Octane and Towing

[69 Post Sedan]

I’m in a discussion with a guy about octane and towing. Up until last week, I had a 2015 Silverado with 5.3 Direct Injection. When I would tow my Chevelle in my 24’ enclosed trailer, I would run high octane because the engine is working harder.

I realize the timing will adjust to prevent engine knock but my thought, and the way it was explained to me, is that the higher octane will prevent detonation. If that’s the true, the timing won’t back off which in turn will help prevent power loss.

Am I way off........too old school??? :dunno:

Kurt

[wheelhop]

Get a diesel and lower your octane!

[PxTx]

I agree. When towing heavy loads I often fill up with hightest. No need to reduce timing and power with higher loads.

These engines are tuned so lean for federal emissions, that they are always on the ragged edge of detonation. Keep doing what you're doing.

[69 Post Sedan]

Get a diesel and lower your octane!

I upgraded to a 2016 with a 6.2L, 8-Speed, 3.42 rear with Max-Towing Package. What a difference this setup is compared to the 5.3L, 6-Speed with 3.42 rear.

[Mr. Chevy]

I can tell you from experience that if you run junk, low octane gas when towing you will definitely get detonation. I had it so bad once it activated the knock sensor on the motor.

Rich

[Big Block Bill]

Congrats! You will love it going forward. On the Octane / Towing question, I've owned a Gas Station for the past 33 years and this question comes up a lot. My experiencen is that increasing the octane on any late model computer controlled vehicle will more times than not work against you. Vehicles today are pre-programmed to deliver timing and fuel @ the octane recommended. When you increase octane, the computer will not adjust. Higher octane makes for a slower burn, not faster as most people think. When higher octane is put into a vehicle designed to run on lower octane it will experience longer cranking upon start up, harder starting when hot, and less performance overall. Don't waste your money.

The only time a higher octane will increase performance in an engine designed to run on a lower octane is when an engine has a high carbon build up on the pistons and combustion chamber resulting in essence raising the compression ratio. We use GM top engine cleaner to clean engines when this occurs. Late model GM 3.6 V-6's are common with this condition. It will cause the check engine light to come on for a random or cylinder misfire codes.

Hope this helps, ENJOY your new ride! Feel the power!

Bill

[PxTx]

I respectfully disagree on it being a waste of money.

My wife has a 2011 Denali with the 6.2. It really is a great set-up. I can only imagine it is even better in 2016. I thought here owners manual said to run premium fuel. Maybe she is waster her money since I did not confirm what the manual says about fuel, but I can't say we're experience any of the negatives listed above.

This could get into a log debate, but on the dyno you can absolutely push the limits of timing with higher octane. If you actually look at the timing maps programmed into the PCM, they vary for tow mode and regular, and have a range of retard once the knock threshold is crossed. Better fuel will let you stay in the more powerful part of the timing map when pushing the engine.

Granted, light load, modest throttle and the higher octane will not be nessisary on many engines. My experience towing with the Chevy V8 is the better octane is worth it.

[Big Block Bill]

I do not know what GMC recommends for grade of fuel in a 2011 Denali, but my 2015 Denali XL must run on Premium according to GMC. I agree on a Dyno when the timing can be adjusted, it will increase performance, but in a stock programmed ECM in a late model vehicle timing is set by the factory programming and increasing octane will not help performance, only hurt the drive ability. FWIW, That's my opinion / experience. I make more money on Premium than I do on regular so I hope everyone buys Premium. Not trying to be a know it all here, but in my world it's just a waste of money unless required by the manufacture. Once again, ENJOY the new ride.

Bill

[69 Post Sedan]

Thanks for the replies guys....much appreciated!!!!

[markjohnson]

I would've thought that higher octane fuel lets the motor run max timing without fear of detonation or killing power when pulling timing out. BTW, anybody else remember the story about the loose, dry trailer ball rattling around in the trailer hitch and triggering the block sensor into thinking the motor was in detonation? Crazy stuff!

[69 Post Sedan]

I would've thought that higher octane fuel lets the motor run max timing without fear of detonation or killing power when pulling timing out.

My thoughts exactly......but I’ve been wrong before....lol

Kurt

[x33rs]

When I tune the LS engines, there are 2 sets of timing tables. One with much lower timing figures. The computer will revert back to the lower numbers when the knock sensors pick up anything. Generally the slight loss in power and MPG isn't even noticed by most owners.

I know the truck timing tables are extremely conservative due to the intended purpose the trucks are built for. I haven't been into the tunes on the newest trucks much past 2006, but I would assume not much has changed.

Some tuners will copy/paste the high octane timing tables over the low octane timing tables to keep everything consistent, and still leave the knock sensors active to pull 3-4 degres when knock is present. But at this point I wouldn't recommend running the cheapest fuel in it.

[martinbrown239]

I respectfully disagree on it being a waste of money. In my opinion, its waste of money.

[Canuck]

I have been running the higher octane in my 2003 Yukon XL2500 from about 60,000 miles, I noticed a performance difference and slightly better fuel economy by constantly running 91. It now has 140,000 miles and have only had to replace the map sensor.

[PeteLeathersac]

I respectfully disagree on it being a waste of money. In my opinion, its waste of money.

Disagree + Agree...sounds like a political statement?
:hmmm:
~ Pete


.

[dustinm]

I have been running 87 in my 6.2 (not towing with it) as the price for premium has escalated higher than diesel. With the lower octane I have managed a new MPG high score on the display (33.5 for last 25 miles, 29.5 last 50). When I go to tow again I will def fill up back up with 91. But whats to say we are getting 91 out of the hose? Esp when there is only 1 hose for three fuel grades. I know they dont dedicate a truck for each fuel either.

[69 Post Sedan]

I have been running 87 in my 6.2 (not towing with it) as the price for premium has escalated higher than diesel. With the lower octane I have managed a new MPG high score on the display (33.5 for last 25 miles, 29.5 last 50). When I go to tow again I will def fill up back up with 91. But whats to say we are getting 91 out of the hose? Esp when there is only 1 hose for three fuel grades. I know they dont dedicate a truck for each fuel either.

Is it possible that the engine timing is backed off with the lower octane and the result is better fuel mileage? Although power will be down in that scenario also.

On a side note, I’ve gotten 28.5 on a 25 mile average.

Kurt

[southernfriedcj]

Get a diesel and lower your octane!

This.

Get a Cummins tow pig and never look back.

[69 Post Sedan]

This.

Get a Cummins tow pig and never look back.

I only pull my trailer 3 or 4 times a year. I can’t justify the extra money
PLUS the maintenance on a diesel. My 6.2 suits me well.... :beers:

Kurt

[dustinm]

Is it possible that the engine timing is backed off with the lower octane and the result is better fuel mileage? Although power will be down in that scenario also.

On a side note, I’ve gotten 28.5 on a 25 mile average.

Kurt




I think the load is light enough, that it isnt detonating and is able to keep the higher timing table.