An Engine's Power Output

I have never had as much fun in a big car as a small one. The ability to throw small cars around corners with the energetic lightness and ease of use. I find little justification in the use of larger cars either in there utility or there styling, I used to own a plain jane Diahatsu Charade G10 5 door, which is by anyones standards a small car, yet I was able to fit a kitchen table and chairs in the back with the seats down, acheived 52 MPG (open road and 48 around town) and due to it;s high torque 3 cyl NA engine still suprise people at the lights, and still had some entertaining company space as well :oops:
By todays standards the P6 is becoming a small car which is a shame......21st century progress?

Graeme
 
If, last year, you would have predicted that this year I would be driving a 1.2 engined car, I would have slapped your silly head! :LOL: But, on my drive is a Skoda Roomster 1.2 tsi 105 dsg. Driving around France in Sept and driving to all maximum speed limits I averaged 49.8 mpg. On returning to GB and encountering the madness that is the English motorways on a Saturday afternoon I averaged 43.9 back to Lancaster from Portsmouth. This was probably due to my wanting to get home and the madness that is the outside lane in GB. The car is responsive, quiet, and free revving. Mated to a 7speed DSG transmission it is also economical. I have driven 5k miles from new and not used a drop of oil. I consider this low capacity turbo petrol dsg trans the current best option for performance and economy. The Roomster is sadly a pig with lipstick to look at but very functional, and it can startle people off the lights. (but heaven help the owner of it when something goes wrong out of warranty!)
 
Tom W said:
I'm afraid you're way off the mark Richard
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At the same time, your Jag is thirteen years old. Since that time, Eaton have grown by a significant amount and have developed their superchargers to a significant extent, such that their efficiency is vastly improved over what once was. These days they add over 120bhp to Jag's 5.0 litre V8 (380hp/ft lbs plays 503hp/461ft lbs) - and the supercharged engine has a lot more to come from it. A stock XFR with a big wing nailed to the boot lid and tweaks to the blower was recently pushing 650bhp and set a new saloon speed record of 226mph at Bonneville. That's, what, a couple of years back - I think the record was recently taken by Dickie Meaden of EVO magazine in a highly tuned Skoda Octavia, but only by a small margin. So it would seem that the latest blowers are capable of producing quite a lot of power and torque! Add in my idea of driving them from a small electric motor rather than the engine (especially if that's driven by regenerative braking) and it ought to 'blow' today's variable-geometry twin-scroll turbochargers away for efficiency.
 
John said:
On my drive is a Skoda Roomster 1.2 tsi 105 dsg. The car is responsive, quiet, and free revving. Mated to a 7speed DSG transmission it is also economical. I consider this low capacity turbo petrol dsg trans the current best option for performance and economy. The Roomster is sadly a pig with lipstick to look at but very functional, and it can startle people off the lights. (but heaven help the owner of it when something goes wrong out of warranty!)
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I love the Roomster's looks - partly because it dares to be different. However, what on EARTH were you thinking getting the DSG box? Have you heard nothing of how troublesome those are? You'd have been far better off with a manual...
 
my guess would be a warranty! I know a few people who own them, none of whom have had problems but all say they wouldnt buy one if it didnt have a warranty...

Rich.
 
IAmTheResurrection said:
Tom W said:
I'm afraid you're way off the mark Richard
Click to expand...

At the same time, your Jag is thirteen years old. Since that time, Eaton have grown by a significant amount and have developed their superchargers to a significant extent, such that their efficiency is vastly improved over what once was. These days they add over 120bhp to Jag's 5.0 litre V8 (380hp/ft lbs plays 503hp/461ft lbs) - and the supercharged engine has a lot more to come from it. A stock XFR with a big wing nailed to the boot lid and tweaks to the blower was recently pushing 650bhp and set a new saloon speed record of 226mph at Bonneville. That's, what, a couple of years back - I think the record was recently taken by Dickie Meaden of EVO magazine in a highly tuned Skoda Octavia, but only by a small margin. So it would seem that the latest blowers are capable of producing quite a lot of power and torque! Add in my idea of driving them from a small electric motor rather than the engine (especially if that's driven by regenerative braking) and it ought to 'blow' today's variable-geometry twin-scroll turbochargers away for efficiency.
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The latest range of Jags also have a whole raft of other raft of developments to improve efficiency, which mine doesn't have. Direct injection, variable intake geometry and as you say, a more efficient supercharger. Of course things move on.

