[shadycuz]

The engine is the size of a push mower.

> XTS-210 is about the size of a basketball, weighs in at 19 kg (42 lb), and displaces 210 cc.

So you are talking about a 26HP lawn mower.

While the Camry might make more power at its normal size. It would not if you scaled it down to the size of a basketball. I'm guessing it would make 1-3HP at that size.

[93po]

A Traxxas 5407 TRX 3.3 engine used in RC cars makes 1.42 horsepower, weighs 305 grams, and fits in the palm of your hand.

This is 1hp per 0.46 pounds of engine weight, nearly three times better than the camry engine.

Granted an RC engine runs on a mixture of fuel and nitromethane, and doesn't have any reasonable durability compare to a Camry engine. But it also only costs $200.

[seabird]

You can't just make the Traxxas 18x bigger and get linear performance improvement. Trying to compare power/weight between engines with radically different weight constraints is silly.

[93po]

Ok, a Kawasaki H2R engine makes 326 horsepower and weighs about 160 pounds running regular fuel. That's almost identical to the Traxxas - 1hp for 0.49 pounds.

[seabird]

That engine is 4x heavier and supercharged. You're not comparing apples to apples.

[93po]

my point is that this ratio exists both much smaller and also somewhat larger. it makes sense this same ratio would be possible in the middle of the two as well. also diesels have super/turbo chargers all the time on production engines, why is that cheating?

[syrrim]

If you had 18 such engines it would get you precisely 18x the performance, at precisely 18x the weight.

[Retric]

No, because you would need to add structural elements, some way of combining power output, and cooling if you’re aiming for a similar form factor.

[seabird]

That's why there's all sorts of widely produced performance vehicles with multiple independent engines!

[aidenn0]

And precisely 1/18 the MTBF

[93po]

In a way, sure. Often when a car engine fails people just replace it. If you were to replace all 18 when the first one failed, the same way you would with a regular car engine, it's not 1/18 the MTBF. And if it was just 1 failing prematurely and you replaced only that one, you also see that same dynamic with car engines when a single component of it fails that's worth fixing.

[pas]

but it fails gracefully, right? (only one engine fails at a time)

it's like RAID, great until the RAID card itself fails

[aidenn0]

It's probably most like losing power in a single cylinder; the effects vary from engine to engine.

[kortex]

> Granted an RC engine runs on a mixture of fuel and nitromethane

That's a huge difference. The main limiting factor in engine power is mass air flow, not fuel. Engines are as much air pumps as they are containers for extracting expansion from explosions. Nitromethane provides extra oxidizer in liquid form, putting nitro engines in some ways closer to rocket engines in terms of power-to-weight ratio.

[cjbgkagh]

I've read about a lot of people complaining about the difficulty of getting the mixture right, perhaps that might be a show stopper for a UAV that must reliably work unattended for a long time. Though the military should also be able to get such mixtures down to a science - so I don't know.

[m463]

I'm not familiar with that engine, but I remember having little glow-plug engines and they didn't even have piston rings. (and were not efficient)

[bluGill]

Every motorcycle mechanic I've seen has a sign in the shop: speed costs money, how fast do you want to go. That sign isn't referring to the costs to modify an engine to go faster so much as the cost to constantly rebuild the engine after they modify it to go fast. I've seen two identical engines, one rebuilt to stock and one rebuilt to max speed - the cost for both rebuild jobs was about the same (the parts for speed were more - but not much more compared to the labor which was the same), but the engine rebuilt to stock ran for thousands more hours, while the one rebuilt for speed has the mechanic bragging that it lasted a whole 80 hours!

[sliken]

My dad used to say the perfect race car would explode into a million pieces just after it crossed the finish line. Anything more robust is wasted weight.

[0cf8612b2e1e]

What is done to modify an engine for speed? What kind of improvement can be seen for speed (accelerates XX faster? YY higher top speed)?

[sliken]

Normal cars are designed from wide temperature ranges (something like -30F to 130F), -100 to 14k feet altitude, with a wide range of sand, dirt, snow, ice, hail and a wide variety of roads surfaces and steepness. Generally they seem designed to last 100k miles under normal use and terrible things don't happen if you forget an oil change.

You can do a chip tune that might get you more HP across a wide range of RPMs, but you won't be as robust, will need maintenance more often, and will likely wear through oil, gas, differentials, clutches, and related more quickly.

There's MANY things you can do that all basically come down to burning more gas+o2 in less time. Higher intake airflow (turbo, supercharger, better/missing air filters, scoops, etc), bored out cylinders for more engine displacement, more gas (increased fuel pressure/pumps), increased RPMs, and decreased exhaust pressure (better pipes, decreased or missing cats).

Trick is, more gas+o2 burned = more heat, more wear, more stress, hotter oil, faster clutch wearing, faster tire wearing, and generally faster brake wearing. Turbos are driven by exhaust, spin at crazy RPMs, increase air intake pressure, and generally are harder on the engine and oil and make cooling more of an issue. Higher RPMs require more precise timing, better valves+springs, better balanced cam shafts, etc. So what might seem like a cheap/easy change like increasing turbo boost from 10psi to 15psi might like a good idea, but have major impact on engine life and maintenance costs. A single blown head gasket from the increased temp, increased vibration, and increased pressure can be very expensive.

Much like CPUs of today, cars are generally designed carefully for their performance level and there's less spare performance left to be easily tweaked. Much like how older CPUs could be overclocked for substantial performance gains. Now both cars and CPUs will throttle if they don't have enough cooling or any of numerous other sensors detect potential problems. It's pretty common these days to see a car with 300hp, but 350hp for up to 10 seconds before the sensors reel you back in.

[mcronce]

Simplifying things in this comment a fair amount, but...

Extracting more power is, most commonly, a matter of burning more fuel, which requires more oxygen. This increases combustion chamber pressure, which drives the piston down with more force; that force is converted to rotational torque and ultimately drives the wheels harder, pushing the vehicle forward faster.

More oxygen can be added in any number of ways; less restrictive intake/exhaust parts, larger valves, cams that are more optimized for whatever load/engine speed you want to produce peak power (or are more optimized for output than, say, economy or emissions), supercharger, turbocharger.

Adding fuel is more straightforward: A higher capacity pump and/or bigger injectors/carbs.

You can also switch to pistons that will compress the air/fuel charge more. This also increases combustion chamber pressure.

You can also run the engine at a higher speed, which will often warrant different cams, stronger valve springs, etc. May also require bottom end uprated components that can handle that task (connecting rods, pistons, bearings, crankshaft).

On the subject of bottom end components, depending on how much you increase cylinder pressure, you may need to upgrade those.

You can also increase output power by reducing losses - a lighter flywheel is a common example with enthusiasts.

Every single one of these involves a trade-off. A lighter flywheel impacts drivability; removing intake/exhaust restrictions and adding forced induction components will both make more noise; etc.

[madog]

Right. Generally more air and more fuel, produces bigger explosions and bigger forces, so the engine would output more power and torque.

These greater forces cause more stress to factory engine components, so generally at a certain level you will need to replace engine internals with uprated parts e.g. stronger rods and pistons.

[qup]

Bigger cylinders, forced air systems, lighter weights, etc.

[ww520]

The Camry engine has 4-6 cylinders for its size. A single cylinder is not much bigger than a basket ball.