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Discussion Starter #1
Does anyone know what actual horsepower the Insight requires to travel at 60 MPH?

It occured to me that someone here may be able to do a test that would answer the question. :idea: If one was able to find a hill that they could coast down at a steady 60 MPH, and if they could measure the angle of the hill or use a GPS to determine their loss of altitude with respect to time, it should be relatively simple to calculate the energy used (knowing the weight of the car and driver).

This information would be very usefull in determining what the ultimate mileage of a plug in Insight could be. It could also determine the size of motor required for an electric conversion, or it could be used to determine the tank to wheel efficiency of the Insight.
 

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Reads like a lot of variables in your proposed testing scheme Kip. ;) IIRC its been discussed and roughly calculated to upper teens to lower 20 HP's.

Of course your rate of acceleration will be anemic at best with such power under the hood.

In regard to EV conversion and HP AFAIK other design criteria become more significant. Range, battery load and sustainable drain rates etc. Been "thinking" about doing an Insight EV conversion myself. A couple of years of acqusition of parts / funds. For me a primary design factor is range and speed. IMO and with Ricky's feedback a 60 MPH top speed with 100 mile range is going to highly prefer some _expensive_ LiPoly's. Makes the cost impractical at this time. Oh well. :/
 

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Discussion Starter #3
There were hills in the Berkshires near Mike's that were suitable for this. Nothing near here is suitable, no GPS either, or I'd try it myself. . :cry:

Not going to loose much sleep over it though. ;)
 

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Well, here's what I have observed with my EV conversion which is a 92 Saturn SC2 at probably about 3200 pounds, LRR tires, a 0 toe in allignment, removed rear wing, and soon to have brake modifications to reduce disc brake drag. At 144 volts nominal I can maintain about 58mph on the freeway pulling approximately 65 amps (this used to be 80 before some of the efficiency modifications, which is a huge gain). So take about 1000 watts per hp to account for losses.

144 volts X 65 amps = 9360 watts

so less than 10hp to pull my car down the road. Somehow it's seeming as though this car is very efficient. The Insight should be able to do better than this. The problem is you won't be able to carry much battery weight in an Insight, even with all the IMA components removed there's room, but the weight is going to be the limiting factor. Not a car to convert to be a lead sled (70's Porsche 914's make a good car for this).
 

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Discussion Starter #5
Thanks Rick, you are confirming what I have suspected for some time that the Insight requires less than 10 horsepower to move at 60 MPH. I seem to recall that the original VW was only 25 HP and that the Triump Spitfire was 22 or 33 HP, and these were not power measured at the wheel.

Must find a good hill. :D

NO....NO, don't put lead in an aluminum chassis! :shock: The next generation Prius is rumoured to have Lithium designed in. Perhaps a used Prius pack in a couple of years?
 

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I've tried some informal coast-down tests and it is VERY HARD to get repeatable results. Even a tiny breeze, or a slightly different road profile makes a huge difference.

The way I would look at it is this: The top speed is around 110 MPH, limited by aerodynamic drag. Wind resistance goes up by the square. The maximum HP is around 70. So to go 55 requires 1/4th the power that it does to go 110, assuming that it's all wind resistance (which isn't quite true, but it's probably close at these speeds). That works out to about 17 HP.
 

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I seem to remember reading somewhere that at 60 flat road, no wind, that only 9 hp was needed.
I looked but could not find the source of that info though, but would expect that it is close.
As far as additional weight, climbing hills is where that has the biggest effect, as well as during acceleration, on a flat road, the weight is only effecting rolling resistance, and only if the tires are not fully inflated.
Very terrain dependant.
 

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Yes, I think that's correct Mike. I've owned 3 brand new Insights, and this type of rolling resistance/horsepower factor has often been on my mind. Car and driver magazine, when they did their standard performance test of every car, used to have this as one of their criteria.

My best estimate, based on a comparison with other cars and from experience, is the Insight with maximum air in the tires, only requires about 8.5 HP to maintain 60 mph. On concrete it may even require slightly less hp, on asphalt slightly more. Actually, I believe Honda states in some official literature that the Insight requires 20 % less HP than the Civic?
 

