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914World.com _ 914World Garage _ Ultra effecient combustion cars, under 1.5 litre
Posted by: pete-stevers Feb 25 2010, 12:38 PM
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
Posted by: Jon Fernandes Feb 25 2010, 12:52 PM
Europe has always used small engine in small cars, think 1.2 litre gas engines and small efficient diesels. I dont understand why this country feels the need to have massive v8 cars and trucks and not enough compact cars. 
Posted by: pbanders Feb 25 2010, 01:00 PM
The original Audi A2 was a remarkable car:
http://www.audiworld.com/news/01/A2TDI/content.shtml
Kind of like a Honda Fit, but with a 1.2L TDI, for 2.99 L/100 km fuel economy (78.7 mpg). There's a new A2 out in Europe:
http://www.allautoreviews.com/auto_reviews/audi/audi-a2.htm
... but it seems more focused on performance than economy.
Posted by: underthetire Feb 25 2010, 01:00 PM
A guy here is putting a Turbo hyabusa 1300 in his triumph, although I don't think for fuel efficiency 
I was wondering how much the E85 sensors are to run a flex fuel in my 914.
Posted by: RobW Feb 25 2010, 01:03 PM
I fully expect to convert my Dad's car to electricity someday.... just not in the next 10-15 years...
Posted by: patssle Feb 25 2010, 01:09 PM
Europe has always used small engine in small cars, think 1.2 litre gas engines and small efficient diesels. I dont understand why this country feels the need to have massive v8 cars and trucks and not enough compact cars.
Most Europeans also only own 1 car. I don't understand why this country feels the need to own 3 914s instead of just one
Posted by: 6freak Feb 25 2010, 01:11 PM
Woodgas ...
Posted by: pete-stevers Feb 25 2010, 01:11 PM
Europe has always used small engine in small cars, think 1.2 litre gas engines and small efficient diesels. I dont understand why this country feels the need to have massive v8 cars and trucks and not enough compact cars.
Most Europeans also only own 1 car. I don't understand why this country feels the need to own 3 914s instead of just one
lets skip political conjecture
and focus on high effeciency combustion cars 
Posted by: RJMII Feb 25 2010, 01:14 PM
I was reading some information on GDI (Gas Direct Injection) the other day.
They were getting better fuel mileage, and better torque by injecting the fuel directly into the combustion chamber. It allowed for leaner mixtures because of less 'wet-walling' and more precisely controllwed injection timing. The fuel was able to keep squirting while it was still burning.
Posted by: kwales Feb 25 2010, 01:25 PM
More power in diesel fuel which equates to better mileage which is why they are all over Europe.
Want ultra efficient? Don't drive a large vehicle the size of your living room.
In Spain a few years ago, the largest normal car on the road was VW Jetta sized.
Most vehicles were sized like that Audi A2, and in that environment, a Smart car looked not so out of place.
Posted by: rick 918-S Feb 25 2010, 01:34 PM
100hp factory rated 1.3L twin cam Suzuki Swift GTI engine bolted to Samurai 5 sp. Custom header, Fuel injected, chipped.
Attached image(s)
Posted by: 6freak Feb 25 2010, 01:36 PM
size matters in a car wreck ..theres more to life then mileage
Posted by: JJ914GT Feb 25 2010, 01:43 PM
That's an MG Midget.
( Oh, wait,.. this isn't the "guess that car" thread ;-) )
Here's a likewise car, under 2 liters, over 200bhp.
http://www.kmidget.co.uk/photos-enginebay.html
Posted by: Brett W Feb 25 2010, 01:46 PM
Can't tow 16K lbs with a 1.4litre toy. Don't want to drive 2000 miles in a trip in a beer can. Don't want to get flattened by soccer mom in suburban. This is America. Free market determined they want cars you can fit several people in and gas mileage be damned. In Europe the government decided what would be sold. The rich didn't want the average Joe riding around in a big car possibly upstaging them. That would be bad.
