alanbell

iTrader: (6)

The last time I was at York raceway , I went against a new Evo >> Dont know model number >> It was well stickerd up and looked the part ?? I got 11.9 , Evo 13 .0 But thats just the drag strip ??? Im there tomorrow >>> Must get better times , ?? Must change gear faster ?? LoL cheers Alan.

spec-cie

Eh? They're both directly related so it can't really be about just one or the other. You're right in that its the torque that, in the instant you floor it, gets you moving but its not about peak values of either: its all about the curve. Diesel engines (particularly the new BMWs) have massive peak torque but like all diesels this drops off rapidly giving a low rev range and, hence, a low BHP figure. So a 330d (360+ lbft) at the right revs will surge forward like a scalded cat but rapidly run out of steam and require an upshift.

High peak values for both are the best indication of a good torque/power curve: high torque sustained across the whole of a (large) rev range. My spec C produces 350/350, peak torque coming in around 3000 rpm and only dropping off a little all the way to 8000 rpm.

Weight and gear ratios also make a difference but, of two cars with similar weight and similar gearing, the one with well balanced power and torque figures will drop cars with much higher figures in one that have lower figures for the other.


So you got rid of your spec C ... what did you replace it with? Does this now make me the longest running spec C owner on here (30 months and counting)?

TonyBurns

iTrader: (3)

It depends on what you mean by directly related.... 2 similar sized/weighted cars with similar bhp but differing torque levels will not act the same, so that means they are not directly related? (one is basically power output from the engine and the other is a measure of the engines pulling power).
The torque will give you the advantage higher up the rev range when your doing xxx mph, the car will keep on pulling (unless you mean its related to this?) so where car A will slow down, car B will carry on going


I replaced it with a 2.5 TD omega due to the miles im doing, and no, your not the longest Spec C owner on here yet

Tony

spec-cie

Directly related as in they are part of the same calculation and you can always work one out given the other:

power = (torque x engine revs)/5252

(assuming you're measuring power in bhp and torque in lbft.

High peak torque figures don't necessarily indicate that torque is available high up the rev range ... thats why I used a diesel engine as my example: very high peak torque figure but nothing above 5000rpm. The converse is also true: a high-revving engine like a rotary or Honda VTEC has a great headline peak power output but relatively low torque.

You're right that two cars with the same BHP but differing torque will act differently ... but that's exactly the same as saying two cars with the same torque but different BHP will act differently (I give away 16lbft of torque to a new 330d but there is no way it will keep up with me from a standing start to any speed over 25mph and its not the weight or the gear ratio making the crucial difference).

TonyBurns

iTrader: (3)

Are you sure about that calculation? it doesnt seem to work?
For example, te RB320 produces 332lbs of torque at 3700rpm, so doing that ends up at about 233, doesnt seem right at all.....

Tony

spec-cie

Yes, I'm certain about the calculation ... its been established for a hundred years or so (and the general power/output relationship for a lot longer than that)!

This is the point I've been trying to make about the torque and power curves: neither torque nor power are constant across the rev range (take a look at any dyno printout and you'll see both start low, peak and drop off). Your figures for the RB320 are quite correct for 3700. According to the review I read, peak power is 317 bhp at 6000 revs which, using the same formula, means torque has dropped off to about 280 lb ft at this point. This is pretty good and a characteristic of turbo-charged engines: many other engines will have lost a lot more than 15% of their torque over this kind of range.

So, having good figures for both BHP and torque typically means that you have a lot of acceleration low in the rev range and can maintain this level of acceleration right up to the limiter (sound familiar? ... this is exactly how your spec C would have been). This is pretty much what you said in your post above: good torque high up the rev range is good ... but that gives high BHP so you can't say its about torque and not BHP as they're directly related.

Because non-racing naturally aspirated petrol engines used to have very similar looking torque curves and tolerances, BHP was pretty much all you needed to get a good picture of how fast a car you were looking at (hence our obsession with BHP and BHP/tonne). Now we have many super/turbo-charged cars and cars with VTEC or other variable timing systems, plus the huge surge in diesel popularity, you really need to know both figures to get an idea of the curve ... and a picture of the curve plus gear ratios, weight to get a decent picture (plus throw in transmission losses, wheel sizes, etc., etc. if you want a truly accurate model).

Hoppy

Have I got this wrong? Seems simple enough to me.

Accelleration and top speed are dictated by one thing, and one thing only - BHP. But not necessarily peak BHP - the amount of BHP you have available at the wheels at any given time. This varies with torque output and engine speed, ie gear ratios, and different engines produce very different results.

But at the end of the day, the car delivering most BHP at any given road speed (all other things being equal, which of course they rarely are) will accellerate more quickly.

