Ultra effecient combustion cars, under 1.5 litre, thoughts, pics, comments, designs, concepts Options

[pete-stevers]

Given todays economic climate, possible scaricity of fuel, and of course just the raw challenge of building a car with high mpg,
we should have a thread on cars of this nature, in production,prototypes,homebuilts, concepts and pictures.
( I wish i had the time and energy to build a car with a sub 1 litre engine, and maybe one day i will)

but lets keep it to combustion power, for now

[zymurgist]

One of the reasons that diesel cars aren't all that popular in the US is that diesel fuel costs more than regular unleaded. I did the math a few years ago and I couldn't make the VW diesels work for me, economically speaking. So I ended up with an old Toyota and then a used Acura.

[Bleyseng]

My 2003 1.8T Passat got 35-40 mpg without problem if you drove normal or freeway driving. Great car, quiet, roomy, airbags and would cruise at 100mph all day and still get 35mpg with the AC on.
Sold it to a friend...
The euro in-laws say they buy diesel cuz they are cheaper to operate/maintain. Lots of Audi A3 1.4's, 1.9TDI's, VW TDI's in the extended family and you can harely tell they are diesels, very quiet.

[pete-stevers]

Hey Geoff...good to see you!

[Dave_Darling]

Interesting about the diesels in the UK. And I did not mean to imply that taxes were the only reason to go diesel in Europe; I thought the fuel economy benefits were obvious.

Ken, diesel is cheaper than supreme unleaded gasoline in some areas of the US. But unless the diesel fuel is 20%-30% higher cost than the gasoline, the dollars-per-mile still favors diesel due to the superior economy.


I, too, tire of the electric car hype. It is not the answer--it is an answer, but there is no one answer. Ditto the hybrids; they have their place but they are not the be-all-end-all.

The alternative-fuel and high-MPG worlds are pretty interesting places when you look around...

--DD

[pete-stevers]

Dave thanks for your contribution
I am of the mind that if one can build and maintain a 914
one could take that skill set and build a high mpg car, not just a 40 mpg commuter( my 79 rabbit can do that)
but 80-100+ mpg with a common combustion motor, common parts, common tools, and even maintain a factor of saftey, with acceleration and speed for common traffic.
....and possibly carry two people...

[zymurgist]

Ken, diesel is cheaper than supreme unleaded gasoline in some areas of the US. But unless the diesel fuel is 20%-30% higher cost than the gasoline, the dollars-per-mile still favors diesel due to the superior economy.

Dave, I don't doubt that. But when I took the purchase price of the vehicle into account, also considering how long I keep my cars (with very low residual value due to high mileage), all that factored into my calculations. It's the same kind of analysis that caused me to decide that a hybrid would not be a good choice for me.

I'm not saying that a diesel wouldn't make sense for other people... I couldn't make the numbers work for me.

[pete-stevers]

I think the route i would go in a build up of this nature would be
250 cc with gearbox( not sure which brand but it would mostly be dictated by gear box)
light weight large dia motor cycle wheels
tube frame chassis built with saftey in mind
aluminum or glass skin
redesigned atv suspension
two alum seats
five point harness
helmets
the thing i have not figured is the drive wheels

[pete-stevers]

i wonder what jake could do to a 1.7 to make it even more fuel effecient

i am still wondering what could be done to a 1.7 to make a 914 get 50 mpg...
or would i have to put a tdi in???
any thoughts

[johannes]

There was a thread about that where Jake explained how he can build super eco type 4. Not cheap ...

http://www.914world.com/bbs2/index.php?showtopic=82761

...

[VaccaRabite]

i wonder what jake could do to a 1.7 to make it even more fuel effecient

i am still wondering what could be done to a 1.7 to make a 914 get 50 mpg...
or would i have to put a tdi in???
any thoughts

It would not be too hard, but would cost a little money, and may not be "sporty" to drive any more. It might also overheat, due to lack of airflow from keeping engine revs low.

You would need:
Modern FI
Tall transmission gearing
Electric cooling fans
A more slippery body kit

Goal would be to have the engine turning under 2000 RPM at freeway speeds, and not have to drive it faster then 65mph.

