How much power is reqd to maintain an Insight at 30mph on the flat in good calm conditions? BHP? KW?
Assume tyres at say 50psi.
Any offers?
Assume tyres at say 50psi.
Any offers?
How much power to maintain speed?
retepsnikrep
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2.8 HP at idle is particularly interesting as it illustrates the difference between neutral coasting with the engine idling and engine off idling. In my calculations for lower speeds I had assumed all losses to be wind resistance which was certainly erroneous, thus my optimistic results. This data is extremely valuable for those planning electric conversions as well as those calculating the gains from energy saving mods and driving techniques. Thanks for everyone’s input and for any additional data we can post here. We might finally be able to answer the question as to whether it is better to downshift to fourth gear when cruising at 30 to 40 MPH due to transmission losses for in overdrive and efficiency losses due to running the ICE at less than optimal RPM. 
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If I could find a long flat road, (not easy in NE) I should be able to just run with the e-wheel @ 30MPH and measure the voltage and current delivered to the motor to do a real world HP measurement. I can run the motor alone with the wheel lifted to get a baseline current.
The losses in a toothed belt 4:1 reduction should be quite small, and the motor torque and efficiency curves of the E-Tec motor are here: http://www.thunderstruck-ev.com/etek_curve.htm
The losses in a toothed belt 4:1 reduction should be quite small, and the motor torque and efficiency curves of the E-Tec motor are here: http://www.thunderstruck-ev.com/etek_curve.htm
I wonder if the scangauge calculates HP using instantaneous fuel consumption, air mass flow into the engine and temperature along with some other info.
I imagine this method might provide a HP value maybe within 20% or 30% of reality which is not bad.
I imagine this method might provide a HP value maybe within 20% or 30% of reality which is not bad.
But should it go down under lean burn? Think about it: say you're going down a level road at constant speed, and by wiggling the accelerator a tiny bit can go into or out of lean burn without your speed changing much at all. That says the engine must be producing the same horsepower in either state. It's just using less fuel to produce that power when it's in lean burn.
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Thats why they test cars on a dyno.
I would agree that Iamian's approach is probably best and think that 1 bhp for 30 mph is about right, probably 5 bhp for 50 mph.
There is another way of thinking about this too, by working backwards from the engine efficiency and the miles per gallon - although far too many "fudge factors" get involved for it to be anything close to scientific. As a result it only really works for higher speeds, as at low speeds the proportion of the petrol consumed going to parasitic losses and not actually driving the car is quite high (alternator, control systems, lights, entertainment, power steering etc).
Say you can manage 80 mpg at a constant 60 mph and the engine is at 25% efficiency. Gasoline contains about 132 MJ per US gallon, so you are burning (132/80) = 1.65 MJ of chemical energy per mile. However, the engine is only 25% efficient, and the remaining powertrain say 90% efficient (to take account of parasitic losses etc), and it looks like you are using 1.65 x 0.25 x 0.90 = 0.37 MJ, or 370,000 Joules at the wheel to travel each mile.
As it takes 60 seconds to travel 1 mile at 60 mph, the power used at the wheel is around 370,000 / 60 = 6200 W, or 6.2 kW, roughly 8.4 hp.
Like I said though, this method probably won't work well for speeds as low as 30 mph and requires quite a bit of "guesstimation" regarding the engine efficiency.
There is another way of thinking about this too, by working backwards from the engine efficiency and the miles per gallon - although far too many "fudge factors" get involved for it to be anything close to scientific. As a result it only really works for higher speeds, as at low speeds the proportion of the petrol consumed going to parasitic losses and not actually driving the car is quite high (alternator, control systems, lights, entertainment, power steering etc).
Say you can manage 80 mpg at a constant 60 mph and the engine is at 25% efficiency. Gasoline contains about 132 MJ per US gallon, so you are burning (132/80) = 1.65 MJ of chemical energy per mile. However, the engine is only 25% efficient, and the remaining powertrain say 90% efficient (to take account of parasitic losses etc), and it looks like you are using 1.65 x 0.25 x 0.90 = 0.37 MJ, or 370,000 Joules at the wheel to travel each mile.
As it takes 60 seconds to travel 1 mile at 60 mph, the power used at the wheel is around 370,000 / 60 = 6200 W, or 6.2 kW, roughly 8.4 hp.
Like I said though, this method probably won't work well for speeds as low as 30 mph and requires quite a bit of "guesstimation" regarding the engine efficiency.
