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Old 05-21-2010, 10:50 PM   #1 (permalink)
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Default Some lean burn thoughts, 80mph LB.

It's been reported that the Insight can't lean burn past 72mph. Well, that must be a matter of road load rather than VTEC, because mine accelerated from 65ish to 80 in lean burn, albiet down a hill.

But the Insight can't tell the difference between a hill and a boat tail. Therefore, a streamlined Insight ought to be able to pull off lean burn at speeds that are more appropriate on today's faster interstates.

I set a new record today: fastest I've gone in an Insight: 80mph in a 70mph zone.
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Old 05-22-2010, 04:15 AM   #2 (permalink)
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It's been reported that the Insight can't lean burn past 72mph. Well, that must be a matter of road load rather than VTEC, because mine accelerated from 65ish to 80 in lean burn, albiet down a hill.

But the Insight can't tell the difference between a hill and a boat tail. Therefore, a streamlined Insight ought to be able to pull off lean burn at speeds that are more appropriate on today's faster interstates.
There may not be a speed above which lean burn cannot occur. I think lean burn is determined by engine load, above a certain level of which lean burn cannot occur.

So anything that can be done to reduce engine load would make lean burn possible at speeds above 72 mph. You demonstrated this by maintaining lean burn at 80 mph down a hill. Others have demonstrated that lean burn is more difficult to enter with non-OEM tires due to greater rolling resistance and thus greater engine load.

Reducing aerodynamic drag would reduce engine load and increase the speed at which lean burn is attainable.
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Old 05-22-2010, 09:18 AM   #3 (permalink)
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Just because the FCD indicated high MPG doesn't mean your in "Lean Burn".

Try a downhill run in neutral @ idle and watch the FCD soar! In fact there's no "easy" direct way to tell from behind the wheel to find lean burn's limits. Sure, the smack dab solid middle is clearly see / feelable. Simply drive on a relatively level route and play with the gas pedal. A slightly lighter touch vs. a heavier foot for the same grade and speed (not slightly accelerating) and you can see / feel lean burn kick in. But find its limits? See my first scenairo above (its not lean burn)

Yes its a niggling highly technical difference, but it is a difference none the less.

The physics and chemistry of combustion and the design of the Insight's engine and control systems preclued "Lean burn" above 72MPH in 5th gear.

Stated another way: When VTEC transitions to its high output valve operation lean burn is _gone_(.) period.
Its engine RPM and engine load dependent. Speed is influenced by grade (hills), If you could monitor the applicable engine control paramaters it would become apparent when high FCD readings are due to conditions other than lean burn. Very hightly technical and IMO only an acedemic "argument".

HTH!



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Old 05-22-2010, 09:40 AM   #4 (permalink)
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Originally Posted by Insightful Trekker View Post
Just because the FCD indicated high MPG doesn't mean your in "Lean Burn".

Try a downhill run in neutral @ idle and watch the FCD soar! In fact there's no "easy" direct way to tell from behind the wheel to find lean burn's limits. Sure, the smack dab solid middle is clearly see / feelable. Simply drive on a relatively level route and play with the gas pedal. A slightly lighter touch vs. a heavier foot for the same grade and speed (not slightly accelerating) and you can see / feel lean burn kick in. But find its limits? See my first scenairo above (its not lean burn)

Yes its a niggling highly technical difference, but it is a difference none the less.

The physics and chemistry of combustion and the design of the Insight's engine and control systems preclued "Lean burn" above 72MPH in 5th gear.

Stated another way: When VTEC transitions to its high output valve operation lean burn is _gone_(.) period.
Its engine RPM and engine load dependent. Speed is influenced by grade (hills), If you could monitor the applicable engine control paramaters it would become apparent when high FCD readings are due to conditions other than lean burn. Very hightly technical and IMO only an acedemic "argument".

HTH!
Best way to determine lean burn is the SGII!

I took a highway run yesterday, 81 mpg, about 50 miles! The SCII has about 1-2 second delay. But even when FCD is high, you are not always in lean burn. It is harder to tell by just looking at FCD.

On the return trip, including getting out of the parking lot, I was at 74 mpg, over 100 miles.

I travelled up to the speed limit and occassionally, 5-10 over (70-75)and 5-10 under (climbing hills). No hypermiling tricks other than gentle acceleration when possible (without clogging up traffic).

Keeping it in lean burn is very important. It seems when it "purges", if you don't adjust the throttle, (TPS indicator) it will clear the purge in about 5-8 seconds, and go right back to lean burn!

I also noted I can get up to about 32-33 TPS before it drops out of lean burn.

