I have only ever had 8v diesels; another thread mentioned a 16v HDi (A new revision I guess.)
I'm intriuged: What was the first 16v diesel released, and how does it effect the driving characteristics (If you think what 16v did to petrol engines I'm baffled as to what it will do on a diesel).
What are they like to drive?
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Basically if you've driven a non turbo 1.9 for instance, and then driven a turbo version. Then you would have noticed the power/torque increase.
The same applies going from a 8v turbo to a 16v turbo, but with improved mpg too.
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First 16v HDi was the 2.2 used in the C5, then the 1.4 used in the C3.
The difference is certainly not as profound as moving from a NA to a TD, 16v engines tend to keep the power on for longer, where 8v's run out of puff about 4000 RPM.
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The first 16v diesel I can think of was the 82 bhp (later 100bhp) 2.0 DT GM unit that replaced the Izuzu 1.7 in the Vectra in IIRC 1998, the previous Izuzu (as fitted to the Cavalier) was more refined.
The advantages of 16v in diesels is more in being able to optimise the layout of the combustion chamber rather than ultimate valve area as in some petrol engines.
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IIRC, the move to 16 valves on a turbo-diesel has little to do with "breathing" ability, as the turbo provides all the oxygen required, and more, as the engine runs lean. The use of a 4-valve head allows the injector to be placed centrally. Maximum power and torque is at roughly the same revs (4000 and 1900 or less respectively) as a conventional head, and is determined solely by the fuel injection settings of the ECU.
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8v deseal vs 16v deseasel? Slow car vs not-quite-so-slow car I think. I exercised my small yet perfectly formed stable of Brit nearly-classics today, all top down, all sub-20mpg. A day to remember.
I can't remember the last time I enjoyed a day driving a diseasel.
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Same for me with petrol. Far too sluggish off the cam. If the hp is good to go, what matters the type of engine?
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">Far too sluggish off the cam.<"
Then get it on cam!
But that's the problem with diseals, far too sluggish off cam, (where off cam>5000 rpm) And who would ride a Norton deasesl? ;-)
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8v deseal vs 16v deseasel? Slow car vs not-quite-so-slow car I think. I exercised my small yet perfectly formed stable of Brit nearly-classics today, all top down, all sub-20mpg. A day to remember. I can't remember the last time I enjoyed a day driving a diseasel.
I had great time bowling round in my car today in the sun, windows down, tunes up, short shifting up through the gearbox on the torque.
One of those days that would have been good in any car, really. The fact it was a diesel certainly wasn't detrimental...
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My car is VW, so has been at the garage for the last few days, missing all this polishing weather. :o(
Courtesy corsa is OK for taking things to the tip. Her indoors wouldn't be seen dead in a Corsa driven by a man she says.
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"> tunes up, <"
But with the top down and howling revs, how does one hear these "tunes"? Too many people out and about as always in the Home Counties, the day is done by 0800hrs for those who wish to make good progress.
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But with the top down and howling revs, how does one hear these "tunes"? Too many people out and about as always in the Home Counties, the day is done by 0800hrs for those who wish to make good progress.
If I wanted wind in the face and engine noise I would've taken the motorbike out ;o) as it was I was quite happy in my normal saloon car...
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Audi 2.0TDI 140 16v vs Audi 1.9TDI 130 8v - the 16v is more free revving, fuel economy a little worse but probably because the engine is less resistant to being driven briskly.
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I'm not going to comment on the technical reasons but I believe that the Renault Laguna had a 2.2 naturally aspirated 16v engine with about 90 bhp in 1995 or so. Similarly, I think the slightly earlier Mercedes C220D was a 16v non-turbo diesel, also with 90something brake. Both were tough but slow and the only quick thing about them was how soon they were replaced by turboed units.
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Personally I prefer diesel cars to petrol ones - maybe that's because I used to drive lorries! I prefer the mechanical
rumble of a diesel to the buzzing exhaust of a petrol engine, I prefer the torque and the low revving characteristic.
4 valves per cylinder were used on some heavy truck engines prior to finding their way into car diesels, but I can't remember (or don't know) which.
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Rolls Royce Eagle - splendid engine, tweakable to some quite remarkable power outputs.
659.
