But st1, you're comparing a 130bhp 1.9 diesel with a 193bhp 2.8 petrol!
Compare the BMW 330i and 330d (as has been done to grrrrreeeeaaaat length on this site), and i believe it simply comes down to driving style. They are as quick as each other, just they both require different techniques to fully utilise that speed.
As i have driven neither, i don't really feel qualified to comment on the BMW's, but having had one petrol and one diesel car (each 90bhp), i have established that i prefer to drive at lower revs than most people, change up at around 3-3.5k revs when accelerating normally, and that therefore my style and type of driving is better suited to a diesel car.
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A big, torquey diesel for me, anyday!
.....preferebly with an automatic transmission.
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groups.msn.com/honestjohn - Pictures say a thousand words.....
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But st1, you're comparing a 130bhp 1.9 diesel with a 193bhp 2.8 petrol! Compare the BMW 330i and 330d (as has been done to grrrrreeeeaaaat length on this site), and i believe it simply comes down to driving style. They are as quick as each other, just they both require different techniques to fully utilise that speed. As i have driven neither, i don't really feel qualified to comment on the BMW's, but having had one petrol and one diesel car (each 90bhp), i have established that i prefer to drive at lower revs than most people, change up at around 3-3.5k revs when accelerating normally, and that therefore my style and type of driving is better suited to a diesel car.
This answers the original question - what is best for PERFORMANCE (which I guess means acceleration, top speed, etc) - quite nicely.
As pointed out above 330i and 330d have similar performance (o-60 etc), what factor do they have in common??? (Hint: It's not peak torque...)
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The diesel's got a lot more torque. I don't have any figures to hand, but if both cars have manual gearboxes, you may be able to do typical overtakes with a flex of the right foot in the diesel, where you'd require to drop a gear or two in the petrol and make it sing.
Again, depends whether you want to have to 'drive' all the time to get maximum performance, or just squeeze and let the car do the work.
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Take modern 2 ltr petrol and 2 ltr TD engines, both produce around 130 to 150 bhp though the TD does it a 2000 rpm lower and produces at least 50% more torque. Enough said!
Only performance benefit of a petrol engine in real world road use is hanging out longer in one gear when over taking.
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Just a tailpiece on this thread: I went to a seminar at M-B in Milton Keynes last weekend. They presented the S600 V12, whose torque curve is flat between 1800 and 3500 rpm -- at 800Nm! Now, that's what I call "grunt".
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I own a petrol V8 and a 2L diesel. The characteristics are almost the same. The V8 has about 160Bhp with 220lb/ft of torque with a red line only slightly higher than the diesel at 5500 rpm. The diesel has about 130Bhp and 200lb/ft and reds at 4750rpm. The V8 will pull from 15mph in 3rd all the way to about 80mph which can make for some big smiles. The diesel flattens out very quickly at about 55mph requiring a gear change.
Give me a large engined petrol with a good Bhp/torque curve over a diesel as it can power away from stationary whereas diesel are great in a narrower band.
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3500S: apples and pears time again! Compare a V8 diesel, or even a 6 cylinder, with comparable capacity to your V8: pull away in 4th from 10mph, if thats your criteria. top speed at least equal. But a 2litre of any design is going to struggle against a 3,5, except on fuel costs!
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Reply to Roger Jones: If the S600 V12 was a turbo diesel it would produce around 1000nm torque.
Reply to 3500S: Interesting that the diesel is nearly half the capacity of the petrol though stands comparison, now if your diesel was a 3.5 as well it would produce around 220 bhp and 330 lb torque and still use 40% less fuel than the petrol.
Dont get me wrong, I love hanging on to the red line in a crisp high revving petrol engined car however for 90% of daily motoring diesel makes sense.
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I drive a 2 litre 306 xsi 16v with 135 bhp and 133 torque. It pulls nicely above 3500rpm and a quick start is not out of the question. However if I am already rolling and into 2nd doing 10 - 15 mph and want to accelerate quickly, I can't. What can one do to improve this situation? Is it a torque, bhp or both issue? Are any of these aftermarket filters, induction kits, or 'piggy back' ECU chips (which confuse the computer into sending more air or fuel or something into the engine) any good? Are they harmful or illegal?
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>What can one do to improve this situation?
Sell it and buy a DTurbo, then get the TD engine warmed over to about 110 BHP and it will wipe the floor with the XSi (except perhaps on the drag strip) :-) Oh, and probably close to double your MPG into the bargain!
>Is it a torque, bhp or both issue?
Both, since they are intrinsically linked. A high torque figure at low revs merely signifies that the engine produces plenty of power at low revs (diesel case). Sadly there is little you can do to increase the low end power of a petrol engine without sacrificing high end power - unless it uses variable vale timing (eg VTEC or VVTi) which gives you effectively a cam for low revs and one for high revs. An induction kit MIGHT make it pick up bit better, but is unlikely to liberate significant horses. A tuning box might liberate a few more horses, but you are limited with a non turbo engine. A turbo combined with an ECU to give you a flat (diesel like) torque curve is the only real way forward (as the 2l Turbo CT petrol engine fitted to some PSA cars - CT stands for Constant Torque).
