150 HP 50 MPG two cylinder engine

by Will Thompson

The late Smokey Yunick (1923-2001) was one of the greatest automotive engineering minds the world has known. Smokey was also notorious for cheating and being so full of BS in NASCAR that stories about him are legendary. One of Smokey’s most legendary engineering feats (and rule violations) was building a 7/8 scale Chevelle and racing it in a NASCAR race.

It’s no surprise then, that one of his most significant accomplishments has people who doubt it’s very existence. The adiabatic engine project by Smokey was an engine design that promised unreal feats from a carbureted gasoline engine. The claims of a 150 horsepower, 50 miles-per-gallon, two cylinder engine are enough to set the tin-foil hat brigade chattering about a possible government-big oil conspiracy to keep Smokey’s invention out of the hands of Joe Consumer.

After a few Google searches and a few days looking around to see what I could find, I didn’t come up with much beyond theory and anecdotal evidence. I did notice a few patents, with this one being most likely the one that sets everyone’s brain gears a-whirring. Here’s the only diagram of anything remotely related to an adiabatic engine:


It seems this guy probably did more research than just about anyone, but most of the links are broken now, and the site’s a bit hard to read due to a language barrier.

Nearly every Smokey Yunick historian remembers the adiabatic Fiero, but no one can find evidence of it’s existence or an actual guide to the technology it possessed.

After reading a few days about Smokey, it seems to me that he would have enjoyed the controversy.

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20 Responses to “150 HP 50 MPG two cylinder engine”

  1. Brad Says:

    You are looking at at diagram that details an engine that has forced induction via a turbocharger, and apparently preheats the fuel/air mixture, which doesn’t really make a whole lot of sense, given you ideally want your fuel/air mixture to be as cold, and therefore, as dense as possible.

    I am not familiar with Smokey Yunick, but horsepower and fuel efficiency are limited by the chemical power density of gasoline; if your engine can burn less fuel per second, it is more fuel efficient, however, this also limits power. The practical application to this is to increase the horsepower of your engine, you must force it to burn more fuel in a given amount of time. This is why people that have a two liter turbocharged four cylinder are often surprised that they get the same gas miliage as a car with a 5 liter v8 when they drive with a lead foot. Granted, some engines are more efficient than others in terms of power loss through heat and mechanical friction, but the only practical way to increase fuel efficiency is to effectively decrease your overall power output.

    Conspiricy theories abound, but look at this from a purely physical/mathmatical standpoint; there is a maximum amount of energy that is liberated when you combust gasoline, anyone can run the numbers and find out fuel economy.

  2. Smokey Yunick and the adiabatic engine « News Coctail Says:

    […] Smokey Yunick and the adiabatic engine Filed under: Uncategorized — recar @ 1:14 am Smokey Yunick and the adiabatic engine Did Smokey Yunick actually create a regular engine that got 50 MPG in a Fiero? Some say it was never built, and we may never know[news] [general sciences] [science] […]

  3. Jessica Breckenridge Says:

    Actually there was an article in either Pop Sci I believe when he had a column detailing his plans for the engine. Although heating the air intake was counter intuitive, he was said to demonstrate a working model for them, however it ran on 108 octane gas to prevent detonation.

  4. Flunkysama Says:

    The idea is to is minimize the amount of heat going out the radiator and exhuast. If you are not loosing as much heat there it must be going to create more power, right?
    In his autobiography, Smokey admits it had high NOx numbers, meaning it was probably running lean as well. He may of had cranked in alot of miller cycle in the cam timing too. Who knows?
    I don’t think there is any conspiracy going on here. The engine was not clean enough and cheap enough for detroit. His MPG claims don’t mean anything unless checked in controlled circumstances.
    Anyway, I recommend reading his autobiography. It kinda rambles, is short on hard facts, but pulls no punches. He was a great man.

  5. Brett Johnson Says:

    I saw Yunick’s Fiero on “HorsePower TV” (TNN, Spike) a couple of years ago. The current owner demonstrated how it uses rapidly spinning cylindrical brushes to atomize the hot fuel. The thing looked like a roots-style supercharger with brushes instead of screws. They didn’t put it on the dyno, tho. [The PowerBlock did not have their in-house dyno back then.]

