A hypothetical question here for the techies. I remember back in the mid 90s a supercharged Mazda 626 Diesel that only had 70 bhp but quite high torque. So let's imagine a car with say 90 BHP from 2-2.5 litres but with say 280 lb ft of torque. What would it feel like on the road?
I'm not that technical but would be interesting to read your views.
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Like a high torque but lower powered diesel from the 90s.
It depends on the power and torque curves. Direct injection turbo diesels have been very usable for while with relatively low power. Now they have high power as well. My brother had a Citroen 1.7 TD that seemed to go okay (it was the more powerful diesel at the time and more powerful than the non-turbo 1.9).... replaced by a non-turbo 405 Mi16 which was faster!
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let's imagine a car with say 90 BHP from 2-2.5 litres but with say 280 lb ft of torque.
Waiting for the techies here, but I suspect that is mathematically impossible. Anyone know how many bhp a Victorian beam engine had?
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I'm too young to have driven the 90s vehicles.As for the possibility, I don't know.It is one of the crazy things that just crop up in my head!
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I suspect that is mathematically impossible.
Not impossible, but, such an engine would have to have a very low rev limit. (In the units, as given, the power figure must be greater than the torque figure when above 5200 revs or so)
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I suppose a diesel engine producing those sorts of figures would be very truck engine like in driving.
Off the top of me head, my last Cummins 14 litre diesel (1984) was rated at 320hp at something like 1500rpm, but developed around 1100lbs.ft of torque at 1100rpm, and wouldn't rev above 1850rpm anyway.
Going by memory there, but not far out i'm sure.
Driving wise, it was wonderful IIRC 90% of peak torque was available from 800 or 900rpm, and would pull cleanly from tickover at 500rpm, so obviously very flexible.
I've driven newer vehicles, and still do with quoted figures far higher than that old Cummins, driving wise or useable power wise not a patch on it.
I suppose you need a large swept volume to create that sort of power to torque ratio, and that sort of unstoppable torque is very addictive, difficult to find in normal cars, but some 4x4's come close.
The Mazda 626 diesel mentioned was a very unloved car i seem to remember, but i nver drove one so couldn't comment.
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I've been driven in (but unfortunately not driven) a Dodge Ram Pick up with a Cummins 5.9 litre Diesel that had 320 BHP and about double that in lb ft. Red line was at 2200 and it really shifted. I guess you are right gordonbennett.
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a Dodge Ram Pick up with aCummins 5.9 litre Diesel that had 320 BHP
I wonder if thats the same Cummins that LeylandDaf used in their 7.5 tonners for some years in the 90's.
Apparently a very powerful and rugged engine.
I wonder if professional engine makers eg Perkins, Cummins etc help in the designing of current car diesels.
I know Perkins had huge input with the Leyland/Rover diesel cars in the 80's/90's and up to demise, whether they were made at Peterborough and shipped to factory i know not.
Seems a valuable knowledge base being missed out if companies like that arn't contributing, i seem to remember the Perkins diesels in Maestro's and the like being hellishly noisy, but had economy unheard of at that time.
Did those engine's maybe deserve a little better shell around them?
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a Dodge Ram Pick up with a >> Cummins 5.9 litre Diesel that had 320 BHP I wonder if thats the same Cummins that LeylandDaf used in their 7.5 tonners for some years in the 90's. Apparently a very powerful and rugged engine.
The Cummins B series engine was indeed used in Leyland/Daf trucks, there was also a 4 cylinder, 3.9 litre version of this.
From memory, as Cummins only considered this a medium duty engine it was only guaranteed for 250,000 miles!
Holset Engineering, which made the turbochargers, set up a factory in Charleston USA which made the bulk of the Dodge Ram turbo's as well as supplying a Case/Cummins engine plant in North Carolina.
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It would depend to an extent on the overall gearing. It's torque at the driving wheels, not engine output torque, that matters. This is something of which most motoring journalists (and the general public) don't seem to be aware.
Edited by L'escargot on 28/02/2009 at 06:17
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I think the current versions of turbodiesel engines have gone too far towards BHP figures, at the expense of low-end torque.
The VAG 1.9 130bhp AVF PD motor was probably the last to offer really strong grunt from 1500rpm. OK, there was no real point revving it beyond 3,000 and it was gruff and grumbly, but the sheer slam of the torque delivery made it fun to use and very relaxed.
The current generation of diesels (I've driven the latest VAG, Ford / PSA, and Toyota variants) are a bit weak under 2,000 rpm in comparison.
However, I suspect part of this is to protect the clutch and gearbox ... it's probably hard to make these car-sized components last a reasonable mileage with very high torque outputs.
