Octane vs mpg again...

[DGXR]

Static compression ratios matters most when the throttle is wide open, getting maximum air intake charge and the engine can actually achieve something close to that number in dynamic compression. So yes I believe in a towing application where there is heavy load, a higher octane could significantly help performance and MPG. In everyday driving and moderate throttle input, where the dynamic compression rarely approaches static compression numbers, you can generally run lower octane with little impact although GDI engines are proving troublesome with this approach. A good example is how fuel stations at high elevation can sell lower octane (85) than sea level locations (87) because the cylinders just aren't getting a full charge. Just my $0.02

 

[Hermann]

Filled up today at Hy-Vee Gas
653.8 miles / 14.855 gallons = 44.0 MPG
A bit below last fill. Refilled with another tank of 91 octane E0
Had 97¢ in fuel savers from Hy-Vee
Mileage monitor on the truck was way off, 8.25% optimistic
The 0 miles to empty came on at 650.4.
How I get 14.855 gal in a 13.8 gal tank is weird. I added 27¢ after the first click off

 

[wpod]

Higher octane allows more timing advance which could most likely produce an increase in MPGS. Who knows what the MPG increase would be.

 

[jetman]

Higher octane allows more timing advance which could most likely produce an increase in MPGS. Who knows what the MPG increase would be.

@jetman and @swathdiver etc know. See post #s 30, 33, & 34, etc here is this thread.

GM "recommends" 91/93 unleaded in my 2007 6.2L all aluminum L92. It's NOT a flexfuel vehicle. I've run all the various grades of unleaded. I get 15-20% improvement on premium vs unleaded.

 

[FZ1]

Brother in law has a 2021 Silverado 2500HD with the 6.6 gas motor and tows a 32' fifth wheel with a GVWR of 10,000 lbs. No idea what his actual weight is. He said was averaging 7.1 mpg towing in NW Pa. on 87. He decided to try 93 since this is a 10:1 engine and he had to run 93 in his 10:1 stock car motors BITD. He claims his towing mpg is now 8.6, a 21% increase and the truck runs better. Not getting into a YOU CALLING ME A LIAR? situation with BIL but that seems like an amazing improvement. 87 is specified by GM.

I believe it. He gets what he gets ,with, the fuel he uses. .02

 

[Hermann]

Higher octane allows more timing advance which could most likely produce an increase in MPGS. Who knows what the MPG increase would be.

So far the hand calculated figures for 2 tanks of 91 octane E0 has raised my average MPG over 8 tanks by .7 MPG. First tank of E0 was 45.4 and the second was 44.01. Running E10 fuel I was averaging 41 MPG or so most tanks of normal driving. My question is the higher octane or the lack of alcohol responsible for the increase. The truck runs noticeably better with the 91 octane. My trips for the lady friends house used to be about 37-38 MPG are now 41-43 and 2/3 of these trips are at interstate speeds, for me which is 70 MPH.

 

[kschachn]

0.7 MPG you say? You’re able to isolate one relatively insignificant variable deep in the noise of everyday driving? I sure couldn’t do that.

 

[Hermann]

0.7 MPG you say? You’re able to isolate one relatively insignificant variable deep in the noise of everyday driving? I sure couldn’t do that.

It helps that I have only burned 8 tanks.

 

[FZ1]

So far the hand calculated figures for 2 tanks of 91 octane E0 has raised my average MPG over 8 tanks by .7 MPG. First tank of E0 was 45.4 and the second was 44.01. Running E10 fuel I was averaging 41 MPG or so most tanks of normal driving. My question is the higher octane or the lack of alcohol responsible for the increase. The truck runs noticeably better with the 91 octane. My trips for the lady friends house used to be about 37-38 MPG are now 41-43 and 2/3 of these trips are at interstate speeds, for me which is 70 MPH.

Less alcohol is better than more alcohol. If the 91 E0 runs better, heck, I'd run the 91 E0.