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MAX Update No. 16: Charmed Looks vs. Fuel-efficient Design

11/5/2008 10:26:35 AM

Tags: MAX, Auto X Prize, gas mileage, 100 mpg, aerodynamics

OK, fun's over, time to get back to work.

I am getting so spoiled. When MAX's gas mileage drops into the 50s, I get grumpy.

I wanted to put 5,000 miles on MAX before the weather got wet (next project — a convertible top), a somewhat arbitrary figure, but it's been my experience that 5,000 miles (or 100 hours) is enough to say, “Yeah, it looks like this is going to work.” So for me it's a benchmark. I made it, but it involved a lot of road trips, and those involved a lot of freeway flying.

The freeways are not my favorite environment — one reason is they tempt me to go too fast for fuel efficiency. At 70 mph, MAX is no more fuel efficient than a ... well, actually, there aren't any production cars that get better than 50 mpg at 70 mph.

MAX does (barely), so I guess I shouldn't kick myself too hard. But heck, MAX is supposed to be spectacular, not just good. With its upcoming streamlined body (currently in that gray area between the drawing board and the highway), it's going to be spectacular. But gosh, can't it be kinda spectacular and still have the look-and-feel of a classic sports car?

MAX front viewI sure hope so, because — I know, I know, I should be ashamed of myself — I'm greatly enjoying driving MAX around in its Vintage/Prisoner/Escape from Berkeley regalia. Everybody digs “Classic MAX”, and I love all the attention. Total strangers say, “Ooooh, that car is so cute, can I take a picture, can I get in it, can you take a picture with me in it?” and I know I'm going to lose some of that attention when MAX goes all streamlined and serious.

Sadly, the lovely, swoopy front fenders are part of MAX's visual charm, I say “sadly” because recent fuel consumption figures indicate that those fenders have increased MAX's drag at cruise by about 10 percent.

As you can see, those fenders make up a lot of MAX's frontal area, and that has to translate into lots of drag. I don't know how much drag, but there are ways of finding out. Tune in next week, and I'll show you how to do wind tunnel testing when you don't have a wind tunnel.

 


Photo by Jack McCornack


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Jim_94
4/16/2010 10:22:29 AM
I have been intrigued with the Max project for quite a while. I even bought one of the books on building a cheap sports car. I love the looks of Max and have ever since I was a kid and watched The Prisoner--the opening was better than the show. As I've been doing research I've found that Max has a C factor that is worse than a Hummer and that at speed those beautiful fenders act like lifting wings. So for my project I am looking at designing a body that would make the care as wide as the outside dimensions of the fender wells, this would give more interior room and some more room for side impact protection. I don't think the weight would be all that much higher. The old TR4 had an electric overdrive-have you ever considered a similar option? That might provide zippier pick up and the low rpm cruising as well. I've seen some of the footage of 7s flipping on the race track under really extreme conditions and going end over end with the driver walking away. Amazing. I used to drive a Triumph GT 6. Not exactly a comfortable car but it wasn't a killer on long trips either. The worst thing about it was the road noise. Hard to talk or listen to the radio. Jim

Jason Phillips
7/31/2009 9:57:59 PM
Seems to me that MAX could benefit from some added turbo boost. Diesels, unlike gasoline engines, can get more power AND better fuel economy from higher boost. A single stage centrifugal compressor (like a turbo or a Paxton-type supercharger) has a hard time achieving more than about a 4:1 pressure ratio. Now, that's about 45 psig (or 60 psia). I'll wager you're not even close to that now. Pump up the turbo boost to get more power AND improve fuel economy. THEN raise the final drive gearing to get the revs down (thereby improving fuel economy even more). THEN fit MAX with taller, narrower wheels/tires to reduce rolling resistance and bring cruising revs down even MORE. After that, well I'm sorry but improving aerodynamics is gonna be your best bet. It's free horsepower and fuel economy really. Manage your airflow wisely and you'll go farther, faster, on less fuel. What about closing off the front end and putting the radiator in the "trunk" lid with an electric fan drawing air down into the radiator and exhausting that air out the rear? That might help kill the low pressure area behind the car, thus reducing aerodynamic drag and improving fuel economy....just a thought. Still want that classic car look? What about the Lotus 49 that Jimmy Clark drove back in the late sixties? Clean, simple, compact, elegant, and timeless. ORRRR go a different direction and look to the Ferrari P4 and/or the Ford GT40 and/or the Lola T70 of roughly that same era. All gorgeous, all "aerodynamically friendly", and all classic. What about a waterless cooling system? Evans NPG and NPG+ can run at atmospheric pressure and never need to be changed. No corrosion with those propylene glycol-based coolants (unlike the ethylene glycol stuff most of us are using). Also, NPG and NPG+ will happily run at around 270 deg. F all day since they don't boil until about 370 deg. F at atmospheric pressure. Higher coolant temps reduce cylinder wall friction

