14 replies to this topic

[Joe555]

I have a power loss 17.7 hp from the engine to the wheels, I am sure thats more than average. I will re-check the front wheel alignment, but I am sure it is correct.
Would the gearing affect it, I have an economy input gear and 3.1 FD.

[sonikk4]

Whats your power at the flywheel to give us an idea of the engine output.

[JustSteve]

power at the wheels and fly?

That sounds about right for a high powered motor with a standard 'box

[jaydee]

Pump up the tyres?

[Pigeonto]

20 hp on mine

[tiger99]

How are you guys measuring the power loss? Have you measured the engine on an engine dyno and the gearbox/drive train output on a rolling road?

Dynos, even the better ones, are notoriously inaccurate and by measuring the basic engine on one and the whole drivetrain on another the results are not going to be very reliable. When tuning on a rolling road, you are using one dyno, so all the measurements will be correct relative to each other, but not absolutely.

And, how do you get the engine on its own to produce exactly the same power on an engine dyno as it does in the car? Think about what might be different, such as the exhaust, alternator, fan.....

If you are not relying on the engine having been measured while detatched from the transmission, please explain how you know the power loss, as I am rather intrigued as to how else the measurement could be performed.

Oh, and 20 bhp is about 15kW, and I can't see how the transmission could dissipate that amount of heat without something melting. I am very interested in knowing what the losses actually are. I am even more interested in how much power is lost in the idler gear alone.

Edited by tiger99, 16 August 2012 - 07:35 PM.

[Dan]

Rolling roads claim they can measure the power losses through the drive train while the dyno is in over-run after a power run so both figures usually come from the same machine at the same session. Probably not all that accurate, but since its from the same machine its just as accurate as the power figure. BHP isn't a real unit anyhow as you know so provided that it's measured in a sensible way it's as useful as any other figure.

[bmcecosse]

Sounds about right to me...... Mini transmission is notoriously inefficient...

[Pigeonto]

Tiger, I asked exactly that when mine was done and the response was just as Dan says.I did start to wonder tho.... did he say 20 to make me feel better so that adding it back on to the ATW figure raises the ATF'wheel figure !!

[tiger99]

Dan,

Thanks for that. I should have guessed that they would estimate it that way. I suppose that with clutch disengaged it is more or less measuring transmission loss. Clutch engaged, you would get transmission loss plus engine internal friction and pumping losses, plus water pump, fan and alternator, and that I could believe might be 20 bhp total. But these figures still seem too high, considering how much trouble I would have to go to to get rid of 15kW of heat. There are not many cooling fins on the transmission, which makes me think that the oil would overheat fairly quickly if run at that kind of power loss for long. A small radiator such as an oil cooler can't shift that much heat either.

I guess it would be very bad to run a decent tuned Mini flat out for hours at a time. I did that regularly with standard 998s, without ill effect, maybe 7 hours flat out on the motorway, but due to less torque and speed I would have been expecting maybe only 4 or 5 bhp.

All of this is very interesting to me because I do occasionally cruise on the autobahns, and am hoping to have another Mini within the next year, so I will need to know what sort of extra cooling it may require. It would be really nice to be able to reduce the losses, but building a new, super-efficient gearbox is not a DIY job, if indeed possible.

I would like to turn the engine around, like the original prototypes, and get rid of the idler gear to reduce losses, but that is a very complex task involving a great deal of accurate machining. Nowadays, there are ways of having the carburettor at the front without icing problems, the alleged reason for reversing the engine, although the real reason is that the inertia of two large gears instead of three smaller ones would have caused problems with the syncromesh. I have wanted to do that ever since my first Mini in 1968, but I doubt that it will happen now. Fitting a "foreign" powerplant, especially a turbodiesel, would be a better use of time, I think.

bmcecosse,

Yes I agree is is not wonderfully efficient, and not just because of the idler gear.

Pigeonto,

Yes, figures can be manipulated to mean a lot of things, but if you have that much loss, it seems to follow that you have quite a lot of power available, which is no doubt what you want.

Edited by tiger99, 16 August 2012 - 08:43 PM.

[bmcecosse]

They could have used a chain - or a belt........

[tiger99]

Yes. I have recently been looking for suitable chains, but the various manufacturers web sites don't give the kind of information that is needed. You probably have to talk to them, and likely end up paying a small fortune for a prototype, rather than just ordering a standard part. But there is still development potential in the Mini, even after 53 years, so I would not be surprised if a chain conversion did come eventually.

[cooperrodeo]

Slarks measured 13bhp on mine

[jaydee]

I was reading about that some time ago and probably someone already tryed that IIRC
Saab also used chain transmission in production cars.
Back to the OP question, when the RR reads 18bhp transmission lost i'd check tyres pressure first.

[Joe555]

Thanks for all the replies, it will take me a wile to absorb them. I just didn't want to wase power; it was a case of one thing leading to another. First I was getting a loud noise from the car on the motorway so I thought I could try a new exhaust system. I went on the Maniflow web site and there is a graph on there, so just for curiosity I compared it to mine (I know you can't compare, but there you go "I was bored"). My car is nothing special, (1275 Metro engine). The Maniflow one was 79.7 engine, 66.2 wheels; loss 13.4 mine was 75.2 engine, 57.5 wheels, loss 17.7 . It had been mentioned to me on a later RR session that I had more than normal losses. Maybe it's all OK but if I can get a bit moor power or save some fuel I might as well.