Works like this... Turbo tooo big so NO boost pressure. The thing is Turbo boost actually sustains itself IF you can start it off. Revs dont matter much.
So you use say 70bhp nitrous gas off the line, INSTANT go! -- And this makes turbo boost even at low revs.. A simple pressure switch stuck into the plenum sees the boost arrive (oil pressure switch as it happens) and turns the nitrous off over 15psi... So now we have an engine on full boost in any gear at any rpm and it sustains itself as long as WOT continues. So if you want to pass a car in top gear at 50mph you can pull out hit WOT which gives it nitrous, boost, and off you go! As boost rises above whatever half your max boost is the gas gets turned off as its no longer needed.
Of course you can have a "overide" switch for taller gears and use it for power as well as to fill in the lag.
Nah, its the older shape than that, and came out of the factory that way, and iirc it had done quite a fair few miles! It was an Import from Japan, 1 litre, turbo charged, and supercharged. Last he posted it blew up and he was rebuilding it for higher boost and stuff i beleive.
I have an A6 2.5TDI straight 5 like yours Peter, (Upsolute) chipped to
175bhp. It drives very well, good torque at low revs, not all peaky like the A3 (sorry - rebadged Golf) TDI 130 I used to have. Are you sure yours is in the best of health? Mine's done 126,000 miles and still goes like hell off the lights, not that I'm any kind of racer. Fuel economy has slightly improved too since getting it chipped.
If you like an engineering challenge then the advice given seems really interesting. If you don't, buy a Merc pimpmobile.
When you say good torque at low revs, how low are you talking? From just below 2k mine picks up very nicely indeed, and the short 1st gear helps it get onto boost nice and quickly - I'd just like more V8-like lazy torque all the way from idle. Mine's in pretty good health - it's got 122k on the clock, and was serviced every 10k up to 50k (Audi main dealer) and from then up to 94k it had oil/filter, air filter and fuel filter done every 6k. I then had the oil changed at 105k and 114k (I really would have liked to do it sooner both times, but laziness got the better of me, and a lot of the mileage was motorway stuff, so I don't think it's suffered too much as a result), and it's due another oil change now. Fuel filter hasn't been touched in the last 28k (I know, I know) and I really want to do that very soon, along with another oil change (did the air filter recently). So I'd say it's in pretty good health.
Good advice. I think I'll save both until I've got enough time and space to make either a viable proposition.
When you say yours goes like hell off the lights - well "goes like hell" is pretty subjective. Mine can be pretty quick off the lights if I want it to be, but the tracking's slightly out so I'd rather not at the moment, plus it's got a really short first gear, meaning you don't get much chance to pull away before you need to change up. The performance is definitely there for when you need it, and it does come in handy. I'd rather save used the performance for a big long 3rd gear overtake though - veyr handy overtaking slow cars up hills.
Btw, is yours the 140bhp version? Saloon or Estate? What sort of economy do you average?
My solid fuelled 9mm diameter lead drag/road projectile does 0 to Mach 2 in a few milliseconds. Unfortunately it's not very practical for carrying me, 3 mates and all our rugby kit to the game on a Sunday, including having a bit of fun when the road/traffic allows it. In fact I have real trouble staying on it and it just won't go around corners.
I'm sure your bike is great fun to design, build and ride. I'm sorry if I gave the impression of one-upmanship, I was just trying to give some idea of how my old TDI bus goes, which is all subjective. For a big heavy diesel estate car it feels pretty quick compared to the other car I drive regularly.
I agree that below about 2k it drives like a 2.5litre normally aspirated diesel with slightly low compression. With a turbo engine this is pretty much unavoidable without clever tricks, which cost money and are thus not desired by the majority of drivers. Lazy V8 torque is really just due to capacity. If you had a 5litre 5cyl 'm sure it would have similar lazy torque.
"Going like hell" is subjective, I meant "goes like hell" in the context of a big diesel estate! I can stay with most of the traffic light chavs/kevins if I feel like it.
I was wondering whether you had some little problem, maybe a sender playing up for instance, that was making the ECU go into safe mode and spoil your fun. I had a glitch one night on the motorway on my way to work that suddenly cut power and I couldn't get the car over 90mph. When I got back in to go home after work, it seemed to have fixed itself and was fine on the way back. I haven't been able to repeat the occurrence. From what you are saying though, your engine performance sounds pretty much like mine.
My car is/was a 140bhp 6 speed manual estate, AEL engine. With the different engine management programme it pulls harder throughout the rev range, is great for typical overtaking manoeuvres and does 135+ (on the clock!), but it can't do much about the torque just above idle - that is just the way it is with the laws of thermodynamics!
We have never formally monitored fuel economy, but before chipping the long term average on the display used to settle around 34.6mpg. Now it settles down to 36 or even more sometimes. Most of the car's use is on my husband's commuting between Northampton and Bedford, with occasional night thrashes by me to London and back (I'm an engineer, working on the underground at the moment).
Hang on, this is verging on an alt.autos.audisadbastards discussion, we're going to get told off if we keep going....
Hey Burgerman, what do you think about me NOSing my Uno turbo powered X1/9?
Heh, yeah suppose so (that's regarding the bit about the lazy torque and bigger engines).
chavs/kevins
Oh yeah, me too. Having the torque right in the middle of the rev range is a great thing!
Nope - that's never happened to me luckily! Maybe something to look forward to, lol!
