[predrag]

Hi guys,

Please have mercy if you think this issue has already been covered: I pledge that I did have searched the forum, and haven't found a satisfactory answer, nor topic that is devoted to this.

In short wording, I am concerned that chasing the best mpg number could be damaging to the Insight's engine. (This obviously seems a bit paradoxical, right?) What I frequently find myself doing is driving around 1500 rpm, gas pedal floored to maximize the assist (like when my speed drops on a hill, and my battery is full).

Now every normal gas engine would suffer from this kind of lugging practice, loading it to the max at low rpm's. My question is purely technical: is Insight engine in any way designed to handle this abuse better? Perhaps the VTEC valve system helps a bit, or perhaps it is just tuned to work ok at low rpm's...

Does anyone feel competent to speak for the engine designers? I would be most thankful, and would sleep better too!

Thanks!
Predrag

 

[Insightful Trekker]

The best MPG comes from _not_ using the IMA system at all :!:

"Lugging" the engine has _some_ additional wear issues, but there are many more significant. VTEC is a wide RPM advantage (don't have to compromise a low end cam vs. a high end one). It doesn't significantly change engine "wear".

Simply stated for _best_ MPG AND engine wear rollercoaster the hills and downshift to minimize IMA usage (and WOT (wide open throttle).

I'd recommend searching the MPG section too :!:

HTH!

 

[Guillermo]

When using full throttle at 1500 RPM the shift light should be telling you to downshift :!:

 

[james]

"...driving around 1500 rpm, gas pedal floored to maximize the assist..."

I know it seems paradoxical, but trying to maximize assist doesn't really give you the best fuel economy. This is in part because of the way Honda designed the logic of the controller: as far as I can tell, you don't get assist at all until your mpg has dropped below about 50-55. You also get "hidden" charging when the battery drops a few bars below full, and this (assuming you have a 5-spd) is often enough to keep you out of lean burn.

Maybe MIMA will change this, but until I get mine, I think I do best mostly ignoring the battery, and paying attention to the mpg bar.

 

[Mike Dabrowski 2000]

John correct me if I am wrong here:
I think the answer is that with modern Fuel Injected computer controlled engines, the issues with engine lugging are not the same as when pressing on the throttle at 1200rpm on the older carburated engines. The fuel management system in the Insight does not just dump more fuel in the engine to try and increase power, it does it in response to the feedback from the emission control system, so only gas that can be efficiently burned is delivered to the engine, to maintain low emission, so the negatives of engine lugging are not in play.
With MIMA, I sometimes find my self driving at 30MPH at 1200rpm in 5th. I maintain momentum with short pulses of IMA.

 

[predrag]

Thank you gentlemen for the thoughts on the subject!

After a moment of logic, I agree that VTEC is here to widen the powerband (keeping more constant the speed of the intake/exhaust gasses), and wouldn't help much with the possible damage while lugging the engine. On the other hand, a properly delayed ignition timing would do that (or in other words, too advanced ignition could cause damage), and I would believe that Honda has mapped that right from the idle speed up.

Also, it is obvious that the whole system of storing the kinetic energy into the batteries and later using it through the electromotor is far from 100% effective. I understand the tip for "not using the IMA at all for the best mileage".

However, some nagging thoughts:

1) If I don't let go off the throttle on downhills (and therefore avoid going into charge mode), car picks up speed that is wasted on wind resistance, so at some speed (70-80mph?) it might be better to shave off the excess and store it into the batteries. (By the way, I just love the rollercoaster driving style...!)

2) When it is definitely beneficial to use the IMA (in my belief) is when facing a short hill on the highway with a full battery - then one can just floor it for the moment, and get over it with the battery that fills up "invisibly" - or without any green charging bars. I guess this opens up a discussion if the resistance (on the generator/alternator) during this invisible charging stage ever stops, even when battery reads 100% full...

3) I am a fan of WOT driving techique, trying to keep it either wide open or on lean burn, not much in between - I have noticed that to improve the mileage. But of course then I will be pushing the engine at low rpm's as well - since it is quite fine to do 30mph in 5th on a 5% throttle, but 40mph at 100% feels like could be damaging (the old school I have been thought says that the combustion gasses are pressing against a relatevely static piston and invites more blow-by, reduces compression).

Any thoughts?
Thanks.

Predrag

 

[Guest]

Hi Predrag:

___Just my $0.015 on the threads topic … You should be just above lugging of the ICE for maximum FE whenever possible! 28 - 32 mph in 5th through a relatively flat - good road - suburban area is perfect for excellent FE. Use DWL and if she drops much below 1,100 RPM while ascending even the smallest of inclines with a continually decreasing throttle input, it is time to downshift if you like it or not. Even after a downshift, keep those RPM’s down to a minimum in that next lower gear and so on and so on. You will know when you are approaching a lugged ICE and when you feel that initial hesitation, drop her down a gear and do not give her more throttle … Lugging is not good.