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A dyno does not have wind resistance.Mike Dabrowski 2000 said:
You can simulate that with a mathmatical model... just like the ScanGauge ( uses a model),
But it's still a guess... a bit closer though, I'm sure.
I think we only care about how many gross HP does it take to move the car down the road.
WITH all the losses with the transmission, tires, wind, etc.
You will still have all that with an EV or PHEV conversion.
I'd be willing to bet a tank of gas that the SG is within 10% of real on the HP reading.
I've used it in enough cars and situations to be confident in this.
The horsepower is 25% to 30% lower than indicated when in lean burn mode.
All your power for everything, including the radio comes from the gasoline.
If you use less gasoline, you naturally make less power.
The lean burn is really, like a 6th gear on the car.
Since there is no 6th gear to lower RPM, (which would in turn lower fuel used per minute) the car lowers fuel used per minute without lower RPM by changing the ratio. It's a clever trick to get less power, without adding heavy ( and costly ) extra gears.
-John
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Since my math skills are weak, my approach to any question like this is to devise a test that will determine the answer, and include all the variables involved.
The current drawn by an electric drive system is a measurement of required power, which can be easily converted to HP.
Several EV insights have been built, so performance data should be available that would answer this question.
The current drawn by an electric drive system is a measurement of required power, which can be easily converted to HP.
Several EV insights have been built, so performance data should be available that would answer this question.
"If you use less gasoline, you naturally make less power."
No, IC engines don't have a fixed efficiency, so that X amount of gas always gives Y horsepower out. The efficiency depends on a lot of factors. For instance, using the choke (on a older engine) gives you a richer mixture, which burns more gas to produce less power (but runs when the engine is cold). Likewise, if you've ever flown a small plane, you'll know about the mixture control, and how to use a rich mixture for takeoff, then lean out to give optimum power/fuel consumption in cruise.
"The lean burn is really, like a 6th gear on the car.
Since there is no 6th gear to lower RPM, (which would in turn lower fuel used per minute) the car lowers fuel used per minute without lower RPM by changing the ratio. It's a clever trick to get less power, without adding heavy ( and costly ) extra gears."
Not at all. When the Insight engine goes into lean burn, it's developing exactly (well, pretty close to) the same amount of power, just using much less gasoline to do so. If it wasn't developing the same amount of power, you'd see a noticable speed drop on going into lean burn. Instead, the only change is to the instantaneous mpg display
No, IC engines don't have a fixed efficiency, so that X amount of gas always gives Y horsepower out. The efficiency depends on a lot of factors. For instance, using the choke (on a older engine) gives you a richer mixture, which burns more gas to produce less power (but runs when the engine is cold). Likewise, if you've ever flown a small plane, you'll know about the mixture control, and how to use a rich mixture for takeoff, then lean out to give optimum power/fuel consumption in cruise.
"The lean burn is really, like a 6th gear on the car.
Since there is no 6th gear to lower RPM, (which would in turn lower fuel used per minute) the car lowers fuel used per minute without lower RPM by changing the ratio. It's a clever trick to get less power, without adding heavy ( and costly ) extra gears."
Not at all. When the Insight engine goes into lean burn, it's developing exactly (well, pretty close to) the same amount of power, just using much less gasoline to do so. If it wasn't developing the same amount of power, you'd see a noticable speed drop on going into lean burn. Instead, the only change is to the instantaneous mpg display
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Yes James. Lean burn gives you SIGNIFICANTLY LESS POWER. It sounds like you have not driven a MT Insight with lean burn. This would be blantently obvious otherwise. Once the engine is to normal temp, and you are into normal cruise mode, lean burn = 25% to 30% less power and, not by coincidence, 30% less fuel is used. It may not be an exact 1:1 ratio for power to fuel use, but it's pretty darn close. If you run rich, you do not get more power because you waste fuel out the tailpipe. Running rich is like taking two Vitamin pills a day. You just piss one away. But running lean FOR SURE has a proportional loss in power. ( taking half a vitamin pill when you need a full one )james said:"The lean burn is really, like a 6th gear on the car.
Since there is no 6th gear to lower RPM, (which would in turn lower fuel used per minute) the car lowers fuel used per minute without lower RPM by changing the ratio. It's a clever trick to get less power, without adding heavy ( and costly ) extra gears."
