Bhp Levels

[kyepan 291]

I am of the understanding acceleration will be at its greatest at peak torque,

Yes that is the point when the engine is capable of the most accelerative force.

 

but...

 

Once you factor in all of the real world frictional elements and gearing it may not be, the actual peak acceleration felt by the person in the car may be at a slightly different.

 

And this is one of the only sensible posts from the many up here.

 

As it's isolating how modeling the engine output is simpler than modeling the real world.

 

which also may be why power and torque at the wheels is an important thing to think about, as that gives you a real indication of how your effort will be applied to the road, rather than how it will be applied to the clutch - then gearbox - then diff - then driveshafts then - wheels, each with their own frictional componenet, that may differ in it's effect or manifestation.

 

i'm going to remanifest myself into the bedroom where i should have been an hour ago getting sleep before my trip into the big smoke tomorrow.

 

 

 

night all

[Cameron 16]

Oh, on a slight tangent, that reminds me of a point I meant to make. Let's not forget that you can only accelerate as fast as your tyres can transfer the force to the tarmac. So an engine that makes buckets of torque down low will either have to be throttled by TC or sit in a cloud of smoke. Whereas an engine that makes less torque at higher revs (a "peaky" engine) will be able to translate 100% of its torque to acceleration.

[DrSarty 90 1 Cars]

Oh, on a slight tangent, that reminds me of a point I meant to make. Let's not forget that you can only accelerate as fast as your tyres can transfer the force to the tarmac. So an engine that makes buckets of torque down low will either have to be throttled by TC or sit in a cloud of smoke. Whereas an engine that makes less torque at higher revs (a "peaky" engine) will be able to translate 100% of its torque to acceleration.

 

Oi Cameron (and tangent point noted), no tyres or gearboxes or we'll wander off again. We are rating an engine, nowt else. Not even how fast it can go; it's bolted to a frame to the floor. It's rooted.

 

Now is this engine any good? OK: scrap that. Let's have that engine, let's call it Vicki's engine standard ex-works, and a clone of that engine that has then had Vicki's mods done on it. Let's clone the floor, frames and dynos too and sit them side-by-side, with us all in a booth watching dials and guages.

 

Now, which engine is better? They are both available for Vicki to choose to hoon in; the same hooning, so the application is the same. Explain how we determine the performance of these two engines and compare them.

 

There were some comments earlier which would mean in our booth would be people saying that torque isn't important, it's BHP that counts. Let me state again that I'm not saying BHP is not important, I'm saying it only comes from torque and how it's delivered. But we seem to have people saying that the torque is not important as long as it has the power, and I am saying this cannot be true. In fact I'm saying the phrase in itself is nonsense.

 

Even from the motorbike article link above, which let's face it is equally applicable as it concerns physics, it says:

 

Accelerating and maintaining top speed both require force and power. At speed, there's no more acceleration to be done, but you have to push all that air out of the way. So "Torque gets you moving, Horsepower = MPH" isn't true either.

 

Even phrases like this, which kind of side with the torque crowd in effect, baffle me as BHP doesn't even exist without torque. It is purely the torque viewed in relation to engine speed, which in itself factors in time and is therefore just a 'power' rating, summing up amount of work done in a certain amount of time. The work IS the torque. So everything in this argument depends on the torque the engine produces. I didn't say peak, I said what torque it produces, which means looking at the whole delivery across the rev range, which gives us a nice plot or graph. As a result, everything else can be valued, rated, specified what have you, but ultimately it all relates to the torque. There is no (horse)power without torque. This means to achieve whatever power or characteristics we want from an engine, we tailor the torque curve and that's all.

 

What else can there be?

[Mandic 0]

As long as You are talking and comparing torque alone so be it, but as soon as You enter another variable in equation, You have to look at the whole thing from different point of view. Now You have two variables in and to see their correlation You start looking at power. You are right at saying that if we want to achieve certain power curve out of our engines we have to tailor torque curve ACROSS the rev range.

 

Now, if we want to compare engines, since like I said, we have 2 variables now, torque and omega. In order to compare these two engines we HAVE to fix one variable! So to compare 2 engines we need to fix omega to a certain point and then look at the standardized torque and power.

 

Only so we can compare things.

 

Let's take F1 engine for example, in "only" produces 350Nm of torque, same as lets say 2l TD engine, how are we going to compare these two then? We HAVE to take a look at power, no other way, or torque if You want, assuming they rev to the same RPM point (standardized torque). Either case, You have to fix one variable (make it the same for both), only then You can compare things. And all that can be easily be seen if You look at area under power curve which will be the same in both cases!