You won't be able to drive a supercharger from a small electric motor. They can easily take 100+bhp to drive. So you now need a big motor, which is quite heavy. And a big alternator to power it when you don't have any regenerative braking power left, and some batteries to store the energy in when you do. Sounds heavy and over complex to me.

Anyway, your original comment was that superchargers are good for efficiency and economy, and now you've shifted to power and torque. There's no doubt that superchargers generate a lot of power and torque, go and look at any top fuel dragster, tractor pull engine, WW2 aero engine etc. Their benefits there are not a new thing. Go and drive a Supercharged Jag and you'll see what the're all about, but believe me it's not economy.
 
also as you note the electric super chatrger require a whale of power to run and they are definatly NOT a small electric motor, the ones that have been touted about in the media are not producing real power, there is no such thing as a free lunch, those watts come from somewhere.

Graeme
 
Catching up here after a day away. A splendid debate!

First off a supercharger as the sole forced induction method is really pretty unacceptable these days. The reason is quite simply that it breaks the something for nothing rule. The turbocharger works by liberating energy from the exhaust. The supercharger consumes energy in losses that have to be provided by the engine. So there have to be some pretty compelling reasons to use a supercharger. These could be to mask some other deficiency in the engine. But since we have been talking super efficient engines, that's unlikely nowadays. So my assessment would be that they are the lazy man's way to big horse power and have no place near an engine with efficiency pretensions.

IATR and others mention several times that the back pressure generated by a turbo is a serious problem in the engine design. I'm afrais I beg to differ. All engines have some degree of exhaust back pressure to cope with - otherwise the exhaust gasses wouldn't flow down the exhaust system from a high pressure area to a lower pressure one! A higher back pressure is inherent in a turbo installation since energy is being liberated from the exhaust gas and the thermodynamic equation "pressure X volume / temperature = constant" needs to be satisfied.

In a naturally aspirated engine back pressure is a killer. However this is not necessarily an issue for the remainder of the engine design for a pressure charged engine. That's because it is possible to tweak the valve events so that the incoming high pressure air is used to purge the cylinder of remaining exhaust gas. So there is more than normal valve overlap - the inlet valve opens before TDC and the exhaust closes after. Since the piston is moving slowly at around the top of the stroke this is very effective. Clearly it is a disaster in a petrol engine where the fuelling is carried out outside the cylinder - the charge air that will be going to waste carries fuel as well. But for a direct injection petrol and for diesels, the purging part of the cylcle comes free (except that you lose some of the energy recently gained by the turbo from the exhaust). And when the engine finally gets to fire it is carrying a fully uncontaminated load of fresh air and fuel. So power is up! I suspect that this is how these very small capacity petrol turbos are achieveing their power outputs.

Chris
 
I agree, small effiecient turbo charged petrol engine, quiet, light in weight, does not need a dpf to hide the fact that it is dirty, then the dpf regen crap burning cycle is not used, again to hide the soot from type approval emissions testing. This matched with a semi auto box like the dsg is the way forward on modern cars. The torque starts low and stays as the speed increases and the gearshifts are sublime to the point of being invisible. The dsg is far from perfect, but it is economical, excepting when used in sport mode or the throttle is mashed by a leadfoot (it is more economical than a conventional auto)

IATR, I drive a dsg because i am a semi raspberry and my left side decides when IT wants to work, the car is on a cripability contract so if it breaks, I don't care :LOL: It is still a better drive than the manual as the mpg is only marginally less and it is more relaxing.
But if I owned it I would still be trading in at 3yrs as I have always done wirh modern cars. I have also previously changed my classic cars at 3yrs as I am usually bored with them by then.
 
IAmTheResurrection said:
Add in my idea of driving them from a small electric motor rather than the engine (especially if that's driven by regenerative braking) and it ought to 'blow' today's variable-geometry twin-scroll turbochargers away for efficiency.
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why bother to convert wasted kenetic energy from braking into electricity to power a motor to drive a supercharger to increase the pressure of the air entering the cylinder to boost engine performance (and thus wasting energy at every step heat, losses etc)...... when you could just feed it into the system via an electric motor, reducing losses, allowing you to only boost performance when required (rather than all the time). F1 KERS systems only produce 80BHP because they are limitted to that in the regulations, reality is that you could produce much more power from the same system (or similar)

the only (HUGE) issue you have is that you can only harvest energy under braking, therefore a good thrash down the motor way would drain the system, or you could cart round batteries toyota prius style, but then battery technology simply is not 'there' at the moment...........

at the moment, small capacity turbo engines tred a balance between available technology (and not just availablity COST is a huge factor here) and performance/efficiency.
 