___If you have the opportunity to regen because there is nothing else better to do then throw energy away, by all means grab a steady amount of it. It will help keep your lights on, Computer(s) booted, ventilation running, or simply to play the radio … Coasting down a hill at 70 + and using the kinetic gain to blunt the upcoming potential hit of a climb is the better way to maintain maximum FE then grabbing a bit of regen to keep your speed down unless it is not safe to travel at 70 + running down whatever hill/mountain you may be coming off of. If it is a mountain you are coming down from, you have to keep your ICE live and Regen w/ Fuel Cut can make a difference but if you know you can hit the bottom at 70 and have a long flat section or climb afterwards, I would FAS and let that Kinetic gain give me everything she’s worth for the long slow deceleration into the upcoming flat or climb ahead.

___The one area where MIMA has my blessing and would work wonders is in your self-described scenario of a shallow hill where you would drop out of lean-burn anyway. If there is too much potential to overcome in a DWL scenario before lugging shows its ugly head, throw a little IMA at her while maintaining lean burn for the shallow/short climb and your set for excellent FE through the climb/descent cycle. As long as you aren’t dragging down the pack by a significant amount imho. When I say significant, I am talking more then 1 - 2 bars although the Mima guys will jump all over me about that one given I have never driven an Insight with it installed Unfortunately, when Honda designed the Insight’s IMA, they only had an inkling as to what they were doing. Honda should have let IMA maintain lean-burn instead of punching it out whenever IMA assist was invoked. You can see the change in Honda’s IMA design philosophy in the AH where IMA is used to maintain ECO at lower loads vs. an overly expensive electric supercharger under all scenarios as it is used in the Insight Mike’s Mima setup has corrected this design shortfall …

___As for a WOT technique, you may be a fan of it but you are killing your Insight’s longevity and it is not maximizing FE by any means.

___You can learn from those that have “been there and done that” or you can beat your head against the wall. The choice is yours

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email:2ncb2uce][email protected][/email:2ncb2uce]

 

[flunkysama]

I agree with Mike on this. The myth that luggiing can hurt an engine formed decades ago. Carburators do a poor job with slow, pulsey air flow, causing engines to run too rich or too lean which could damage them. Engine knock also most likely occurs under full throttle at low RPM.
Poor engine mounting and internal balancing caused lots of shaking at certain RPMs too.

Result: "Do not lug your engine! It's bad for it!" That's what my grandfather used to tell me.

All these problems are solved in modern electronically controlled fuel injected engines.

Sometimes, accelerating from a stop I use full throttle with 2K (or lower) shifts points. Acceleration is about the same as normal traffic. The advantage is getting to cruising speed and lean burn quickly. The result is about the same MPG as normal throttle and shift points.

 

[Mike Dabrowski 2000]

Hi Guys
While pondering this question, and fulfilling my need for a 100 mile trip over a mostly rural rolling New England secondary highway this afternoon. (CT RT 12), I made the 100 mile round trip with 79.9MPG. Average speed 36 mph, max of 50. The road goes through several small to middle size towns, with lots of traffic and traffic lights, I hit some school busses on the way back, the road is never flat, with two hills that without MIMA, to maintain 40mph, you would need to be in 3rd. My speed was with traffic, and at the speed limit +- 10MPH.
Take off from a stop was always with gentle throttle, and full manual assist, to get to speed with minimal gas usage.
The technique I settled on for cruising was to be in 5th as much as possible, even down to 30 mph. RPM 1000 to 1400. I had PIMA tuned so that the assist setpoint was at ~95 MPG, and the regen setpoint at 115 MPG. Come to a hill, gently change the throttle so the MPG was down to 70, and I already had full assist. Over the hill, back off the throttle to 130-140 MPG, and I got from 10-30 A of regen, with 150mpg giving full regen.
All so intuitive that I forgot about it.
With the stock IMA, if you press down the throttle to get acceleration or to compensate for slowing down on a hill, with the RPM at 1000-2000RPM, you must push down to ~ 40MPG before full assist comes in if it ever does. One look at the torque curve for the IMA, and you will see that the ICE only puts out about 20HP down there, and the electric puts out 13.Therefore the need to down shift.
I could top all but the big hills never dropping my MPG much below 60, all in 5th. Dropped to 40 on the two big ones.
The battery SOC got to 2 bars, after the big hills, but was at 40% when I got back.
I would bet that if anyone of you got into a 5 speed MIMA equipped Insight, and did a MPG run over a familiar road without MIMA, then did a duplicate run with propertly tuned PIMA, that your MPG would go up 5-15 %. No special techniques needed, just go easier on the throttle that you would without MIMA.
The best part is that the speed range during the runs would be higher with MIMA, acceleration faster, pulses of power shorter, and speed closer to the speed of traffic flow while matching or improving on the straight IMA MPG.
The engine was down to <1000 rpm several times, it even stalled then restarted once at 22 MPH in 5th, abut the electric torque was able to accelerate right from there with no need to downshift.
MIMA really makes a difference, and I know that if mostInsight drivers tried it, they would want one.
IMBO (In My Biased Opinion)
:wink:

 

[Mike Dabrowski 2000]

With all discussions of comparitive MPG, the following things :
terrain, speed, traffic, stops, wind,weather,temperature, AC, and other factors would need to be comparable for a meaningfull comparison.
The minimum for me to feel comfortable with a comparison
would be average grade, average speed, max speed, number of stops, elevation change start to finish, round trip or not.
Why don't we come up with a standard way of defining a trip that will allow some good fair comparisons of terrain in particular.
Delorm topo usa allows a route to be plotted on a map, then a profile of the elevation changes can be plotted for the trip. it cost less than $100.
Here is one of my trip today:
http://pages.cthome.net/genesisone/Mikesouthrt12.pdf
what do you think?

