93 octane gas

texasnavy05 · October 30, 2019

Any benefit for running 93 octane in the new 6.6?

About $0.55 difference between 87 and 93. 2mpg boost would make the $per mile the same. But, I feel like a 2mpg boost is ambitious.

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CamGTP · October 30, 2019

Who is claiming a 2mpg increase though?

If you were going to beat the absolute piss out of the truck every second and day of it's life, running 93 octane would likely benefit the engine just a little. Because it's less prone to knock and would be better if that engine is under extreme stress/hot temps all the time.

Otherwise running 87 or 89 octane will be no different than 93 octane for running around town and cruising on the open road. I prefer to run 89 octane in the DI engines because from watching data logs with my tuner it ran smoother than with 87 octane. No noticeable mpg change between the two fuels.

texasnavy05 · October 30, 2019

Who is claiming a 2mpg increase though?

If you were going to beat the absolute piss out of the truck every second and day of it's life, running 93 octane would likely benefit the engine just a little. Because it's less prone to knock and would be better if that engine is under extreme stress/hot temps all the time.

Otherwise running 87 or 89 octane will be no different than 93 octane for running around town and cruising on the open road. I prefer to run 89 octane in the DI engines because from watching data logs with my tuner it ran smoother than with 87 octane. No noticeable mpg change between the two fuels.

I don't think anybody would claim a 2mpg boost. I was just saying it would take 2mpg to make the $ per mile the same. If there's no other real advantage...I guess that answers my question.

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Grumpy Bear · October 30, 2019

I spent a good deal of time and money on this topic over the last year testing in 1 octane units mpg and KR reduction between 87 and 94 octane. Results were zip. Repeated with different fuel sources. Again zip. Each run several thousand miles and multiple tanks averaged until I was satisfied to a statistical certainty. I tired octane boosters a few years ago and also, zip.

The only thing fuel wise I've found that 'can' make a difference is a PEA based and fuel tank used cleaner such as, Chevron Techron, Gumout Regane or Red Line SI-1 and only if the system was dirty enough to actually cause a decrease in fuel efficiency. Double down on the dose for one full tank to clean.

Other "cleaners" such as Seafoam will keep clean systems from getting dirty but IMHO and stat's say it won't clean a dirty system.

A dosing about every 5K will keep it from degrading to begin with.

SierraHD17 · October 30, 2019

With the stock timing curve of an HD gaspot you have absolutely zero reason to run premium fuel. Until tuning is available (which I honestly doubt it ever will be) run regular.

CNY_AT4 · November 2, 2019

Without doing the research, running premium gas only would have noticable benefits if you are running variable timing as the vehicle will pull timing on perceptible knock. Higher octane would raise this limit and gain you more power. As grumpy bear stated, typically the detergents in the fuel can play a factor but those shouldn't yield anything on a new vehicle.

Not an HD but with my F150, I run premium when towing as it will give a noticable gain to power on hills, etc but it is the EcoBoost and adjusts power/boost based on a wide variety of things which higher octane helps. I wouldn't have the same benefit with the 5.0.

diyer2 · November 2, 2019

My brother in law has a 1988 Chevy 2500 350 4 speed. 160 K miles. Motor hasn't been touched. Trans rebuilt and rear end also.

Here in Colorado we have 85, 87, and 91 octane due to the altitude.

Normal use he uses 85 octane.

If he tows a heavy load it spark knocks bad unless he uses 91 octane.

Truck can't adjust timing enough to stop the spark knock due to the old technology.

newdude · November 2, 2019

Almost 11:1 (10.8 to be specific) compression it wouldn't hurt anything that's for sure. The 5.3 is 11.1 and is 87 octane but at 11.5:1 the 6.2 is 93 octane.

Edited November 2, 2019 by newdude

Grumpy Bear · November 2, 2019

Back in the day we used a rule of thumb that said a point of research octane per point of compression. Research octane was the number on the pump and the lower of the two. The motor number is a more severe test and 8 - 10 points lower than the research number. This link will give more detail.

https://www.pei.org/wiki/octane-number

That research number is based, as the article states on the results of a fuels knock limit to a blend of two know fuels in a variable compression motor. I have some hours on these motors. They have a fixed camshaft profile and there in lies todays variable that wasn't back in the day.

On the head of this motor is a transducer that records BMEP (brake mean effective pressure). Same number you would see on a compression test, that is the average of all four cycles. While the reported octane numbers are referenced to the mechanical compression ratio the logs record the BMEP and compression pressure as well and this is a really big deal because octane limits are based not the mechanical compression ratios but the dynamic ratio. That is the Compression pressure / atmospheric absolute pressure. THAT number is highly influenced by the inlet valve closing angle which determines the 'cylinder trap' or how much of the mechanical number is kept.

