The Modern Diesel Driver - "The Race"

Soldato
Joined
16 Jul 2004
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I've said a number of times on OcUK before that my pet hate is the modern-diesel driver. The type that assumes his or her car is a rocket ship because the in-gear acceleration is much greater than the equivelant cc petrol. This sense of overawing power generates a level of confidence in the cars power abilities as, day-to-day, it seems very fast and relatively, it is.

At the average traffic light grand prix, the sort that my mother, aged 51, will take part in while driving her 74hp Astra, the modern diesel driver will literally "blow away" the competition, as, like my mother, petrol drivers feel where the torque begins to drop and shift, rather than changing at or a little past the maximum power point. This gives the modern diesel driver the edge as their torque hits with a sharp punch and doesn't let off a newton metre until around 3500rpm in the average TDCi/CDTi/D-4D etc. car. This means that the modern diesel driver is extracting a much larger proportion of the accelerative potential of their vehicle than the petrol driver who will probably shift at around the same rpm, thus often losing the "race".

The above also gets applied to the major roads as well, where because of the torque advantage the driver can leave most other vehicles in the plume of smoke that gets excremented with a bit of a full throttle and be off in to the sunset.

As few may know, I retired from driving the 300hp Citroen Xsara with condoms for tyres and am now the pilot of a 98 2.0 Mondeo Ghia. Performance, handling and ride are surprisingly similar, but the Mondeo succeeds when it comes to general comfort. With the working AC as well, in this heat the Mondeo has the edge.

The 2.0 Mondeo Ghia is by no means light on it's feet. A quick glance at the back of the owners handbook reveals the kerb weight of the "LX" vehicle being 1328kg (Including 75kg for driver, 90% full tank of fuel and all required fluids). For starters, I only weigh 54kg, so that's down to 1307kg and for the purposes of the calculation, at the moment I have a 25% full tank of fuel so we're down to 1278kg. Unfortunately, it isn't an LX, so we need to add on a bit of fat. If Fox's GhiaX baby weighs 1400kg with all his stick on bits and a bottle of coke, then I can't see 1360kg being unreasonable. So 1360kg it is. With 128hp and 176Nm, we have 94hp/ton and 129Nm/ton respectively.

If I were to pick a car at random, say, an 05 plate 2.2 ST TDCi Mondeo Estate, we have some more figures - 1574kg, 152hp and 360Nm - 97hp/ton and 229Nm/ton. Look at that juicy torque figure - 265 lb/ft for the elderly here - enough to make the modern diesel driver's head dizzy with excitement. But is it any good? In short, it seems, no.

I've just been out for a drive, you see, and despite an aggressive attempt from the exact same ST, he couldn't get his car in front from 0-50mph and only match my performance. This demonstrates what I've been trying to say all along. The "Modern Diesel" isn't necessarily fast, it just uses a bigger percentage of its fast-ness day-to-day than a petrol equivelant. Despite the ST having more than twice my trifling 176Nm, it was all lost in pulling the extra weight, turning the massive drivetrain and because of the small ratios needed to be able make the car driveable without having to change gear every 10mph.
 
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You weigh 8 Stone!?? WTF?

EDIT: and 229NM is only 168.9 lb/ft

So...............Diesel 4tw! :D
 
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Interesting post.

Reminds me of when I raced a Laguna DCi off the lights.

I was expecting it to be quick off the line, but I got almost a cars length in front of her over quite a short distance. Does this mean, had we kept on going, she would have had the edge when we got to higher speeds?

Oracle said:
You weigh 8 Stone!?? WTF?

Oi, what's wrong with that :p
 
Oracle said:
You weigh 8 Stone!?? WTF?

EDIT: and 229NM is only 168.9 lb/ft

So...............Diesel 4tw! :D
I was intentionally converting absolute torque rather than per ton!

And I weigh 8 st 6 lbs, which is up from about 7st 9 lbs earlier this year. I'm only 5' 6", so it's not as bad as it sounds, but still pretty rake like :p
 
agw_01 said:
Interesting post.

Reminds me of when I raced a Laguna DCi off the lights.

I was expecting it to be quick off the line, but I got almost a cars length in front of her over quite a short distance. Does this mean, had we kept on going, she would have had the edge when we got to higher speeds?
The edge at high speed, where aerodynamics make a substantial impact, would, basically, have depended on who had the higher absolute power relative to their aerodynamic effeciency (Though there's not a lot of difference, aerodynamically, between everyday cars). There's no question that eventually that ST TDCi would have shifted off in to the distance had we kept going, although not by a huge amount...

