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I keep reading about "1.5L mode" on some of the new Hondas. Could someone explain what that is?

Is it VTEC running on the fuel economy cam? Or something else? Or the FE cam plus something else? Cylinder deactivation?

Specifically, why is it called "1.5 liter" mode? Is that the consumption per 100km, or the effective displacement of the engine at that point, or ???

Just curious. Thanks for any answers!

-soD

I don't know who calls it 1.5L mode, but they're talking about the i-vtec economy cams.

"when driving conditions are right, like during cruising, the new engine (R18A)achieves particularly high fuel economy, on a par with that of a 1.5-liter engine when VTEC activates the fuel-economy mode."

It's from this article. (http://asia.vtec.net/Engines/RiVTEC/index.html)

The R18A is in the 8th Gen (2006+) Civic DX, LX, and EX. The hybrid and Si have different engines.

1.5L mode was coined by psyshack. It's more of an analogy than an actual name I think.

Thanks, I'll check the article. :)

-soD

Thanks for asking the question soD!!
I was in 'honda' last night and kept reading same and was
totaly confused:o

Yeah like they said above, it's not really 1.5 mode, just the mileage is on par with a 1.5l engine.

Basically, the engine operates on the atkinson cycle when in "i-vtec mode."

It is a basic 1.5L active combustion charge.

If you study around on it. Drive the car you start understanding the hows of it all.

The basics. The intake valve is help open a milsec. longer and a portion of the 1.8L charge is pushed backinto the intake. The throttle plate moves to a position to limit pumping loss. At the same time the sensors in the intake tract are changing there setting along with the timing. If the low load condition continues then fuel deliver changes. It would make no sense to keep pumping fuel in the cyclinder just to eject some of its resulting mixture in the intake.

If you have a SG and are able to keep low load going you will see a dramatic increase in real time mpg. Much like lean burn but not as drastic. With basic lean burn you decress the amount of fuel to the ratio of air. In the 1.5L mode as I call it. The car maintains a basiclly reduced air and fuel charge. The drive by wire throttle plate or butterfly helps with controling the air volume. Also if you watch Hondas video on the operation of i-vtec/1.5 you will notice the intake valve holding open for a milsec longer thus decressing ave. compression from the stroke from the point the intake valve close's. On a SG you will see the timing retard at this point. Instead of a more advanced state when you are in normal mode. And thus seeing the full 10.5:1 compression ration spec'd in the R-18.

The R-18 is a very trick engine. It is a work of art. The only thing missing is lean burn. I was hoping CR-Z would get a lean burn hybrid R-18 off shoot. But it looks like it will get another engine. Honda can build some of the best engines made.

Don't over complicate the R-18 or dismiss it. When one learns how to work with it good things happen. :)

Yeah, I think I got the gist of the idea from the article. Pretty nifty indeed!

I've been thinking about other ways to deal with load changes than with a throttle butterfly, but I haven't come up with anything worth thinking of, yet. You can monkey with the cam in many different ways (perhaps by managing the overall amount of lift, or by managing the timing as Honda is), but that doesn't get you any further than the R18 currently is. But I keep thinking that there might be somewhere that we can go with that.

Perhaps a strategy to vary inlet air temperature depending on load settings, in conjunction with a throttle butterfly or some kind of valve management strategy? Sort of a built-in on-demand WAI . Hmm....

-soD

Yeah, I think I got the gist of the idea from the article. Pretty nifty indeed!

I've been thinking about other ways to deal with load changes than with a throttle butterfly, but I haven't come up with anything worth thinking of, yet. You can monkey with the cam in many different ways (perhaps by managing the overall amount of lift, or by managing the timing as Honda is), but that doesn't get you any further than the R18 currently is. But I keep thinking that there might be somewhere that we can go with that.

Perhaps a strategy to vary inlet air temperature depending on load settings, in conjunction with a throttle butterfly or some kind of valve management strategy? Sort of a built-in on-demand WAI . Hmm....

-soD

A true lean burn is the next step. If you start playing with cam grinds. You gain in a area and loose in another. IE Why vtec was invented. Switch cam profiles. R-18 does respond to a quicky WAI and its bone idle simple and cheap to install. A must for any winter driving. Also IMHO the R-18 responds to higher octane fuel in the winter. But turns into a dog in the summer/warmer temps on higher octane fuel.