Bad mpg?

[Antonm]

You can make the same power as a 6.2 with smaller displacement. But the engine has to be operating at higher and higher VE levels and more fuel has to be added ( beyond 14.7 afr) to make the power.

Nothing about that statement is even remotely true , or makes sense in any way.

Volumetric efficiency is dependent are hard parts design, you can't just decide to run at a higher and higher VE without psychically changing parts.

Like some F1 teams have actually managed to get their engines VE above 1.0 (into a slight supercharging effect even though they are naturally aspirated) by using reflected wave tunning of the exhaust and intake pulses at the extremely high RPM those little 1.6 liter engines run.

But for the time being at least, that's still F1 technology that hasn't made its way into production cars.

And as discussed above, fuel is what makes the power, take the fuel needed to make the power you want, add in the air needed to burn that fuel, mix them together in the correct ratio , then bam, you got the power you asked for. And power doesn't take a real hit between 13.0 and 14.7 in gasoline anyway, 13.0 is just a lot safer for the engine.
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[blanchard7684]

Nope, you have to add more fuel AND more air to burn that more fuel. Power comes from the fuel, the air is needed to burn the fuel.

If you add enough fuel to make a given power, you also have to add the equivalent portion of air to burn that fuel, regardless of engine displacement.

An easy example of this is small displacement forced induction engines that are popular now. Like the little 2.7 four banger that's in the Silverado making 310 hp. That engine injects enough fuel into the cylinder to make 310hp, then crams enough air into that same small *** cylinder via a turbocharge to burn all that fuel.
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If I add more air the afr rises and I make less power . It is a ratio.

This is again why peak power is at lower air to fuel ratio. There is incrementally more fuel added to a given mass of air.

This is because the combustion process requires it for achieving maximal energy release.

Your turbo example is only proving the point I’m making.

The turbocharging increases an engine’s volumetric efficiency which has the same effect as adding displacement.

 

[Antonm]

And also for the same throttle position ( depending on throttle body design) the 6.2 will be drawing in more air. 6.2 has 87 mm TB, 5.3 has 80mm. So for the same pressure drop through intake runners, the larger area flows more.

Yeap, just like mentioned above, the 5.3 might need 30% throttle to achieve the same power the 6.2 does at 20% throttle.

So for all use cases that don't call for more than 355hp (the amount the 5.3 makes), the 5.3 will have the throttle open slight more than a 6.2 making the same power.

Once the 5.3 hits wide open throttle, its done, can't draw in any more air, so injecting more fuel wouldn't do anything to make more HP. Whereas the 6.2 can draw in more air thanks to its larger displacement, so it can inject and burn more fuel, making more hp.
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[blanchard7684]

Nothing about that statement is even remotely true , or makes sense in any way.

Volumetric efficiency is dependent are hard parts design, you can't just decide to run at a higher and higher VE without psychically changing parts.

No kidding… what do you think a throttle does?

Are you under the misguided assumption that engines operate at 100% ve all the time?

 

[Antonm]

If I add more air the afr rises and I make less power . It is a ratio.

This is again why peak power is at lower air to fuel ratio. There is incrementally more fuel added to a given mass of air.

This is because the combustion process requires it for achieving maximal energy release.

Your turbo example is only proving the point I’m making.

The turbocharging increases an engine’s volumetric efficiency which has the same effect as adding displacement.

You don't have a point because you either simply don't know what hell you're talking about or English is a second language to you and you're having a hard time getting a point across.
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[Antonm]

'and using the same amount of fuel' cannot ALWAYS be true,
otherwise GM would not have been willing to accept the tooling costs difference between 5.3L and 5.7L in the late 90s, followed by 6.0L, followed by 6.2L.
(Also note the low uptake rate of, as well as the eventual demise of, the 4.8L.)
CAFE MpG testing scores are obviously a thorn in GM's side, not only because CAFE MpG results and real-world results have predictable differences.

GM is a business, and business have one purpose in mind, to make money. As long as it legal and people are willing to pay for more power so their heavy *** SUV's can accelerate like the sports cars of just a few years ago , GM will tool up to make whatever they can to get that money.
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[Marky Dissod]

It has been accepted fact for the past 19 years that the AFR is usually stoichiometric (14.7to1 for pure petrol, 14.1to1 for E10, 9.9to1 for E85) -
except for a brief transition immediately after the driver totally lifts off the go-pedal which is mitigated by electronic throttle 2nd-guessing.
Those who do not accept this fact should stop bogging this discussion and take their remedial efforts elsewhere.
OK
There WERE two exceptions. Lean Cruise is no longer a 'thing', since 06.

There comes a point where driver power demand exceeds the point where 'stoichiometric' can sufficiently control cylinder combustion temp.
If cylinder combustion temp goes up, NOx goes up. The EPA is willing to 'waste' fuel to control NOx!
At that point, the ecm goes into Power Enrichment mode (aka funtime).
Once the ecm has accepted that fuel economy is no longer desired, the ecm is STILL (ALWAYS) trying to reduce (eliminate) NOx emissions.
When it goes into Power Enrichment mode, it can no rely on the O2 sensors (which were aiming at stoichiometric a moment ago).
The ecm checks its previous stoichiometric calculation results and applies Power Enrichment fueling as follows:
If it was guessing 'a bit lean' recently, in addition to Power Enrichment, it ALSO applies the %age previously used to correct the previous lean moments
It it was guessing 'a bit rich' recently, it only applies Power Enrichment.
Power Enrichment is NOT as simple as calculating for a specific AFR or Lambda, but for our purposes saying
'Power Enrichment generally aims for between 12.5-13.0 AFR' suffices.

 

[Marky Dissod]

GM is a business, and business have one purpose in mind, to make money. As long as it legal ...

CAFE MpG test scores are part of the legality framework that directly affects (not only) GM's bottom line.

... and people are willing to pay for more power so their heavy @$$ SUVs can accelerate like the sports cars of just a few years ago, GM will tool up to make whatever they can to get that money.

I agree.
So why, after decades of 5.7L V8s for sports cars AND pickup trucks / suvs, did GM decide to debore the pickup truck / suv engines?
Why not just use a smaller cam / different heads / different valves / different valvesprings? Oh wait, they did all those things,
and ALSO debored the pickup truck / suv bread'n'butter engines ... and also 6L80, 8L90, 10L80, variable cam timing, direct injection, a turbo 4-cylinder ...
I blame CAFE, is my point.

 

[Antonm]

The EPA is willing to 'waste' fuel to control NOx!

The EPA is willing to waste A LOT of fuel to control NOX.

I know this isn't a diesel discussion, but modern diesels DPF regen uses a bunch of fuel to burn off / clean the DPF , and that's fuel (complete with all its road taxes) that isn't pushing the truck forward.

These DPF regens in 3/4 ton and larger pickups often result in a loss of 2 mpg or more, proof the EPA doesn't give two sh!ts about MPG's
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[blanchard7684]

You don't have a point because you either simply don't know what hell you're talking about or English is a second language to you and you're having a hard time getting a point across.
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Do you know what an air fuel ratio is?

Do you know that they vary depending on power demand?

You have a really really hard time with this.

Your response is amusing and immature.

Which reflects your knowledge of this subject.