On a water cooled engine it is easier. You shift from 1-3-5 skipping 2 and 4, and moving to higher gears as soon as you can to keep engine revs low. Nothing is done fast. Cruise some of the hypermiling websites for more ideas (and lots of home built aero bodies.

Zach

[johannes]

It would not be too hard, but would cost a little money, and may not be "sporty" to drive any more. It might also overheat, due to lack of airflow from keeping engine revs low.

You would need:
Modern FI
Tall transmission gearing
Electric cooling fans
A more slippery body kit

Goal would be to have the engine turning under 2000 RPM at freeway speeds, and not have to drive it faster then 65mph.

On a water cooled engine it is easier. You shift from 1-3-5 skipping 2 and 4, and moving to higher gears as soon as you can to keep engine revs low. Nothing is done fast. Cruise some of the hypermiling websites for more ideas (and lots of home built aero bodies.

Zach

- Tall transmission gearing / In my opinion the 914 already has a very long gearing
- Electric cooling fans / What for ?

[VaccaRabite]

- Tall transmission gearing / In my opinion the 914 already has a very long gearing
- Electric cooling fans / What for ?

If the motor is turning under 3000RPMs for long periods of time, you will overheat the motor.

Tall gearing and low motor RPMs will be making the engine work harder, increasing head temps. Low engine rpm means that less air is getting pushed by the fans for cooling. The combo will lead to quick overheating.

I guess you could use a mechanical fan, but it would need some sort of gearing to keep the fan velocity up even though the engine speed was down.

Oh, tall skinny tires on lightweight wheels would also help raise MPG.

Zach

[Brett W]

There is nothing wrong with turning some rpm. My Civic would get better mileage with a high rpm than it did with a lower one. I changed transmissions around a couple of times and found better mileage with more rpm. Remember the more the throttle is closed the higher the pumping losses. The engine has to work harder. Hence part of the reason diesels work better in many cases.

[Todd Enlund]

Dave thanks for your contribution
I am of the mind that if one can build and maintain a 914
one could take that skill set and build a high mpg car, not just a 40 mpg commuter( my 79 rabbit can do that)
but 80-100+ mpg with a common combustion motor, common parts, common tools, and even maintain a factor of saftey, with acceleration and speed for common traffic.
....and possibly carry two people...

In the early '80s, someone built a car using a Triumph Sptifire frame and a foam/glass composite body, with a 17 hp 3 cyl Kubota diesel tractor engine.

I have the original article somewhere, but here is a summary:

http://www.rqriley.com/cent.html

[underthetire]

I don't understand why everyone thinks low RPM=better mileage. You need more throttle to keep speed then. More-throttle=less vacuum=less efficiency. Think somewhere I read you want to be in cruise speed at 60% range of your max HP RPM. You would need to build a super torqy, low RPM engine to gain anything. I remember going from 4:11 to 4:88 gears on my Toyota PU and the mileage went up about 5 MPG.

[johannes]

Low RPM means less friction that means better efficiency.
You can see on Jake's curves that you have an efficiency ratio. The best efficiency often matches with the torque max rpm.

[Dave_Darling]

I don't understand why everyone thinks low RPM=better mileage.

Because, in general, it's true. Higher RPM for a given speed (i.e., shorter gearing) means more combustion events per mile. That means more fuel burned per mile. This does break down at very low RPMs where the engines get very inefficient, but that range is usually below 2000 RPM.

Check some BSFC maps. No, not the single-line curve we've seen before, I mean a full map of torque vs. RPM (or nearly equivalently, BMEP vs. RPM) plotting BSFC for the full range of those two. You'll see that the minimum consumption is around 2000-2500 RPM and 70% throttle in most cases.

Now, just to confuse things further, remember that most cars need on the order of 10-20 HP to cruise at "freeway speeds" on a typical day. (You can reduce that required power by lowering your speed, by lowering your rolling resistance, by lowering your CdA, or some combination of all three.) So for steady-state cruising, the question becomes "what RPM does your car most efficiently generate 15 HP?" Which may not be the same as "where is the most efficient range of operation for the engine?"

It's an interesting subject, and the hypermiler and ecomodder crowds really have some pretty decent ideas of what is going on. Doing some research (or at least some reading) on http://ecomodder.com can provide more info, including instrumented repeatable real-world tests.

--DD