Want to overtake quickly? Change down a gear. Your torque will probably not change much, but the multiplication factor of the lower gear ratio means the engine is spinning much more quickly and therefore delivering more BHP to the wheels, therefore faster accelleration.

If you're comparing two similar Scoobs, and have a reasonably accurate dyno graph, check the BHP at a given engine speed. The higher the BHP figure, the faster the accelleration of that car. Torque is a vital factor, but not the deciding one. More revs make a huge difference by increasing BHP.

Other factors with a big influence on straight-line accelleration and speed are weight, which is significant up to, say 100mph. After that, it's aerodynamics which play the biggest part, and both Scoobs and Evos are hopeless in this department. Don't take on a quick Porsche on an autobahn

Richard.

swtmerce

I think to put it a very simple way, the more area under your torque and power curves, the better!

spec-cie

Hoppy, you're close but you're also missing the fact that, at a given engine speed, BHP and torque are related by a constant ... the 'amount of BHP you have at the wheels at any given time' - i.e. engine speed - is the very definition of torque (well, actually its the other way around as power is derived from torque) ... you can't say it is about one and not the other.

Engine BHP and torque are unaffected by road speed or gearing. When you shift down a gear you actually increase the torque at the wheels: torque is a turning force and that's exactly what the wheel exerts on the road. BHP is a derivation of torque and doesn't actually 'do' anything ... is a different measure of the same phenomenon.

Having a higher-revving car is an advantage because, unless your torque falls off massively, the torque at the wheels will be greater at high revs in, say, fourth than at the equivalent engine speed (the one you 'get' when you change up) in fifth. But with diesel engines you often have to short shift for maximum acceleration because the torque at the wheels, at the top end of fourth, is less than that at the equivalent engine speed in fifth. Here, the extra revs aren't helping even though the BHP measured at the engine is greater than after you've shifted.

Quoting peak figures is generally for kudos but, given some idea of the engine type, you can make a guess as to what the curves will look like, and peak figures for both gives you a good set of parameters to work with.

spec-cie

I'm beginning to wish I'd put it that way myself

Hoppy

I know what you're saying, but in the context of Scoobs, the higher and wider the area under your BHP curve will give you the fastest, easiest to drive daily motor.

Of course, this motor will also have a nice high and long torque curve, but my point is that it's the BHP at any given speed that makes you go!

Sorry top be pedantic

Regards,

Richard.

smartuki

wot about a smart car ???

Hoppy

I disagree. This may be semantics and I suspect we may actually agree, but some of what you have said is contradictory and your point about short-shifting diesels is, with respect, wrong, and illustrates my point about the importantce of BHP. When you short-shift a diesel at high revs, it is because the torque curve has fallen of a cliff and the increased revs are insufficient to compensate for that loss. You then actually get more BHP by changing to a higher gear. The dyno curves will show it.

I don't know if this helps, but if you re-phrase my use of the term BHP to "turning force at the wheels" maybe we are saying the same thing?

Regards,

Richard.

spec-cie

Yes, except (and being very pedantic here so apologies) the definition of 'turning force' (whether at the wheels or at the engine) is torque. BHP is a measure of power (work rate), not force.

andythejock01wrx

Does this thread come with instructions for the hard of thinking ?

Hoppy

Yes, we agree. Our difference is just semantics

Torque is turning force and, I think, any confusion in this thread relates to where that torque is measured. Ie, at the flywheel (usually manufacturer's figures - bench dyno) or at the wheels on a rolling road dyno, which at best, is a calculated guess which varies enormously (and can be easily manipulated for dyno queens).

Bottom line is that the amount of potential speed/power you have available, is, obviously, dependent on how hard those wheels are turning vs the resistance (weight, rolling resistance, aerordynamics etc).

Ultimately, it's the stop watch or speed trap that tells the whole truth. Dyno numbers just give you a clue if you know how to read them and without meaning to sound arrogant, most people don't

Good evening,

Richard.

Hoppy

Sorry Andy, but at this time of night, no. (Snooker final's on telly )

But I am frustrated by this thread and others that rabbit on about torque and BHP as if it was somehow a complex subject. It's actually simple and obvious.

Somebody should write a brief 'sticky' post about it. Not me

Richard.

andythejock01wrx

The sticky's on Wikepedia, but cheers anyway.

h4rry

iTrader: (3)

Just going back to the saxo thing earlier on in this thread, it is possible the scooby driver came across one of the few z car honda civi type r engined saxos that are about. These seem an awesome bit of kit, so much so that i was thinking of getting rid of the scoob in favour of one but the practicallity of the scoob totally outweighed the saxo.