Not at all. When the Insight engine goes into lean burn, it's developing exactly (well, pretty close to) the same amount of power, just using much less gasoline to do so. If it wasn't developing the same amount of power, you'd see a noticable speed drop on going into lean burn. Instead, the only change is to the instantaneous mpg display
-John
Lean burn does give more power for the same amount of gas, or the same amount of power using less gas. If it didn't there would be no point in putting it on the Insight in the first place. It is a costly modification as it requires an extra catalytic converter and does require special software to control. Hypermillers accellerate to a speed slightly higher than what they hope to maintain, back off the thrittle untill the IMPG Gauge indicates lean burn mode, then gradually increase the throttle so as to remain in lean burn at the speed they originally intended to cruise at.
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But a Dyno will give the actual exact HP output of the Engine... if you are reading it with the SG at the same time you can see the difference.gpsman1 said:
I'll take that bet :badgrin:gpsman1 said:
Although to be fair I will say that I already know it is more than 20% off... because I just called them and asked a few minutes ago how accurate the HP reading was... They said that their reading is usually around 20% higher than the actual net HP... :badgrin:
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I also think that people are confusing two very different things....
#1> Power the Engine puts out in HP which is at that time.
#2> Work the Engine does with 1 Gallon of gas.
Lean Burn is more fuel efficient so more energy and work is done with the same 1 gallon of gas.... but over a longer period of time... the fuel to air ratio goes from as low as ~13:1 up to as high as ~25:1 almost 1/2 the fuel is being used per engine cycle... in order to get the same amount of power per engine cycle out of that much less fuel the lean burn would have to double the efficiency of the ICE... And while it does increase the ICE efficiency I seriously doubt that it is doubling the efficiency ... if it did we would have read a long time ago about the wondrous 60+% engine Honda made.
"Yes James. Lean burn gives you SIGNIFICANTLY LESS POWER. It sounds like you have not driven a MT Insight with lean burn. This would be blantently obvious otherwise."
Sorry to burst your bubble, but I've been driving a 2000 MT Insight since (IIRC) June 2003. Put about 70K miles on it, with 70.2 mpg average since I found out how to reset the LMPG counter.
As for reading about the wondrous Honda Insight engine, do a little searching and you'll find articles about it and the awards it has won. Not as many as it should have, of course, since it doesn't have 12 cylinders and put out 600 hp, but it got recognition.
Sorry to burst your bubble, but I've been driving a 2000 MT Insight since (IIRC) June 2003. Put about 70K miles on it, with 70.2 mpg average since I found out how to reset the LMPG counter.
As for reading about the wondrous Honda Insight engine, do a little searching and you'll find articles about it and the awards it has won. Not as many as it should have, of course, since it doesn't have 12 cylinders and put out 600 hp, but it got recognition.
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Lean Burn ALWAYS produces less power. Always. Period.
I'm surprised, shocked in fact, that after all those miles you claim to have driven James, you contest this fact.
I'm shocked we are having this conversation.
You cannot change the laws of chemistry and physics just because you think you have a cool car.
( Ok, I agree it IS a cool car... but you still can't change the laws of physics... )
Does lean burn use less gas per mile? Sure you bet. THAT IS THE POINT.
Is lean burn just as powerful as the stoichiometric ratio? Absolutely not.
Can you accelerate quickly in lean burn? Absolutely not.
Why? It is less powerful.
Can you climb a large hill in lean burn? Absolutely not.
Why? It is less powerful.
Can you maintain high speed indefinately in lean burn? Absolutely not.
Why? It is less powerful.
Does gasoline 'diluted' with ethanol give you as many miles per gallon? Absolutely not.
Why? It is less powerful.
Does gasoline 'diluted' with water give you as many miles per gallon? Absolutely not.
Why? It is less powerful.
Does gasoline 'diluted' with air give you as many miles per gallon? Absolutely not.
Why? It is less powerful.
Lean burn is gasoline vapor diluted with extra air. Air is not a fuel.
Lean burn is always, by law of conservation of energy, LESS POWERFUL.
If the car was permanetly set to lean burn, you would have terribly low MPG.
If lean burn could be maintained full time, that is how Honda would have built it!!!!
Fact is, lean burn is a method to turn down the power, when low power is all that is needed.
Fact is, lean burn is like adding a 6th gear to turn down the power to the wheels, which is why I made the analogy earlier.
I think you should investigate why the CVT does not use lean burn.
I think you will find "emissions" is not the reason. ( while this is often mis-quoted as the reason... it may be a contributing factor, but it is not the main reason... )
I hate to preach/teach but I thought this was blatently obvious to anyone who owns a 5-speed.
Practical real world driving should show you it is less powerful. You really don't need a chemistry degree.