Suppose so, but maybe my idea of a supercharger to help with the lower revs could be an idea - don't want to overstress things though.
I take it with that sort of economy it gets driven at quick-ish motorway speeds regularly. Mine very rarely falls below the 40mpg mark (as per the trip computer, though this is usually around 1-2mpg optimistic), and that's with a commute that's around 15 miles motorway at around 95-ish (honest guv) and then about 9 miles of NSL A-roads in the morning, and going somewhat slower due to the traffic on the way back. I did average 47.9mpg on a trip to Peterborough and back once (220 miles round trip) not going above 80, but that's no fun :-). I even got it showing a 62.5mpg average once, but that was sticking to 60, and I'd really rather not do that all the time!
I dunno, it's good to have another 5-cyl TDI nut on here, up until now it's just been me raving about them!
Well I am a bit biased! I think everything should have it as standard... I even have a nitrous fridge made from a polystyrene fish box off the docks...
All Turbo engines are gutless off-boost - that's part-and-parcel of how they work.
But again, why would you drive it off boost ? If you're finding it sluggish in normal use, then you're in too high a gear !
My Turbo also only makes decent boost from 2000rpm upwards - but seeing as the amount of time spent below 2000rpm on a normal drive is zero, then it doesn't matter one jot.
They don't !
Turbo spins up properly when there is enough exhaust-gas-flow to make it do so. See Burgerman's posts - you can't trivially alter this, without knackering the higher-up power (cos you're now restricting the flow).
It's to do with the flow of your exhaust gasses, which drive the Turbo. More revs = More gas.
Plus, driving a diesel engined car is different as they generally dont rev as happily and produce gobs of torque further down the rev range relative to a petrol engine. I reckon it'd be quite easy to drive my works van all day below 2000rpm.
The cost of the good performance of many modern turbo diseasels is f*ck all benefit from the turbo higher up, they put pretty teeny turbos on. My works van (mercedes 311CDI) feels restricted over about 2800rpm but it boosts from almost idle. It also has fly by wire throttle, it revs more like a petrol engine when you give it a quick stab on the gas in neutral, I think the ECU gives it more oomph to make it feel a bit peppier. On old skool mechanical injection diesel engines, the throttle pedal is the governor whereas with modern ones (merc CDI and Pugt HDi for example) its all done with electrickery.
I dunno how advanced your Audi is in the engine electronics stakes.
Around town. It's nice to get a nice smooth progressive delivery of power right down from tickover, like you get in n/a engines.
Yeah, true. Suppose I want V8 performance all through the rev range with diesel economy. I'll have to make do with the compromise on offer I suppose :-)
True. One day when I was using it for courier work in London, I spent a whole day keeping it on boost (or just below boost, if the other option was screaming the engine a bit!) pretty much all of the time, and it didn't use any less fuel, possibly a bit better off.
I know what you mean, the short first gear on mine means that it gets on boost nice and quickly, and it's not that difficult to keep it there in all honesty, I just quite fancy more torque right down low.
Yep, read Burgerman's posts, also about the bit where you could improve gas flow at lower revs, but it'd involve altering the timing of the exhaust valves, and adjusting the timing of the injector pump accordingly, which would all in all result in lower efficiency.
I know that much, but I keep on hearing about more modern TDs that really come on song as low as 1500rpm (Merc CDIs, Vauxhall CDTIs, etc) - I don't know if that's purely to do with improving the flow of gases that actually drive the turbo, or actually improving the turbo itself so that it speeds up quicker, and responds better to slightly smaller amounts of exhaust gas. I wonder if it's possible to put one of these new modern fandangled turbos on mine and the engine coping?
I still really like the idea of supercharging it at low revs, with some sort of clutch that disengages it when the turbo kicks in (as in Ed's Micra), but that's a lot of time, expense and effort.
I believe its cos the throttle cable is not directly linked to any mechanical part of the engine, it works a potentiometer which tells an electronic brain how much juice to give the injection system. You may already understand this bit.
The term comes from planes, some big-assed planes made up untill recently still use cables gears and levers to operate the control surfaces. Some probably still do. Someone had the bright idea of linking the controls to some electronics and sending the signals to electrickery controlled hydraulics.
Ah, I thought those CDI engines had it all. Turns out they don't. My Audi revs happily up to the redline. I suppose on balanace I'd rather it do that than run out of puff before 3000rpm. I dunno, maybe, maybe not.
Why do people call it fly-by-wire? I've heard it called drive by wire as well, surely that makes more sense as cars don't fly! Well, unless you're playing darts with them as on Top Gear!
Nor do I. It's about half way between the two I think. It's got a drive-by-wire throttle though, I think.
This isn't so much to do with the turbo, but there's a guy on the mg-rover.org forums (Rover Ron I think his name is), who's made a device to amplify the MAF signal on his Rover 45 TDI. The result of this is heavier fuelling off-boost, which he claims has virtually eliminated the off-boost gutlessness of his L-series. Last I heard he was wanting other people to try the device out on their derv burners, so it might be worth getting in touch with him.
A small test to do to see if it will make any difference is to unplug the MAF sensor to force the ECU to fail-safe to default MAF/fuelling values. This will take off some of the top-end power, but _should_ result in better low-down heave. Give it a try.
Goodo, I'll keep it in mind. I'd much rather wait until someone's done a genuine long-term test on it (i.e. over 50-100k+++) to see if there are any long-term side effects before doing anything like that to mine though!
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