Important factors in accelerating from a stop:

Absolute grip at the drive wheels, which is affected by tyre width, engine placement (Distributes weight) and overall weight, which positively affects grip
Power
Power distribution - FWD/RWD/AWD, in reverse order of launching ability
Weight, which negatively affects acceleration

Important factors in accelerating generally:

Weight
Power
Power distribution - AWD/RWD/FWD, in reverse order of accelerating ability

Important factors at high speed:

Aerodynamic effeciency
Absolute power
Power distribution - AWD/RWD/FWD, in reverse order of maximum speed ability
Weight plays a factor, but becomes less and less important the faster you go. At 150mph, they'd be little difference in power requirement if you weighed 1200kg or 1400kg.
 
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ST TDCi's are not particularly quick off the line becuase they are torque limited in first and second gears, and if you try really agressive starts and cut the traction control in its even slower.

Diesels have never been much good from a standing start.
 
There is another huge factor in acceleration that's not been mentioned so far. Gearing.

Acceleration of a car is governed by torque and power at the wheels, not at the flywheel, and a gearbox is basically a torque multiplier.

Slow revving engines have longer gearing to create higher speeds at lower revs, which reduces wheel torque.

Diesels only really excell at in gear acceleration when people can't be bothered to select the most appropriate gear in a petrol driven car (eg 30-70mph in 5th).

-Dolph
 
What are you boys on, I'll take any of ye on in my 144k mile 306. It pulls to around 3500 rpm now (I don't know because the rev counter doesn't work) and the turbo makes a screaming sound. This means I am running around 60 extra bhp.

I will kick your backsides and you will be nowhere to be seen (leaves a handsome smoke screen now too)

Heh diesels suck ;)
 
isnt it obvious that a diesel is slow at TLGP due to the 4000rpm rev limit, you have to change gears too often for standing start sprints etc hence id not bother with a standing start race in a diesel.

did anyone see 5th gear when they put a diesel astra against a tarted up vx astra. not a lot of difference at all.

diesels annoy me with their instant shove in most gears etc. small petrol engines dont have the torque delivery to be flexible enough to just shove you down the road
 
The ST shifted out of first only a fraction before I did, which I think's at about 37mph indicated. Even though it has, say, a 4000rpm rev limit vs. my 7000rpm, they do exactly what Dolph pointed out and alter the gearing to suit. If you put a 1.75 gear on that 4000rpm diesel, it will hit the same speed in the gear as my 7000rpm petrol. The 1.75 gear has the effect, however, of dividing the torque output by 1.75.
 
I was trying to work out what this ST tdci would do in first ^^

First it eats through, its just every other gear ;)
 
I find it hard to do spirited starts, say from the lights as the turbo wallops in and then its over quite quick, when the turbo fully goes in in first gear it does shove you forward but its a bit of a pain to launch them compared to a petrol. I never "race" anyone and have no interest in it, its usally the other way around. Foci and corsa's try it on the most.

The torque im mine you can feel though and i can imagine going through a set of fronts quite quick, torque should be around 290 after revo, just need to find £500 :eek:
 
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The extra torque generated by diesels is required to pull the taller gearing, due to the lower revving engines and the difference in power bands.

This usually negates any benefits from the extra torque output.

<edit> I see Dolph has already said this :)

Part of the reason why I don't like some modern petrol engines (smaller ones particularly) is they're not as flexible as the older ones. My 1300cc small bearing crank straight four was a lively little thing, that would rev to 8000 (slightly uprated) and would pull strongly in all but top from low RPMs (had to be past 3000 to get into 4th acceptably).

The Sprint engine will move off perfectly happily in 3rd, which makes for excellent lazy driving :D
 
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PMKeates said:
What? I'm reading 130ps from the handbook! :p

Yea, no idea why Ford said that. There were two versions of the 2.0 Zetec - one with a Silver camcover, the earlier engine, rated at 136bhp, and the other with a Black camcover, rated at 130bhp (bhp, not ps). For some reason Ford put '130ps' in all the handbooks irrespective of the actual power of the car. Although the Silvertop Zetec engine officially develops 136bhp, there is confusion as to the output of the Blacktop engine - although minor revisions were made to the engine there wasnt really anything that could account for the apparent 6bhp drop in power, so some people suspect it was maybe an insurance thing or something.

FWIW, RR'd Blacktop Zetec engines produce similar power to the Silver ones - Pete's old 2.0, for example, was 136bhp. The unladen weight of a 98 2.0 Ghia is, IIRC, 1250kg, with 1280kg for the Ghia X. Quite where the extra 30kg comes from I dont know, but there we go.
 
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