Car Hacker Hacks Lawn Care Carb Into Hot Rod Car

Internal combustion engines have often been described (quite correctly) as air pumps, and because of this nature, they tend to respond very well to more air. Why? Because more air means more fuel, and more fuel means more power- the very nature of hot rodding itself. [Thunderhead289] is an accomplished car hacker, and he’s decided to take things the opposite direction: Less air, less fuel… more mileage? As you can see in the video below the break, [Thunderhead289] has figured out how to mount a single barrel carburetor from a lawn mower to the four barrel intake of a Ford 302– a V8 engine that’s many times larger than the largest single cylinder lawnmower!

The hacks start not just with the concept, but with getting the carburetor installed. Rather than being a downdraft carburetor, the new unit is a side draft, with the float bowl below the carb’s venturi. To mount it, a 3d printed adapter was made, which was no small feat on its own. [Thunderhead289] had to get quite creative and even elevate the temperature of his workshop to over 100 degrees Fahrenheit (38 Celsius) to get the print finished properly. Even then, the 34 hour print damaged his Ender printer, but not before completing the part.

The hackery doesn’t stop there, because simply mounting the carburetor is only half the battle. Getting the engine to run properly with such a huge intake restriction is a new task all its own, with a deeper dive into fuel pressure management, proper distributor timing, and instrumenting the car to make sure it won’t self destruct due to a poor fuel mixture.

While [Thunderhead289] hasn’t been able to check the mileage of his vehicle yet, just getting it running smoothly is quite an accomplishment. If silly car hacks are your thing, check out [Robot Cantina]’s 212cc powered Insight and how they checked the output of their little engine. Thanks to [plainspicker] for the tip!

45 thoughts on “Car Hacker Hacks Lawn Care Carb Into Hot Rod Car

  1. Gasoline engines are not going anywhere for a LONG time to come. Electric doesn’t yet work for everyone for a multitude of reasons, electric cars are currently still very expensive (especially compared to an “old banger” like a 302 Ford) with lots and lots of supply chain issues meaning their availability is not great. Making existing gasoline ICE cars go further on less go-juice is a very relevant endeavor and will be for the foreseeable future (at least the next 20 years)

  2. One of the issues that exists however I cannot comprehend and thus eloquently describe is the burden on infrastructure to a singularly electric future. In cities with town has and electricity the shift to a single energy source will likely cause supply issues as the burden on electricity supply increases. Further the relatively immediacy of refilling fossil fuelled vehicles cannot be reasonably replicated. Fast charging as far as I am aware for a significant fleet of vehicles is an unknown burden. Battery replacement is a possibility however how long has it taken to sort of standardise domestic chargers? I forgot my laptop charger. It now sits there dormant. Electric everything is a noble concept. It will take a long time if ever. Perhaps there is a better solution that will percolate in time.

    1. Just need to make some trades and compromises. Turn off the heat and air conditioning and your 80-inch TV set. Now there’s plenty of amps to charge your car. Stop clustering all the business in one place and the housing in another place. Mixed use zoning. No more 100-mile commutes. Tax people based on their commuting distance. Make a few lifestyle changes or find a new planet to plunder. Electric cars or fossil fuel cars work don’t work too well under water.

      1. Nothing you suggest would supply the massive energy required to charge a electric car. You would however lower the standard of living and potentially kill the most vulnerable.

  3. Smaller carb means less air and more pumping losses. If it gets better economy, it’s because they can’t open the throttle. Better would be stock fuel injection with intake air heated by the exhaust so it’s less dense and we can spend more time with but using less fuel.

  4. During the oil embargo shortages of the 70s, lots of people we’re trying stuff like this to save gas. As a young 3m process engineer, I occasionally visited a 3m plant where the plant’s station wagon was outfitted with blocked off cylinders, and dummy pistons to maintain balance in the name of saving gas. The conversion was written up in a company “program for profit” document that was used to document cost savings. As it turned out, it did save gas but resulted in a vehicle with no acceleration and that was prone to stalling at critical times when you wanted to accelerate. Perhaps its greatest savings were due to no one wanting to use it. During my plant visits it was always available and ended up sometimes the only vehicle we visiting engineers could get because no one else wanted to use it. After a year or two later the car was converted back to its original condition. I suspect that this project may have a similar life cycle.

