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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 abou

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 3y ago
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 3y ago
  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.
  - syrrim 3y ago
    If you had 18 such engines it would get you precisely 18x the performance, at precisely 18x the weight.
    - aidenn0 3y ago
      And precisely 1/18 the MTBF
      - pas 3y ago
        but it fails gracefully, right? (only one engine fails at a time) it's like RAID, great until the RAID card itself fails
        aidenn0 3y ago
        It's probably most like losing power in a single cylinder; the effects vary from engine to engine.
        jacquesm 3y ago
        They tend to seize and when they do and you gang them they'll likely break stuff in the other ones unless you add a freewheel or some other luxury like that.
      - 93po 3y ago
        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.
    - Retric 3y ago
      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.
      - deleted 3y ago
        [deleted]
    - seabird 3y ago
      That's why there's all sorts of widely produced performance vehicles with multiple independent engines!
  - 93po 3y ago
    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 3y ago
      That engine is 4x heavier and supercharged. You're not comparing apples to apples.
      - 93po 3y ago
        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?
- cjbgkagh 3y ago
  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.
- kortex 3y ago
  > 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.
- m463 3y ago
  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)
ww520 3y ago
The Camry engine has 4-6 cylinders for its size. A single cylinder is not much bigger than a basket ball.
bluGill 3y ago
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!
- 0cf8612b2e1e 3y ago
  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)?
  - mcronce 3y ago
    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.

93po 3y ago

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 3y ago
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.
- syrrim 3y ago
  If you had 18 such engines it would get you precisely 18x the performance, at precisely 18x the weight.
  - aidenn0 3y ago
    And precisely 1/18 the MTBF
    - pas 3y ago
      but it fails gracefully, right? (only one engine fails at a time) it's like RAID, great until the RAID card itself fails
      - aidenn0 3y ago
        It's probably most like losing power in a single cylinder; the effects vary from engine to engine.
        jacquesm 3y ago
        They tend to seize and when they do and you gang them they'll likely break stuff in the other ones unless you add a freewheel or some other luxury like that.
    - 93po 3y ago
      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.
  - Retric 3y ago
    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.
    - deleted 3y ago
      [deleted]
  - seabird 3y ago
    That's why there's all sorts of widely produced performance vehicles with multiple independent engines!
- 93po 3y ago
  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 3y ago
    That engine is 4x heavier and supercharged. You're not comparing apples to apples.
    - 93po 3y ago
      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?
cjbgkagh 3y ago
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.
kortex 3y ago
> 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.
m463 3y ago
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)

ww520 3y ago

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

bluGill 3y ago

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!

0cf8612b2e1e 3y ago
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)?
- mcronce 3y ago
  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.