 

 

Cheers

 

Ziga

[Batfink 201]

I think what we can sum up is that Vicki needs to let her car rev as high as possible to find her true peak power and get 45's on

[DrSarty 90 1 Cars]

I agree totally with what you have said Mandic, because in isolation, torque as a comparative between engines is meaningless....however, so is horsepower. Now here we are talking just about rating an engine based on one figure alone, which is also something I said can't be done.

 

Don't get frustrated at me, as I'm saying you can't have these two engine's of Vicki's side-by-side on the dynos as I suggested, with two BHP screens showing a figure each, where one says 150bhp and the other says 145bhp, AND INSTANTLY STATE OR ASSUME that the 150bhp engine is better.

 

As a result, these people that were saying earlier 'pish to torque, it's horsepower that counts' and I said 'well no that's not really correct' are wrong, and in an argument inevitably somebody is wrong or has to succumb to another point of view. That is why this is being debated I believe.

 

So your good torque example earlier comparing an F1 car's (apparently meagre) 290lb.ft of torque wouldn't make it - on that measurement/statistic/figure alone - stack up very well against a 2.0litre diesel Mondeo. Agreed? But, the 900bhp of the F1 engine makes it sound much higher, more sexy, more impressive than the Mondeo as it is something we can associate with, i.e. 900bhp is much higher than 150bhp, so therefore it IS a more poweful engine. It is therefore a good 'at a glance' reflection of an engine's power capabilities and you can therefore see why it is helpful in situations where higher appears better, such as sales and rolling road days.

 

But it is (in isolation as I hope we're agreeing on now) only telling part of the story, because how does that 900bhp F1 engine stack up against the 900bhp diesel engine of a large construction vehicle such as a truck. Like I said, it's meaningless.

 

So in conclusion I am saying this. *And allow me to say I have found the whole discussion fascinating and I hope some others have too. I'm going to buy a book today on engine technology to read on my trip down to Australia tomorrow I've found this intelligent debate so interesting. One thing I'm going to look up today is why F1 engine's rev so high? I think I have my own sensible reasoning for it but I'll see if that's vaguely correct when I get my book.*

 

I am saying that comparing Vicki's two engines on the dyno, one factory spec 'versus' one we can tinker with instantaneously and change anything we like (what a dream that would be for giving back to back comparisons....oh hang on, that's what engine developers do), the BHP and the torque figure alone, in isolation are fairly useless. Yes, we can see 'errr...that one makes more X'. But a true comparison is done by looking at one of the two engine curves. Why did I say that? Well, I am saying that EVERYTHING about the engine's characteristics are a function of its torque. It's power (bhp) curve is merely derived mathematically from the torque curve; it simply doesn't exist without it. Therefore the distinction between torque and BHP as shown here several times, particularly as separate items is incorrect, as they are intrinsically linked. However it all starts with torque; not peak, but delivered, spread torque, which is then tailorable to generate the horsepower desired, which in itself is just a measure of a rate of work. BHP makes a good quick description of an engine or a perceived engine improvement, but ultimately the deciding factor is what torque the engine produces at what RPM, where you look at it collectively, hence IMHO the torque graph/curve (and the area below) describes and dictates the performance of any engine.

 

So please no more fights or comments about horsepower being better or winning races, and certainly not torque is irrelevant, because as I see it, it simply is everything.

Edited December 10, 2008 by DrSarty

[Mandic 0]

Look mate,

 

All I'm saying is that if You start to compare engines You have to have the same starting point. That's why You need to fix omega! And then You look at torque curve, which will all be down to application this engine would be used in. For example, ideal torque curve of a locomotive engine will certainly look different to the one powering ventilating fans for example! But when You standardize the torque to a certain RPMs then You can start talking about power as well as is the only one which can be compared between mechanical, electrical, heat power, ...

 

 

So when comparing two engines, first make sure You are comparing same stuff! Next, see which of those torque curves suits You best and choose appropriate engine for Your application. That's it. BUT the area under power curve will stay the same.

 

This is general rule. But since we are comparing similar sized engines, for similar applications, with similar gboxes, tyres, same cars driven on similar roads, ... We can just look at power for easier comparing. As soon as one variable is not the same, for example road type (open roads or tight twisties) we can no longer say which is better just from power, but if we alter another variable, say gearbox, then power is back in the game So again. Make sure You compare same stuff and then look which engines suits best for given application.

 

Cheers

 

Ziga

Edited December 10, 2008 by Mandic

[DrSarty 90 1 Cars]

Agreed again Mandic.

