Honda K20C9 Atkinson cycle

[melk]

So my daughter and son in law traded in their clunker of a 2019 Jeep Cherokee for a 2025 Honda Civic with the 2.0

I’m researching the engine and it looks like for 2025 they have moved to a “simulated” Atkinson cycle using some modified form of VVT. I’m only vaguely familiar with Otto vs Atkinson and the implications of such.

The one thing that jumps out at me is the compression ratio is raised from 10.8:1 to 13:1 which is a pretty big jump. Still NA so no turbo which I’m glad for. It is fully DI only, no hybrid setup there.

Location is SoCal and they rack up pretty good highway miles on the car, 50-100 miles a day. Hopefully there’s not too many first-year teething problems with new tech but I guess somebody has to be the guinea pigs…

 

[Pablo]

Ask Toyota how that worked in the 2GR-FKS.

Kinda odd, noisy and not very good MPG. But not massive fuel dilution, but I run an OVT MT tune.

Here's to hoping Honda has it figured out!

 

[OneLonelyBurrito]

The one thing that jumps out at me is the compression ratio is raised from 10.8:1 to 13:1 which is a pretty big jump.

Most of the engines with high compression ratios like 13:1 will never actual achieve that while running, i.e. the Atkinson cycle. I know my Mazda with the 2.5 N/A engine has a static 13:1 compression ratio, but while running, it never actually achieves that compression ratio.

 

[Nessism1]

The compression ratio is the compression ratio. How that effects the engine depends on the valve timing, thus the "trapped" compression pressure. With Atkinson, the intake valve closure is delayed, and so the trapped compression is less.

 

[fantastic]

Would that design & compression ratio require premium fuel?

 

[melk]

Supposedly not, Honda recommends 87. After some more reading it seems basically what’s it’s doing is leaving the intake valve open past BDC and closes late in the cycle.

 

[meep]

If they get the tuning right it will provide quite impressive mpg.