Yes, thanks to that site I have memorized all the 100% stations around here

 

Just recently managed 26MPG (all highway) on a couple tanks on my recent road trip.

In roughly 2,400 miles I averaged 22MPG mixed overall.

I was thoroughly impressed.

Mike

 

This past week we took our winter drive and enjoyed the smoothness of the new motor mounts and tires. The prior week it did 25.8 MPG for a San Diego loop. The barge this time turned in a reasonable 23.8 MPG on the way up. Tanked up with Shell V-power while up there and immediately the car felt down on power. The usual 35 mile run I saw the gas gauge drop. The rough calculation was it was getting 11 MPG in town and 19 MPG highway, that's definitely off. No CEL and at the tail pip it didn't smell rich. Called the service guy about possibilities for the bad MPG. We both thought O2 sensors. Can't do anything being 200 miles away so it would have to wait till back home.

That 11 MPG in town ran the tank down quickly so this time I chose a different station. 12 gallons of V-Power and the car felt pretty good again. As I'd experimented long ago, each grade drop yields about 10% decrease in MPG for ours. When we didn't have ethanol the car did great at about 27.X MPG but with 10% ethanol the usual is in the 25 MPG range.

Additional comment: Either the station is purposely deceiving the customer or their fill guy put regular gas into the premium tank. I paid $3.09 so it wasn't one of those moments I pushed the wrong button.

 

My last long drive I pulled 490 on a full tank.

 

I've taken two long trips, mostly highway speeds, with the Cascade Mountains to cross going and coming, and have gotten close to 29mpg both of those trips. Combined mileage on a tank with some highway and town driving seems to be near 20. Premium Sinclair or Chevron. Not a lead foot!!!

 

So, I spent two weeks driving only around town, all distances that were too short to fully warm up the engine and my average fuel economy was 17 mpg, so I thought there might be something seriously wrong with my engine. However, it seems to run fine. It has lots of power. It runs smooth and quiet. So, last night I decided to see what my highway fuel economy was. Here are the results!!!

 

The average of all those numbers turns out to be 28.75 mpg!!!

 

Actually, the only reason cars used to get the best fuel economy at 55 mph is because they were designed to do so.

Internal combustion engines become more efficient as you increase power output, but, drag increases with the square of the velocity. Therefor there is an efficiency curve that was designed to peak at around 55 mph.

But then gas became cheap and plentiful, so we didn't care any more. Therefor we started designing engines exclusively for more power. These engines have way more power than we need to drive 55 mph. It only takes about 25 to 30 hp to keep this beast going at 55 mph and these engines are capable of producing somewhere between 250 hp an 290 hp depending on the year. At 25 hp to 30 hp, these engines are incredibly inefficient. If you double the velocity to 110 mph, the force required to maintain that speed will quadruple and the power required to maintain that speed will increase by a factor of 8. That's 200 to 240, which is closer to what these engines are able to produce. So these engines will be much more efficient than at 25 hp to 30 hp. But fighting so much resistance is a waste of energy.

110 mph is probably beyond the peak of the efficiency curve, so peak efficiency is probably somewhere between 55 mph and 110 mph.

Below the peak, faster is more efficient, but above the peak, slower is more efficient.

Does anyone have any idea where this peak is?

My guess is that it's not 55 mph, or less than 55 mph. It's probably somewhere between 65 mph and 80 mph.

 

Reviewing this post suggests general consensus that 100% gasoline provides better MPG over gasahol due to higher heat (BTU) content (same octane)

New car window stickers provide EPA mileage ratings .....

My question is whether auto manufacturers EPA compliant ratings reflect MPG using 100% gasoline or gasahol (10%)?

Anyone know definitively EPA guidelines with supporting documentation??

Thanks.

 

I just did a round trip drive to California and back to AZ and drove 752 miles with cruise set @ 75mph and averaged 26 mpg with my 97 LS on some 18" SC430 wheels w/ 235/45/18 tires. I used regular unleaded, 87 octane, had a fresh oil and filter change and also popped in my K&N filter in the intake that had also been cleaned recently. This was also in 95% heavy rains and some 20-30mph windy gusts at times on the I-10. On the way back I was loaded with some 17" wheels and tires in the trunk so probably an added 200lbs of stuff. Basically driving with 2 people in the car.

my last fill, I went 442.1 miles on 17.199 gallons of gas (~25.7mpg), so I could've easily hit 500 if I wanted, but there were no available gas stations for the next 60 or so miles so I didn't want to push it. I bet if I spent the extra $8.50 a tank for premium, I could average 27mpg no problem. Since they charge a 50 cent premium for premium, I don't feel like I'm doing harm with 87 oct vs. the crappy 91 we get out here.

 

^^^^
Wow. Really good MPG. I've never ran 87 octane in my LS...your making me think I should...

Mike

 

Initially when I bought my LS, I would only run premium, but I got tired of paying more for it each week, at the time I had an 80 mile commute M-F for only a 1-2mpg increase, typically only at hwy commutes, so I tried 87 and I didn't notice anything knocking, pinging, a power loss or anything detrimental to the engine. I may be making only 255hp instead of 260hp, but with an engine w/ over 277k, that power loss would probably be negligible. My LS still drives the same, and still passed emissions perfectly fine in my state on the first try, still fires up with the same quickness.

Here's how my fuel gauge looked at fill-up, didn't even hit the low fuel light yet

 

These engines operate optimally with 91+ octane fuel...

To compenste for lower octane fuel, the ECU retards the ignition, and enrichens tge fuel mixture to prevent engine damaging detonation...

I can always tell who was using low octane fuel...the enriched fuel mixture causes increased carbon build-up in throttle body, intake, valves, pistons etc...

An over rich fuel mixture tends to increase wear on piston rings, cylinder walls, valve stems and valve guides..

Engine oil does not last as long..

The catalytic converter also has to work harder to catalyze the over-rich exhaust...and the oxgen sensors degrade faster in that scenario

Fly now, pay later

 

^^^^
Yeah, that's what I thought and why I've never ran 87.

My best tank was 520 miles with 2 gallons to spare (All FWY). My last tank was 472 mixed.
All 91 Octane.

Mike

 

I always thought fuel 20 years ago isn't as nice as fuel is now. Detergents and additives are a lot more advanced in today's modern fuels available at the pumps and I always use Top Tier so I figured it would be ok.
I usually average only 385 or so due to being in the city so much, but I'm ok with that, its the car I always go to when I just want to cruise and get there in comfort. My Accord is for acting like a hooligan and shifting at 8k to hear VTEC scream