DYNO QUESTION

[Mr Revhead]

BTW do you really believe that a 500hp engine will lose 100hp through transmission losses? If so then where does all that lost energy go?

exactly.

if you have a stock engine then mega work it, and use the same gearbox... its not magiclly gunna suck more power is it.

imo each car will have different losses, some really good boxes may only use say 20hp to turn and 3000rpm. others may use 50. so as fivebob has stated the only TRUE way to tell, is measure both with the same equipment.

(figures above were plucked from thin air)

[ROBODISCO_20v]

[
BTW since when was 15%=17%, or 17%=20% or even 22%=25%, they're all different by a large margin, but if that's your idea of accurate then I hope you don't set you torque wrench with the same tolerances, or you will be spending a lot of money on helicoils.

2%-3% is a huge difference is it
I think you need to get that heli coil out of you arse coz it's affecting your brain

[fivebob]

2%-3% is a huge difference is it

Yes it is,in this case more than a 10% error, just like .0005" is a huge difference when it comes to bore clearances. I suppose you wouldn't think such a tiny amount would affect anything either

I think you need to get that heli coil out of you arse coz it's affecting your brain

Ahhh so that's my problem, and here's me thinking it was a haemorrhoid

[jondee86]

Well...... um...... yeah. The efficiency of a gearset is obtained by
comparing the power in with the power out, and expressing the result
as a percentage or efficiency. For helical gears the accepted figure is
typically 98% for each pair of gears in the gear train.

So if you are in a gear that has two pairs of gears in mesh, and you
stick 100 kW up the box, about 4 kW will go to transmission losses.
Double the input to 200 kW on the same box, and you will lose 8 kW.

As a matter of interest, having a car that can put down 500kW at the
wheels doesn't mean you are in any danger of melting your gearbox.
Not unless you can find a way of running it at full power continuously.
Such a car would accelerate from zero to loss of licence in less than
5 seconds, and reach warp speed in 10. So most of the time it will be
be making 50 kW or less, just running round town at legal speeds.

The only cars that come close to running balls out continuously are
the ones that race on the high speed ovals in the USA. And you can
bet your pocket money they run engine, trans and diff oil coolers

Cheers..... jondee86

[RedMist]

Well...... um...... yeah. The efficiency of a gearset is obtained by
comparing the power in with the power out, and expressing the result
as a percentage or efficiency. For helical gears the accepted figure is
typically 98% for each pair of gears in the gear train.

So if you are in a gear that has two pairs of gears in mesh, and you
stick 100 kW up the box, about 4 kW will go to transmission losses.
Double the input to 200 kW on the same box, and you will lose 8 kW.

Cheers..... jondee86

I know its easy to pick on others theroys, however you are well off track here. 98% for each pair of gears in the train.... okay in a six speed gearbox there are 6 pairs of gears in mesh, (NOT TWO!!) in the train so I loose 12% of my power to the box alone? Plus whatever I loose in the diff, cv's, bearing friction? And where does that power go? As energy cannot be distroyed, it must be turned to heat and sound... as the gearbox doesnt create that much sound we can surmise that a majority of that energy must be turned to heat. As such a 12% loss to our 6 speed tranny with a 200kw engine results in a 24kw heater as the transmission and any subsequent cooling device attached to the tranny.... mmmmmmm.... Thats one shyte load of heat.... I know I'll reduce it dramatically by having only 4 gears... thats still 16kw..... nope... thats still enough to crispy critter my nads in milliseconds.

See how the maths doesnt work? As, in reailty, I rest my nads on my gearbox after a heafty race session and only have a mild toasting. Probably 1 kw heat, which in race conditions we could expect a max of 2kw.... out of 130kw engine.... 1 + 1 <> 32.9

[Adamal]

There you have it ladies and gentlemen, you've heard of the "butt dyno", now we bring you the "Nads Heat Test!"

Love your work, RedMist

Very good info to know though.

[RedMist]

A Gartner poll recently surveyed 100 people and 92% believed the the "Nads Tranny test" (I think it needs a rename) to be more sensitive than the "Butt Dyno"

[jondee86]

OK.... you may have six pairs of gears inside the box, but only two
pairs will be transmitting power to the wheels and generating heat.
Gears in mesh but not carrying any load can pretty much be disregarded
in this context (as mentioned in a previous post).

Heat from friction does not get stored up inside the box like a pizza in
a hotpack. Due to the difference in temp from inside to outside, there is
a continuous flow of heat energy being transferred from the surfaces of
the box to the air. The higher the airflow, the greater the heat transfer,
and the lower the temp of the box.

Try running your car on the dyno for an hour and then get your nads in
there.... Would you like fries with that sir ??

Cheers..... jondee86

[RedMist]

You seriously need to study how a gearbox works. Unless you have access to testing F1 technology only one gear pair is engaged at any one point in time.
Your synopsis in regards to thermodynaics, although very rudimentary is somewhat correct. There is heat transfer to other contact surfaces (not only air) which will reduce the heat energy in the box. But your scale is well off. If I double my HP and run it through the same mechanical solution (IE the same box) do I double the friction of the box? What about quadrouple?

But no matter how you manipulate your original calculations it still doesnt anywhere near match reality.

[jondee86]

Take a look inside a typical front engine RWD gearbox, one with the
input and output shafts inline. Then explain to me how 3rd gear works
with only one pair of gears engaged

Granted, there are some fixed and some variable losses involved in
gear transmissions, so the efficiency will tend to drop off a little when
the box is operating at less than rated power.

I don't have any reference data on what happens to the efficiency
when a box is operated at twice it's rated power. I'd guess that it would
probably drop, as the tooth loading would most likely exceed the ability
of the lube to keep a film between the sliding surfaces, and metal to
metal contact would occur.

What I can say with some certainty, is that if you take a box rated
for 100 kW input @ 96% efficiency and feed it 100kW, it will reject 4 kW
primarily in the form of heat. Take a second box rated for 200 kW input
@ 96% efficiency, feed it 200 kW and it will reject 8 kW. Input speed,
ambient temp and other conditions being equal.

Operation above and below the rated conditions, with cyclic loads and
widely varying speeds and temperatures, will affect the efficiency and
the amount of heat rejected. How much affect is pure speculation.

Cheers..... jondee86

[barryogen]

OK.... you may have six pairs of gears inside the box, but only two
pairs will be transmitting power to the wheels and generating heat.
Gears in mesh but not carrying any load can pretty much be disregarded
in this context (as mentioned in a previous post).

only disregarded with regards to heat production, they will however help to dissipate the heat to the surrounding area(gearbox) and anything attached to it.

Try running your car on the dyno for an hour and then get your nads in
there.... Would you like fries with that sir ??

heh, just drop them in the oil... deep fried mountain oysters... well, kinda.