Ah, Valentine’s Day! The day we expect our significant others, lovers, and expensive sex mannequins to gamely pretend to forget about our many, complicated flaws and remember why they got into this mess in the first place. We express this, commonly, by giving one another our hearts—usually symbolically. Since we have all these hearts now, and hearts are pumps, it’s worth asking: can you replace your car’s fuel pump with a human heart?
Now, I’m aware that there’s some significant ethical and bio-technical issues why you either can’t or shouldn’t seek out human hearts to replace your fuel pumps with. But, for the sake of this little thought-experiment, let’s say you’ve been given all the hearts you need from willing donors who died for just, beautiful causes, and that you figured out a way to run 12V from your alternator into the heart to keep it pumping.
Maybe you even wired the heart up through your parking light or DRL circuit so that your lights pulse with the heartbeats, too. Why not, right? What’s the point of adding human organs to your car if you can’t have a little fun?
I’m also going to say both systems are roughly equal as far as restriction goes; fuel lines tend to be much higher diameter, but there’s many parallel capillaries and veins. And I have no idea how to compare the two, so we’ll call that a wash.
So, now that we’ve established it’s ethically acceptable and technically feasible to connect human hearts to your car, the question is will a heart be capable of replacing your fuel pump?
Let’s look at some of the specs of a human heart as a pump to get an idea. Most importantly, I think we’d like to know what kind of fuel pressure we’ll be able to get from a heart. Luckily, we measure this all the time, just with blood instead of fuel.
Average human blood pressure is usually taken to be 120/80, where the 120 (systolic) number refers to the pressure the heart exerts when it contracts, pumping blood out, and the second number (diastolic) referring to the pressure when the heart intakes more blood, between beats. The units for those numbers are in millimeters of mercury (mm Hg).
We usually measure a car’s fuel pressure in pounds per square inch (psi). One psi is equal to 51.7 mm Hg, so a heart can pump about 2.3 psi on the systolic contraction and 1.5 psi between beats.
I’m not the only one asking the question of what a heart is capable of pumping in psi, it looks like. But it looks like people on medical websites don’t like these kinds of questions:
Man, lighten up, people.
So, it looks like a heart’s actual pumping ability should be able to hit a bit over 2 psi, at least in pulses. For our bodies, pulses are fine, but cars like steady pressure, which is why most cars already have fuel pressure regulators.
So, with that in mind, it looks like on some carbureted cars, around 2 psi should be fine. In fact, on my ‘73 VW Beetle with twin Kadron carbs, it seems that 1.5-2 psi is just what it expects. So, I should be able to replace my boring old metal fuel pump with a nice, glistening human heart!
Of course, if I had a Weber carb, I’d need 3-3.5 psi, and it looks like most carbureted engines would need about 6 psi. And that’s not even close to what a fuel injected engines require, which is around 35-50 psi.
That’s a lot more psi than a human heart can provide – so what’s a romantic to do?
The answer, as always, is love. The answer involves hearts coming together, my friends, only this time they’re not drawn together by waves of passion, but rather by being connected in series to increase their head, or pressure.
So, since the world is full of love and hearts are being given out freely, you’ll want to grab at least three hearts and connect them one to another in series, superior vena cava to aorta. So, fuel tank to heart input vena cava to output aorta to input vena cava to output aorta to input vena cava to output aorta, and then back. Three hearts, connected together, making a healthy 6 psi of fuel pressure.
Now, for your fuel injection setups, you better get one of those big picnic coolers, because you’re going to need around 15-20 hearts, at least. For higher pressure setups, you’ll need even more, maybe up to 25 beating hearts.
Make sure you think about packaging before suturing all those hearts together in series; my suggestion would be to pack them in a box and zig-zag them in rows.
So, there you go, young lovers. That heart you have beating in your chest is strong enough to feed an old Volkswagen all the fuel it needs. You and your lover, together bound by the power of eternal romance, are able to power most carbureted cars—well, if one of you can talk the other into a three-way.
And, for a modern fuel-injected car, you’ll need the love-power of some kind of very substantial plural marriage, or maybe some kind of sex cult.
Now, I have to pause here before I get too excited, because this all just means the hearts can provide the needed pressure – what about the actual flow of the fuel?
It appears that a human heart provides about 14 liters per minute of flow. That works great for bodies, but how do we figure out how much fuel flow an engine requires?
Optimal LPH = (Max. HP x BSFC) / 1.585
So, we can see here that this is horsepower-dependent, and it’s in liters per hour. First, let’s get our units the same. A heart does 14 liters per minute at its peak, so we multiply that by 60 and get 840 liters per hour. That seems like a pretty big number, right?
That almost seems too good. Some other sources put the rate at about 5 L/min, so, if we multiply that by 60, we get 300 L/hr. Still pretty good!
The other variable in there, BSFC, means brake-specific fuel consumption, which the people at Holley say requires 0.5 pounds of fuel per horsepower per hour at full throttle. This is basically how much fuel consumed per unit of power of the engine.
I asked David Tracy, our on-staff ex-OEM engineer, what carmakers used as an average BSFC, and he said 300g/kWh because he likes to force me to do math. So, when converted to the units I’m working with here, that comes to 0.45 lbs/hp/hr. That seems to make sense, as I figured Holley probably skews to thirstier, higher-performing engines.
Okay, so, let’s run the equation for a car with, say, 200 HP:
Optimal LPH = (200 x 0.45) / 1.585
Which gives us an optimal fuel flow of 56.78 liters per hour! Can that be right? If so, a heart seems more than up to the task, even at the lower 5L/min flow rate!
Okay, so with this in mind, it looks like we can use human hearts to pump fuel to engines with up to 900 or so HP! Holy crap.
Now, turbocharged engines want more fuel, so the max HP on a turbo is probably less, so, you know, keep that in mind for your next project.
But it’s technically possible, at least in terms of simple mechanical output, to run your car’s fuel system with hearts. All thanks to the power of love and/or the mechanical fluid-pumping ability of a mammalian heart!
Happy Valentine’s day, everyone. I love you all.