    1. A better choice would have been to put in a long stroke inline 4, Higher gearing, and a low restriction intake and a header. Less weight, friction, and pumping loses. Of course if you had say a vax in the back and fuel injection you could replace the throttle plate with an EGR system. Today you could do it with an ARM m0

      1. Or not only replace the carburettor, but replace the whole engine with the engine from the lawnmower.. :D No accelleration, huge mileage, and hopefully enough torque to pull that overweight American car.

        Ow. And there we come to the real issue I think: overweight cars. Bring the weight down and you mileage will go up, even if you have a big engine.

        Of course, if you bring the weight of the car down to let’s say 600kg, but keep the big engine, you’re going to run into another overweight thing: your right foot, hahahahaha. :D

        So what you should basically do to get a high mileage, is to keep the lawnmower intact, add some cabin to it so that you stay dry and can take your groceries with you, and use that to drive around.

        Bottom line: the Japanese were on the right track already since the ’80’s. ;)

      2. Holden tried that in Australia. Their Commodore family sedan had always come with a 3+ litre 6 or 8 cylinder engine, then during one of the fuel crises (late 70s? It was before my time) they put a 1.9L 4 cylinder in it. When I got into cars 20 ears later that car was still a joke.

        Then again, with modern computerised engine management and a turbo, the “small engine in a big car” model can actually work well.

  5. It’s good to see that the “magic carburetor” urban legend continues to inspire fiddling with engines even now.

    The volume of air moving into the engine at a specific RPM is fixed by displacement, so using a tiny carburetor will cause higher velocities in the carb throat but the Stoichiometric air-to-fuel ratio can’t change all that much, requiring high fuel feed rates (as he’s done with pressurization).

    The “how” seems to work – you can run an engine by dripping gas into the intake maniforld – but the “why” remains. Intake restriction was one of the first gambits of Detroit in the early 70s in an attempt to create efficiency but as above there are real (and very small) limits to the gains that are possible. Have a look at the work that it took to create the Honda Compound Vortex Combustion Chamber (CVCC) engine (also the root of the “Civic” model designation) to cheat this game at all, and a lot of the intense work that got us to current fuel-injection/turbocharged engines with better efficiency.

    That these efficiencies are then used to make higher horsepower engines for bigger/faster vehicles that just nudge CAFE standards rather than producing sensible, efficient vehicles says more about marketing/human nature than any kind of engineering or technology and probably belongs in another column.

  6. Two rules to good fuel economy:
    1. Never exceed 2000 rpm. Throttling and windage losses are murderous at higher engine rpm. Shift early, shift often. Make sure that throttle is as wide open as you can make it, or closed tighter than a ***’s ***, nothing in between, but just keep the rpms low. If you drive an automatic, well, I’m sorry for you.
    2. Never touch the brakes. They just turn fuel into heat. Plan ahead so you don’t run into stuff. If you must, use engine braking so at least the injectors turn off instead of idling and burning gas while you heat your brakes.

    FWIW, it costs $0.10 to $0.20 of fuel to bring a car from a stop up to highway speed.

    1. Though for anything with forced induction you often have to keep it at “normal driving” RPM for the afromented forced induction system to be effective and not being a burden.

      Unless we’re talking about the early 80’s turbo’d econo cruisers, they were built for driving just like that.

      They also weren’t making significant amounts of boost, though that meant they didn’t need neither charge air cooler nor high octane fuel.

    2. “FWIW, it costs $0.10 to $0.20 of fuel to bring a car from a stop up to highway speed.”

      That doesn’t tell us anything. At what price per gallon? Would be more useful to know the quantity.

      1. Useless to give specifics. Left as an exercise for the reader. Intended to encourage thought and discussion.

        Or assume a big-ass american car and american gas prices (and american dollars), or a small european car and european fuel prices. Outliers like autobahn speeds or saudi arabian fuel prices are obvious outliers.