I have nothing against ultra efficient vehicles, but realize not everyone wants them or cares and that doesn't make them bad people. I don't want to get in a wreck driving a shitbox smart car. I really don't want to get hit in my Prelude, Civic, 914 etc. But those are much bigger cars. Plus I like going fast. so 1.5 litres and less is boring.
Posted by: wayne1234 Feb 25 2010, 01:55 PM
We have a 08 Toyota Yaris it is 1.5 liter 106hp. can actually fit 4 adults, comfortably. I almost got a smart car, but test drove it and the yaris the same day, in the smart it was a shoulder to shoulder experience.. the is quite alot of room in the yaris. it has good crash results, also. I dont drive in "eco mode" by any means and get mid 30's for mpg with mixed driving.. on highway trips we get over 40mpg, thats not in the slow lane, keeping with the flow of traffic. it is a awesome well proven drive trrrain, it is the same basic engine that has been in the echo for quite some time... 200k miles are very common with no mechanical repairs. I did drop it with TRD springs and MOMO Winter alloys, and a jl audio system to make it a little different.
Posted by: turboman808 Feb 25 2010, 02:10 PM
I was reading some information on GDI (Gas Direct Injection) the other day.
They were getting better fuel mileage, and better torque by injecting the fuel directly into the combustion chamber. It allowed for leaner mixtures because of less 'wet-walling' and more precisely controllwed injection timing. The fuel was able to keep squirting while it was still burning.
Thats what my solstice has. I can drive like a maniac and still get 18mpg and thats with 330hp and 350lb. If I drive it normal it gets 30mpg.
Small motor in a more aero body and lighter as well and you would have a pretty low mpg car.
Posted by: Phoenix-MN Feb 25 2010, 02:13 PM
I started driving a 2005 Scion xB a few years ago for my daily driver. 1.5l engine has ~100 hp and moves it faily well and gets 34 - 35 mpg. Very roomy even with 4 adults and it isn't the smallest thing on the highway. The looks/styling has to grow on you though 
Paul
Posted by: wayne1234 Feb 25 2010, 02:13 PM
As far as small not being safe, I believe it all matter on the situation,,, small low car vs big full size truck, head on or side impact... truck will win mostly due to bumper car height. Into a fixed object is a different story, I rember a youtube vid of a smart car into concrete wall, the smart car look liker a crushed beer can , but the interior cabin was completely intact, the door still opened and closed fine, and interior g's on the occupant was less then half that of old tank cars. the body absorbed the impact like it was designed to do. I do believe you must drive more defensively in a smaller car, But everyone should drive what they feel comfortable in, thats what makes America wonderful,
Posted by: Andyrew Feb 25 2010, 02:14 PM
A friend of mine has a 93 honda civic "lean burn". He gets near 50mpg...
Seriously why arent we utilizing THAT technology??? Damn things got like 230k miles on it as well.
VW/Audi uses direct fuel injection on all their new engines. Lots of company's do.
Posted by: davep Feb 25 2010, 02:23 PM
The best mileage of any car I've ever owned was the '73 914 1.7 back about 1976 or so. Stock 165 tires, Imperial gallons (25% larger than a US gallon), and the gas of the day that I believe was somewhat better than today. I would get about 40 MPG highway, and sometimes 50 on a long cruise.
Not only that, but the 914 was more fun and laughs per mile than any other car as well.
Posted by: pete-stevers Feb 25 2010, 02:34 PM
i wonder what jake could do to a 1.7 to make it even more fuel effecient
Posted by: pbanders Feb 25 2010, 02:35 PM
FWIW, my commute car is a 2009 Honda Fit Sport, with the paddle-shift AT. It replaced my '98 M3, which while enjoyable, was the most expensive car to maintain I've ever owned, used premium fuel, and got about 19 mpg on my commute. I replaced the skinny OEM tires with 205/50's, which helped handling and braking. It's a really fun car, I can drive it flat-out with barely anyone noticing, and still get 30 mpg on my commute. On flat highway drives it gets 40+ mpg. Extremely practical, gobs of front and rear seating room, fold-flat rear seats for a huge cargo area. Full of safety features, too. 5-star crash ratings, airbags galore, seatbelt tighteners, and active front headrests. It's also reasonably cute looking and fun to drive. 100K miles before the first tune-up, too.