Bottom line; the required octane number is pressure sensitive not compression ratio sensitive. You could literally have a motor with a 14:1 ratio running knock free on 85 R straight run fuel IF the inlet valve closing point was late enough to set the cylinders BMEP low enough. You could also have a motor with an 8.5: ratio that required 97 points if the inlet angle is shallow enough.

This is why the are 'rules of thumb' and not absolutes and now that we have VVT/VVL and KR and soon even VCR all former knowledge is muddy. Oh those rules will always apply but getting them will be more and more difficult for anyone but the designing research lab to obtain.

The good news is; we know have motors that run the highest possible cylinder pressures for the fuel available assuring efficiency for cost effective operation, motor power and emissions requirements.

Edited November 2, 2019 by Grumpy Bear
Spelling, Grammar.

Cowpie · November 9, 2019

It would take a little more than a 2 mpg improvement to make premium break even with regular. For instance, regular in my area is 2.39. Premium is $2.94. If I was getting 15 MPG on regular that is about 16 cents a mile. To make premium break even, it would require getting over 18 MPG.

I would concur that the 6.6 L8T could probably benefit from higher octane since it has a compression ratio of 10.8:1. It is hard to imagine that there would be times where, when using regular, the ECM would have to alter timing and whatever to prevent occasional pre-ignition. And that is one of the major problems with DI gas engines.... LSPI (Low Speed Pre Ignition). It is such a problem among DI engines that even motor oil formulations have been altered a little in an attempt to mitigate it, when a little more octane would noticeably prevent it. Just the slight combustion chamber carbon build up would elevate the compression ratio over 11:1.

To that end, if one has access to E85, mixing a 1 gallon to 4 ratio of E85 to E10 regular would end up being a 25-30% ethanol blend and a octane rating of 94 (1 to 3 of E85 to non ethanol regular). That could be a cheaper solution. Many in the high performance car community at doing this sort of thing with good success. Most vehicles will not get a CEL with blends up to 30%. These pickups are designed to deal with E15 already. They can deal with E30. If one could find a blender pump in their area that would be great. Just select E30 at the pump. Either way, the total price would be less than regular gas with the benefit of premium gas and burn cleaner.

Edited November 9, 2019 by Cowpie
Spelling

SierraHD17 · November 9, 2019

Doubtful octane will do a thing. There is a lot more to octane tolerance than static compression ratio... and direct injection is key. The timing curve will be pathetic like how it is in the current 6 liter trucks and dumping premium in these on the stock tune will not do a damn thing.

Cowpie · November 9, 2019

Still it would be worth a try by running a higher octane mix. If it doesn't help, then go back to regular. My wife's 2017 Equinox with DI 2.4 with 11.2:1 ratio definitely runs better on E85 compared to regular or even mid grade. That is why it has been on E85 exclusively for quite a while now.

SierraHD17 · November 9, 2019

Just spending more money lol. Enough people whine about the mileage as is so paying more for the same thing isn't going to help... and ethanol will just make that mileage even worse. The numbers on 87 posted by guys look decent for an HD gas truck so I doubt they will see an improvement. These aren't set up for ethanol so the timing adders will not be there for higher content nor will it know what the ethanol content is so it will do nothing for power.

Cowpie · November 9, 2019

Yeah, ethanol can make the MPG worse, but the does not mean on a cost per mile basis that it is a poor choice.

For instance, my 2015 2500 6.0 has been on E85 for over 3 years. Currently at $1.90 a gallon. Premium is $2.94 a gallon. I average, for all miles (city, highway, rural gravel, hauling, towing, etc) about 11-12 mpg on E85. 13-14 mpg on road trips. At $1.90 a gallon and 12 mpg, that equates to 15.8 cents a mile fuel cost. If I was using premium, I would have to average 19 mpg for ALL miles. That is never going to happen even on road trip mpg. So E85, while delivering lower mpg, is substantially cheaper to use on a cost per mile basis.

Folks need to get beyond just the mpg numbers and find out what they are doing is actually costing them.

And E85 at $1.90 with E10 at $2.39 in my area, blended at a 1 to 4 ratio would make 94 octane fuel and be cheaper than regular E10 per gallon. So again, while the mpg would be lower with ethanol, it is a substantially cheaper than using premium gas on a cost per mile basis.

I am really surprised there isn't more talk about doing this with the 6.2 in the 1500. Many HP car enthusiasts do this mixing. But for some reason pickup owners suffer from an economic brain fart and enjoy spending higher money for Premium fuel.

Edited November 9, 2019 by Cowpie

SierraHD17 · November 9, 2019

There is plenty of chatter on E85 conversions on performance oriented forums. This place isn't really a performance forum so you don't hear about it.

E85 is also limited and only available in certain areas so its consideration is pretty null. I can buy it in drums... but I can buy race fuel in drums too and would rather use that for all my performance stuff.