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Bhp Levels


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#41
danpug

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By fastest do you mean ultimate top speed or fastest accelerating?

#42
B1ack_Mi16

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By fastest do you mean ultimate top speed or fastest accelerating?


Well it really does not matter if you take into account my statement of using gearboxes that will give the same top speed for both cars, at the maximum revs of each engine.

Lets put it this way instead.

Both cars are geared in such a way that they can only make 100mph top speed at the maximum engine revs.

The answer is anyway that the one with most BHP will be fastest accelerating.

Torque just describes how much "work" the engine can do, while the power describes how fast it can do the work.

Work = Force * length (N * m)
Power = Work / Time

It's quite simple physics.

#43
weejimmy

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no i dont think its irelivent, that was a bad choice of words, just not as important as bhp


thats why race cars whos sole point is to go faster than the other guy have peaky , no mid range torque , high bhp engines

heres a good wright up explaining bhp and torque, from more my point of view
http://forums.mg-rov...d.php?p=2506850

please dont ignore it as its on a mg rover site lol

thi

#44
danpug

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thats why race cars whos sole point is to go faster than the other guy have peaky , no mid range torque , high bhp engines


Wouldn't that depend on the type of curcuit though? I can understand high bhp engines on say for an example an oval curcuit but on twisty curcuits torque will be essential i would have thought.

#45
Batfink

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no - you just need more gears to keep it in the peak powerband :lol:
If you think about most road cars, 1st gear is all but useless except for pulling off so you only have four gears you will use on track (or if you have a gti-6 - 5 gears)
but on a racecar you can gear 1st so it can be used on slow corners. I think the smallest ratio for my gearbox gears me up to 70mph in first! - so as long as I can get moving I have 6 gears to use on track which means I can keep my car in the correct powerband easily.

K.

#46
DrSarty

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I found the article very interesting, but I'm afraid even on topic we're wafting off topic.

Again, I said there were many variables in comparing cars and their performance, i.e. what they do in the road in the real world.

What I'm bangin' on about (yet again), is that this topic is talking about an engine in a certain state of tune delivering a measurable amount of performance. Please forget gearboxes, power to weight, suspension and handling orientated geometry and all that, as they are the next tuning areas to create a better performing car for whichever application.

Under the spotlight was a car lashed to a dyno reading power through the wheels. The dyno and associated hardware and software calculated back to take into account drivetrain losses and determine its version of what the engine was producing at the flywheel; in this case 140BHP.

Vicki wanted to know if that was good or acceptable based on her mods TO THE ENGINE!! Hence I started saying/suggesting getting hung up on horsepower figures was perhaps not the best measure of the engine, whereas the torque and fashion in which it is delivered is key. The BHP figure is derived from the engine producing T torque at R rpm, so is purely a function of torque; the other number just being a convertor for imperial or metric measurement.

I am putting my neck on the block, as I discussed with Jas E earlier, who works in engine tuning and watches dyno runs, saying that the only variable an engine tuner can introduce/manipulate/tune if you like is to alter the shape of the torque curve. Wait! Yes, components can be balanced, toughened, lightened or hardened etc to allow the engine to achieve or sustain different RPMs, and also the tuner can simply apply more throttle. But as BHP is calculated from torque, then surely my neck is fairly safe, as an engine produces a rotational force and that's all.

Components which alter fuelling, airflow, exhaust gas extraction or tasks related to that such as altering cam timing, are not directly increasing the power of the engine, they are altering the shape of the torque curve, WHICH IN TURN, based on selection of RPM produces a BHP figure, which is not entirely irrelevant as the customer may want to see that and perhaps can see the difference and understand it better. But even Jas said at his work the engineers/technicians are looking at the torque produced, i.e. the real 'work' done by the engine.

Horsepower - in my mind and commented on similarly in other locations, even Wikipedia - is a rating or measurment of work because it involves the factor of time, but that is solely based on manipulation of the torque curve to meet a desired manner of performance, delivered entirely IMHO by torque.