By far my best mileage and my first tank with 93 octane. Car also seemed not to have as much surge transitioning to assist or transitioning out of lean burn. Coincidence?

Regards,
Jerry
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Old 05-22-2010, 09:47 AM   #5 (permalink)
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By far my best mileage and my first tank with 93 octane. Car also seemed not to have as much surge transitioning to assist or transitioning out of lean burn. Coincidence?

Regards,
Jerry
In my Insight smoother hyper MPG has always been the case using higher octane fuel.

HTH!



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Old 05-22-2010, 10:13 AM   #6 (permalink)
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So maybe high octane fuel could be better? But I assume it doesn't offset the extra cost, right?

Also, how does the Xgauge for the SGII monitor Lean Burn? What are the parameters? And can it be programmed to measure VTEC engagement?

What RPM is it that we're at when we are at 72MPH in 5th? I assume that is when VTEC kicks in? Is it a solid kick in, always on after X RPM and only engages when it reaches X RPM?
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Old 05-22-2010, 10:44 AM   #7 (permalink)
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It might not always be obvious when the car goes into lean burn but I don't see how someone couldn't notice the sudden surge and gauge change when the engine drops out of lean burn. I've been above 72mph in lean burn, managed 74mph a few times. If it definitively drops out of lean burn with VTEC engagement at 2500rpm then mine is doing it a little late because without moving the throttle I've been able to get 74mph multiple times before the surge and MPG loss happens.

What would happen if we pulled the connection(or connected a remote switch) to the VTEC solenoid to try and take a long trip where we want to try and take advantage of the downhills? We might not get such a definate immediate dropout right at that ~2500rpm point.
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Old 05-22-2010, 10:47 AM   #8 (permalink)
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As Insightful Trekker says, when you're at >75mpg it's somewhat academic whether you're in LB or not.

Actually to get the amazing mpg's the Insight-I was built for, it's better to be in NB (No Burn) than in LB wherever possible. That's one of the keys to really high mpg's. On the looong downhill on I-90 into Springfield, MA, I bet one could reach 80mph in NB. Probably other downhills elsewhere in the US would work too.

I bought the car for mpg, not mph, so to me anyway going 80mph is irrelevant, not utilizing its full performance capabilities.

And now for even better mpg than I can get in the Insight I'm off for some FB (Fat Burn) on my bicycle.
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Old 05-22-2010, 11:39 AM   #9 (permalink)
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So maybe high octane fuel could be better? But I assume it doesn't offset the extra cost, right?
Many experts contend that buying higher octane fuel than what an engine is designed to burn is a waste of money. The Insight was designed to run on regular unleaded gasoline.

Higher octane delays the onset of pre-ignition knock which occurs only under high-load engine conditions. Pre-ignition knock can be minimized using a knock sensor that retards ignition timing. Retarded timing reduces power output, so maybe under high engine load, higher octane gasoline might result in a bit more power. A race car runs under high engine loads almost always, but the engine in a normal car spends only a small percentage of time under high enough load to cause knocking. So I don't consider high octane gasoline to be worth its higher cost.

That said, several Insight drivers are convinced that their fuel consumption decreases when they using higher octane gasoline. I've never understood a mechanism that would explain this, but I don't question their beliefs.

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What RPM is it that we're at when we are at 72MPH in 5th?
Using this graph, I estimate that the engine is spinning at 2,500 rpm.

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I assume that is when VTEC kicks in? Is it a solid kick in, always on after X RPM and only engages when it reaches X RPM?
According to this,the transition to high-power VTEC-E mode occurs between 2,500 and 3,200 rpm (72 - 90 mph) during acceleration (depending on engine load) while the transition back to economy mode occurs at 2,300 rpm (60 mph) during deceleration.

The engine load might be light enough on a steep downhill grade to be able to enter lean burn mode at 90 mph. But on a flat highway, the engine load might be high enough at 72 mph to transition to high-power mode thus preventing lean burn at higher speeds. But this is just speculation on my part
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Old 05-22-2010, 11:48 AM   #10 (permalink)
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Many experts contend that buying higher octane fuel than what an engine is designed to burn is a waste of money. The Insight was designed to run on regular unleaded gasoline.
True. There is no cost / mile benefit with premimum fuels even in an Insight and in the hyper MPG range, _at_ the current price differential of .20 c / gallon in my location.

But

There is a difference in "Designed to", "Required to", or simply gets better, "smoother", hyper MPG!





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Last edited by Insightful Trekker; 05-22-2010 at 11:52 AM.
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