Quote:
Originally Posted by gwyllion
I don't know where you live, but VW never produced a Golf II with a 1.9 TDI engine. The GTD had a 1.6 turbo diesel engine with 70-80 hp.
It might surprise you but the Peugeot 908 HDI engine has a compression ratio of only 14:1 (see here). That is not a lot more than modern direct injected petrol engines. For instance, the Ferrari 458 has a CR of 12.5:1. |
Sorry my mistake... was Golf III... a picture worths a thousand words( though that was not my car)
http://www.metacafe.com/watch/256724..._acceleration/
81Kw ie ~ 110 HP
" have it on good authority that the Peugeot engine has 84x82.5mm bore/stroke, 146mm con rod length, 14:1 CR "
the
rumor might be close to reality alright, but there was another rumor that stated that Audi had a 17:1 CR... now if you count the additional pressure of the turbochargers, that might give with 2 bar 28:1 and 34:1 respectively...
Quote:
Originally Posted by gwyllion
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" Regardless, given the torque function, there is an associated power 
. So if the torque is known at all speeds, the power is known at all speeds (and vice versa). You can't have one without the other."
Where you get confused is this...
" The peak power is very important for reasons I'll get to later, but the peak torque is essentially useless all by itself "
which is very misleading; ... because it discards the action of the loads on the engine in any time. If the engine has no load, or negligenciable load, then torque matters nothing, give it a constant=1 and power is a direct function of the RPM of the engine... which is theoretically correct but describes nothing useful.
If not a contradiction; .... because if You can't have one without the other. then how came one is all things and the other nothing.
Hard time getting this : POWER = torque x engine speed, you cannot have 10 Nm and 1000HP unless your engine revs at 200.000 RPM( or much more)... but on the other side you can have 20000HP in only 300 RPM... yes 300 RPM !... in those 5 store high, big freight ships, diesel engines... those engines can rarely be said that accelerate, yet imagine their peak power ???
Simply you can't have power without torque... the better your initial specific torque, the better anything "power" related... only that max power attainable, as a number trowed on the table, is completely irrelevant when you pass a certain threshold. OTOH torque is always more relevant because the faster the car goes, the more the aerodynamic LOAD, and so the better the torque the faster it gets to those higher power levels and higher speeds.
Quote:
Originally Posted by gwyllion
Because you have been a Golf owner, perhaps the previous Golf GT is a good example. VW made the car with a diesel and a petrol engine: - petrol: 1.4 TSI (supercharger + turbo), 125 kW @ 6000 rpm, 240 Nm @ 1750 rpm, 1268 kg
- diesel: 2.0 TDI, 125 kW @ 4200 rpm, 350 Nm @ 1750 rpm, 1303 kg
Guess which car is faster. These are the performance numbers for the DSG gearbox: - petrol: 0-100 km/h in 7.7 sec, top 218 km/h
- diesel: 0-100 km/h in 8.2 sec, top 218 km/h
Both cars have the same top speed because they have the same power. The petrol car accelerates faster because of its lower weight. The higher torque of the diesel can not compensate for this weight disadvantage.
Finally, the fuel consumption numbers, again for DSG gearbox: - petrol: 7.3 liter/100 km
- diesel: 6.4 liter/100 km
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Do you sell cars ????... it seems you do!... Is like OC in computer chips. From the factory those diesels are "cut", by an order of things, including the marketing notion that they are economic and don't have to be fast.
But sorry to disappoint you, but i would prefer the TDI anytime, the money i save in fuel, will be enough, in 4 year after the guaranties expire, to transform it into a 300 HP "sport" car... the same cannot be done with the TSI, without marrying the daughter of a gas station company owner, to conclusion... and spend more money in the transformation, to begin with.
Quote:
Originally Posted by gwyllion
Yes, the diesel car has better fuel economy. However, if you take into account that diesel has a 10% higher energy density (see here), the difference is not so big. |
Yes your link is correct more or less... if we don't account for premium fuels. Race fuels don't have anything to do to those numbers... and i'm pretty suspicious that diesels don't have an advantage here... or very little if they do.
Quote:
Originally Posted by gwyllion
A diesel engine revving to 8000 rpm  How high must the cetane number be to achieve such high rpm? Race diesel engines don't produce power by revving, but by injecting more fuel (= more torque). |
Again: POWER = Torque x Speed of engine(RPM)
Higher RPM is NOT ONLY achieved basically by "brute force"= more fuel, stressing more the engine, but much better by reducing in-balances in all moving parts and by reducing "parasitic loads"... your engine takes a lot of energy only to move itself = the bigger the engine the worst this might get=... petrol engines are better in here, diesel and others will catch up... you are laughing of yourself... Peugeot and Audi have started a little above 5K RPM, but already passed the 6K RPM in 2009 and 2010... and could had been more( perhaps above 7K RPM) if they weren't forced to restrict the engine more and more every year.
Back to R18... i very much doubt, by these long dissertations, that Audi will go for Petrol with it. The passage to a V10, giving Peugeot the upper hand in torque, 5 power strokes per revolution against 6 power strokes for peugeot, should had been balanced by a better fuel consumption which was hardly noticed and a higher RPM ( a lighter engine )... a tough bet, remaining in conclusion to learn HOW and WAHT downsizing the number of cylinders will give you.
So after this lesson learned is hard to believe they will discard it... and if it is a "winner" factory that goes electric-petrol hybrid is Peugeot... but which i doubt also, because they must know how electric motors are not good yet to balanced the losses by going petrol... and batteries still weight a "ton"...