Edited by DrSarty, 08 December 2008 - 05:13 PM.


#47
DrSarty

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BTW this link was in Weejimmy's post a while back. Quite good, and surpisingly like my suggested method of measurement for representing the true capabilities of an engine. I can assure you I conjured up the idea myself, and only saw this description or anything remotely similar tonight.

Link from WeeJimmy's link.

:lol:

#48
casanova2007

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i believe that torque is more important, my friends got a little turbo diesel skoda vrs thing thats been tuned pushing out somwhere around the 160-180bhp mark and somwhere near 250-270lbft of torque, ive raced him in my stripped out mi16 205.although i have the weight advantage he always gets a better start and stays ahead till he pussys it at 130, which says to me that because of his amount of torque he has the upper hand so it really must be the most important factor.

#49
Moz_Goodwood

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your all torque you are sarty :lol:

#50
DrSarty

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No, I'm BHP too, it just don't think it truthfully reflects an engine's output, and neither does torque in isolation. That's why I agree totally with suggesting Vicki posts her RR graph up.

Remember, I'm not saying one is better than the other, as I'm not actually saying they're different. My power rating could equally use BHP as the figure instead of lb.ft or Nm, but all I'm disagreeing with is some people saying 'no BHP is better' or 'more important', when the two are intrinsically linked, and to change BHP you ultimately are changing the torque behaviour of the engine as that's all it produces, nowt else.

Yes Moz, that was funny BTW.

#51
large

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I have just had my 205 rally car on the rolling road

The spec is

1.9 standard bottom end
Big valve head
grp a piper cam
Ported and polished head
Dellorto twin 40s
Magnex 4 branch manifold

Itís producing 145bhp at the flywheel

I personally thought I would get a bit more bhp

Iím interested if anyone thinks that this is good or bad

Thanks

!st question should have been, did you rebuild the bottom end and did you R,R, the car befor you did the work. You should do this befor doing any engine work as it gives you a starting point. Also dont use the fly wheel fig as it is just a calculated guess.

#52
Batfink

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Please forget gearboxes

you can only do this if the engine is on an engine dyno. Otherwise the gearbox greatly affects the calculations depending on the gear used. We are assuming the nearest gear to a 1:1 ratio was used, but we can't be certain.


Vicki wanted to know if that was good or acceptable based on her mods TO THE ENGINE!! Hence I started saying/suggesting getting hung up on horsepower figures was perhaps not the best measure of the engine,

If bhp is directly related to the torque then it is something that should not be ignored (but obviously to build the best engine should not be used in isolation)

Components which alter fuelling, airflow, exhaust gas extraction or tasks related to that such as altering cam timing, are not directly increasing the power of the engine, they are altering the shape of the torque curve, WHICH IN TURN, based on selection of RPM produces a BHP figure, which is not entirely irrelevant as the customer may want to see that and perhaps can see the difference and understand it better. But even Jas said at his work the engineers/technicians are looking at the torque produced, i.e. the real 'work' done by the engine.

but the amount of fuel and air, swirl etc will directly affect the burn, and the resulting ignition in the cylinder chamber will push against the piston. more fuel and air in the chamber produces more torque, hence the use of forced induction.

We have digressed somewhat as the only way you will really know is when the car is taken out on the stages. Is it competitive or not. TBH the only thing i'd be interested is the wheels figure. I think flywheel figures tend to disappoint. For example my mi16 came out at 174bhp at the fly, which seemed crap when people were saying that I should be getting 190bhp, but it had 146bhp (roughly) at the wheels and more importantly was bloody rapid on the road

Edited by Batfink, 09 December 2008 - 09:04 AM.


#53
DrSarty

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but the amount of fuel and air, swirl etc will directly affect the burn, and the resulting ignition in the cylinder chamber will push against the piston. more fuel and air in the chamber produces more torque, hence the use of forced induction.