 

For your (I mean everyone's) viewing pleasure, it seems this debate, perhaps like 'why are women so hell bent on controlling us males?' has been going on since time immemorial - well at least since Otto invented the internal combustion engine anyway - and therefore I present you this extremely entertaining read. It is clever, humourous and as random as some of our stuff on here, which makes me feel we're not as strange as I sometimes think we are.

 

It's worth sticking it out as it gets quite 'spaced out' later on and extremely philosophical.

 

Now, my final words <forum sighs in relief> I can now clearly see having read up on F1 engines having to rev so high to generate high horsepower that HP is certainly a very important factor in tuning an engine. I have learnt from people's comments and explanations and this ^^ article (and others), that the rotational speed of the engine (read: output shaft) is critical to performance; I accept that and I understand that I may have come across as saying it wasn't.

 

And it is implied in making comparisons that it's done fairly, which implies the use of some constants; so again I totally agree.

 

This is why I remain confident that in Vicki's two engine comparison, if you're totally nailing down every last element for consistency such as revs (which of course are critical in power (HP) output - something I've always conceded but then I've never really understood the relevance of power in itself until now), then the only way to increase power output is to alter (increase) the torque, the actual force that the engine generates. That is really what I've been saying all along.

 

Just to clarify that, if we free up the element of revs for this side by side comparison, then we can manipulate power output even on revs alone, as the maths for the power calculation will mostly always be in the favour of RPM. So engine B at 7200rpm versus engine A at 7000rpm, now taking torque as a constant, means the actual power output will be higher. So we have our higher HP figure: great. But based on engine application, as we all know is ultimately the most relevant matter in all this waffle, Vicki might not be able to access that higher RPM for several reasons such as it doesn't suit her driving needs or it stresses the engine unnecessarily. On that basis the higher HP wouldn't be much good. Sure, she can say her car produced standard plus 25bhp, but as stated it might not be any good to her. Conversely, if she was able to generate an extra 25lb'ft of torque then that would much better represent an improvement in the engine IMHO.

 

Likewise, instead of being able to increase the RPM by 200rpm, we can also liberate more power by generating more torque and settling the revs back to an even, constant level. This means you and I are in total agreement Mandic and most likely Black Mi16 too. But if you think I'm hell bent on disagreeing or being flippant, then please accept my apologies and enjoy the link to the F1 forum debate above, as it's technically fascinating as well as being easy to digest and pretty funny.

 

Rich

Edited December 10, 2008 by DrSarty

[tony perks 1]

I think the engine is a little down on power here's mine same spec cam proper head Magnex, but with 45's

 

http://i162.photobucket.com/albums/t269/to...pg?t=1228904690

 

Sorry about the link but i couldnt shrink the file to upload it here.

 

The engine in question had just had the 38mm chokes removed to improve low end pick up as we were at caerwent very tight and twisty, next weekend this it did and improved the whole feel of the engine, This engine when built and dyno'd put out 196bhp and over 150lb/ft of torque this run was after 5 rallys and was showing signs of breathing, so is really in need of rings and valve seat tidying.

Edited December 10, 2008 by tony perks

[Henry 1.9GTi 36]

just use bmep?

 

way I see it you need to look at each engine speed seperately, at any engine speed more torque = more power so to get back to the OP as said above get it to rev more if the graph is not tailing off yet.

not sure if its been said but a few omegas have been typed. this is 2piN where N is engine speed rev/sec so to compare a torque to a power output is silly as for a given torque figure power will not change at a set engine speed and visa versa. More = More

 

k i just typed loads but deleted it, cba

 

good luck with the car vicki

[B1ack_Mi16 67]

This means you and I are in total agreement Mandic and most likely Black Mi16 too.

 

That is true, I just wanted to be a little diffictult because I happened to be in the mood for it ..

 

And to prove the point that in general if you want to compare two cars with two different engines it's really the power you need to look at, as it's definately the most important factor in this case.

 

But enough about this now I think

[guffe 2]

Offtopic, but I think this is a stupid thread.

[Batfink 201]

well I learned some interesting stuff

[DrSarty 90 1 Cars]

Offtopic, but I think this is a stupid thread.

 

You're entitled to your opinion Guffe.

 

But hey, ram it! I know you crazy Finnish, as I've just divorced one .

 

Thanks Kev. I enjoyed it too. I'm off to learn off the Ozzies tomorrow, as Eeyore recommended I listen to them as in some respects, their general engine tuning knowledge at street level is way up on ours.

 

And about BMEP, I know Sandy prefers that as a comparison method...I do too. But this conversation specifically went with Vicki's original post and the good old BHP is better than torque argument.

 

Speak to you next from Sydney!!

[weejimmy 1]

this thread is as stupid as a pub conversation,

theres some sence in it if you look hard enough.