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I think the current versions of turbodiesel engines have gone too far towards BHP
I agree completely, there are some low rev high torque diesels around, but they tend to be large volume (a common theme?), i'm thinking of German 6 pots as stuffed into their higher priced cars, but the BMW 320d does buck the trend, and pulls very well from much lower revs.
I dislike having to drive diesels hard to get the power out, its just not diesel driving, and i'd like to see a bit more balance in drive-ability.
Maybe its the manufacturers bhp (it sells cars i suppose) contest, many think bhp is the be all and end all, and have no notion of the much more important torque figures with diesels.
Our pick up gives max torque from 1400rpm, but thats 3 litre 4 cylinder, and is very pleasant to drive as a result, but it probably loses out on top end performance by not being 6 cyl, and possibly wouldn't sound the part in a large car.
Don't get many car diesels with 750cc per cyl.
I think you may be onto something with the drive train components suffering.
One particular manufacturer offers diesels in various power outputs in a certain model, i've noticed that the lower powered versions have very little low speed torque and its a job to get them to climb the truck without being cruel to the clutch.
I've often wondered whether over so many thousand miles this would result in heavy clutch use with associated problems, well it appears so from technical questions with very short clutch/dmf life reported.
But the higher powered versions of the same cars just romp away with no clutch slip needed, and those high output versions don't feature at all in the threads.
Maybe just coincidence.
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Intrestingly enough, on a site called rri.se there is a huge list of engines with their torque/power outputs over their rev range. The latest twin turbo 3litre BMW diesel units appears to produce very close to max torque from just 1200rpm.
Also what's interesting about the BMW unit is that it reaches max power by around 3600rpm.
Edited by smokescreen on 28/02/2009 at 15:16
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Intrestingly enough on a site called rri.se there is a huge list of engines with their torque/power outputs over their rev range.
Jolly interesting site that, thanks for posting.
Some makers claimed power doesn't actually get to the wheels, the BMW you quote does very well in that respect.
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Not that hypothetical really - most vintage and earlier cars had long-stroke low-revving engines with relatively few horsepower, but plenty of grunt. A neighbour of mine had a large 1911 Renault that must weighed two tons, but probably no more than 20-30hp. However, the engine had a 6" stroke (IIRC) and was, I understand, quite easy to drive.
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Not that hypothetical really - most vintage and earlier cars had long-stroke low-revving engines with relatively few horsepower but plenty of grunt.
Was not the original R-R Silver Ghost driven from London to Edinburgh in top gear under RAC supervision in 1911, and then lapped Brooklands at 75mph to prove top was not an unnaturally low gear?
7.75 litres and probably weighed at least 30 cwt.
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My old Rover 420 diesel had only 86 bhp from 2 litres but could easily pull away even on moderate inclines in 3rd gear without using any revs aslong as you were progressive with the clutch.
It was running outta puff at 3000 rpm but change at 2500 and you could gather speed pretty quickly.
My old Astra van with the LPT diesel engine was much the same - loved both vehicles.
Both had turbos, but not highly strung ones.
Low pressure turbos can make lovely combinations with biggish diesels.
On the petrol front, my mums V6 Hyundai has only 171 bhp but it pulls strongly from low revs - you can slot it into 6th gear at 25mph and leave it there until you dip below that speed. That is about 1250 rpm. It also has punch from 3000 rpm though when it seems to find another burst of power. Alot better engine than the figures suggest.
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As power is a torque x RPM, the area under the torque curve/graph is all that really matters. If an engine has very high torque but low BHP, then the torque curve will be a column at the lower RPMs. The column would have to be very tall to get that area under the graph.
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My login name came from the fact that many years ago I owned a 1972 Mustang V8. This had the then standard 302 cu/ins engine, around 5 litres as us Euro folks measure.
This large engine was equipped with a carburetor of miniscule dimensions, such that it produced about 110 bhp at about 4000 rpm.
To drive ( 3 speed auto with straight through "mufflers" ) it would take off with a nice roar and squeal if you floored it, and pull well up to about 50 mph, after this you are aware that you are near full throttle, and you can wave the pedal about with little happening. It felt ok at about 60 mph, but 70 was about it.
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"carburetor of miniscule dimensions"
What was the fuel consumption like? I imagine that with a manual transmission and a higher top gear, it would be quite reasonable...
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"my mums V6 Hyundai"
Is that a Sonata? If so, I have a feeling that's the same engine as in the Kia Magentis (another underrated vehicle), but I'd be interested if anyone can confirm.
Edited by J Bonington Jagworth on 28/02/2009 at 20:07
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No, its the Coupe, but the engine is from the Sonata I believe.
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