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I worked it out as something under 17 HP. I have about 10 miles of consistent downhill that I drive frequently (US 50 from Lake Tahoe to Carson City). I'll consistently hold about 60-65 mph going down it,
so given elevation change & distance, it's pretty simple to get a ballpark figure for power.

The catch is that I've got 5-6 bars of regen most of the way down, and I don't know how much of the 17 HP is driving that. It does want to speed up considerably if I get to full charge before the bottom, though.
 

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Discussion Starter #11
Dougie, it was reported here that the Insight was still accelerating at 2 MPH per second when it hit the speed limiter, indicating that the engine was putting out more power than required to maintain a constant speed. One would also have to determine if the engine was at the right RPM and the IMA pack sufficiently charged and unlimited to produce peak power. I suspect that after putting out current for the time required to hit 113 that the IMA pack would be limiting the current to the electric motor.
 

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Sounds good Mike, except accelerating TO 60 mph is alot different than maintaining speed AT 60 mph. Especially the part from 45 up to 60, when wind drag is a larger factor. By the time you get to 60, what will be the battery SOC??
 

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It could well be that the top speed (not limited by the computer) is higher, but it's not going to be that much higher. The drag goes up quite quickly at higher speeds.
 

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Discussion Starter #15
Here is the raw data:

At 50 degrees F, dead calm, 3 degree slope, straight asphalt road, the Insight tops out at 76 MPH!

I have no idea what this means, but it is a lot faster than I expected. :shock: Now where is that old physics text now that I need it?

P.S. Don't believe any rumours that I had to drive 50 miles and take 3 runs on a deserted road to get these numbers. ;)
 

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Discussion Starter #16
(Edited for reasons noted in following posts.)

1 horsepower = 550 foot-pounds per second

76 MPH = 111.5 feet per second.

(Sine 3 degrees) .0523359 x 111.5 feet per second = 5.83 feet per second vertically.

Insight and pilot weigh 2,049 pounds x 5.83 = 11,946 vertical foot pounds per second

Divide by 550 = 21.7 horsepower at 76 miles per hour.

Finding the cube root of 21.7 (2.79) and dividing by the ratio of various speeds, then cubing the result yields:

(at 50 degrees)

6.2 horsepower at 50 MPH
10.7 horsepower at 60 MPH
25.3 horsepower at 80 MPH
49.5 horsepower at 100 MPH
71.3 horsepower at 113 MPH

Presently my tires are not at max and I have the engine aerodynamic cover removed for mods. I need a warmer day, and a longer and gentler hill to do a better test, but for now........
 

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I just realized that I am guilty of spreading a false description of the relationship between drag and power. Drag is a force, and power is force times velocity. Aerodynamic drag goes up as the square of velocity, so the power needed to overcome aerodynamic drag goes up as the cube of velocity.

This means that to double your speed, you have to multiply the power by eight, not four. (Assuming it's all aerodynamic drag.)

So if the Insight has, say, 80 HP and a top speed of 120 miles per hour, then it takes only 10 horsepower to go 60 miles per hour.
 

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Discussion Starter #18
Good point Dougie. I recalled that the resistance of water went up as a cubed ratio. I had also calculated that the Insight could go 193 miles per hour with a 140 HP Civic engine! :shock: :lol:Somehow the light didn't go on. :?

Thank you for revisiting the question. I'll review my calculations and edit my conclusions.
 

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Interesting Post

Kip,
Very interesting post. One thing I do not see mentioned here. If we were considering this for an EV then 10 hp might be enough. Electric's are not known for their hp though, it's their foot pounds of torque for accelleration. I believe a large diameter electric motor (leverage) of say 20 hp will produce about 78 ft lbs (Civic) and should be plenty to get you to cruising speed.
 

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Discussion Starter #20
Thanks Jack. As I mentioned there were several good reasons for wanting accurate info, and I think we have a better idea now. I'm close to having a Twin Latch Circuit installed, and am really keen to do tests. This mod like many others would benefit from a power saving analysis related to the total energy used at cruising speed.

A while back I tried a circuit that disabled the power steering in 4th and 5th gear. Had I done an analysis of the power saved before hand, I would not have even built it. (I soon abandoned that mod for safety considerations.)
 
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