Posted by: RoninEclipse2G Feb 25 2010, 02:35 PM
There is a lot to be said for the guys that are dropping newer engines into older chassis. I've seen reports from a few of the guys that dropped Suby STi engines into 914's that were getting mid 30's for their highway MPGs. Normally that engine would only get mid to low 20's for highway mileage in the much heavier STi and that's a 2.5L engine.
Posted by: pete-stevers Feb 25 2010, 02:45 PM
How about the VW Polo, 1.3 G40?
that would be a nice hot hatch!!
Posted by: Dave_Darling Feb 25 2010, 02:47 PM
Lean burn is no longer in favor because it produces more NOx than current standards allow.
Diesels are vastly popular in most of Europe in large part due to the fuel taxes; diesel fuel is taxed much less heavily than gasoline. In the UK, where the two are taxed a closer amount, gasoline cars are still more popular.
Small lightweight low-powered aerodynamic cars are the most efficient, in general. Ever been in a Geo Metro? Think about using one every day on your commute. And think about the late-chugging makeup-applying screaming-at-children soccer mom in her Expedition. (Or, conversely, the breakfast-eating still-shaving newspaper-reading man in his F150 King Kong Cab pickup.)
I really like my CRX, and it gets by far the most use out of any of the cars we have in my household. But it's definitely not for everyone...
Google "ford probe iv" to see a very aero-slick concept car that got good fuel economy. Wander over to http://www.aerocivic.com for a look at a serious home-brew aerodynamic Civic which is ugly as hell but quite functional. It would be interesting to see what could be done in that vein by someone who wasn't trying to do it as cheap as humanly possible... If we could lose the currently-standard ideas of what makes a car good-looking, we could have cars that got significantly better freeway mileage. But I still couldn't drive the Aero Civic on a daily basis.
Sandy's Sprite (pictured above) should be a hoot to drive, and get at least half-decent mileage. The aero won't be great, but a nice modern modestly-powered engine and light weight should help it get decent numbers.
...Oh, gearing! Can't forget gearing! For cruising steady-state you want the absolute tallest possible gearing you can get. (You can go too far with it, but you are unlikely to with any reasonably-available OEM gears.) One reason the current Vettes get 30 MPG on the freeway is because they can cruise at 60 MPH at something like 1500 RPM. If you had a smaller engine with the same gearing, you would have to use more throttle to maintain that but you'd get even better economy.
More research you can do: Google "throttle pumping loss" and "BFSC map" to get an idea of how efficient different throttle openings are. (Hint: About 75% open is generally better than almost closed.) For tons and tons of ideas, see http://www.ecomodder.com and look for the "master list of modifications" that save gas. Most of them are things we wouldn't choose to do for various reasons (aesthetics, convenience, etc.) but some of them are quite easy and not that obvious.
--DD
Posted by: messix Feb 25 2010, 02:53 PM
my get to work beater is a '95 geo metro, i drive like i stole it and get 39mpg back and forth to work 9 miles one way. i took it on a roas trip over the mountains and got 48 mpg. it has over 116k miles and is definately built like a disposable car, but it was cheap to buy, has saved me a shit load in money for gas when i had to drive my daughter 240 miles a week to school, and it seems to be the magical parking spot finder for going to big events where parking is scarce [some one always leaves 14' between cars that i can tuck it in to].
now if i could find some thing that rode quieter and better and still got 30- 40 mpg i'd be all over it. but nothing like that is cheap enough to buy.
Posted by: messix Feb 25 2010, 03:10 PM
talk about old cars new engines... i'd love to do a '64-66' mustang with a modern 2L fuel injected 4 cyl with a 5 speed tranny. they got high teens mid twenty's with the old 190 cid inline six adn a 3 speed manual!
Posted by: patssle Feb 25 2010, 03:17 PM
My college car was a 1996 Chevy Beretta. A decent sized car that got 37 mpg. Granted it was only 120 hp or so with a manual transmission...but it wasn't a shitbox shoebox sized car. And it was a little more stylish than most cheap cars (ignoring the Corsica style front).
