Back in the 1960’s my Dad was really into go-karts. Built his own, went to meetings, raced it at this place near Road America, got the magazines, you name it.
He had 2 engines on his and I’ve always wondered what the advantage was to that.
Should of asked him years ago but didn’t and now he’s much too busy being dead to ask so I’m asking you.
Power would be added together. More power = faster top speed and, depending on the weight of the engines, more acceleration.
Also, if one breaks down, you can still make it home/pits on the other.
But how much power? And is that power worth the extra weight. How much extra speed could 2 engines actually provide even if they are running at equal performance? It’s not like it’ll make the kart go double the speed of just one engine.
Total power=power of engine 1 + engine 2, assuming perfect coupling.
Double speed is unlikely due to aerodynamics. But certainly a higher top speed (assuming geared correctly) vs. One engine.
Without knowing the power to weight ratios of the engines, and weight of the car and driver, it is impossible to tell if it it increased acceleration at all.
Extra weight will definitely affect handling negatively. So for it to be worth it (lower lap times) the track would need a lot of/ longer straights to take advantage of the higher top speeds.
Or the two engines give a lower CG, or better aerodynamics, than a single engine of comparable weight and power.
Lower cg is a valid point. Tho not so sure how it could give better aero.
And of course fuel consumption goes up and thus range goes down. Unless you add a bigger tank. But then weight goes up again.
If you do a search you will see that this is not uncommon. You would get twice the horses giving you quicker acceleration, and you could use a bigger gear to raise the max speed.
Cars use multiple ‘power units’ today… and they are on the road, but it’s not two internal combustion engines (ICE). It is typically an ICE and two electric motors (for example) driving different wheels. Exotic cars add this weight and complexity for power, and some other things.
The electric motors add weight, complexity, change the driving dynamics, the the balance and create other design compromises. But they add power, to more than offset the things I just mentioned, and you can really take all those issues, which are resolved with hundreds of engineers, and reduce it to a Kart with two engines, and the person doing such a modification will sort out the issues, on a smaller scale, and change things like gearing, suspension set ups, and determine if the pros outweigh the cons.
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No. Same top speed notionally.
Its all about acceleration … When I drove an identical kart against my brother in law, I beat him because I was 95 kg and he was 115kg… my sister kindly noted “he was faster because he weights less” I had the better power to weight ratio because an extra 20kg (44lb) is a lot, especially when you only have 12 hp …
Aerodynamic drag force is roughly proportional to the square of speed.
Power requirement is force x speed, so the power required at any given speed is proportional to (speed)[sup]2[/sup] x speed - that is, power requirement is proportional to the cube of speed.
Flip that around, and speed is proportional to the cube-root of power.
So if you double your power output (without changing anything else), your drag-limited top speed increases by a factor of 2[sup]1/3[/sup], or 1.26. So if one engine just barely gets you to 25 MPH, two engines will get you to 31 MPH.
That cubic relationship between speed and power explains why there are so few cars that can go 200+ MPH. If you’ve got a 300-horsepower sport coupe that can hit 150 MPH, it’ll take 711 horsepower to hit 200. If you want to hit 250 MPH, you’ll need nearly 1400 horsepower. You can also get there with just 1000 horsepower with some aerodynamic improvements.
Back to the kart…
Two engines doubles the weight of the engines, but it doesn’t double the weight of the entire vehicle. The driver still weighs the same, and it’s likely there wasn’t much weight added to the chassis itself. Putting some rough numbers on it, if a one-engined go-kart and its driver together weigh 300 pounds, and a second 50-cc engine adds 30 pounds of weight, then you’ve got twice the power and only 110% of the total weight: you would expect 1.8 times the acceleration that you had with the single-engine kart. That assumes ideal gearing, which you probably wouldn’t have. I assume they were using a CVT, which would offer a fixed range of drive ratios. If you stuck with the same primary drive ratio, yes, you’d achieve that 1.8X acceleration, but you’d probably run out of RPM before you hit the drag-limited top speed. OTOH, if you change the primary drive ratio so you hit top speed when the engine is at its peak power output, you will have compromised the acceleration at lower speeds. If you’re a good racer/tinkerer, you can choose which of these attributes to give priority to. Racing on a tight twisty track? top speed be damned, tweak your car for best accel at lower speeds. Racing on an oval, or a track with long straights? Top speed is your friend, even if it takes you a little longer to accelerate.
There are no karting formulae which permit CVTs. Karts with multiple gears invariably have conventional manual transmissions.
I raced go-karts when I was in my early teens. Ran a junior unlimited class. Only real rules were a centrifugal clutch with no transmission was required and something like a maximum 35 cubic inches. I remember some dual engine karts but they never did well. Biggest issue was balancing the engines between the rear drive wheels.
Could cost possibly enter into this? Perhaps he could obtain 2 engines at a lower cost than a single large engine of the same total horsepower.
Often the biggest, newest, fastest is quite expensive.
For example, for many years I have used 2 average size computer monitors at a great cost saving over purchasing the newest & biggest monitor available.
I don’t know which type of engine your dad used, but I think that the Briggs & Stratton 5hp horizontal shaft was pretty common for fun karts. I seem to recall my B&S 5hp engine weighing around 40 pounds. The entire kart (with a steel frame and floor pan) weighed well over 100lbs before adding a rider. Adding a second engine would probably increase the total weight by maybe 15 percent.
Another problem is that a simple centrifugal clutch setup usually just drives a single rear wheel (the left rear, if I recall correctly.) I used to be able to slide left turns for fun, but I probably was faster turning right with the weight transferred to the left power wheel (I also flipped the kart a few times when turning right under full power–oops.) Most races are run in a counterclockwise direction, so putting a second engine on the outside (right) rear wheel would give a better transfer of power in turns.
Having a separate engine for each drive wheel also eliminates the need for a differential.
I recall racing with a “live axle” in the 80’s. The gears, or gearbox, drove the axle. I don’t think dual engines would have been possible.
Wouldn’t it be better to just have 1 larger more powerful engine than mess around with having 2?
If 2 engines contribute so significantly, why are there no regular racing cars with 2 engines?
There are. All F1 cars are now, and have been some form of hybrid since…2010? I forget the first year KERS was mandatory. The top endurance prototypes are hybrids too. Some of the unlimited hill climb competitions had cars with two engines.
But ultimately the short answer to your first question is “it depends”. A longer answer is “it depends on a LOT of factors”. The biggest one is if it is allowed in the regulations for whatever series in which you are competing.
Back in the day, when you built your own, you built it using lawnmower engines. Which didn’t come easily and cheaply in mid-sized versions.
Machine Elf got it all. The aerodynamic drag, the total power, the weight and acceleration considerations, the choice of gearing, everything.