Donald A. Meyer
12/24/2008 4:18:34 AM
New to your 100mpg MAX project, and noted your concern about Max's front fender drag. Have you thought about a simple light weight fiberglass flap (baffle) in front of the fenders, angled back 45 degrees on each side of the nose opening (similar in looks to a large air brake)? They could be supported by aluminum tube braces off of the nose cone area. That would deflect a lot of the air gradually past the tires and fenders, and thereby significantly reducing air drag due the fenders.

Brian A. Stewart
11/19/2008 5:39:48 PM
Spoil sport! Yeah, pretty much any of them from that era (the one I was thinking of might have been the '37, which had the headlights in a different location." When I suggested (only half-seriously) it as a possible fairing for a quad-cycle (4 wheel "bi"-cycle), I got a suggestion for carving the body out of Styrofoam, and forming the body out of fiberglass over it, and using gasoline to melt the 'foam out of the shell. (Or something like that.) I'm probably not going to try it, either, since I have never worked with fiberglass in my life, and that body would be a very difficult place to start! Still, I can see why it is cited as one of the most beautiful cars ever!

Jack McCornack
11/19/2008 1:09:42 PM
Let me guess, Brian--the Talbot-Lago T23 Teardrop Coupe. Folks, that's the name to google if you want to see the classiest ride of the '30s. Inspirationally it's tempting, but man, we sure wouldn't hit our under-ten-grand cost target with a body like that. And frankly, some of its swoopier features are more pleasing to the eye than they are to the air...but what a marvel for 1938.

Brian A. Stewart
11/18/2008 6:04:00 PM
Hey, if you want a streamlined car and a classic body, you could always model it off of the Talbot-Lago. The Talbo-Lago was supposed to be very aerodynamic and one of the best looking cars ever. (I came across when trying to find inspiration for a different looking velomobile body.)

Jack McCornack
11/18/2008 6:31:36 AM
William, you may be right that taller gearing will improve our mileage, but we're currently geared to cruise at 55 at 2300 rpm, which according to the manufacturer, is right in the efficiency sweet spot for this particular motor. Bigger engines get their peak efficiency at lower revs (a container ship diesel runs best at about 100 rpm) but they weigh more per horsepower delivered. There's a slower engine in our power range (25 hp at 1500 rpm) but it weighs 450+ pounds more than MAX's Kubota, and at that weight we'd need 40 horsepower...and then we'd need a heavier chassis to carry the heavier engine. The weight goes up as the revs go down, and soon we'd have a much less efficient car with a slightly more efficient engine. You may be right about the streamlining too, maybe I'm hoping for more than I can get. Since aerodynamics is my forte, this may be a case of "Give a kid a hammer, and everything looks like a nail," but for me the big question is, can we get it slippery enough and still keep it cheap.

william_1
11/15/2008 8:45:10 PM
Yes the streamlined body will improve gas millage but i believe it will not be as much as you expect. Probably not over 80mpg. Optimal mpg for a diesel happens at 500-1000 rpm. To break the 100 mpg barrier You will need to slow down to 30mph or change the gearing to get low rpm's at 50 mph.

Jack McCornack
11/14/2008 9:57:07 PM
Oops. Sorry, AL, I misunderstood your question. On second reading, I gather you're asking what can be done to improve the fuel economy of your truck, not the fuel economy of my MAX. For starters, if you drive over 55, slow down. Keep your tire pressures up to spec. But most important, and you are a perfect candidate for this, drive the vehicle most appropriate to the trip. If you're carrying sheetrock to a build site, take the truck, but if you're carrying yourself and a lunchbox to a build site, take your Prius. I'd guess your truck is more comfortable, but a Prius is comfortable enough for most trips, and at better than triple the fuel economy.