The reason ( I think ) why this may be hard for some people to realize is... While the horsepower IS about 30% less in lean burn ( the chemistry says so ) we are not cutting some 250 HP beast to 175 HP. I'm sure you would notice that.
In the case of the Insight, lean burn is most often cutting 15 HP down to 11 or 12 HP. And I suppose, that could be invisible to people not paying close attention.
Cheers.
Hope that clears it up.
-John
P.S. I was getting 84 to 94 MPG the first week I owned the car... and oh... BTW... in 25 years of driving, I've never ever owned a manul transmission car... in fact, before last month, I've never even driven one before. *( Thus I keep rolling to a stop in gear.... newbie... I know... bad.... ) Best trip... 129 miles at 97 MPG... No MIMA.... yet.... and I'm starting to wonder if things really can get better! :lol:
I'm surprised, shocked in fact, that after all those miles you claim to have driven James, you contest this fact.
I'm shocked we are having this conversation.
You cannot change the laws of chemistry and physics just because you think you have a cool car.
( Ok, I agree it IS a cool car... but you still can't change the laws of physics... )
Does lean burn use less gas per mile? Sure you bet. THAT IS THE POINT.
Is lean burn just as powerful as the stoichiometric ratio? Absolutely not.
Can you accelerate quickly in lean burn? Absolutely not.
Why? It is less powerful.
Can you climb a large hill in lean burn? Absolutely not.
Why? It is less powerful.
Can you maintain high speed indefinately in lean burn? Absolutely not.
Why? It is less powerful.
Does gasoline 'diluted' with ethanol give you as many miles per gallon? Absolutely not.
Why? It is less powerful.
Does gasoline 'diluted' with water give you as many miles per gallon? Absolutely not.
Why? It is less powerful.
Does gasoline 'diluted' with air give you as many miles per gallon? Absolutely not.
Why? It is less powerful.
Lean burn is gasoline vapor diluted with extra air. Air is not a fuel.
Lean burn is always, by law of conservation of energy, LESS POWERFUL.
If the car was permanetly set to lean burn, you would have terribly low MPG.
If lean burn could be maintained full time, that is how Honda would have built it!!!!
Fact is, lean burn is a method to turn down the power, when low power is all that is needed.
Fact is, lean burn is like adding a 6th gear to turn down the power to the wheels, which is why I made the analogy earlier.
I think you should investigate why the CVT does not use lean burn.
I think you will find "emissions" is not the reason. ( while this is often mis-quoted as the reason... it may be a contributing factor, but it is not the main reason... )
I hate to preach/teach but I thought this was blatently obvious to anyone who owns a 5-speed.
Practical real world driving should show you it is less powerful. You really don't need a chemistry degree.
The reason ( I think ) why this may be hard for some people to realize is... While the horsepower IS about 30% less in lean burn ( the chemistry says so ) we are not cutting some 250 HP beast to 175 HP. I'm sure you would notice that.
In the case of the Insight, lean burn is most often cutting 15 HP down to 11 or 12 HP. And I suppose, that could be invisible to people not paying close attention.
Cheers.
Hope that clears it up.
-John
P.S. I was getting 84 to 94 MPG the first week I owned the car... and oh... BTW... in 25 years of driving, I've never ever owned a manul transmission car... in fact, before last month, I've never even driven one before. *( Thus I keep rolling to a stop in gear.... newbie... I know... bad.... ) Best trip... 129 miles at 97 MPG... No MIMA.... yet.... and I'm starting to wonder if things really can get better! :lol:
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Lean burn is not unlike cylinder deactivation... you know... those large cars/trucks with a V8 that can run on 4 when cruising. That is, in a way, the same as lean burn.
In those V8, you feed air/fuel to 4 cylinders, and just air to 4.
Thus, really, taken each full Revolution at a time, you have just changed the A/F ratio to 28:1.
( The Insight Lean Burn was measured by one owner to be 26:1 )
So, how many people think a V8 with 4 cyl fueled is "just as powerful" as the full V8?
:badgrin: Don't tell me it's not the same. It is mechanically different, but SAME IN FUNCTION and end result.
-John
In those V8, you feed air/fuel to 4 cylinders, and just air to 4.
Thus, really, taken each full Revolution at a time, you have just changed the A/F ratio to 28:1.
( The Insight Lean Burn was measured by one owner to be 26:1 )
So, how many people think a V8 with 4 cyl fueled is "just as powerful" as the full V8?
:badgrin: Don't tell me it's not the same. It is mechanically different, but SAME IN FUNCTION and end result.
-John
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