  6. Ben Says:

    I remember reading about this in Popular Science (probably) ‘way back when.
    This blog entry lacks not only a conclusion but does not even define “adiabatic” or explain how the engine was supposed to work.
    The article was written by someone who claimed to have gotten a ride in the prototype, which was powered by an engine which somehow was able to capture waste heat and use that to enhance combustion efficiency. He said Yunick was constantly on the phone with a lawyer to determine what he could and could not reveal. And there was an anecdote about the unusual torque of the engine involving being stuck in a high gear with oncoming traffic, and the engine responding well. But that’s just my memories of something written possibly 25 years ago.

  7. Will Thompson Says:

    Brad - from what I read the idea Smokey tried to capitalize on was to be able to actually warm the fuel-air mixture before it hit the combustion chamber. Supposedly this made a condition that allowed an extremely lean air-fuel mixture.

    For those of us who have always had the idea that a cooler, more dense air-fuel mixture in order to get better performance and efficiency. When you think about it, the idea is intriguing. Turbochargers and superchargers (and even cowl induction hoods by virtue of cooler air being more dense than warmer air) have always worked by adding in more oxygen to the mix, more fuel is added so that a lean condition won’t exist, subsequently grenading the engine. While I don’t pretend to know if a heated air-fuel mixture would perform better and more efficiently than a cooler mixture, the idea isn’t one I can dismiss out of hand. If a combustion condition could be attained by using more air and less fuel, that would be considerably more efficient than more air and more fuel.

    Either way it’s a really hard concept to get your mind around, and the fact that we’re all doubting that the technology even existed and functioned says to me that maybe the idea wasn’t perfect or practical.


  8. Will Thompson Says:

    Brett, I think Powerblock (specifically Horsepower TV) was where I first saw the story of the adiabatic engined-Fiero also.

    The exhaust-driven “homogenizer” in the intake tract isn’t a turbocharger, but rather the brushes you mention to better atomize the fuel-air mixture and supposedly allow for warmer air and less fuel.

  9. Lenny O Says:

    I read the original articles in one of the hot-rodding magazines in the early eighties. According to Smokey, the turbo had two main functions; pressurization of course, but mainly “homoginazation” of the air/fuel mixture through rapid and constant mixing. This was supposed to minimize detonation and maximize the heat efficiency of the engine, allowing great power with fuel efficiency. I never saw any followup after that

  10. Johnny2Bad Says:

    All turbo and super chargers cause the fuel-air mixture to heat; you are compressing a gas after all. The Germans even call it a “Komptressor”. It’s not the heat that is a problem. There is such a thing as “too hot” which will result in combustion, such as how a diesel engine works (no spark; just 20+ :1 compression) but below that you are fine.

    Cooler intake charges (not cooler charges period) help because air is denser as the temperature falls, and since all internal combustion engines burn air (not gas, or whatever; they just set up a condition where we can make the air burn) you get more “fuel” per volume (and engines are volume-limited) because you can pack a denser air charge. Denser air equals more power but it also burns more fuel and fuel has problems atomizing at low temps, making the engine burn more fuel and waste more fuel (unburned fuel in exhaust) as temps fall.

    However all that is moot once the engine has taken in it’s “gulp” of air and fuel; what happens after that can’t change the amount of charge you have. You can compress it (which heats it up) or whatever.

    Smokey was working on capturing the heat of combustion and turning it into work; thus his research taken to it’s ultimate would result in ambient temperatures at the exhaust and in the engine compartment. it’s not easy but since most any petroleum engine wastes a considerable amount of the fuel as heat rather than turning it into work (ie horsepower) this is clearly an area where any advances does result in better efficiency.

    Modern engines use advanced coatings to retain heat in the combustion chamber (piston tops, valve faces, intake runners, head chamber surfaces, etc) but it’s tricky work managing heat; you also need to shed heat created by friction or else engine life suffers.

    Very interesting man, Smokey.

  11. Will Thompson Says:

    Johnny2Bad, that was a very good comment. I wish I knew all there was to know about Smokey’s invention. Shoot, I wish I knew what to believe.

