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engine files - crank or rear wheel horsepower

Started by h106frp, December 11, 2015, 09:45:01 AM

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h106frp

I just want to confirm, but i am assuming the engine files are for crank horsepower not rear wheel.

Thanks

HornetMaX

Correct as far as I know (there's a transmission efficiency coefficient that gives you the wheel power from the crankshaft power).

C21

Correct.
crankshaft power -> -2% -> clutch power -> -5% to8% -> rear wheel power
Thats why the efficiency is set to 0.92  ;)
# Member of the CAWS Racing Team #


Hawk

Is the efficiency at the crankshaft for 2 stroke engines slightly better than a 4 stroke? I only ask because I'd have thought with less moving parts(and therefore less inertia/friction drag) the 2 stroke would come out as slightly more efficient on the crankshaft power output?

Hawk.

HornetMaX

Short answer: no.

Relatively longer answer: the efficiency only models the power loss between the crankshaft and the rear wheel, so that's due to the transmission (clutch, gearbox, chain) so I see no particular difference between 2 and 4 strokes. Extra parts in 4 strokes (wrt 2 strokes) have side effects like additional rotating inertia, smaller specific power etc.

Power at crankshaft already includes the power that is lost to operate other engine components (valves, pumps etc).

Hawk

Quote from: HornetMaX on December 11, 2015, 01:58:27 PM
Short answer: no.

Relatively longer answer: the efficiency only models the power loss between the crankshaft and the rear wheel, so that's due to the transmission (clutch, gearbox, chain) so I see no particular difference between 2 and 4 strokes. Extra parts in 4 strokes (wrt 2 strokes) have side effects like additional rotating inertia, smaller specific power etc.

Power at crankshaft already includes the power that is lost to operate other engine components (valves, pumps etc) .

That is exactly why I would've thought that the power output at the crankshaft would've been slightly different between the 4 stroke and 2 stroke engines - simply because the power at the crankshaft already includes the "power that is lost to operate other engine components (valves, pumps etc) ", being said that the 4 stroke has obviously a lot more engine components the power can be dissipated through?

Therefore in my thinking, because there are more engine components in a 4 stroke than a two stroke then surely it must follow that the power output at the 2 stroke crankshaft must be more for a given capacity than a 4 stroke? Or am I totally misunderstanding the term "power output at the crankshaft" and the way it's calculated?  :-\

Hypothetical example of my thinking due to more components in a 4 stroke engine:

4 stroke power-loss at crankshaft = 2%

2 stroke power-loss at crankshaft = 1.5%

Hawk.

HornetMaX

Quote from: Hawk on December 11, 2015, 03:54:27 PM
That is exactly why I would've thought that the power output at the crankshaft would've been slightly different between the 4 stroke and 2 stroke engines
The output at the crankshaft is different (in our GPB case) if the .engn files are different, no matter of 2 or 4 strokes (or whatever else). All is included in them (in terms of output power).

Quote from: Hawk on December 11, 2015, 03:54:27 PM
Therefore in my thinking, because there are more engine components in a 4 stroke than a two stroke then surely it must follow that the power output at the 2 stroke crankshaft must be more for a given capacity than a 4 stroke? Or am I totally misunderstanding the term "power output at the crankshaft" and the way it's calculated?  :-\
It's not calculated, it's measured on a bench most of the time. And what you measure is the engine output, with all it's component (but no clutch and gearbox).
Asking how much power a 4 strokes loses due to it's "extra" components is not very relevant as without the "extra" components, it wouldn't work.

Quote from: Hawk on December 11, 2015, 03:54:27 PM
Hypothetical example of my thinking due to more components in a 4 stroke engine:

4 stroke power-loss at crankshaft = 2%

2 stroke power-loss at crankshaft = 1.5%
There's no such a thing as a "power loss at crankshaft", at least not in practice.
The power loss (efficiency factor in GPB) is for the transmission.

Hawk

Quote from: HornetMaX on December 11, 2015, 04:14:26 PM
Quote from: Hawk on December 11, 2015, 03:54:27 PM
That is exactly why I would've thought that the power output at the crankshaft would've been slightly different between the 4 stroke and 2 stroke engines
The output at the crankshaft is different (in our GPB case) if the .engn files are different, no matter of 2 or 4 strokes (or whatever else). All is included in them (in terms of output power).

Quote from: Hawk on December 11, 2015, 03:54:27 PM
Therefore in my thinking, because there are more engine components in a 4 stroke than a two stroke then surely it must follow that the power output at the 2 stroke crankshaft must be more for a given capacity than a 4 stroke? Or am I totally misunderstanding the term "power output at the crankshaft" and the way it's calculated?  :-\
It's not calculated, it's measured on a bench most of the time. And what you measure is the engine output, with all it's component (but no clutch and gearbox).
Asking how much power a 4 strokes loses due to it's "extra" components is not very relevant as without the "extra" components, it wouldn't work.

Quote from: Hawk on December 11, 2015, 03:54:27 PM
Hypothetical example of my thinking due to more components in a 4 stroke engine:

4 stroke power-loss at crankshaft = 2%

2 stroke power-loss at crankshaft = 1.5%
There's no such a thing as a "power loss at crankshaft", at least not in practice.
The power loss (efficiency factor in GPB) is for the transmission.

Highlighted in your first paragraph is what I was thinking(I think. Lol) So that's good to know.  :)

Thanks for explaining Max.  ;) 8)

Hawk.

Vini



Vini

i thought we were talking about transmission losses, no?

HornetMaX

Ah OK, I thought there was something else in frits' post.