BHP vs Torque

Post 140661 by nealer on 2006-09-08 00:43:18

hello all ... probably a question that has already been answered already on this forum, but I can't find an answer ... What is the difference between BHP and torque ... am asking because I'm fed up being smoked by my mates Golf TDi (and other coal / peat burners) - granted the S60 is a heavier car (and has a heavier driver) but I have 200bhp and he has 150bph ... surely the weight difference wouldn't make it that much quicker? To be honest - I'm not bothered about the old 'my car is faster than yours' arguement - but am fed up with his mythical stories of 40+ mpg (can cars really do this ??) and performance. cheers!

Post 140678 by Rnash2002 on 2006-09-08 08:27:54

I always thought its the torque that gives you the acceleration,more torque the quicker the car will pull,see the turbo diesel's have alot of torque mid range,i had a play with a new 307 diesel in my rover,stayed with me on some back roads,but once we had stopped for a car turning it was bye bye to the pug:)

Post 140684 by TwistedSanity on 2006-09-08 09:21:54

Torque is the stuff that gets you off the line quickly, i have a harley which is only 30bhpish but has masses of torque, two up i can surprise many sportsbike owners at the lights, but once i hit 30mph all i see is there tail lights, i hear there is a smart car(not for sale in england) that is diesel and does about 120?mpg, now thats economy, brighton and back for a fiver

Post 140686 by Unknown on 2006-09-08 09:26:36

Torque is the "turning force" of the engine. The longer the stroke in a engine (how far the piston travels from top to bottom), the more turning force or Torque a engine has. Our engines 5 cyl petrol have a long ish stroke, coupled by the fact it has a extra cylinder than a conventional 4 cylinder, giving large torque, and also, the extra cylinder we have gives the engine more momentum, so thats more torque and horse power combined advantage. Plus 5 cylinder is the "perfect balance" technicaly speaking. We got bags of torque with a narrow power band, power band being the pull in rpm if you like, ours fizzle out at 5000 rpm, which is low, the skylines for example pull continualy upto 7-9rpm. Horse power then is almost the opposite of the longer stroke in the engine, the shorter the stroke the faster the engine will turn, thus rev higher (like the mazda rx8, yes this is a rotary engine, but it revs really high with a wide power band, yet, fudge all torque). barbs

Post 140768 by Straker on 2006-09-08 16:11:38

Technical definition of power is "rate of doing work" therefore if your engine revs higher you (generally speaking) aren't putting so much force into the piston but because the crank speed is high you are dissapating more energy and your engine is more powerfull. Diesel engines physically can't rev much about about 5K (the diesel doesn't burn fast enough) but the combustion pressures are higher so you get more force on the piston which translates to torque. F1 cars don't develop much torque but they rev to about 20K (because petrol burns much more quickly than diesel) so generate large amounts of power. Turbos, engine size, fuel type all affect pwoer and torque but again very generally speaking small revvy engines are powerfull but low on torque whereas large lazy engines are (pound for pound) not as powerfull but they make up for it in torque. personally speaking Petrol is still the best :rice: :thewave: :B_steerin

Post 140777 by volvotuning on 2006-09-08 16:44:36

[QUOTE=nealer]hello all ... probably a question that has already been answered already on this forum, but I can't find an answer ... What is the difference between BHP and torque ... am asking because I'm fed up being smoked by my mates Golf TDi (and other coal / peat burners) - granted the S60 is a heavier car (and has a heavier driver) but I have 200bhp and he has 150bph ... surely the weight difference wouldn't make it that much quicker? To be honest - I'm not bothered about the old 'my car is faster than yours' arguement - but am fed up with his mythical stories of 40+ mpg (can cars really do this ??) and performance. cheers![/QUOTE] Forget about the difference in power and torque. To explain why the Golf is faster, you need to look at either power or torque on their own and where in the rev range it's delivered. Lets use power cos it's easy... Say you have 200 bhp @ 5000 rpm. The Golf will have say 120 bhp @ 5000 rpm. At 4000 rpm you may have 170 bhp, but the Golf may have 150 bhp (peak) At 3000 rpm you may have 120 bhp, but the Golf also may have 120 bhp. Now this is where the big difference is... At 2000 rpm, you may only have 60 bhp, but the Golf may have 100. At 1500 rpm, you may only have 40 bhp but the Golf may have 70. That's why it can beat you UNLESS YOU ARE IN THE RIGHT GEAR and making more power than he is at any moment in time. Gearing plays a factor too because it applies a torque multiplication factor to deliver a higher or lower force at the road. Hence why if you have 2 identical cars with same power and torque, the car in 2nd gear will accelerate faster than the other car in 4th gear. Below is a dyno chart of an S60 D5 v C70 2.5 LPT. Only power is shown (at the wheels of course). Both were done in 4th gear. Notice how the D5 has more power up to around 3800 rpm. So the D5 will always be faster if both cars are under 3800 rpm. For the C70 to be faster, the driver needs to make sure he is always over 4000 rpm else the D5 will whop his ass. So, just cos you have more power doesn't mean you are quicker. It depends on where the power is, and more importantly how you use it! Same goes for torque - just because you have more torque doesn't mean you will be faster. It depends on where the torque is. To win a "race", you need to know where the power and torque is of the other car and what gear it's likely to be in for the stretch of "private" road you are on. You can then choose the best gears to be in for your own car. Get it wrong and you lose. Get it right and you win. Adam.