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Quote>>>>>IIRC, the move to 16 valves on a turbo-diesel has little to do with "breathing" ability, as the turbo provides all the oxygen required, and more, as the engine runs lean. The use of a 4-valve head allows the injector to be placed centrally.<<<
4 valves allows a larger valve area than 2. On a turbodiesel, surely admitting compressed air into the cylinder more easily or pushing exhaust gas out to the turbo more easily will improve performance through slightly reducing the work done by the piston during induction and exhaust strokes.
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>>will improve performance through slightly reducing the work done by the piston during induction and exhaust strokes.
Indeed, this is the mechanism by which an increase in volumetric efficiency can also increase mechanical efficiency.
Put another way;
Indicated power - Friction power = Output power (as would be measured on a brake)
Number_Cruncher
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I'm not a diesel fan for a number of reasons so have little experience in driving them but please help me with the following - do 16V diesels rev higher than 8v diesels then ? As the diesel rev band is less than the equivalent petrol - although I do recall reading somewhere that Honda reckon they can do a vtec type diesel if they wanted to - but with the inherent torque of s diesel they felt it was not necessary.
Just as a side point I am looking forward to seeing the subaru diesel.
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I believe diesel's slower burning properties mean it is the speed with which the fuel combusts that limits them to 5000rpm.
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So what subsequently gives the torque in a diesel - is it the greater energy released in the combustion process - even at these lower revs.
(As you can see - diesel technology is not my strong point)
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Good question - I have no idea of the answer but I'm just as interested as you - the thought had never crossed my mind!
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I'm not a diesel fan for a number of reasons so have little experience in driving them >>
Why not try one. You might be pleasantly surprised.
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Maybe on the exhaust, but no real benefit as the exhaust is positively pressured, and recycled anyway on part throttle due to the EGR function. The overpressure from the turbo is far greater than a piston induced partial vacuum, so the work of the piston induced partial vacuum is small, especially as there is no throttle to augment the negative pressure. If there is a gain it might be by reduction of pumping losses, but this is likely to be very minor. The limit is set by the turbo capacity, and the variable vane function, which maintains gas speed. On petrol engines, without turbos, the intake tract length is sometimes modified to keep gas velocity high, to enable better part throttle response, but as the diesel has no throttle there is no need for this device. No doubt there are better informed posters on this?
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my comment above was meant to be addressed to Sofa Spuds point. It got out of sync.....):
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What about 12v diesels?
---
Xantia HDi Exclusive.
XM 2.1 VSX.
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you can't get a diesel to rev much above 5K because the fuel doesn't burn quickly enough.
Torque figues are high because diesels are more thermally efficient than petrol engines and because of the ultra-high compression ratios possible (typically 18:1 or 19:1), which enables more complete mixing & combustion.
But the fact that combustion efficiency falls away fairly sharply over 4750 rpm means that POWER is limited, as power = torque x rpm
In a petrol car you can't get much above 12:1 compression without risking uncontrollable detonation, but of course you can rev a lot higher, which overcomes the lower thermal efficiency.
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The "fill factor" of the combustion chamber (useful valve area as a percentage of chamber roof area) is not critically important in a turbocharged engine, although it can offer some help with a short stroke naturally aspirated unit.
Other than allowing a central injector nozzle position, the real advantage of a 4 valve head is the increased rate of change of valve orifice area per unit time. Because there is a greater total valve circumference in a 4 valve head the engine is effectively throttled over a smaller crank angle during the periods of valve opening and valve closing.
659.
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Actually its the inbuilt limiter that restricts the revs, and the ECU limits the fuelling also. Otherwise the engine would run into trouble due to the greater reciprocating weight of its heavier components. I beleve smaller diesels, such as model engines, can run up to 18,000 rpm.
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My brothers RC car ran on nitro which isn't the diesel you get from the pump! They are compression ignition though.
No doubt that fuel is designed to burn quickly.
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>mss1tw
You are confusing model glow engines which run on nitromethane ignited by a glowplug and model diesel engines which run on a ether/paraffin mix and are compression ignition...
madf
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But the glow plug is only used for starting, once it's running and warmed up you take it off and it keeps going...
So it's either compression or carbon deposits keeping the thing going ;o) The only electrics are for the fuel and steering servos.
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Once the engine is running, the heat from combustion keeps the fine platinum wire glowing. This is the ignition source, AFAIK.
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Once the engine is running, the heat from combustion keeps the fine platinum wire glowing. This is the ignition source, AFAIK.
Ah! Thanks for that!
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Cheers craig - I understand a bit better now.
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