These things have a type r engine dropped into the rear and converted to rear wheel drive, running circa 220BHP with the remapped zcar ecu, but if supercharged can be anything 300+ BHP, and whats worse, they look completly bog standard!

There is one for sale on a track and road car website i was on the other day (cant remember site now ) it was a grey one, someting like an s reg and was running 310bhp (RRproved) for £9000. Claimed 0-60 time of 3.8sec's

I think we really need to start looking out for these cars before we get embarrased by them, they seem to be coming a lot more popular these days, and the worrying thing is, some of the kids will have them but not declare the changes, and have it insured as a bog standard 1.6 VTR or something stupid, then we are in the **** if anything goes wrong!!

AudiLover

For all you know it could be tuned. Its like those pesky 350hp ibiza cupras that show up Evo's!

kingofturds

iTrader: (1)

I kept an evo at bay on the way back from alton towers the other day in a saxo vts He was sat on my *** driving out of the park, but in the "twisties" he could not keep up for ****. Its easy to slag off saxo, in fact I have plenty in the past. But for a small fwd car they handle pretty well.




Once I got on the A50 though he blitzed me

h4rry

iTrader: (3)

Exactly, i aint slaggin them off, in fact they are a great little toy if youve got the money to spend on them. My mate had a tuned VTS about 2yrs ago, 188BHP (RRproved) and that was fast as ****, Seen off a big dirty merc 500 on the m53 one night, i rekon we were doing 155mph easy ( in my younger stupid days - note, i dont condone high speed public driving any more!)

The point is, theres lots of faster cars about these days and your never sure how fast any car can be anymore with todays technology, next, we will have 1000bhp road cars!!

GazTheHat

Aye, but it's still a Saxo.

andythejock01wrx

You starting to pick a bit of Jockanese mate ?

GazTheHat

Nae

andythejock01wrx

No, no, no Gaz !

A've got nae breeks on - correct.

Aye and nae - wrong !

Aye and nah, nut - correct !

We'll have you trained before you know it !

Andy McNicoll of the clan McNicoll (goes without saying, but I like the flow of it. ).

GazTheHat

I stand corrected. now gae get us some bucky ya fud.

andythejock01wrx

"Fud" . Aint heard that in years !

LG John

It's actually 100% the other way around as others have alluded to. Torque is a static measurement of force. Notwithstanding no one would design an engine like this for a car application; it's entirely possible to have monster torque for a very short range but poor performance. Take a tractor for example - sh*t slow! But it's got enough torque to rip your scooby in half and it’s not the weight that's letting the side down (although it doesn't help) it's the lack of power.

Power is a more important measurement because it refers to work. If you really want, you can convert bhp to calories/hr as they are both a measurement of power as is KW/h, etc. Power takes some account of the passage of time but torque does not. If you want to move a 1.3 ton object from rest to 100mph you need to apply work it. The application of force (torque in the sake of cars) is the method of applying work to the object but a peak torque figure only indicates what the maximum force that can be applied is but gives no indication of the overall work that can be done. Power on the other hand does give an indication of work. Of course it's not even as simple as that since an STI doesn't just produce zero or 265bhp but rather must be operated at its most efficient rev range to produce peak power. Nevertheless, it’s fair to assume that any manufacturer worth its salt will have matched gearing and other components to allow the vehicle to accelerate with around and about peak bhp being applied most of the time.

An analogy might help (figures totally made up):

A weedy guy approaches a gym monster and challenges him to a punching contest. He stipulates that using a special force detecting pad each contestant must apply as much punching force as they can in 10 seconds. The beast agrees and goes first. His first punch is 7lbft, he's second he really lays into it and generates 12lbft and the same for his third. His forth is down at 6lbft and his 5th 4lbft as he’s now pretty tired. In total he lays 41lbft into the pad across 5 punches with a peak of 12lbft, an average of 8.2lbft and an average of 4.1lbft per second.

The weedy guy goes next and quickly smashes out 15 punches at a consistent 3lbft each and is immediately announced the winner. His total is 45lbft with a much lower average of 3lbft but an average force per second of 4.5lbft. Simply put, he worked the pad more.

The beefcake is a classic scooby, the weedy guy is a Honda S2000 and the punching was actually a 10 second run rolling from 40mph

The sure fire way to take account of all of the above is to look at the area under the curve. That’s not entirely practical when sat next to someone at the lights though so its best to have a handle on what his power is, weight is and transmission method. Case and point is LetsTorqueBHP - Home which I find to be really quite accurate (considering) and it only looks at these 3 factors as they are by far the most important.

P.S. The EVO probably had basic mods to 400bhp

Hoppy

Good explanation, SB