In this age of high gasoline prices
it would be interesting
to take two Chrysler 318 V8 vehicles
and do 'convoy' style MPG test trips
where lean burn was used on one vehicle for the first trip,
then the lean burn was swapped to the 2nd vehicle and its system swapped to the 1st vehicle, and the same trip repeated.
This is the SAE/TMC Type 4 MPG test that can detect down to as little as a 2% difference with high accuracy.
Chrysler's short lived Lean Burn had a bad reputation,
but how much fuel did it really save?
Members here on Moparts are uniquely qualified to do such a volunteer experiment. It might really give a MPG gain, unlike so much of the hokum & fraud circulating on the Internet right now (Acetone, HHO generators, Tornado swirly-gigs)
Since Honda claims to have recently created a new style of catalytic converter than can reduce NOx in lean AFR like used in diesels, people are looking at lean burn again. This article reviews the history:
http://www.designnews.com/article/9710-Thirty_Year_Quest_for_Lean_Burn.phpNote that the current 5.7 and 6.1 V8 twin plug engines are very similar to the Nissan NAPS-Z, in fact the old NAPS-Z emissions data published in the SAE Journal allegedly convinced Chrysler to go ahead with the 'crazy idea' Hemi revival.
With a SCT tuner,
how lean could a 5.7/6.1 V8 go at highways cruise?
In Australia models of the Insight
Honda used lean burn at Highway cruise when throttle movement had been gentle for awhile:
http://www.autospeed.com/cms/A_110187/article.html?popularArticlesample quote
The Insight, unlike the Prius, also has a lean cruise mode. In this mode, the air/fuel ratio goes leaner than the stoichiometric 14.7:1 that the Prius runs all the time. In addition, the Insight can also switch out of closed loop, running rich air/fuel ratios of around 12.5:1 under full throttle at high revs.
So, how lean does lean cruise go? Thereby hangs a story...
Air/Fuel Ratios
Despite plenty of tech information on the Insight being available on the web, it appears no one has ever directly measured air/fuel ratios and then posted the data. I used a professional MoTeC air/fuel ratio meter to determine the above information – that the Insight runs in closed loop 14.7:1 (or around 14.7 – say 14.5 to 14.8) a lot of the time; that the air/fuel ratios go richer at high load/high rpm; and that lean cruise is significantly lean.
Most cars that run lean cruise use an air/fuel ratio of about 16.5:1. (Incidentally, lean cruise is now outlawed for conventional new cars here in Australia because of the high NOx emissions that occur when running lean. Car companies used to configure lean cruise to come into action only at loads and speeds not achieved in the emissions test cycle. More on NOx in a minute.) Compared with stoichiometric (14.7:1), a 16.5:1 air/fuel ratio means that – all other things being equal – about 12 per cent less fuel is used.
Tech resources on the Insight suggest that lean cruise air/fuel ratios can be as lean as 22:1. However, when I put the very accurate MoTeC meter on the Insight, the real story was revealed. Out onto the freeway and the air/fuel ratio stuck at 14.7:1. Then, after a few minutes of 110 km/h, the air/fuel ratio numbers started changing.
To sixteen to one.
Then seventeen to one.
Eighteen to one.
Nineteen to one.
Twenty to one.
Twenty-one to one.
Twenty-two to one.
At this point I exclaimed out loud – never had I seen such a lean air/fuel ratio on a running engine. Never.
Twenty three to one.
I gasped “$h1t!”
Twenty four to one.
I laughed out loud.
Then, a stunning twenty-five to one!
That’s right, the Honda happily trundles down the highway with a measured air/fuel ratio of 25:1! To anyone with any knowledge of contemporary car tuning, that’s a jaw-dropping figure. In fact, perhaps more than any other readily observable characteristic of the Insight, the 25:1 lean cruise shows the brilliance of Honda’s engineers.