They can make decent sized cheap cars that get good gas mileage and don't look like crap. They just don't want to.
Posted by: RoninEclipse2G Feb 25 2010, 06:17 PM
DD, that article on the AeroCivic got me thinking about how so often designers and engineers don't really take the drag coefficient into account. My 95 Eclipse has an unusually low CD which helps it get ~40 mpg highway with a heavy 2.0 NA engine. I know a couple of guys that have gone to the crazy lengths of putting a complete underpanel on theirs and have seen a few extra MPG's on the highway. It's something I've seriously looked at for my own vechicle
Posted by: Gigamight Feb 25 2010, 06:43 PM
My favorite gas-sipper was my 92 Honda Civic VX. It has no sound deadening, no carpet padding, hardly any seat padding... basically it was factory weight reduction to the extreme. Thing could SCOOT though. Plus I got almost 50mpg. Wish I still had that thing, they are going for a pretty penny these days.
Posted by: Todd Enlund Feb 25 2010, 09:18 PM
I think that a TDI 914 would be cool, and should be capable of 60 MPG.
I also would love to build an Opel GT with a Toyota DOHC engine.
Posted by: Dr Evil Feb 26 2010, 12:12 AM
Someday I WILL do a respectable TDI into 914 conversion.
Posted by: veltror Feb 26 2010, 04:42 AM
Diesels are vastly popular in most of Europe in large part due to the fuel taxes; diesel fuel is taxed much less heavily than gasoline. In the UK, where the two are taxed a closer amount, gasoline cars are still more popular.
--DD
Statistics etc,
Diesel is taxed HIGHER then petrol but the overall % of Diesel cars is higher then you may think, coupled with the fact that resale prices are better of a diesel.In 2008 44% of all cars sold in the UK were Diesel and in 2009 42%. If you then look into the breakdown across segments the results are even more eye-opening.
Upper medium class 3-series, Audi A4 etc Diesel sales are 70.6%
Executive class 5-series Audi A6 Diesel sales are 77.8%
Luxury class S-class, Audi A8 etc Diesel sales are 54%
MPV class 59%
4x4 SUV class 82.6%
Since it makes little sense to have a small diesel car since by nature thay are runabouts etc Diesel is the way to go. As far as comments about accidents of small cars vs large cars it is not as cut and dried as people make out. It is all in the design and engineering, many large Chineese cars have abysmal accident results, in this case size does not matter.
If ppl want to drive huge cars etc which have crap economy then fine, their choice, however I object to the eco-Nazis telling me that electric is the answer it is not.
The Toyota Pious (not a spelling error) is outdriven, out handled, out economised by a VW Polo Bluemotion, and that is before you have to factor in the cost of disposing of the batteries.
So what do I drive? A Passat 170 TDI, the other half a petrol Tiguan 1.4TSI.
If I had the space i would have and drive a 1958 Plymouth Fury or a huge finned Caddy from 1959.
R
Posted by: zymurgist Feb 26 2010, 05:42 AM
I could get 37 mpg in my RSX if I drove slower. I have a co-worker who has the exact same car, and she reports that she gets 37 mpg if she keeps it at 65 mph or below.
Not gonna happen. 
Posted by: johannes Feb 26 2010, 06:18 AM
Most Europeans also only own 1 car.
That was true in 1950 ...
Posted by: johannes Feb 26 2010, 06:33 AM
This is the concept of the future. http://www.loremo.com/englisch/index.htm
They expect to sell cars next year...
four seats. It will be available with Diesel or Electric engine.
https://www.youtube.com/watch?v=uqkl1Ve_T8c
This one is also a great concept ... but only two seats and only electric
http://www.aptera.com/
https://www.youtube.com/watch?v=r_JV6QUIu5s
Posted by: zymurgist Feb 26 2010, 07:28 AM
One of my friends (who drives an RSX Type S) goes nuts for the Aptera. He wants one in the worst way.
Posted by: RobW Feb 26 2010, 07:55 AM
Lean burn is no longer in favor because it produces more NOx than current standards allow.
