Please can someone help explain what these figures mean in relation
to engine performance? They are the specs for the Yaris Petrol 1.3
versus Yaris Diesel 1.4.
Petrol 1.3 63kW/86bhp 124Nm/4100rpm
Diesel 1.4 55kW/75bhp 170Nm/2000rpm
Am I correct in thinking the diesel will produce 170 doodahs of pull at 2000 rpm
whereas the petrol will produce only 124 doodahs of pull at 4100 rpm?
Strong Diesel. Weak Petrol engine.
The 86bhp of the petrol engine sounds better than the 75bhp of the diesel.
Strong Petrol. Weak Diesel engine.
Please can someone help me to understand how this all relates as it
is quite confusing?
Thanks very much.
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Basically the petrol engine is more powerful, but to get to use this power you need to have higher revs. In this sense the petrol is more peaky and will have worse performance at lower revs compared to the diesel.
The diesel is ultimately less powerful, basically because diesels can't rev beyond 5000 rpm, whereas petrol can probably get to 6500. Power is due to burning more fuel (Think F1 17,000).
Torque (the dodaah figure) is a guide to pulling power. i.e if you put your foot down will much happen. At low revs say 1500 diesel will pull a lot better than petrol. This makes deisel better in traffic as you don't need to change gear as often.
In real life these engines will make similar prgress.
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Don't forget that much of the difference, even though the performance is similar, will be in the way the car feels to drive. As James says, the diesel will probably be more relaxing in traffic. Because of the power being delivered at lower revs, it may also be quieter at speed than the petrol, and therefore happier on the motorway. It will also be at least 25% lighter on fuel.
Chris
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Except that the diesel has a smaller useable rev range, as soon as it comes on boost, it's not long before it's all over, therefore it needs taller gearing. Which then blunts the torque figure somewhat.
This is best diplayed when pulling away. There is next to no torque or power before boost, which can make for scary pulling out at roundabouts etc.
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Butdo not forget we buy fuel by volume not mass ,Diesel weighs far more than petrol for a given volume so fuel savings are not as great as first appears and if the tax system is altered then any benefit is nulled.But in the UK where their is no or very little difference in price it must take a long time to recover the extra outlay for a diesel motor.In Germany where we have a 25% difference you need to travel around 50000km a year to break even slightly biased to petrol due to most petrol cars paying no road tax in the first two to five years and diesel having no free time
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Yes, you have to get used to driving a diesel, and learn to use the power band efficiently. The tendency is just to keep pushing the revs up; press the pedal to go faster, right? But there are times with a diesel when changing up a gear and letting the revs drop gives you bags more acceleration. That takes some getting used to. Once you do though, there are no more scary moments than with a petrol engine. And the overall experience is much calmer. I think so, anyway.
Chris
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Agreed, having used diesels for the last decade. And you don't have to waste breath asking for a receipt in the filling station, they assume you are a business user and offer you one anyway.
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If you are a business user the petrol is the cheaper option according to recent what car tests , the diesel best with the larger cars.
To fully understand the torque readings you really need to see graph of it ,
diesel engines are usually very peaky giving lots a torque from 1500rpm and peaking around 2000 however after that its rapidly down hill. Hence they can be slow of the mark but pull well on the move, the narrow power band is offset by taller gearing so for motorway driving can be quite.
The petrol engine below 1500rpm will probably have more torque than the diesel (this should get some expert comments) with torque rising steady now I'm guessing here because some engines have a good flat torque over say 2000 to 4000 before dropping off, or as in the case of the primera i had although max torque was at a high 4800rpm the curve actually peaked almost at maximum at about 2500rpm dropped off slightly st 3500 then up to a max at 4800 rpm. so a high maximum torque does not mean a poor puller (but can some Hondas are until high revs ).
if you only drive locally get the petrol you will see 40+ anyway and is probaly cheaper to buy. if you use motorways a lot then i pity you , buy the diesel.
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My diesel Lupo gives 56ish to the gall on driving lessons. If you show me a petrol engine that can get near that I will gladly buy it.
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Pete,
My real life experience doesn't bear this "petrol for local journeys" theory out.
Many short local run petrol cars (say 1.6-2.0 family hatches) are capable of returning less than 30mpg. Drift round in a 1.9-2.1 turbo diesel and the same use can give 45-50mpg.
A family I service vehicles for have just gone from a 2.0 petrol Espace to a Mondeo TD, their fuel bill has halved.
David
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It's all been said before on his forum! Whilst some drivers may not like the different driving characteristics of diesels, the economy of said vehicles is beyond dispute.
Modern turbo-diesels have a great combination of torque and economy. Combine this with high gearing/relaxed cruising/long life/strong residuals and you've got a winner. For most people, anyway!
Viva la difference! (no Vauxhall pun intended)
Pat
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The choice of petrol for local driving stop start idling at lights was not taken on the basics of petrol economy , no one disputes diesel gives more mpg, what it does not give is a quite tickover and a vibration free through the pedals /wheel/seat. Diesel clatter is present .
Given a £1000 increase in purchase over a petrol car of similar performance for a low mileage around town driver makes no economical sense , hence one of the reasons for What car declaring the petrol the best option.
I am not anti diesel , i intend to have one on retirement when economy is more important than refinement.
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THe "long life" issue of the diesel needs perhaps more attention too, doesn't it, in terms of value for money?
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The engines might last longer (because they have to be built to withstand the internal stresses) but the catalysts won't. HJ's section today has a Mercedes one giving up at 43k...
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Pick the right diesel and your noise/vibration point is not a problem. My (very much regretfully now sold) Mitsubishi double cab Strada 4WD turbo was extremely quiet and smooth. Frequently riders asked me was it really a diesel. Get the Isuzu similar model though and I agree with you. A real bag of nails clatter-wise.
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Peugeot & Citroen diesels are remarkably smooth even at tickover; not so the Fords of a few years ago which could be heard two streets away when running at idle speed. Not having all that ignition gubbins to let you down on damp mornings is also a big advantage.
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Has it been statistically and practically proven that diesel 'cats' will not last as well as petrol? I did see the mention of the 43k Merc. cat that James referred to, but that is only one. I wasn't aware that there was this major liklihood of early derv. cat failure. More info requested please.
KB.
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I thought HJ in his column categorically said two way diesel cats were rather more reliable. Will have to read it again methinks to see if I am going completely batty. If that is what HJ did say that's good enough pour moi.
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