    If it were Steven Hawking, I could probably believe all of it. The BSer that Smokey Yunick was, though…


  12. Richard Brooks Says:

    The basics behind this engine were published in a series of articles in Hot Rod magazine (I think) back in the early eighties.
    The ‘turbocharger’ was indeed called a homogenizer because it blended the air-fuel charge. More importantly, it acted as a one way ‘check valve’ which ensured the heat-expanded air-fuel charge didn’t back up through the carburetor (throttle-body fuel injection was still a relative novelty then).
    The engine exhaust was used to preheat the intake charge just like in the picture. “BS, the engine would detonate to death!” you say. Not so. What Smokey discovered is that, once you heat a fuel-air charge beyond a certain temp (300+ degrees, I think), it truly becomes homogenous and burns with no hot or cold spots to cause detonation. From what I recall, it ran on pump gas and a fairly high 9-10 to 1 compression ratio, and put out ridiculous power for its size. The NoX emissions, however, prettymuch nixed the engine, as there were no catalysts available at the time to take care of it, and synthetic oils cost about $15 a quart.

    Smokey also taught Detroit that a powerful engine could also be an efficient engine. Buick’s 3.8 liter started as an anemic 90 hp V-6 which shook and rattled badly. Smokey taught GM how to split the crankshaft pins to smooth it, and (eventually) triple the power output while STILL getting better mileage from it.

    This is too long already, but your current car probably owes a lot to Smokey Yunick’s genuis and “I’ll find a better way” attitude.


  13. Will Thompson Says:

    Thanks, Richard. Great comment, man.

    So I wonder if this engine could work with today’s commonplace technology (TBI, better catalysts, etc)

  14. Richard Brooks Says:

    Addendums and other remembrances.

    The engine ran a very lean charge (which didn’t help the NoX) of around 20-1 or so.

    Some of the earlier experiments literally melted down :) due to the stock, factory cast pistons. Forged pistons took care of that problem, and allowed more progress.

    Smokey was (in)famous for his ingenuity. To get more traction on southern circle tracks using stock cars, he once engineered an engine to turn backwards (and flipped the rear axle) to change the traction distribution on the rear tires.
    Back then there wasn’t any rule about the size of a fuel line, so he snaked about 30 feet of 5/8 fuel line all around the car - because it added a crucial 2-3 extra gallons per race! :)

    The 7/8 scale car is also true - and also the reason templates became standard to ensure that a stock car was really a showroom model - and not 7/8 size.

    Sneaky and underhanded? Maybe. But you can’t say he didn’t think outside the box.


  15. Motoroller Says:

    Back in my younger days, I studied automotive engineering. I had one semi-genius professor and fuels and lubricants was his specialty. The class was often like mythbusters, and smokey yunick was only second fiddle to STP. Heated, agitated mixture is easy, put a roots type blower on a turbocharged engine.

    Think about it. If it were REALLY that easy to get HP+MPG, you would see every shadetree mechanic doing it.

    Smokey Yunick. Lotta smoke, but no fire!

    BTW, I am a fan of old smokey. RIP.

  16. Motorcycle Guy Says:

    Umm have you ever heard of Ducati? They are pretty much there at both those marks the mpg might be around 43 and the hp should be about right on with their new 1098.

  17. Will Thompson Says:

    Yup, sure have. I suppose I should have mentioned that I was talking about four-wheeled vehicles. Obviously motorcycles have a bit of an advantage because of their lower weight, excluding Goldwings and the like.

    On a side note, I hold firm to my belief that Ducatis are the best sounding bikes made. Makes the hairs on the back of my neck tingle thinking of that sound.

  18. Automotive Blogger » Blog Archive » Followup to the Smokey Yunick Fiero Says:

    […] to the Smokey Yunick Fiero May 25th, 2007 by Will Thompson A couple weeks ago, I wrote about the existence, or lack thereof, of Smokey Yunick’s famed adiabatic-engined […]

  19. Hostgator » Blog Archive » Smokey Yunick and the adiabatic engine Says:

    […] a regular engine that got 50 MPG in a Fiero? Some say it was never built, and we may never knowread more | digg […]

  20. Leonard Ochs Says:

    Just remember, the hotter an engine runs relative to the ambient temperrature the higher its efficiency - apply the Carnot cycle to see. So, if the engine was running hotter then its efficiency was higher then it gets better milage. This was the principle for all the work that went into the ceramic engines in the 80’s. Materials of construction for high temperature internal and external combustion engines will always be a problem. Application of Carnot yields an efficiency of about 35 to 40%. Can’t get much better until we can run hotter; and we can’t run hotter until we can find material that won’t fatigue at the higher temperatures.

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