        1. You are entering the autobahn from the right because the rightmost lane is the slowest. If there are vehicles limited to 80 km/h (all semitrailer tractors), they drive on that lane. So that’s the speed you usually have to achieve to enter the autobahn. You are allowed to use the autobahn when your vehicle is capable of accelerating to 60 km/h, but everyone will hate you if you can’t go faster than that. Above 130 km/h you automatically become partially liable for accidents you are involved in.

        2. OK.

          Potential energy of car is 1/2 * m * v^2

          for 3000 lb car (m = 1360 kg) and v of 70 mph (31 m/s)

          gives 653480 joules of energy

          Energy density of gasoline is 127 MJ per US gallon

          653480 joules / (127 MJ/gallon) = 0.00515 gallons (forgive me for the SI to gallon conversion!)

          Then account for 20% efficiency of combustion, transmission, etc
          0.00515 gal / 20% = 0.0257 gallons

          0.0257 gallons * $5 /gallon = $0.129 or a hair under 13 cents.

  7. The biggest issue i have with this is that at the end of the day you might be saving a few gallons of fuel but you are still running your engine lean. Running a 4 stroke lean does the same as a 2 stroke and will eventually cause the engine to burn up way earlier than designed. Is it a neat test yes and I’ve been watching it, is it a long term solution absolutely not because of the previously mentioned issue.

    1. I have to agree. If you think that the power of a larger engine is wasted then you should try driving in a higher gear ratio. you could change out the differential for a different ratio or put larger wheels on the car.
      I have been wondering why manufacturers don’t put two engines in a car. that way if one breaks down you have the other to get you home, plus you have lower fuel consumption only using one engine. maybe there is a vibration issue. it would be have the advantage of the volkswagen dual clutch gearboxes for changing gears. i.e one engine is clutched while the other is in gear.

      1. Because the added complexity and mass of having two engines vastly outweighs both the fuel savings and the incredibly rare (for most people) risk of an engine failure that’s related to the engine itself (engines rarely fail, and when they do, it’s more likely something external to the engine anyway)

        I think some cars can turn off some cylinders for economy. That’s a simpler and smarter option.

        1. I’ve heard about the cars that turn off their cylinders on /r/justrolledintotheshop. they are invariably a disaster, coking up the cylinder head and vacuuming oil out of the sump.

          I don’t think two engines need be heavier than one, for instance you could eliminate the differential and have one three cylinder engine with even gears driving left front wheel and the other three cylinder engine with odd gears driving the right front wheel.

          That way you would have better traction in snow with the same number of gears as a typical manual car. many parts are already duplicated in engines like the v8 so it’s not a deal breaker to have two flywheels which would be smaller due to the lower horsepower.

          the alternator and starter would need to be duplicated for each engine however, but again smaller designs would suffice.

          I get your point though, for most people reliability is not an issue. It’s different in sea going boats where redundancy is the norm.

    2. That’s just a common myth, at least on factory engines. Yes, fuel does help cool down the cylinder, but running lean means making less work and less work meas less heat.

      Air cooled or boosted engines are different though, because lower AFR help keeping intake and cylinders cool, so that means less konck.

      1. The reason people think lean = hot engine is because in a sense they’re right, just for the wrong reasons(like with alot of myths, they have some basis in fact, like the exhaust ‘backpressure’ myth). Ideal ratio or rich charges tend to be alot cooler, a lean charge will invariably be hotter and more prone to detonation, which disturbs the gas boundary layer between the piston/cylinder wall and transfers heat alot more efficiently instead of just pushing it out into the exhaust. Running lean can also increase EGT, because it will not burn fully(or sometimes not at all) inside the combustion chamber, only igniting once it reaches the much hotter exhaust system.

        None of this matters if the engine(usually just the combustion chamber design) is specifically designed to run lean, though.

    1. Yes, but it’s a far different story if you run at 40% efficiency and 7% drivetrain loss or 5% efficiency and 25% losses.

      Also, not only you can improve efficiency of the engine, so it can use less g of fuel for a given kWh (also known as BSFC) you can also improve how much power you need to keep a certain speed. Aero, weight, drivetrain losses, rolling resistance, accessories all contribute to final MPGs.

