Bad mpg?

[B-train]

Welcome to my 09 Esky 6.2L in town driving on e85

View attachment 448062

I wanted a 10 SP for Xmas but they only had 6 SP last year.

How much DOES your right foot weigh?

 

[petethepug]

Funny you should mention that.

 

[swathdiver]

I find it interesting that most normal people driving as they normally do,
tend to get less MpGs / consume more fuel per unit of time compared to the CAFE MpG test scores.

That being the case, why hasn't the test been amended to correlate more closely with how normal people drive?

Because they are terrible drivers. Zooming through traffic, making lane changes every few car lengths and then running towards a red light at ten over the speed limit until the last seconds. They're nuts. Not to mention the swill they fill their tank with and lack of maintenance that kills their fuel efficiency. They rarely pay attention to the air pressure or tire rotations either.

My pickup meets its EPA estimates. My Yukon XL was not rated by the EPA, big fat blanks on the window sticker and no listing for it at FuelEconomy.gov. I emailed the EPA as to why, they had no answer for me.

 

[swathdiver]

Welcome to my 09 Esky 6.2L in town driving on e85

View attachment 448062

I wanted a 10 SP for Xmas but they only had 6 SP last year.

Must be related to Wes! @Doubeleive

My wife is back in the 9s again on E85. She loves the new gears and likes the newfound acceleration.

 

[Doubeleive]

Must be related to Wes! @Doubeleive

My wife is back in the 9s again on E85. She loves the new gears and likes the newfound acceleration.

I actually had mine up to 13.4 yesterday taking my daughter to the airport, cleared everything out and didn't floor it except once lol
on the way back I was little more frisky and was down to 12.6, it's down to 11 now and it will be back down to 10 in not too long

 

[Marky Dissod]

Because they are terrible drivers.

Can't argue with that. However ...

Zooming through traffic, making lane changes every few car lengths and then running towards a red light at ten over the speed limit until the last seconds.
They're nuts. Not to mention the swill they fill their tank with and lack of maintenance that kills their fuel efficiency.

This is actually why I'd let cabdrivers and other people who 'drive for a living' submit their MpG records,
and compare those against the CAFE tests.

I've noticed that the 'cheapest no-name' petrol I can find tends to get slightly worse MpGs
compared to petrol priced closer to the local average. Hmmm ...

My pickup meets its EPA estimates.

Your driving meets your vehicle's CAFE estimates.
MY driving, for example, is consistently 2/3rds of the city rating, and 4/5th of the highway rating.

My Yukon XL was not rated by the EPA, big fat blanks on the window sticker and no listing for it at FuelEconomy.gov.
I emailed the EPA as to why, they had no answer for me.

Is it a 2500? If its curb weight is high enough, it doesn't get tested.
My guess is you'd have to extrapolate estimates based on similar vehicles.

 

[Antonm]

Error 1. Overall you are using an overly simplistic equation of state to describe a system that operates via heat and mass transfer.

I thought you didn't believe in Boyle laws or Charles law,, but now you'v eflip flopped again. And the internal combustion engine absolutely has a heat transfer component (that's where Charles law comes), but not a mass transfer component.

Guess where the heat transfer component is accounted for in you own power equation,,,that's right, in the thermal efficiency term. Seems like I've typed out a few time words to the effect of " the same efficiencies"

 

[Antonm]

Error 2. Pressure is a measure of restriction in a flowing system. You are conflating mass flow of air with a measure of upstream pressure (in the intake manifold).

It would appear as though you are not familiar with the concept of proportionalities. We often use things that we can directly measure to determine other things.

A great example of this is what started this whole argument about AFR. We don't actually directly measure AFR you know, we measure the concertation of the oxygen in the exhaust (post combustion event) to determine what the AFR was before combustion. That's a proportionality we use so commonly that we often refer to the o2 senor as telling us the AFR is, when it not actually a direct measurement. But just because its derived from a proportionality, doesn't mean it isn't accurate.
...

 

[Antonm]

Error 3. You are assuming manifold pressure is equivalent to pressure at BDC of intake stroke. If it was the same, then how is anything flowing if there is no additional motive force from pressure drop?

True, I was/ am using an ideal example. Whatever restriction that's in one engine, is also in the other and would affect both engines nearly identically
And guess what,,,do you know where this is accounted for in your own equations ,,,, that's right, in the combustion efficiency term.
Seems like I've said a few times, "engines with the same efficiencies" a few times

Which a 5.3 and 6.2 are dang close in their efficiencies, close enough to be called the same for all practical discussion.

I'm surprised you went for pressure delta vice time delta to point out a potential difference in Pbtc, although time delta is also accounted for in an efficiency term as well, but that hasn't stopped you yet. Guess that one slipped your mind.
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[Antonm]

Error 4.



The natural and logical inference from this is that, for every increment of displacement I remove, I gain cylinder pressure at BDC. The higher pressure at BDC means the smaller engine maintains the same power as a larger displacement engine.

We are talking about part throttle cursing here, so assuming it always takes the same amount of force (horsepower in this case) to move the same amount of mass (the mass of a Chevy Tahoe in this case) at a given velocity (say 70mph on flat level ground), then yeap it sure does.

If it wasn't possible for two engines of different displacement to make the same power at part throttle, then two Tahoes (one with a 5.3 and one with a 6.2) would never be able to drive at the same speed.

Power comes from the fuel (think if said that before too). So if both engines are capable of taking in enough air on the intake stroke to burn the same amount of fuel during the combustion event, then those two engines (assuming they have the same efficiencies) will be making the same power.

This is not a wild concept, we see this literally everyday of our lives. Very little of the time are we actually using all the power available to us.
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