Such genius, use the vacuum created by the gas flow to spin the turbines and effectivly slow the the air charge volume and speed such pure genius, if we follow there inspirational logic maybe we could also put air volume restrictors in front of the thottle body carb etc :LOL:

graeme
 
ghce said:
Such genius, use the vacuum created by the gas flow to spin the turbines and effectivly slow the the air charge volume and speed such pure genius, if we follow there inspirational logic maybe we could also put air volume restrictors in front of the thottle body carb etc :LOL:

graeme
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What do you make of their claim to improve fuel atomisation?
 
IAmTheResurrection said:
What do you make of their claim to improve fuel atomisation?
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total male cow poo.

it will make not a jot of difference as it's in front of the injectors. On an SU engine it would make it worse, as the airflow would be slower so would generally make the whole thing worse.

They're some of the worst things on eBay, along with the magnetic lead replacement things you put round your fuel pipes! How anyone with any sort of knowledge buys them....
 
They tested these "electric turbochargers" in a mag recently, basically they just introduce a big restriction into the intake. Even at very low rpm they can't flow enough air to keep up with the engine, never mind create boost.

Going back to proper electrically driven superchargers, as suggested earlier, using very rough calculations, if we say it can take 25bhp to drive the supercharger, lets say that roughly translates to 25Kw, at 12V that equals 2083 Amps !!! That's going to require a major rethink on the electrical system :LOL: :LOL:
 
Yeah but it makes you go faster and furtherer! :shock:

These aren't electric Richard, just a fan which is supposed to atomise the fuel better because it spins in the induction stream.

When I had an Audi garage test my A6 as the engine warning light was on, they told me that one bank was a little low on the secondary air system :?: . having not a clue what he was talking about, I asked him to explain. He told me that the little electric pump was designed to pressurise the induction system to heat the engine up quicker. I checked that he did in fact mean the induction system and he assured me that is pressurised the inlet manifold. I then asked him what the turbochargers were doing at this time and he looked a little stumped.

Richard
 
quattro said:
... they told me that one bank was a little low on the secondary air system :?: . ...
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I guess that this one belongs to the list of faults like "weak piston return springs", "worn out silencer bearings" and a "flywheel that does not contain enough flies".

Well, as i grow old, there is always something new to learn...
 
Well apparently the seconday air pump is real, I found this relating a whining noise at startup.

This is the SAI pump .it is designed to come on and blow air into the exhast manifold to burn the rich mixture on exhaust to reduce emmisions until the O2 sensor warms up and trims out the fuel input. It can be a costly repair but it is emmisions related not drivability related. If the O2 sensors do not go " lean" on start up which indicates a lack of air being pumped by the pump it will throw an OBD2 code .. lack of flow bank one and lack of flow bank 2 indicate the pump is dead or dying
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Note it blows into the exhaust, not the intake ! I can't remember for sure which engine you have, but they're talking about the 2.7 Turbo
 
It's the 2.7 Bi Turbo petrol engine, and yes I did discover afterwards that it blows air into the exhaust stream causing a secondary burn which heats the cats up quicker therefore getting them to operating temperature quicker to reduce emissions. As soon as they hit temperature it stops working.

Too much crap on these modern engines 8)

Richard
 
With regard to how much electricity would be required to run a supercharger, I wonder how much a KERS setup generates. Mind you, F1 racers obviously stop much harder, from much higher speeds, than any road car ever could. As for electrically-driven turbos, I've seen reports that various car-makers are developing turbochargers with small electric motors to get 'em spinning more quickly at low engine revs than the exhaust gases could manage, thereby reducing lag... what do m'learned fellow contributors make of that idea?

Someone, I think, mentioned the subject of engines with both super- and turbochargers, like VAG's 1.4TFSI lump - am I the only one who thinks the idea completely batty? Hideously complex (especially what with the supercharger disconnecting as the turbo boost reaches acceptable levels), reportedly not a paragon of reliability and, by all accounts, ruinously expensive to make.
 
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