 

[kapps]

The engine was down to <1000 rpm several times, it even stalled then restarted once at 22 MPH in 5th

wow. 22 in 5th, I thought my mom was crazy when she tried going up a small hill at 30 in 5th. I usually try to keep the engine above the 1200-1300 rpm range when cruising. For me, it takes a little getting used to when jumping between the Insight and MINI Cooper S. The Insight can spin 'em at 1500 rpm while the MINI needs 2k+ before it begins getting into it's power band. And I'd never try driving the MINI in the upper gears below 1800 or so rpm. It just doesn't like it down there.

 

[Mike Dabrowski 2000]

As I said, 22 in 5th was where I stalled, after that I kept it over 1300 most of the time.
The insight with full assist in the 3-6K power band of the ICE makes the car scary fast (by my standards). It will accelerate up a good grade at 90+ mph in 5th. In third at 3K + the Insight just blast off, with the full 13 electric ponies galoping right in there with the gas ones.
The normal IMA limits the assist to 6-7HP when you go that fast, not with MIMA. I can squeek the tires in first and second with out poping the clutch.
Too much fun at first, I had to work the lead out of my MIMA finger.
Now I am trying to get good mileage at normal commuting speed. :wink:

 

[predrag]

Thanks for the thoughts, Wayne.

Manual IMA is an obvious desire for 99% of Insight drivers - I wish someone started manufacturing some nice kits!

As for the whole "accelerate with wide open throttle" technique, it has been reccomended over and over exactly here in this forum - so it must have some effect on MPG.

(I don't want to open up that discussion all over again...)

Anyhow, today I tried not to go full throttle until the engine is reving at least 1700-1800 rpm. Hard to tell if this is making any difference, I don't have a regular route...

 

[james]

My own experience (not with MIMA, yet), is that although I can cruise in 5th at about 25 mph or more on the level (or more usually a slight downhill), any lower and the car jerks & shudders if I try to give it more throttle. To speed up, I usually wind up dropping to 3rd for a few seconds, then back to 5th.

I don't know if this is absolutely the most efficient technique, but it's a lot more fun than trying to nurse a little more speed out of 5th, and not THAT much worse - after about 630 miles, I'm at 80.1 for this tank

 

[predrag]

Yes, driving on minimum throttle at 25-30mph in 5th feels familiar, and then downshifting to speed up. It all depends on the gas pedal position, of course: more pedal to the metal, higher rpm's (= lower gear) is required.

And, by the way, I'm completely jealous of your 81mpg for the tank... Over here there are so many hills to traverse that with the local driving I'm having a hard time maintaining 70mpg! (How is it there by you, James....?)

 

[james]

Hills? Well, when I go to the lake (which I've done about twice a week on this tank), I start out from my place at about 4800 ft, make about a 400-500 foot climb and drop back down into Carson City, then climb to Spooner Summit at about 7200, and drop back to about 6300-6400

80 is a bit over my average, which is about 75-78 in summer, dropping to 70 or less in wintertime, but the hot weather in August* helped, as did not having to go into town as much as normal.

*Yes, I last filled the tank in mid-August. I was abroad most of September, so it doesn't really count. Still, I haven't had to buy any $3/gallon gas yet

 

[predrag]

Wow, James, that's impressive...

I don't want to turn this into a mpg topic - but it seems that I should go to that section and read some more! The only time I ever got 80+ mpg was on the Martha's Vineyard (an island off Cape Cod, MA), where you just cruise up & down little hills at 30-40 mph.

Any real world highway driving for me turns out to 75mpg at best, and if you put a hill or 2 in (we don't have mountains at east coast), then it is struggling to keep it at 70.

(Meanwhile I think of myself as a good driver, my tires are at 45 psi and I have the 2000 manual model, without A/C!)

 

[james]

"...struggling to keep it at 70."

Perspective, perspective... Remember that with at least 90% of the cars on the road, you'd have to work to get 35

 

[Wayne M]

Built for it

Don't worry too much about the 'lugging' with the Insight engine design. It's built for it, with the offset cylinder design which does away with most of the over stressing that one would normally find on a more conventional engine. But, I'm still not that comfortable about getting down to speed / load ratio's like we've got going in this thread. :shock:
And even with figures to the contrary, it still seems less economical to wide open throttle just to get max assist.

 

[predrag]

Oh right, the offset cylinder design, I forgot that one! Obviously, this engine was designed with low rpm loads in mind. So it isn't like driving any other car in idle-level rmp in top gear. Still, I don't feel comfortable going wide open unless I am at least at 1700-1800. Does this match everybody else's emotion too?

We should also take in account that Insight gets largest torque at about 2000 rpm!