New 6.6 gas

TXGREEK · October 28, 2019

Posted the newest TFL Truck video on the 2020 6.6L Gasser highway towing and highway empty MPGs in the 6.6L Forum section.

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Great video, thanks for posting.

Personally, the new 6.6 is perfect for towing in areas not to steep. I can see this truck engine being widely used especially in flatter roads but I’d definitely choose the diesel in mountain regions like Colorado if I’m towing max, especially for safety reasons and LOVE the exhaust brake!

Sent from Above

greatmizzou · October 28, 2019

1 hour ago, SkidooSteve12 said:

Posted the newest TFL Truck video on the 2020 6.6L Gasser highway towing and highway empty MPGs in the 6.6L Forum section.

Interesting they put 85 in it. Manual specifically says to use 87. If the engine is being maxed out, they should really use 87.

Having driven in Colorado, Ive experienced engine pinging and performance problems using 85....regardless of the altitude.

SkidooSteve12 · October 28, 2019

2 hours ago, greatmizzou said:

Interesting they put 85 in it. Manual specifically says to use 87. If the engine is being maxed out, they should really use 87.

Having driven in Colorado, Ive experienced engine pinging and performance problems using 85....regardless of the altitude.

Yeah I was surprised they went with the 85 octane... I wonder if they put 85 octane in the other HD gas engine trucks they tested?

Cowpie · October 28, 2019

I would have issues with running regular in the 6.6 L8T anyway. I has a 10.8:1 compression ratio. I would probably only use mid grade as the base fuel. Maybe even premium in hard working situations. With the compression ratio it has, even though regular is "approved" to use, the ECM likely has to retard the timing frequently to keep knock events at a minimum. And that is not the best deal for pulling a trailer up to the Eisenhower Tunnel. It would be interesting to see the end results of using regular for the Ike Gauntlet and then taking the same setup and using Premium and see if it makes a difference on the pull. This is one reason why it would have been ideal if they would have made the 6.6 L8T flex fuel capable. Then one could use inexpensive 100 octane fuel in it so that the 10.8:1 ratio motor could really reach its fuel potential.

SierraHD17 · October 28, 2019

I doubt the timing curve is aggressive enough to detonate with regular on account of the direct injection. If it's anything like how GM has tuned all their prior heavy duty applications you can run anything you want in it almost and it will not detonate.

Even the previous L96 has such a pathetic curve in it that you could run 80 octane gas and it wouldn't lose any advance. LQ4 and the LY6 were the same deal... this no doubt will be no different. Just leaves a bunch of power on the table you likely will never be able to tune for anyhow.

Edited October 28, 2019 by SierraHD17

kenny_r · October 28, 2019

Idk, I work for our local gov’t and we have a large fuel station. Whatever regular fuel it has isn’t very good. We have a couple 2015 L96’s and they run like complete crap on the stuff

SierraHD17 · October 28, 2019

Datalog them... fleet beaters probably run like complete crap in general. That and depending on how screwed up the virtual alcohol sensor based timing adder table is you will never know otherwise. That lovely "virtual" sensor GM used on these HDs for E85 is junk... same thing they did with the GMT900 half tons and it's not uncommon to have issues with it giving false alcohol content. I own an L96 and have tuned it myself... they have no ignition timing in them stock. 80 octane is an exaggeration but at the same time any 87 octane works in them.. These new ones in all likelihood will be the same as GM would test for that during development. The HD line gas stuff isn't built for Ricky Bobby who drives it like a grocery getter and the "safe" settings in the pcm reflect that. These engines will be in 20 some thousand pound GVWR delivery trucks and whatnot too just like the L96. There is a lot more to octane resilience than just a static compression ratio.

Edited October 28, 2019 by SierraHD17

greatmizzou · October 28, 2019

Wait, did they do the Ike gauntlet using 85 octane??

redwngr · October 28, 2019

On 10/22/2019 at 8:26 PM, greatmizzou said:

60mph flat Light foot in a short test drive I was getting 20mpg average at cruise speed. Granted it was like 15miles.

probably more like 15mpg

I hope it does better than that at a steady 60 once the engine/trans/diffs are warmed up.

(and I understand/agree that typical tank averages are not going to be like the steady state goo-going numbers)

Edited October 29, 2019 by redwngr

ApertureX · October 29, 2019

16 hours ago, greatmizzou said:

Wait, did they do the Ike gauntlet using 85 octane??

I was just wondering that myself. It's already bad enough that they leave it in D when the manual to use L for towing on hills to select the appropriate transmission range.

Colossus · October 29, 2019

At altitude, 85 octane is the same as 87 down at sea level. Fuel burns differently up here, folks. At least that was the case in older vehicles. Newer vehicles might be different, but the reason we have 85, 87, and 91 octane as our only choices here in Colorado has been that fuel burns differently at altitude. Go below 4000ft and you generally get 87, 89, and 93.

i82much · October 30, 2019

8 hours ago, Colossus said:

At altitude, 85 octane is the same as 87 down at sea level. Fuel burns differently up here, folks. At least that was the case in older vehicles. Newer vehicles might be different, but the reason we have 85, 87, and 91 octane as our only choices here in Colorado has been that fuel burns differently at altitude. Go below 4000ft and you generally get 87, 89, and 93.

the air is less dense. it’s sort of like having a lower compression ratio.

greatmizzou · October 30, 2019

I think the issue is the modern pcm compensates for that and possibly still needs 87 octane to take that into account.

there are news stories going back years ago that cover this. My engine, a 5.3 2002, pinged like crazy using 85 at high altitude. That has to hamper performance right? Or maybe my truck was so old with Minor leaks galore it just affected me more?

protovack · November 1, 2019

less o2, less chance of early combustion, so they can get away with lower octane up high

but fuel efficiency will suffer

Cowpie · November 2, 2019

Came across another 2020 6.6 gasser tow video. Guy was pulling 8K travel trailer in the Rockies. Maybe someone beat me to it and I just missed the post, but it is a worthy look see...

Edited November 2, 2019 by Cowpie