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I am not sure if it is my mind playing tricks on me or not, but I feel that the power output of my 3.0 diesel (190 odd bhp) is lacking quite a bit recently and it can only just keep up with a VAG 130PD (which I know is a great unit). Can I check whether this is the case or not? Can the dealer plug in a computer and see what's going on or do I have to go to a specialist?
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You can take your car to a dealer and they can plug in their diagnostic kit to see if every thing checks out, which is always a good start. You don't mention whether your car is still under warranty which determines how you approach the problem. As for measuring the power output the race/rally guys and gals use a rolling road specialist which is a bit over the top when a much cheaper diagnostic check could find if there is a problem.
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I dont think going to a rolling road is necessarily over the top. Ring up a couple and see how much they charge for a power run, rather than a full set-up, it shouldnt cost much. Ignor any guestimated flywheel calculations, and get a power figure at the wheels. 3ltr is that rwd bmw? Anyway for fwd divide by 0.85, & for rwd by about 0.825. In doing this you will find out roughly how much power your engine really is making, and also give you some amo when you approach the dealer.
Ben
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Many thanks for your answers. Car is a rwd bmw and is still under warranty. Therefore, along with sorting out my lights (previous thread) and a few other bits and bobs, I suppose that they should check it with their diagnostic machine.
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CM,
I would say that you are taking the best course. Even though the dealer won't be able to check the actual engine output, an engine diagnostic check should show up anything that might lead to a loss of power.
I suppose allowance has been made for the probability that cars fitted with the VAG 130PD engine are lighter and may have lower gearing?
The constants (0.85 and 0.825) given by Ben for rolling road testing presumably apply to cars with manual transmission. I wonder if they also apply to cars with automatic transmission as fitted to possibly the majority of BMW 5-Series?
Incidentally, I understand that the 530D loses much of its economy advantage as an automatic (though it does drive beautifully). If CM's is an automatic there will also be a power loss of course.
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No - car is a manual.
I know that the Passat is slightly lighter but the power:weight is also quite a lot less. I need a service shortly so will find out.
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Why do you say the dealer won't be able to measure actual engine output? Do you know that for certain? VAG can use a diagnostic computer to measure approximate power output without a rolling road, so maybe BMW can?
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Edgar,
It's possible for the output that SHOULD be seen at the flywheel to be computed from a formula that includes, say, the cylinder pressures that are developed at certain engine speeds and the resistance to rotation of the crankshaft (engine not running).
However I can't see any way of measuring the ACTUAL flywheel output without removing the engine and connecting it to a dynamometer in a test rig.
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Dizzy,
You're right. The computed value shows a guesstimate value of what SHOULD be seen at the flywheel. That may be enough for the purposes of finding out if anything is wrong with the CM's Beemer, compared to another Beemer. If he does a dyno test of his car for £50 quid, the dealer could say "they're all like that sir". But if he gets the dealer to test another car, under the same conditions, as well, using the computed (but free) value, then he'll have a case to argue.
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How does knowing the cylinder pressues of an engine which isnt running tell you how much air is being drawn into the combustion chambers?
Agreed the only real way to know the power output of an engineis to connect it to an engine dyno. However, if an engine that has been on a proper dyno is installed in a car, then run on a rolling road, a good estimate of the power lost through the transmission can be made. This informatin can then be applied to other similar vehicles.
Ben
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Ben,
I did mean that the cylinder pressures would have to be taken whilst the engine is running. It would be only the resistance to rotation that would be measured with the engine switched off.
Measuring the effort required to turn the crankshaft would give an approximation of the frictional losses in the bearings and piston rings, etc. It would also, of course, be affected by the compression of the air in the cylinders unless the injectors were removed.
My examples were exactly that - just imaginary examples - and I've no idea what, or how, the BMW diagnostic equipment would actually measure. My Perkins engine test colleagues could get useful engine diagnosis data from things as odd as measuring the current flowing through the starter cables via clamps applied over the top of the cable insulation. All a black art to me!
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Yeah sorry my message didnt read well- i wasnt knocking you, just intersted in how it all works etc.
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Yeah i should of mentioned the figures i gave are to be used to make appoximations for manual cars.
Automatics of course have higher transmission losses. These can be limited if the car has a lock down feature. On my mums 850 T5 automatic, i locked the transmission into "L" and it behaved more like a manual on the rollers and recorded a figure of 199bhp@wheels which i thought reasonable for a car with a claimed flywheel output of 225bhp. I would imagine RWD auto could 20% or possibly more through transmission losses.
Ben
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Just had a thought have you tried changing where you buy your diesel?
There are all sorts of scams going on regarding evading excise duty on diesel. Some them may result in alduterating the diesel. If my unreliable memory serves me right there is diesel and "Diesel". Just wondering if some of the poorer quality stuff has got into the supply chain.
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I thought that it could be a bad tank but would not have thought that Esso would have duff tanks - or am i being naive? Always in the past have had good fuel from this station (at East India Dock, London) as well as being one of the cheapest.
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The guys at the rolling road will be able to advise the likely output at the wheels for your car.
Car and Car Conversions magazine has a rolling road directory in the back of the mag. Alternatively look under 'engine tuning' in your yellow pages.
Of course, you'll have to pay for a road session (around £50 I expect), but you should be able to get the dealer to do the diagnostic bit under warranty, so try this first.
Let us know what you find.
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I remember many years ago in the US, I think it was "Hot Rod" magazine who took a production 7 litre(400+cu. in.)that was supposed to give 400 plus hp on an engine dyno and at first got 185;considerable tweaking only got it up to 260.Ford last year had to revise the Mustang engine considerably to get near the quoted power.In Japan,the manufacturers always quote high because they know no-one believes them.
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I have to disagree with your comment about Japanese engine the mitsubishi evolution and suburu are both rated at 380 bhp in Japan although the manufacturers know they do produce more power. I was also under the believe that manurfacturers in this country had to give an accurate assesmant of engien power and so as to ensure that all engines are capale of this figure they derate the figures allowing some "better" engine to develop more power than the book claims.
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mitsubishi evolution and suburu are both rated at 380 bhp in Japan
Are you sure of your facts as I am fairly sure that it is illegal to sell a car that has more than 280 or 286bhp in Japan. That it why they only quote 280bhp. (maybe a typing mistake on your part)
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Japanese cars are power limited to 208kw (I think), grey imports from Japan have to be delimited if they are to realise the potential max power form a given engine. The Subaru WRX can deliver way over the 208kw but this is all a Japanese car will give and all that will be quoted for the power (for the japanese car).
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Engine performance in EU is homologated.ie.the test engine is checked on the test-bed by a certifying authority(TUV,DTP,TNO,UTAC) etc. and must be close to claimed performance.Under ISO,production engines must also be close to the quoted figure.Japanese engines sold in the EU must go thro' this process;Japanese engines sold in Japan do not and they always quote "high" numbers.
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I should also have pointed out that the engine will not be homologated if it produces too much power;the limits are something like +/-2% power and +/-4% torque;remember many countries use the engine power for tax/insurance purposes.
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