GCR: is it possible to make MPG worse by downsizing engines TOO much?

[niky]

Originally Posted by MetroMPG

I couldn't help but comment. Then comment again... and again.

Getting Good Gas Mileage Is Hard; Will Tinier Engines Really Help?

I noticed, Anthony posted the link to the article on a gaming forum I moderate. I believe he's joined here under the name "RunningStrong".

I think the premise is good, but needs more research. Anthony knocked it together based on a conversation we were having on that forum about the Ford EcoBoosts.

In part, I agree... sometimes an engine is too small for the work desired. When I did the EcoBoost Explorer, fuel economy in traffic was just as bad as the V6. Whatever the size of the engine, accelerating two tons of metal (however gently) up to speed requires a lot of gas. But I partly disagree, because from my driving, I saw the potential for extra highway MPGs simply by staying out of the boost.

Unfortunately, since part of the premise of the EcoBoost is that you don't give up power for economy, these new engines are tuned to produce lots of boost very early, so most people don't see any benefits.

[gone-ot]

...the 1.4L turbocharger Cruze boost is all-in by 1,850 rpm...and idle is only 800 rpm!

[serialk11r]

Originally Posted by Duffman

No its not because at WOT you are running the engine on fuel enrichment, you would want to run at the maximum throttle opening that permits stoichiometric air/fuel ratio. Maybe thats 80% or 90%, I really dont know the point, but WOT is not where its at for FE on a stock production gasoline engine.

You might be surprised how many cars do not enrich until high rpm. Fairly sure the Prius does not enrich the mix, ever, because its peak efficiency is pretty much at maximum torque output.

[Daox]

Originally Posted by serialk11r

You might be surprised how many cars do not enrich until high rpm. Fairly sure the Prius does not enrich the mix, ever, because its peak efficiency is pretty much at maximum torque output.

I was also going to note this. In most cars I've been in you don't hit fuel enrichment at WOT until maybe 4000+ rpm.

[serialk11r]

Originally Posted by Daox

I was also going to note this. In most cars I've been in you don't hit fuel enrichment at WOT until maybe 4000+ rpm.

Not sure but specifically I think before wideband O2 was popular it was common, I know my 1ZZ-FE is closed loop into the 4000s, never actually logged it in open loop mode!

I think wideband O2 equipped cars are running richer at max torque to reduce exhaust temperature a little bit and make the cats last longer. I followed the BRZ/FRS pretty closely and the AFR goes down to 10.9:1 at high rpm! It dips into the 12s well before 4000. Reflashing that to 13:1ish gains a huge amount of power...