Christmas Road Trip results (87 octane vs 93)

CRTrucks · December 31, 2013

Hi everyone, I thought I would post my results from a road trip I took last week.

Truck specs: 2014 Silverado LTZ Crew Cab 4x4, 3.42 axle started with about 1100 miles on the odometer and ended with about 3200 miles (drove around town in Michigan)

Distance: 1650 miles round trip

Terrain: We drove from Maryland to Michigan so the terrain varied from flat as a pancake Ohio to very hilly Pennsylvania. Nearly 100% expressway / turnpike except for stops.

Weather: Averaged about 40 degrees with a high of about 48 and low of 20

My observations: On our way to Michigan I ran on 87 octane, the truck achieved an average of 18 MPG (calculated by hand). I found that the truck did not want to stay in V4 mode even on very flat roads on the Ohio Turnpike. If I turned cruise control off, I could force it to jump to V4 by babying the throttle but it would hop right back in with the smallest hill. I was rather upset with this fact as the truck was getting pretty poor MPG during the drive (DIC was showing around 16 MPG). On the other hand, the truck rides really nice, it is the most comfortable vehicle I have ever owned and is a pleasure to drive.

After we arrived at our destination I questioned what would happen if I ran on premium for our return trip. I read about how others had observed better MPG running higher octane fuels in these new trucks, and figured it was worth a try. I did a little sleuthing and planned out my fuel stops. I found a gas station (Sams Club) that actually had 93 Octane cheaper than the other local stations had 87 for and it ended up only being 20 cents more than 87 octane at that particular station. I ran the truck down to nearly empty and filled up with 93 octane. After filling up, I didn't see any results right away. After driving about 100 miles on the 93 octane I started to notice the truck was running in V4 mode nearly all the time (even on hills I would have expected to see it jump to V8). We stopped for lunch and when we were cruising around I noticed the throttle response seemed a lot better and acceleration seemed much better. On my next fill up I put 93 octane in again (a bit more expensive this time but I couldn't find a station in the area that was priced like it was a Sam's). The entire ride back, I felt like it was a different truck (I wonder if GM actually intended for this engine to run on higher octanes from the beginning and decided to allow it to use 87 as an afterthought?).

The Results (hand calculated)

87 octane: 18 MPG

93 Octane 21.5 MPG

A lot of this can be attributed to the truck staying in V4 mode more often with the more power from the 93 octane. I could also see that some of it could be attributed to the truck being broken in a little more between the trip to Michigan and back. After this trip, I think I will be running premium fuel for my road trips in the future.

Carder09 · December 31, 2013

I think the manual states a minimum of 87 is recommended. I would look into a tune, black bear is very good, and utilize the full potential of the higher octane. I run premium also, though I have an 06 with a tune, and I average better mpg also. Though a lot of factors play in it, yours still might increase a small amount as the engine breaks in.

Cap'n Pete · December 31, 2013

Interesting!

Thus far, I've only run 2 full tanks of gas through my truck, and I'm sitting just over ~900kms (~600 miles) on the odometer. So far, the mileage technically SUCKS, however, it's got everything to do with the DAMN COLD WEATHER we've had ever since I picked up the truck 3 weeks ago! The truck has spent way more time sitting idling than I'd like (esp. for a new engine) but I'm not jumping into a freezing cold truck and driving away without letting it warm up.

After I ran the first tank empty, I switched to a 91 non-ethanol fuel to see if there would be a difference. It's honestly too early for me to tell. What I CAN TELL so far is that the outside temperature has a huge effect. Once it drops below the freezing mark, esp. by -5°C (25°F or so) the mileage falls off big time. We've had a couple days with the temp just above freezing, and I've been able to see the numbers improve A LOT (ie: 18 litres/100kms when it's bad, down to 13 litres/100kms when it's warmed up ................sorry CANADIAN mileage data, not MPG!!).

I'm curious to see how it performs when the weather warms up. I can see how it can easily get over 20 MPG if the conditions are right. It'll be easier to compare the difference between fuels then too.

HydrogenCyanide · December 31, 2013

Driving East to West will almost always yield worse fuel economy. Although the higher octane gas may have had an impact, so could the wind. Might just be the way the wind blows.

fondupot · December 31, 2013

the truck is designed to run in 87. Running 93 without a proper tune wont make a difference.

The mileage difference you are seeing is most likely attributed to difference in environmental changes. Aka, wind, temp, etc.

crushNchowda · December 31, 2013

the truck is designed to run in 87. Running 93 without a proper tune wont make a difference.

The mileage difference you are seeing is most likely attributed to difference in environmental changes. Aka, wind, temp, etc.

All these high compression GM smallblock V8's like higher octane fuel regardless of what the manual states is the "minimum". I wouldn't say it is no difference, it may not be huge, but I'm sure you'd get slightly better mileage and definitely make a little more power on the 93. Also, particularly w/ winter blends, you reduce the risk of knock entirely.

I agree having it tuned properly for the octane is the ideal, but I don't think it would hurt running 93 regardless. I don't pay for gas, work does, so I run it anyhow.

CRTrucks · December 31, 2013

the truck is designed to run in 87. Running 93 without a proper tune wont make a difference.

The mileage difference you are seeing is most likely attributed to difference in environmental changes. Aka, wind, temp, etc.