Jack McCornack
11/14/2008 9:43:27 PM
Hey Al, I can't guess which one is most comfortable, but if you add a MAX to your fleet, I can tell you which one will be -least- comfortable. :-) Light cars transmit more bumps in the road to the driver than do heavy cars. When selling sports cars, the spin goes something like "The Blahblah gives the driver precise feedback..." and "The Whatsit offers the discerning driver incomparable road feel..." and while I'll admit I like the 'being there' feel of light sports cars, most folks prefer a bit more isolation from imperfections in the asphalt. Do I have any other thoughts toward increasing its mpg? You bet I do, and can probably come up with a thought a week for the next year--right here on MAX Update. Stay tuned.

Leslie_2
11/14/2008 1:27:10 PM
Most any vehicle can be made to get higher MPG with good maintenance and careful driving. I have a 91 Celica GT with near 400,000 miles on original engine and transmission. I use synthetic oils and grease (AMSOIL) all around and changed the plugs to the multi-gap type. I constantly get around 40MPG and on one good test of several tanks I got to 50.1MPG without no more than careful driving and good maintenance. If I can do it in my garage, the manufactures can do it in production. Just using synthetic oils and grease are a major start. Yes they cost a little more but the oil change is a lot longer in miles so in the end you actually save on oil and gas. When, or should I say if, the engine finally dies, I'll do a serial hybrid conversion and see if I can get a 100MPG Celica. Yes the compression is still up there and it will still run like crazy and if I don't care about fuel, it will burn rubber. I just take it easy as this is my main set of wheels and both of us are getting up there in years. Leslie

Al Herrington_1
11/14/2008 12:07:53 PM
Jack- As a long time MEN subscriber and a carbuff, I have followed your MAX efforts with great interest. I have an 08 Prius (52+ mpg), a 97 Geo Metro (42+ mpg), and a 98 Dodge Ram 1500 (14- mpg). Guess which one is the most comfortable? I am attempting to build an electrolysis device for the truck. Any other thoughts toward increasing its mpg (besides selling it)? Al Herrington

John Rockhold
11/14/2008 11:09:47 AM
Hi BJ -- the key part of Jack's statement is "in production." Sadly, Honda ceased production of your little, superefficient hybrid in 2006. But, yes, that hybrid was quite famous for its gas mileage. Thanks for sharing your numbers, those are great. Especially 784 miles on one tank! Kudos. The good news is the Insight is coming back, sort of. Next spring, Honda will start selling an entirely different Hybrid under the Insight name. It's a larger car than your two-seater; it will have room for five passengers. Its design is similar to that of the Toyota Prius. But the new Insight will be less expensive than the Prius, selling for about $19K. Fuel economy numbers are unknown at this time, but odds are they will be in the 40s. I'll be writing about the new Insight in the coming months in the Energy Matters blog and the magazine.

BJ_1
11/14/2008 10:41:51 AM
Not true. (there aren't any production cars that get better than 50 mpg at 70 mph.) Our Honda Insight consistently got 60 mpg @ 70 mph. We regularly got 75@55 and 55@75 with an even exchange of 1 mpg for 1 mph in between. I've even driven, much to my wife's chagrin, the 784 from our home in LA to Albuquerque, NM at 55 mph on one 10.5 gallon tank of gas. If I hadn't made it, my wife would be here now and I'd still be somewhere in the NM desert. ;-)

Tom_3
11/13/2008 5:39:03 PM
I just wanted to let you know that I have been watching your project with a great deal of interest. I look forward to your results with the custom body, I wish I could be helpful but I don't have much experience in fluid dynamics. A big congrats for your escape win. Having an alternative solution which reliably works definitely helps in the energy debate. Tom

Jack McCornack
11/6/2008 12:07:23 AM
Hi Mike, heck yeah I'm familiar with the XR3 -- go to Max Update 5: Keeping the Faith and you'll see an XR3 link and photo. Air drag is the biggest factor for sure, but there are other factors. The XR3 uses a smaller engine (same manufacturer but different in other respects, e.g 2/3 as many cylinders, no turbo) and it's true that three wheels have less rolling resistance than four. And one difference to consider is that I'm reporting the results of non-optimal driving. At this stage I can claim 80mpg, but I get it by slowing to 40mph, and it doesn't reflect how I've actually been using the car.

papastardust
11/5/2008 3:42:00 PM
Jack are you familiar with the xr3 they claim 125 mpg with the same motor your using.Can the difference between your 50-60 mpg and their 125 claim all be due to air drag ?? Mike V







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