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RichardW
Is it illogical? It must be Citroen....
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>Sell it and buy a DTurbo
My Dad would never speak to me again.. The shame..
Thanks for the info, most helpful.
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If you open the throttle in 2nd while rolling at 10-15mph in a TDi your generally greated with a great big fat wad of Turbo Lag - nice.
Diesels are great for economy but I find their complete lack of throttle response and narrow power band annoying at best and down right dangerous at worst - I went back to a gasoline powered car from a Focus TDCi because of this.
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If you open the throttle in 2nd while rolling at 10-15mph in a TDi your generally greated with a great big fat wad of Turbo Lag - nice. Diesels are great for economy but I find their complete lack of throttle response and narrow power band annoying at best and down right dangerous at worst - I went back to a gasoline powered car from a Focus TDCi because of this.
Turbo lag always frustrates. Does the new breed of TDs have the Constant Torque as mentionend above to avoid the big fat wad of turbo lag?
I have driven a TT turbo and a boxster s. Admittedly the boxster has more go, but the 6 cylinders working away produce a wonderful spread of power solving my 10-15mph 2nd gear problem (yes I know it is a 'fast' car so should be quick, but it was the low range pull that impressed, amongst other things..), whereas the TT's lag caused us to get beaten by a nissan pulsar, which was embarrassing. Mind you the Nissan did have gold wheels and a huge spoiler so I guess that helped.
So, is the only (or best) solution a bigger engine with more cylinders? Or perhaps for 'normal' cars a 1.5th gear or 2nd gear 'underdrive' for just such an occasion?
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www.stanford.edu/~voloshin/lhowwhy.html
I have posted this link before on the Discussion forum, but it's such a good explanation of the relationship between power and torque that I may as well post it here in Technical as well.
Enjoy.
Ed.
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I think some people are scared of dropping down to 1st from 2nd when crawling along and needing to spurt some power on. Gearboxes do have synchromeshes on 1st these days, which was often the problem in the olden days; and Mr Driving Instructor always discouraged it.
Having recently driven an HDi engined car, if you floored in in 2nd gear at around 10-15mph, you'll have a long wait while the throttle finally works out whats going on and then the engine plods up to the turbo point before finally taking off. By the time that's happened the milk float has already burnt you off.
While modern TDs seemed to have smoothed out the turbo lag problem reasonably well, so there's less of a binary step change in torque; they still seem to have poor (if not worse) throttle response. I think all the electronics needing to control things and stop puffs of black smoke belching out when flooring it add a lot of delay in the system.
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>I think some people are scared of dropping down to 1st from 2nd when crawling along and needing to spurt some power on. Gearboxes do have synchromeshes on 1st these days
So, I'm not doing any harm by clunking it into 1st at 15 mph? It feels like too much of an effort to get it in to be a good thing.
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Not if you do it smoothly, it shouldn't be any different to any other gear change. Mind you, a lot of cars have a very short 1st gear so you can get a big leap in revs. My old 205 had long 1st and 2nd gears, so I would quite often drop to 1st while moving - and 1st gear was good for 40mph in that car (very quickly and noisily though!).
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"While modern TDs seemed to have smoothed out the turbo lag problem reasonably well, so there's less of a binary step change in torque; they still seem to have poor (if not worse) throttle response. I think all the electronics needing to control things and stop puffs of black smoke belching out when flooring it add a lot of delay in the system.
Have to agree, I used to drive a diesel van years ago, and it was horrid. About 2 years ago, I hired a car that was a new diesel Astra. I hoped diesels had improved, but was very disapointed in the 'around town' response, especially when wanting to go from a crawl to 30mph, eg when slowing behind someone turning left and then trying to get through the next lights.
I still decided to buy a diesel to save money,, and bought a diesel Omega Elite automatic, I expected it to be like a snail, but because it's an automatic, there is none of that lag, none whatsoever. As soon as the lights change, you can floor the throttle, and you are held 'moderately' in your seat after about 0.2secs....The revs go up to 1900rmp in a split second, and it's off like a shot up to 30mph, before most have let the handbrake off, a nice plume smoke to boot! The marvellous thing is 0-30mph, the revs don't go above 3000rpm, before you have to back off and it changes up, so no-one hears a sceaming petrol engine going upto 6000rpm in 1st and thus cursing you as a maniac.
The automatics completely get rid of that awful sluggish low-down lag.
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I love my V8 just for the sound it makes, it's 32 years old but still makes an lovely grunt that will forever endear me to V8's.
My diesel in comparison is the 'daddy' only because it is more modern but has the same properties in a smaller package with twice the fuel consumption.
Now if I could afford the 3.9 EFi V8 as a transplant it would make my P6 into more of a monster that it is.
As a compromise, I'm a diesel convert only down to the 'politics' of the day.
I admit though, a good petrol V8 tuned for Bhp and torque will rule the roost. There aren't many V8s that can do that. Well saying that the new Rover V8 is on song, 260Bhp might sound meagre but 410Nm of torque and it's overtake city.
I guess I want both, I want to able to take my cake and eat it.
Petrol V8 will always win.
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