Post 140784 by GregE102 on 2006-09-08 17:26:20

Hi Adam I have a standard 850 T5R saloon on a 95 plate, I think it's 240 Bhp I'm not sure, do you know what that translates into with Whp and tork? As My Mate has a Renalt Megan 1.9 TD and off the line i bet him up to about 40 then he comes past me, then i change in to 2nd at about 55 and then see him disapear in my rear view mirror and he never gats any closer, but Nealer is right its vfast for a diesel, i have driven it and like your graph shows it runs out of power very quickly. Greg

Post 140785 by BlackBeast on 2006-09-08 17:30:30

Weight also plays a factor in all of whats been said above!!!

Post 140786 by nealer on 2006-09-08 17:32:50

this is Brilliant!! thanks all...

Post 140788 by S60D5 on 2006-09-08 17:43:58

[QUOTE=nealer] To be honest - I'm not bothered about the old 'my car is faster than yours' arguement - but am fed up with his mythical stories of 40+ mpg (can cars really do this ??) and performance. cheers![/QUOTE] The Golf TDi lump should easily get 50+ mpg. I get very nearly 50mpg out of my D5 on most tanks, and WELL in excess of 55mpg on a longer run :Handshake Gotta love diesels!! That said, my next car will be petrol. Volvo, of course ;)

Post 140795 by volvotuning on 2006-09-08 18:00:08

[QUOTE=S60D5]Gotta love diesels!! That said, my next car will be petrol. Volvo, of course ;)[/QUOTE] Are you mad? :cuckoo: Adam.

Post 140798 by S60D5 on 2006-09-08 18:04:27

[QUOTE=volvotuning]Are you mad? :cuckoo: Adam.[/QUOTE] Yes :biggrin: :biggrin: Current plan is that my girlfriend will have my D5 and I'll get a new shape V70R (or S60R...) The price of them at the moment is amazing! (£15k for an S60R with 25k on the clock, late '03 with 2 years Volvo warranty!). Won't be for a little while yet, mind you. Need to finish Uni first ;) That and wanting to enjoy RICA D5 power for a while too......... :B_steerin

Post 140801 by S60D5 on 2006-09-08 18:08:28

Edit - That and the insurance for an S60R is £11.50 more per year than my D5 as standard :cuckoo:

Post 140803 by volvotuning on 2006-09-08 18:09:43

[QUOTE=S60D5]Yes :biggrin: :biggrin: Current plan is that my girlfriend will have my D5 and I'll get a new shape V70R (or S60R...) The price of them at the moment is amazing! (£15k for an S60R with 25k on the clock, late '03 with 2 years Volvo warranty!). Won't be for a little while yet, mind you. Need to finish Uni first ;) That and wanting to enjoy RICA D5 power for a while too......... :B_steerin[/QUOTE] Yes the are great value - lot of car for the money, that is for sure! Adam.

Post 140888 by Wobbly Dave on 2006-09-09 00:31:49

Just to stick my 10p worth in BHP is a mathematical function of engine torque x rpm. The formula is BHP = torque * rpm /5252 It miffs me a bit when Clarkson said about the M5 E60 - "when you push the M button the engine is no longer making 420 bhp, it is making 507" which is codswallop. They quote peak figs which has little bearing on the real world. The car will only ever make that figure at 1 particular rpm. When the engine is idling is hardly making any BHP at all. Diesel engine are torquey and low reving - petrol e.g. VTEC is high rev low torque. In theory both cars can make the same power but in entirely different ways.

Post 140889 by volvotuning on 2006-09-09 00:45:00

[QUOTE=Wobbly Dave]Just to stick my 10p worth in BHP is a mathematical function of engine torque x rpm. The formula is BHP = torque * rpm /5252 It miffs me a bit when Clarkson said about the M5 E60 - "when you push the M button the engine is no longer making 420 bhp, it is making 507" which is codswallop. They quote peak figs which has little bearing on the real world. The car will only ever make that figure at 1 particular rpm. When the engine is idling is hardly making any BHP at all. Diesel engine are torquey and low reving - petrol e.g. VTEC is high rev low torque. In theory both cars can make the same power but in entirely different ways.[/QUOTE] hehe, I'm gonna add my 12 p worth. Technically, it's possible to make an engine produce the same power over many rpm. Just needs a suitable negivative sloping torque curve :) However, you wouldn't want to do that else it will be like a very old diesel. Or you can make a funny shaped torque curve which would results in 3 peak rpms of the same value! Now that would be very crap to drive! But just to demonstrate the fact that it can be done with just ECU software! Both petrol and diesel can make the same torque too! But often, it's in different parts of the rev range. For example, the D5 tuned can make 435 Nm from 1700 rpm to 3500 rpm, whereas the T5 will do it from 3000 rpm to say 5000 rpm. So here, both the diesel and the petrol are making the same torque. Adam.

Post 140891 by Wobbly Dave on 2006-09-09 00:51:40

For my 14p worth I agree. I should have said both make can make torque in different parts of the rev range. I was trying to illustrate the myth that is peak power figs - in so much that they only exist for 1 moment in the rev range - and as such dont give a true indication of a car's performance.

Post 141299 by Straker on 2006-09-10 20:10:43

Post 141502 by Engineer on 2006-09-11 18:11:12

[quote=Straker]Yes but Dave when you press the button the engine will run a different map much like the RICE re-maps so you get more power and torque accross all the rev range and the curves will look different.... Also at the top of the rev range there is a big difference between 420 and 500 BHP.[/quote] About 80 BHP I make that lol. If you want to compare different engines then use BMEP, then just look at the chassis weight saves all the confusion. If you compare the original guys query regarding the Golf its plainly obvious why he's in trouble. See Link and punch in Golf TDI, 110,4000 and 1.9 in the blue columns this car ain't far off a standard S70R Auto, be it an old one http://www.vpcuk.org/forums/showthread.php?t=12506