  8. Honestly, that’s a really dumb way of going about efficiency, especially on an engine like that. What you’re doing is creating more pumping losses (what you certanly dont want if your goal is MPGs).

    A proper way of going about this, if you wanted to keep this old engine is to modernise whatever you can.

    First big gain would be multipoint EFI setup with programmable ignition. Along with wideband O2 sensor, you could run that badboy in a perfect AFR, something you just cant do with carbs.

    Then i’d go for a serious MILD cam setup with appropriate overlap. If you’re really serious you’d also swap out for solid lifters, lighter valves and pushrods along with softer valve springs.

    Now that you actually done something reasonable for efficiency you can go further. Lighter crank, lighter flyweel. Electric water pump and fan. Power steering and AC delete. Higher efficiency alternator.

    And lastly of course. Drive by wire and EGR. You can do some really cool things with this (like running WOT to hit that sweet low pumping losses). Works best with an auto of all things.

    When you’re all done with that, you might just realise you just made an LS :D

      1. Yes, that’s true. What you want is as least parasitic losses as possible. Solid lifters should put less losses on the valvetrain side of things, so there might be a tiny bit gained there.

        There’s lots more things you could do to an engine like that for the sake of efficiency (even crazy stuff like GDI) but that would require so much work and modification that you’d be left with a block that barely resembles what came from the factory.

    1. I dont think you have your priorities in order. I agree with the mild cam thing, but Lighter valves, solid lifters, softer springs? What? I mean theoretically they could improve efficiency, but in the real world i doubt even most dynos would pick up an efficiency gain that small. A lighter crank and flywheel also most likely wont have as much effect on efficiency as you might think. Lightening those components up is more for engine responsiveness than it is for power/efficiency gain. Once the engine is up to speed, a heavier lower end will also have more momentum to keep it turning.

      One of the reasons that the lawn mower carb worked to increase mileage(though he DEFINITELY needs a longer road test and a more accurate way of measuring fuel consumption) was because with such a small oriface feeding such a large engine, the air velocity going through that carb will be absurdly high(the rudimentary carb had trouble metering fuel because of that, hence the controlled vacuum leak device he made to properly control the AF ratio), which will promote a finer mist of gas from the carb jets, and with high velocity comes more turbulence, the finer mist, high velocity, and more turbulence promote a healthier, much more homogenus charge which the engine can burn more completely and extract more energy out of. The end result is increased miles per gallon.

      Also, as great as LS motors are, I’ve never known them for being 40MPG economy motors, even in relatively light cars like what a maverick is.

  9. Crazy comments!! The guy was bored and very ingenious and put a little toy mower carb on a V8! I love how everyone came up with better ideas for more economical solution.
    To me it was all about seeing if it would work, period. If the guy really wanted a more economical means of transportation, just drive a different car!!
    Hats off to you my man!

    1. Basic understanding on how gasoline cars work will tell you, that smaller carby isn’t the proper way for going about this problem. You could have achieved the same exact thing by just not opening the trottle more than 20% and use the smallest pilot and main jets where engine still keeps running.

      1. Or just take 1000kg of weight off that car.

        I don’t know what car that is, but it looks as if it weighs close to 2000kg. So, half the weight and get twice the mileage (well, more or less).

        1. Unfortunally fuel consumption doesn not scale linearly. And i’m pretty sure that car isn’t 2 tonnes. Mavericks of that vintage are closer to ~1,3-1,4tonnes. So lighter than most cars today.

      2. just keeping the throttle below 20% on a larger carburetor would not have the same effect. Air going through a larger bore will invariably slow down more than going through a smaller bore. Slow air means the atomized gasoline will have more trouble staying in suspension. A less homogenous fuel/air mixture means a less efficient burn, which means less power available to be extracted by the engine, which means all that potential energy is just being wasted by being sent out into the exhaust instead of being useful power.

        Modern engine design focuses heavily on keeping the fuel/air charge in as homogenous state as possible before igniting it for a reason. That’s where a majorly significant portion of power/fuel economy resides.

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