MAX: Our Quest for a DIY 100-MPG Car

Progress continues on MAX, the home-built, 100-mpg car (prospectively) that you’ll be able to make for $10,000.

| October/November 2009

100-mpg car

MAX is a sports car powered by a Kubota diesel engine that’s normally used in tractors. After MAX has been perfected, we will have plans available for those who want to build their own.


Last year we introduced MAX, the MOTHER EARTH NEWS contender in the Auto X Prize fuel-efficient car competition (see Here Comes the 100-mpg Car). For those who may have just tuned in, the Progressive Insurance Automotive X Prize is a $10 million competition to create cars capable of achieving 100 miles per gallon in fuel economy. Entries must have a design that would allow for the production of 10,000 cars per year at the price most appealing to the manufacturer’s stockholders. We’re aiming for a more affordable approach: a DIY, fuel-efficient car that you can build for about $10,000.

Part of what I want to prove with MAX is that if I can build a 100-mpg car using off-the-shelf technology, the major automakers should be able to do the same, if not even better. Sure, MAX is different than a family sedan, but those car companies also have different resources than we do here in the Kinetic Vehicles garage. After MAX has been perfected — whether we hit 100 mpg or not — we will have plans available for those who want to build their own.

MAX is a sports car powered by a Kubota diesel engine that’s normally used in tractors. The car has turned heads and drawn crowds everywhere we’ve gone, and shown its heels to far zootier vehicles in everything from “play dates” on the twisty roads of southern Oregon to formal endurance racing from Berkeley, Calif., to Las Vegas (see MAX Wins 800-mile Road Rally, Without Gas).

You may be wondering whether MAX is practical. Well, we have more than 7,000 miles on its wheels now — everything from grocery getting to freeway flying — and it has served us reliably. For fuel, we’ve used everything from jet fuel to olive oil.

I bet I know your next question: Is MAX getting 100 mpg? Not yet. But so far we have the chassis and power source sorted out, so now we can improve MAX’s body, which will really improve its mpg.

Building a Better Body

The only thing holding us back from 100 mpg is air resistance. MAX’s current body looks cool and classic, but it’s an aerodynamic disaster. We’ll never see 100 mpg with this design. Frankly, it’s a bit amazing we’ve been nipping at 70 mpg (which we’ve achieved when cruising slowly). But we know what we need to do: Make a new body that has half the drag of the current one.

jack mccornack
10/18/2009 9:09:55 PM

KeithOliver noted that... > ...anyone trying to copy the MAX concept is going to have to meet emissions regulations in effect at the time that they register. ...and that's true, but there are 50 different regs in 50 different states, and in most states homebuilt cars don't have to meet the same standards as high volume cars. > MAX was started a Loooong time ago... No it wasn't. MAX was conceved in '06, we started collecting parts and fitting things together in '07, and its registration date was '08, which is when MAX first hit the road. It's not registered as a heavily modified older car, it's registered as brand new in 2008. ...prior to soot filters and selective catalytic reduction being required... There are manufacturers working hard on those problems. Some of these manufacturers were quite interested in MAX as a demo platform before the final round of the Automotive X Prize rules were released, and affordable ceramic soot filters are just around the corner, and urea injection is coming out of the labs and hitting the roads already. It's not insurmountable. ...but that will no longer be the case in 2010 and beyond. One big thing MAX has in its favor is it doesn't make much exhaust per mile. I'm not sure how the other American auto manufacturers are doing it, but if they can pass EPA muster burning three times the fuel that MAX burns, our EPA-certified-for-agriculture engine might pass the auto emissions requirements, just the way it is.

jack mccornack
10/18/2009 8:33:05 PM

Hi Bob, > I really feel let down that you are giving up the X-Prize contest. :-) You and me both, man. > The reason that you give that you would have to modify the engine to go from 20 seconds for 60 mmph to 18 seconds doesn't make sense to me. I know I've written a lot of words on the subject, but don't recall writing those. I'll acknowledge that the 0 to 60 performance issue was one of the first clues that the X Prize folks and I weren't seeing eye to eye, but it's not why we withdrew. I could write reams of details, but the basics are in MAX Update #32 in the MAX Update blogs. Improving 0 to 60 times by 10% isn't trivial, and I don't think the body change will do it. The streamlined body will add some weight, and it's possible the will hurt low speed acceleration as much as the streamlining helps it. We can meet their acceleration requirements with engine mods, but then we're getting out of our knowledge base re emissions, and I know the Kubota engineers worked hard to balance power against pollution. And of course, we could have got with the X Prize program and converted to electric, but then the budget would have skyrocketed, as would our carbon footprint. So we're keeping MAX a DIY car and paying more attention to economy (both fuel economy and construction/purchase price economy) than to performance.