 

i like it

[DrSarty 90 1 Cars]

this thread is as stupid as a pub conversation,

theres some sence in it if you look hard enough.

 

i like it

 

GREAT!

 

And that's why we keep going to pubs.....isn't it?

[boombang 2]

GREAT!

 

And that's why we keep going to pubs.....isn't it?

 

No, I go purely for the beer and to escape from the harsh realities of life.

 

On topic though, almost everything posted here is right, just different viewpoints.

 

Personally though, I'd always rather have a 140bhp engine with a decent amount of torque over a wide rev range than a 150bhp engine with a narrow torque band.

 

In practise on the road, my old Mi16 powered 309 was very rapid. Peak torque was between 4k and 7k, and the 1.9 engine with Mi final drive dropped it bang onto the peak torque each change up.

 

Put the same engine on a 1.9 box and it feels slow and laboured. Think this is the point a lot of people have tried to put across on here.

 

I agree with Dr S though, power is nothing, it's all about torque, how wide the torque band is, and THEN about what gear ratios you run it through (and shed loads of other stuff, but hey this is a simple post so lets keep it simple).

[GLPoomobile 958]

I wonder if Vic has had enough yet of being referred to as a lady?

 

And I hope my Christmas dinner is more easily digestible than this topic. I didn't realise you could get heart burn from reading! That's the only thing I've learned from this.

[jengis 0]

So please no more fights or comments about horsepower being better or winning races, and certainly not torque is irrelevant, because as I see it, it simply is everything.

 

Very simply (and accurately) TORQUE is HALF the story, REVS (either a specific RPM or a range of RPM's) are the other HALF.

 

As you quite rightly say it's torque * RPM that gives you the power produced by the engine. if EITHER is zero, then you have zero power.

 

The final piece is the gearing - this is the piece of the physics jigsaw that makes the "theoretical" BHP figure into an actual force that can be used to accellerate the car. If the engine is spinning really fast then it needs a lower gear fot the same road speed - hence the resultant torque at the wheels will be high.

 

Kev

[andychalmers 0]

My mind is in bits after reading this thread

Spanner in works now, I went in Latvolas WRC FOCUS last week, thats 300bhp with 550 lb of torque & that was insane, neck breaking in fact. My road evo is 360 bhp & 330 lb of torque and is'nt even 1/3 as quick, however his car is about a million quid new & mine was prob about 30k new. In rally cars you deffo need the torque as lots of stopping starting so helping the acceleration & grunt low down.

[Cameron 16]

The difference is, in a WRC car the torque is actually tractable due to the super-duper 4WD system and sticky tyres. Try sticking 550lbft through a FWD 205 with an open diff!

[danpug 1]

My mind is in bits after reading this thread

Spanner in works now, I went in Latvolas WRC FOCUS last week, thats 300bhp with 550 lb of torque & that was insane, neck breaking in fact. My road evo is 360 bhp & 330 lb of torque and is'nt even 1/3 as quick, however his car is about a million quid new & mine was prob about 30k new. In rally cars you deffo need the torque as lots of stopping starting so helping the acceleration & grunt low down.

 

Thats the point i was trying to make earlier in this thread.

[jengis 0]

Spanner in works now, I went in Latvolas WRC FOCUS last week, thats 300bhp with 550 lb of torque

 

550 lb ? you sure its not 550 Nm ? (translates to 397 ft lb)

Reason being, its not possible to have that much torque and only 300 bhp peak unless the engine only revs to 3,500 RPM (ish)

 

I agree with your point though, if the torque is good, max power isn't constrained to the top of the rev band, so accelleration is strong from the midrange (though torque tails off quickly as the revs rise, capping power).

[welshpug 1,661]

550 lb ? you sure its not 550 Nm ? (translates to 397 ft lb)

Reason being, its not possible to have that much torque and only 300 bhp peak unless the engine only revs to 3,500 RPM (ish)

 

I agree with your point though, if the torque is good, max power isn't constrained to the top of the rev band, so accelleration is strong from the midrange (though torque tails off quickly as the revs rise, capping power).

 

 

most likely 550Nm, but you're not actually far off with the RPM, most WRC engines only rev to 5500-6k RPM due to the restrictors on the inlet, they are tuned quite differently to an engine that's unrestricted, the torque they produce

Edited December 16, 2008 by welshpug

[vickiw106 1]

I wonder if Vic has had enough yet of being referred to as a lady?

 

And I hope my Christmas dinner is more easily digestible than this topic. I didn't realise you could get heart burn from reading! That's the only thing I've learned from this.

 

 

she maybe if vicki was interested in this forum

 

vicki is just my wife and this user name was available

 

i really wish i had not started this thread