HDI driving techniques - recommendations?

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rabenson
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HDI driving techniques - recommendations?

Post by rabenson »

Hi All,

Having recently replaced my beloved 1.9D ZX with a 2.0 Xsara HDI 90, I'm now starting to come to terms with the very different power characteristics of the two engines and am having to adapt my driving style accordingly. In order to save a lot of trial and error, I thought I might ask the experienced HDIers among us for some driving tips.

For example, if I wanted to make rapid progress in the ZX, I would change up at 4000 rpm which would put me in the higher gear at 3000 rpm ie still nicely on cam for the normally aspirated 1.9D. I notice that this technique doesn't seem to work nearly so well in the HDI and suspect that I should be looking to change up at maybe 3000 rpm or even less.

Any views??

Ron
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Post by deian »

i think the torque would be lower down on the HDI engines, try 2000rpm, not got one myself, but most of the torque is around 2000 - 2500 rpm
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AndersDK
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Post by AndersDK »

You have already noticed the massive differences in the low rpm torque between these two generations of diesel engines.

Depending on your goal with your driving style - you should adapt accordingly.
I'd say you should gear up even a lot earlier - at some 1800-2200-ish - if you would like to exploit the low rpm umph in the HDI. This gives you the option of bottoming out on overtaking or catching up in city traffic. And still have a decent mpg.
You will quickly learn that you dont get thru traffic slower this way. Its just the feeling of it - as you totally miss that high rev noise out there from the front :lol:

You will notice that the HDI do it much better right from the bottom - than the "old" style diesel which had to sort of be spinned up first.

It really is amazing how different a HDI is to an old n/a diesel.
Anders (DK) - '90 BX16Image
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Post by Honda »

My Xantia HDi liked those gear changes at:

- 2000RPM normal driving
- 3500RPM "I am late for work" mode :twisted:

However it was a 136Hp version of the DW10 (with different response to the official 90 and 110Hp versions).
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Post by Kowalski »

Its all about power, ignore the torque.

Rev to peak power and over it, the power will then start to fade. For maximum accelaration the ideal point to change is at the point where the power in the next gear down is the same as the power in the current gear, i.e. the power in the current gear is going down, but the power in the next gear is still going up.

This won't feel fast, because you're not feeling maximum torque and you won't feel the surge, but the fact is the engine produces its peak power at the peak power rpm (4000rpm ish) and not at the peak torque rpm (2000 rpm ish).

The HDI 90 has much the same power curve as the 1.9 TD, so for best progress, wait until 4500 rpm before you change gear and change gear quickly. This isn't good for engine life, fuel economy, emissions or noise!

For absolute fuel economy drive slowly, keep the rpms as low and avoid using more than about 2/3rds throttle, once the turbo comes in, it heats up your intake charge and the HDI has no intercooler so efficiency drops off.
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Post by Honda »

That may be correct for 90hp version but not 110hp and 136hp versions.

On the 136hp DW10 above 4000 you'll be just making more noise an getting no aceleration. Best aceleration times were achieved by changing just after 3500. I am speeking from personal experience.

According to following graphic, for the 110hp version, 4000RPM should be the ideal point. I am not sure of this I have only chronometered the 136hp Xantia, which achieves 9.9 secs from 0-100km/h.

Image

Now, on a Honda S2000, the ideal point is at 9000RPM :twisted:
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Post by Kowalski »

How is the 110 bhp engine any different? You don't change gear at peak power, you go past it, otherwise you're dropping yourself down the rev range into a much lower powered engine speed when you change gear.

Yes it produces more power, but the power curve is the same shape, the same sort of shape as almost every engine that exists. Power goes up, peaks then comes down again.


These two graphs were produced on a dynomometer, they don't agree 100% with the manufacturers figures exactly.
http://www.superchips.co.uk/curves/psahdi90.pdf
http://www.superchips.co.uk/curves/psahdi110.pdf

For performance, you want to use peak power all the time (you'd want to stay at a fixed engine speed) but that isn't possible without a CVT. Instead you've got to start below peak, go over and then come back down again. You're aiming to always be at the greatest power the engine will produce given the road speed and gear ratios.

This is fairly fundamental stuff.
Last edited by Kowalski on 31 Mar 2006, 22:00, edited 2 times in total.
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Post by Kowalski »

Admin!!!

Its done it again.
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Post by deian »

so whats the ideal place to change gear on my car (see below), i find 3000rpm good, thats when the turbo is at it's peak (1 bar).
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fit a dump valve

Post by fivelighters »

fit a dump valve va va vroom :lol: :lol: :lol: :lol: :lol: :lol: :lol: :wink:
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novice qn

Post by roypch »

Hi Kowalski

What is the best place to shift gear (for best fuel efficiency and engine life) on a 94 xantia TD ? I have been playing around a bit never getting it right.

cheers

roy
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Post by Homer »

Kowalski wrote:How is the 110 bhp engine any different? You don't change gear at peak power, you go past it, otherwise you're dropping yourself down the rev range into a much lower powered engine speed when you change gear.
That's fine in theory, and on the racetrack.
Notice that after 3000rpm you are not getting much increase in power, and on the road it's even more noticable. You just get more noise for very little extra acceleration. If you change down into the 3000+ range takes more time to change gear than you get back from extra acceleration.
When you hit 4000 the drop off is very marked and feels like deceleration.

And, unlike a petrol engine, the fuel economy really suffers. Using the full rev range is how I managed to get 20mpg out of the 807.

It depends a lot on gearing but keeping in the 1500 to 3000 band gets the best out of the engine without thrashing it to pieces.
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Post by f00lzz »

Homer wrote:
Kowalski wrote:How is the 110 bhp engine any different? You don't change gear at peak power, you go past it, otherwise you're dropping yourself down the rev range into a much lower powered engine speed when you change gear.
That's fine in theory, and on the racetrack.
Notice that after 3000rpm you are not getting much increase in power, and on the road it's even more noticable. You just get more noise for very little extra acceleration. If you change down into the 3000+ range takes more time to change gear than you get back from extra acceleration.
When you hit 4000 the drop off is very marked and feels like deceleration.

And, unlike a petrol engine, the fuel economy really suffers. Using the full rev range is how I managed to get 20mpg out of the 807.

It depends a lot on gearing but keeping in the 1500 to 3000 band gets the best out of the engine without thrashing it to pieces.

Agreed.... anything over 3k seems wasted... also cruising above 3k makes a big increase in fuel consumption
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rabenson
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Post by rabenson »

Thanks Guys

Much food for thought! I'm not convinced that the gear ratios on the xsara HDI are quite as well chosen as those on the zx 1.9D or at least don't seem to suit the power output characteristics of the engine quite so well - but I'll stick at it. It may just be that this is such a different beast to what I'm used to!

Thanks again

Ron
2007 C6 2,7 HDI exclusive 95k
2004 C5 VTR HDI 103k
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