last tank.

 

[Riccochet]

Are we doing off road fuel economy now?

Pretty sure my Wrangler gets 2-3 gallons per mile when I'm rock crawling.