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Old 04-06-2006, 12:52 AM   #1 (permalink)
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Default Horsepower to the wheels at 60 MPH

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. 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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Old 04-06-2006, 01:15 AM   #2 (permalink)
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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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Old 04-06-2006, 01:38 AM   #3 (permalink)
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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. .

Not going to loose much sleep over it though.
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Old 04-06-2006, 03:52 AM   #4 (permalink)
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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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Old 04-06-2006, 04:26 AM   #5 (permalink)
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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.

NO....NO, don't put lead in an aluminum chassis! 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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Old 04-06-2006, 09:06 AM   #6 (permalink)
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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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Old 04-06-2006, 09:32 AM   #7 (permalink)
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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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Old 04-06-2006, 11:39 AM   #8 (permalink)
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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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Old 04-06-2006, 01:25 PM   #9 (permalink)
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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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Old 04-06-2006, 02:25 PM   #10 (permalink)
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James
5 or 6 bars would be ~25 amp @ say 144V Thats 3600W or nearly 4 HP.
With MIMA, we could get on the long hill, and controll speed with regen, and by knowing the amps of regen, come up with a more exact number?
Better get your harness built.


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