Question for Scuffers re transmission losses

[Exige77]

Many people quote transmission losses as a % but should it not be a number ?

If You attach a 200 BHP or a 400 BHP engine to the same gearbox would the transmission loss not be the same. If you use a number (say 30 BHP)it seems correct. If you use a % then double the BHP has been lost by the transmission.

Can you clarify ?

Thanks

Ex77

[Scuffers]

Exige77 said:

Many people quote transmission losses as a % but should it not be a number ?

If You attach a 200 BHP or a 400 BHP engine to the same gearbox would the transmission loss not be the same. If you use a number (say 30 BHP)it seems correct. If you use a % then double the BHP has been lost by the transmission.

Can you clarify ?

Thanks

Ex77

not that simple....

transmission looses though a gearbox are a combination of things, for example, if it was 30Hp then no way could you turn a gearbox by hand!

if you think about it, the looses are:

1) bearing drag - this will vary depending on load applied to the bearings (including the non-selected gears)
2) oil drag - this is relatively constant (in terms of torque drag), assuming oil temps are stable, clearly if the oil is stone cold, it will be higher.
3) Gear friction - once again this is load dependant, higher the torque loads, the higher the friction.

then there are a few other minor ones, like seal drag etc.

now, there are such things as transmission rigs that can measure all this stuff, but as you can imagine, not many places have them, very much a development tool.



Now, assuming your trying to quantify figured from hub-dyno's, then all you have to go on is collated data from said gearbox, that said, most transverse box'es are really not that bad (compared to gearbox/prop/differential setups), typically, 8-12%.

to some extent, the higher the torque, the lower the % loss, but without hard test data, it's guesswork.

Also, before you jump off and start calculating XYZ, consider that all hub-dyno's don't read the same (although there's less excuse as to why!)

[Exige77]

Thanks Simon, I suppose what I am really asking is if you start with a Genuine 200 BHP (at the Fly)engine which reads 170 BHP at the hubs and you add a genuine 200 BHP giving 400 BHP total and you put it on the same Hub dyno agian what will it show ?

If the loses are a fixed BHP like 30 then will the Hub dyno show 370 BHP.


Many peopel quote a % figure like 15%. This would mean the Hub dyno would then show 340.

I don't think this is correct.

Was look for some guidance.

Thanks

Ex77

[Scuffers]

Exige77 said:

Thanks Simon, I suppose what I am really asking is if you start with a Genuine 200 BHP (at the Fly)engine which reads 170 BHP at the hubs and you add a genuine 200 BHP giving 400 BHP total and you put it on the same Hub dyno agian what will it show ?

If the loses are a fixed BHP like 30 then will the Hub dyno show 370 BHP.


Many peopel quote a % figure like 15%. This would mean the Hub dyno would then show 340.

I don't think this is correct.

Was look for some guidance.

Thanks

Ex77

well, 15% is way high for a transverse box, if your looking at a C64 box, they seem to be more like ~10%.

typically, std 2ZZ's make ~170 (metric hp) at the hubs, so if you assume that they are 192 flywheel (actually somewhat of an assumption) then that's 12.9%, however, realistically, they are nearer 185-190, at which point, 10% is more like it.

[sdd]

Of the half dozen or so 2ZZ's that we put on the same hub dyno last year we had figures that ranged from 168 - 176 at the hubs, these were all engines that were 'standard' i.e. we built them but used totally stock internals with the exception of better oil pump and sump. Suggest this backs up Simons view that the C64 has relatively low transmission losses. We also use an endurance spec competition gear oil to prolong the life of the gearbox which will perhaps have a slight effect to increase losses.

Stephen

www.track-club.com
[e-mail]

[saaby93]

Interesting thread this. Are there any other published figures for transmission losses eg RWD vs FWD and gearbox types Rover vs Honda vs Toyota?

[icepop]

Morning everyone, and a happy new year to you all.

Had similar thoughts to the original poster, but unfortunately nobody seems to have answered the question.

So, in general, if there is a hypothetical power loss of 20bhp, through a transmission, and that reduces a 200bhp output figure to 180bhp, does a 400bhp output reduce by 20x2, (40bhp), or is it reduced no further than the original 20bhp and therefore give 380bhp.

[Scuffers]

icepop said:

Morning everyone, and a happy new year to you all.

Had similar thoughts to the original poster, but unfortunately nobody seems to have answered the question.

So, in general, if there is a hypothetical power loss of 20bhp, through a transmission, and that reduces a 200bhp output figure to 180bhp, does a 400bhp output reduce by 20x2, (40bhp), or is it reduced no further than the original 20bhp and therefore give 380bhp.

short answer, probably not, but in the absence of any hard data, it's all we have to go on.

long answer, it's not as simple as that!

in some box's, the losses (as a %) will drop with load (torque), others will increase, just depends on the box.

to a point, if you plot a graph of torque vs. losses (as %), it will not be a straight line, it will initially be quite high, then slowly drop until the point where the box starts to deform with load, then the line will start to rise again.

(the actual losses in hp terms will always be rising).

Ideally, you need to dyno out a gearbox to establish this kind of thing.