07-02-2012, 03:39 PM
Ruan Wrote:You're looking at ONE component of the torque/power curve...
Darren's engine was exactly the same, just turn down the power a bit to 200 or so, the peak torque would have come at around 4200 and peak power at around 4800rpm... But that's because of the big turbo...
You have to look at the whole graph to get the entire picture...
You could make your PD what you'd call "petrolly" if you wanted... I.e. no torque low down, rising to a big peak in horsepower but giving a low torque figure... All you'd need to do is make the torque limiters pull back all fuel low down, so your torque curve would just go up and up and up until the peak, it'd be a shit engine because you'd have to rev the TITS off it to make it go anywhere, which is kinda pointless, when a Diesel can produce the full 250lb.ft torque from just off idle... That's like saying I want a petrol engine like a Diesel, so I'm going to make the cams so that it can get NO air in up high, but loads of torque down low...
It's just that you're thinking when you see a high torque figure, you assume that's an un revvy, no HP up high... But of course, that's because you had a SPIKE down low... You need to look at the entire graph... Get my drift?
Ahh, yeah I see exactly what you mean!
So theres always gonna be compromises with whatever you try and do to an engine....I want the low down torque of the diesel but then a progressive line right up to the top end, so you're not dropping the toqrue after like 2k rpm, which I think is what makes my car (and diesels in general) feel slow (to me).....cos you can rev it to the red line but its not accelerating any more quickly than when you were at around 2k, whereas the smaller 1.8 which was technically slower pulled hard at 5k+and now driving the diesel seems counterintuitive as you've gotta change gear in the middle of the rev band to get more power. But clearly you can't have a flat constant high torque line, and losing the low down torque which the diesel is so good for would just be completely pointless really.
So basically if I added a larger VNT turbo to mine (from the 150 for example) would that 'keep' the torque for longer or would it 'move' the whole curve further up in the rev range?
I know what I mean.....but that probably makes feckall sense to anyone else as I just can't seem to put it into words! :think: