[Delta Flyer]

This not exactly the subject topic line I wanted to use, but needed to keep this from looking too off-topic.

At lunch, someone was mentioning someone with a go-cart could go 78 mph with a 5.5 horsepower 2-cycle engine. That got me thinking about a couple of things:

- How much horsepower does the Insight need to cruise at 50, 60, 70 mph?

- How much lighter can the Insight be made? I know the Insight2 concept car is about 1500 pounds, 300 less than the Insights on the road.

 

[Yves M.]

As a first draft,
the engine HP curve graph shown in the Encyclopedia:

Shows about 20 HP at 2000 RPM which is about the RPM at 60 MPH. So 20 HP is the max possible.

Considering that the engine at that speed and gear, has no acceleration (without the IMA) if you floor the gas pedal and needs the IMA as soon as there is a slight hill, I would approximate the HP needed to be between 15 and 20 HP

I would add that there is a margin of error of 'just about' 10 HP so....

 

[Delta Flyer]

Thank you for the graphics.

I was thinking: a go-cart probably weighs 200 pounds - an Insight 1800 pounds. Most of 1600 pounds is a shell and protection. If there was only a lightweight method to protect in a collision. Of course a go-cart would be a death trap at highway speeds.

 

[kapps]

It takes very little HP to keep something moving. It is true that a cart can go well over the 70 mph range - the small kid carts can go 70 mph. Remember a cart has very little resistance too...every time they go out, the bearings are lubed and everything is just right.

Also, it's the torque that you need to look at, not HP. Hp is just torque*rpm/5252. This means that if you have the same torque at 2x the rpm, the HP is double - why diesel engines have low HP. The amount of torque the Insight's engine can produce at 2000 rpm is very low. That's why the IMA is there. The most efficient form of driving is to use the gas engine to cruise and the IMA to accelerate.

Making the Insight lighter acutally wouldn't help the HP needed to cruise; although it would reduce the time it needs to get up to speed. The aerodynamics of the car is what determines the HP needed to cruise. Reduce the Cd to <.2 and your highway mpg will rise dramatically.

 

[Delta Flyer]

Now I've come up with an onorthodox application of wartime technology.

The US Navy could fit the Trident ballistic missile in their submarines' silos, but it was too blunt. The solution was to put what looked like a telescoping radio antenna on top of the missile to cut the drag.

Peacetime application: have a telescoping bumper on the Insight. The front one would reduce the drag - the rear one would keep tailgaters off.

 

[Foxpaw]

Making the Insight lighter acutally wouldn't help the HP needed to cruise; although it would reduce the time it needs to get up to speed. The aerodynamics of the car is what determines the HP needed to cruise. Reduce the Cd to <.2 and your highway mpg will rise dramatically.

Not just the aerodynamics - but the total energy losses at cruising. That includes aerodynamics, rolling resistance, and friction within the drivetrain. Making the car lighter might reduce the rolling resistance somewhat.

I'm not really sure how you would go about reducing the weight of the Insight though, because I don't know where all the mass is. Somehow car manufacturers find a way to take a bunch of components that weigh about 700 pounds all together, and somehow make a 3000 pound SUV out of it. :wink:

The obvious one is to remove the jack, spare tire, and tool kit. I don't think those are all that heavy, but muscle car nuts swear by it. 8) The stereo system probrably weighs very little. Hrmmm.. other than that I don't know where all the weight is! The IMA system is like a couple hundred pounds, the gasoline engine and transmission is another couple hundred, the frame is like... I don't know, but I'll guess and say like a hundred pounds. (Guessing, basing an estimate from a Lotus Elise which has a similar aluminum frame.) The tires and rims would be like 50 altogether.... So what's left? The seats? The dash? Cupholders??? We're missing about a thousand pounds! :wink:

 

[james]

Somewhere there's an old thread where I worked it out to be about 17 HP to cruise at 60. Used a different method, based on how fast I coast down a long grade. In pretty good agreement with what Yves gets...

 

[ElectricTroy]

The actual HP depend on the car. A smooth EV1 or Insight would be <20. A brick-shaped SUV is likely 30 hp.



As for the go-kart, I can believe 5.5 hp = 78 mph max. It's low to the ground with minimal resistance.

Likewise VW's 240 mpg car can go 60mph with only 4 hp @ 2000rpm - http://www.seriouswheels.com/top-vw-1-liter-car.htm