10/17/2009 12:11:20 PM

Unless I'm mistaken, there is 1 big problem with the concept, and that is that anyone trying to copy the MAX concept is going to have to meet emissions regulations in effect at the time that they register. MAX was started a Loooong time ago, prior to soot filters and selective catalytic reduction being required, but that will no longer be the case in 2010 and beyond. I think the only chance the rest of us have is to retrofit an existing vehicle with a registration date prior to 2005. The earlier, the better, since the less stringent the emissions regulations. I have been looking and one cabn find Honda Insights with dead batteries for $1-2k. Good areodynamics come right out the box.

jim price
10/16/2009 1:25:11 PM

Yo! Love your project. Big trucks use a two speed rear-end to get 12/16 forward gears; Electric actuated add-on overdrive units are available for cars. With proper transmission/ rear end gear selection your car would be a real hotrod around town and triple overdrive would help your quest for 100 mpg. One of the ultra high performance cars uses an eight speed tranny but their goal is 200+ mph. Good luck,--------jim------

10/16/2009 9:06:55 AM

I really feel let down that you are giving up the X-Prize contest. The reason that you give that you would have to modify the engine to go from 20 seconds for 60 mmph to 18 seconds doesn't make sense to me. Just by adding a streamlined body will give you at least 2 seconds.

jack mccornack
9/30/2009 8:01:22 PM

Interesting points, Kit. Over-the-highway trucks tend to have a higher ratio of rolling resistance vs aerodynamic drag than cars, because they typically have only triple the frontal area of a car but 20 times the loaded weight. They need a lot of power to deal with the needs of acceleration and hill climbs, but once you've got them rolling, they roll pretty takes surprising little to keep them going on flat ground. So as far as fuel economy goes, trucks don't suffer from poor aero as much as cars do. That said, if a trucker can add an air deflector to the top of the cab and go from, say, 6 mpg to 6.1 mpg, and if you drive 100,000 miles a year, that's 275 gallons a year. Over a 20 year service life, that's 5500 gallons.

jack mccornack
9/30/2009 7:35:09 PM

t. brandt, reducing drag does have its limits, but we're nowhere near them yet. For mileage bang-for-the-buck you can't beat small motorbikes, but it is possible to equal the drag (and mileage) of a typical motor scooter with a light and streamlined car. Craig Henderson broke 100 mpg in his Avion a quarter century ago and last October hit a personal best of 113 mpg cruising from Canada to Oregon. Streamlining motorbikes works wonders too. If you scroll down to MAX Update #25 you can link to the Craig Vetter Fuel Economy Contests, which topped out at 470 mpg for a street legal motorcycle at highway speed. Craig (Henderson) hopes to have Avion kits available in the spring, he just finished production body molds for the kit and his target is a car you can build for $30,000. There's no question that 100 mpg cars are possible (the Avion web site is, the question we're trying to answer with MAX is, can you build one for ten grand?

9/30/2009 11:33:12 AM

Love the article guys! However air drag may not be so much of a problem as you think. Consider Schneider Trucking,SLOW,under powered,Cabin overs,aerodynamics of a brick bat and an absolute traffic hazard,get all fuzzy with their 7.5 mpg.! A Freightliner Columbia will get about 5.5-6.5 mpg. Outwardly the Columbia appears more Aerodynamic.Then there is a good friend that has a 1998 Freightliner Classic Condo.550+ to the drivers hp. It is an Aerodynamic train wreck that is almost never driven under 70 mph. His books will show a 7.2 mpg fuel average.Unlike Schneider he stays loaded to the gross,80,000 lbs. almost constantly and does idle his truck when and where he can for either heat or ac. Differences are he put an after market larger turbo on,changed the injector clearances and timing,has a 13 spd. trans.,keeps the engine in its "sweet spot" better,and under the hood the air is dealt with more efficiently than the Columbia. I put a hydrogen generator on a VW Jetta diesel and got 70 return with no other alterations. I really feel your 100 mpg is doable with some more out of the box thinking! Good Luck!

t brandt
9/22/2009 4:06:34 PM

The 100mpg auto is really a pipe dream. There already is a 100mpg vehicle: the 50cc motor scooter. they've been around for 60 years. Some hi school physics: E = 1/2mv^2 + drag + heat. Reducing drag has it's limits. Nature has already figured out the best shape: the fish & the bird body. Unfortunately, the internal combustion engine is inherently inefficient and 90% of energy released in burning fuel is lost as heat. The only thing we can really do is minimize the "m" or the "v" in the equation. That leaves us with the tiny, slow scooter.

jack mccornack
9/19/2009 5:16:34 PM

Thank you, Sam. Your ideas aren't silly at all, but they need to be tempered by our $10,000 budget. Lightweight wheels clutch brakes etc would save fuel (lightweight --anything-- saves fuel, rotating parts in particular) but as far as bang-for-the-buck goes, I think streamlining will give us the best return for our money...hopefully we'll have enough left over to change the trans and axle lubes to synthetic. And Robert, while every state has different rules for homebuilt car registration (some easy, some tough), my personal MAX, which is registered at my home in Oregon, is legal to drive in any state, just like any other car with an Oregon plate. If you register your own homebuilt car in your own home state, the other 49 states will honor your registration as well.

9/18/2009 8:42:21 PM

Do we know if this thing is legal in any state ?

sam strohl
9/18/2009 9:35:49 AM

let me start out by saying i love the max,great idea.if you can build this in your garage and get it to 100 mpg that would be totally awsome! love your new body design,can't wait to see this on the car! this might seem like a silly idea,but i think you could also improve your milage by using aluminum wheels and better tires with less roll resistance.what about syntheyic lubricants? dont know what you have for a driveline but there are several areas this can be improved.lightwieght cluch,driveshaft, brakes and rotors to name a few.anyway keep up the good work.

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