I saw a Dyno chart somewhere where someone found the truck actually does produce slightly more HP on higher octane fuel. I can't find the chart now, but it showed E85 having the best HP and torque followed by 91. Wish I could find it...

MikeNH · December 31, 2013

the truck is designed to run in 87. Running 93 without a proper tune wont make a difference.

The mileage difference you are seeing is most likely attributed to difference in environmental changes. Aka, wind, temp, etc.

Nope. Unless the new trucks have changed which is unlikely, at each fill up the truck calculates ethanol content by playing with timing. Since E85 and premium will likely act similar in terms of timing adjustments you'll likely see the same power gains from 93 as you would E85 without the MPG hit. Regardless of efficiency, even my 2011 ran better on premium before being tuned.

haider320 · December 31, 2013

the truck is designed to run in 87. Running 93 without a proper tune wont make a difference.

The mileage difference you are seeing is most likely attributed to difference in environmental changes. Aka, wind, temp, etc.

Not necessarily. These new ecotec engines have variable valve timing. With my 2011 5.0 Mustang, it also had variable cam timing. The Mustang had an 11.1 compression ratio and was also designed to run on 87. The knock sensors would detect knock by running 87 and retard the timing. Less HP, tq, and mpg. Run 93 in the Mustang, the timing would be advanced due to less knock. More HP, tq, and better mpg.

The Ecotec also has an 11.1 compression ratio. I think it's dumb GM recommends 87 with a high compression ratio. I would bet this engine/ECU operates similarly to the Mustang set up.

The Ecotec can also run E85. More ethonal means higher octane. The Ecotec 5.3 running E85 is rated at 383 HP and 416 ft-lb. Running 87 the 5.3 is rated at 355/380. If that isn't proof the timing isn't advanced in these new motors; I don't know what is..

I believe he got better mpg, along with more HP and tq with higher octane.

http://gmauthority.com/blog/gm/gm-engines/l83/

DanMan_S · December 31, 2013

Not necessarily. These new ecotec engines have variable valve timing. With my 2011 5.0 Mustang, it also had variable cam timing. The Mustang had an 11.1 compression ratio and was also designed to run on 87. The knock sensors would detect knock by running 87 and retard the timing. Less HP, tq, and mpg. Run 93 in the Mustang, the timing would be advanced due to less knock. More HP, tq, and better mpg.

The Ecotec also has an 11.1 compression ratio. I think it's dumb GM recommends 87 with a high compression ratio. I would bet this engine/ECU operates similarly to the Mustang set up.

The Ecotec can also run E85. More ethonal means higher octane. The Ecotec 5.3 running E85 is rated at 383 HP and 416 ft-lb. Running 87 the 5.3 is rated at 355/380. If that isn't proof the timing isn't advanced in these new motors; I don't know what is..

I believe he got better mpg, along with more HP and tq with higher octane.

http://gmauthority.com/blog/gm/gm-engines/l83/

This is correct. The days of saying that adding higher octane fuel beyond what the vehicle requires will have no benefit are over. It has been proven that the new 5.3L responds quite well to higher octane fuel. While the official numbers are with E85, this isn't due to the fuel itself, but due to the higher octane rating. If I had one of the new 5.3L trucks, I'd be running the highest octane available whenever I fill up.

The combination of variable valve timing, direct injection, higher compression and advanced computing and knock sensors allow GM to tune the engine for the high octane scenario, and then just pull back as needed when the low octane fuel is detected. The addition of direct injection also helps avoid alot of the issues with detonation/pre-ignition as you simply don't have a cylinder full of fuel during the compression stroke anymore.

On previous years engines, whether or not the addition of higher octane fuel would make a difference is debateable, on these new ones, GM has officially posted low octane AND high octane hp/torque numbers, similar to how ford does it with the mustang.

On the dyno, the 5.3L of 87 octane produces 302 hp and 332 lbft at the rear wheels, on E85, this jumps to 321 hp and 355 lbft. The links below have acceleration numbers and dyno charts to show how this works.

http://www.lingenfelter.com/LPEforumfiles/showthread.php?2248-2014-1500-Silverado-with-5-3L-L83-engine-work-begins

http://www.gmhightechperformance.com/tech/engines/1306_2014_silverado_solid_baseline/

klrrdr · December 31, 2013

My new AT with 5.3 and 800 miles has yet to get past 14.8 in a combination of town and hi-way. Not really happy with those numbers. Eastern,PA not too cold. Is it that winter gas dragging me down?

bladz1454 · December 31, 2013

My new AT with 5.3 and 800 miles has yet to get past 14.8 in a combination of town and hi-way. Not really happy with those numbers. Eastern,PA not too cold. Is it that winter gas dragging me down?

I'm in the same exact boat, im wondering if I should toss some high octane in to see if it really makes a difference now

'01LS1 · December 31, 2013

Nope. Unless the new trucks have changed which is unlikely, at each fill up the truck calculates ethanol content by playing with timing. Since E85 and premium will likely act similar in terms of timing adjustments you'll likely see the same power gains from 93 as you would E85 without the MPG hit. Regardless of efficiency, even my 2011 ran better on premium before being tuned.

Exactly...

& for those interested, this is worth reading...

http://en.wikipedia.org/wiki/Heptane

&

http://science.howstuffworks.com/gasoline3.htm