Diesels are vastly popular in most of Europe in large part due to the fuel taxes; diesel fuel is taxed much less heavily than gasoline. In the UK, where the two are taxed a closer amount, gasoline cars are still more popular.
Small lightweight low-powered aerodynamic cars are the most efficient, in general. Ever been in a Geo Metro? Think about using one every day on your commute. And think about the late-chugging makeup-applying screaming-at-children soccer mom in her Expedition. (Or, conversely, the breakfast-eating still-shaving newspaper-reading man in his F150 King Kong Cab pickup.)
I really like my CRX, and it gets by far the most use out of any of the cars we have in my household. But it's definitely not for everyone...
Google "ford probe iv" to see a very aero-slick concept car that got good fuel economy. Wander over to http://www.aerocivic.com for a look at a serious home-brew aerodynamic Civic which is ugly as hell but quite functional. It would be interesting to see what could be done in that vein by someone who wasn't trying to do it as cheap as humanly possible... If we could lose the currently-standard ideas of what makes a car good-looking, we could have cars that got significantly better freeway mileage. But I still couldn't drive the Aero Civic on a daily basis.
Sandy's Sprite (pictured above) should be a hoot to drive, and get at least half-decent mileage. The aero won't be great, but a nice modern modestly-powered engine and light weight should help it get decent numbers.
...Oh, gearing! Can't forget gearing! For cruising steady-state you want the absolute tallest possible gearing you can get. (You can go too far with it, but you are unlikely to with any reasonably-available OEM gears.) One reason the current Vettes get 30 MPG on the freeway is because they can cruise at 60 MPH at something like 1500 RPM. If you had a smaller engine with the same gearing, you would have to use more throttle to maintain that but you'd get even better economy.
More research you can do: Google "throttle pumping loss" and "BFSC map" to get an idea of how efficient different throttle openings are. (Hint: About 75% open is generally better than almost closed.) For tons and tons of ideas, see http://www.ecomodder.com and look for the "master list of modifications" that save gas. Most of them are things we wouldn't choose to do for various reasons (aesthetics, convenience, etc.) but some of them are quite easy and not that obvious.
--DD
Nice thesis there Dave.... thanks.
With the open throttle, I swear I got the best mileage out of my 993 in 6th doing 90-110 for long lengths of time... ie 280 between Cupertino and SF. I'm sure the lack of drag helped too...
Posted by: johannes Feb 26 2010, 08:07 AM
That's true but Diesel is also more efficient. A diesel car will have 20% to 30% better mpg. If gasoline and diesel are taxed the same, the only reason people buy more gas cars is beacause they are cheaper.
Posted by: Brett W Feb 26 2010, 08:21 AM
http://www.americanthinker.com/2010/02/congress_toyota_and_cafe_stand_1.html
Posted by: zymurgist Feb 26 2010, 08:25 AM
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.
Posted by: Bleyseng Feb 26 2010, 08:35 AM
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.
Posted by: pete-stevers Feb 26 2010, 01:13 PM
Hey Geoff...good to see you!
Posted by: Dave_Darling Feb 26 2010, 03:15 PM
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
Posted by: pete-stevers Feb 26 2010, 05:15 PM
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...
Posted by: zymurgist Feb 26 2010, 05:47 PM
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.
Posted by: pete-stevers Feb 28 2010, 12:56 PM
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
Posted by: pete-stevers Feb 28 2010, 09:58 PM
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
Posted by: johannes Mar 1 2010, 06:22 AM
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
...
Posted by: Vacca Rabite Mar 1 2010, 08:42 AM
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
Posted by: johannes Mar 1 2010, 10:15 AM
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 ?
Posted by: Vacca Rabite Mar 1 2010, 10:20 AM
- 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
Posted by: Brett W Mar 1 2010, 01:31 PM
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.
Posted by: Todd Enlund Mar 1 2010, 05:12 PM
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
Posted by: underthetire Mar 1 2010, 06:18 PM
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.
Posted by: johannes Mar 2 2010, 06:29 AM
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.
Posted by: Dave_Darling Mar 2 2010, 05:15 PM
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
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