I totally agree with all you've said, which also means you're agreeing with what I said. ;)

The bit :) up there is exactly what I said, i.e. the BHP figure is 100%, TOTALLY & UTTERLY related to torque, but in the order that you manipulate one to generate the other, in this case and all cases the torque. That's what I've said all along.

So if you want a different BHP *from an engine*, you manipulate the torque curve (which means tinkering with things that will create more bang or a different burn) in such a fashion that you match it to an RPM for the power band most desirable for your application, which most times will inevitably involve some form of compromise. Likewise Kev, AFTER we've tuned the engine, we can match and manipulate the gearbox and drivetrain components to do the same thing.

This compromise is apparent unless it's a strict track car only e.g. formula 1, where (and here we are going full circle), high BHP figures will be the order of the day, BUT, and please forgive me for saying this again, that BHP figure is purely derived from torque and where it sits in the rev range. It is NOT a separate entity as it simply can't be.

The link I posted above from WeeJimmy's link I think sums it up quite nicely - and includes lots of stuff about gearboxes so I don't disagree with you Kev - where the highest average power, which you can describe as torque or BHP if you like because ultimately they're the same thing although one is a true measure of a force, is what actually produces the best performing car overall. This is why I proposed the twin figure rating showing how much torque or BHP was available for what useful percentage of the rev range.

And on gearboxes again, the rolling road is a fair measure if cars are tested fairly, i.e. equal tyre pressures and same gear used, providing the cars are pretty similar at worse. This means both/all cars in the 'shoot out' are subject to the same inadequancies to they pretty much cancel out.

Edited by DrSarty, 09 December 2008 - 11:00 AM.


#54
kyepan

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Work = Force * length (N * m)
Power = Work / Time


As previously stated

Power is a rate at which the force is applied at a specific length or length of lever

Plotting both Torque and Power on a graph against RPM allows us to understand mainly where torque rises and falls. The work done by and therefore power developed by that torque will be directly determined by the RPM.

The differing levels of torque across the RPM range therefore explain the power delivery characteristics of the engine.

If you're looking for answers as to how an engine (note engine in isolation) would perform at any given point, look at the graph.

Neither are better, they are both theoretical explanations of applied force and applied force with reference to time. How they manifest themselves determines the behavior of the engine. What people think is the "best" behaviour is subjective, and we could go round in circles until the world stops turning, and the sun runs out of Hydrogen to light up the sky.

I'd like to thank GLPoomobile
The letter A
And the number 7

for todays post

#55
B1ack_Mi16

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I still think bhp is the isolated factor to look for if you don't know any other information about the engine, car or transmission.

For example, 150bhp and 75lbft bike engine vs 150bhp 150lbft car engine.

Put them in the same car with suitable gearboxes letting them hit the same top speed at the maximum bhp revs for each engine.
Assume perfectly flat torque curves on both engines and exactly same weight on both vehicles.

You'll find both will accelerate the same and have the same top speed, even though one has twice the torque than the other.

#56
pip470

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In my head im unsure they will accelerate the same but with the above analogy im sure they will both reach the same top speed. If you could explain why I would be wrong it would be much appreciated.

#57
mfield

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In my head im unsure they will accelerate the same but with the above analogy im sure they will both reach the same top speed. If you could explain why I would be wrong it would be much appreciated.


I presume the difference in gearbox ? :lol:

#58
B1ack_Mi16

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I just have to try to communicate this one a little bit more.

Take a look at attached crappy illustration/picture.

Attached File  power_torque.jpg   35.04KB   22 downloads

I really think this one proves that the only thing that counts when you want to accelerate as fast as possible (or go as fast as possible) is to have as much engine power as possible.

The engine torque is actually irrelevant as you can see from the equations, it's not even used to calculate the Force that will push the car forward, and that is really what is pushing you back in the seat....

I would like to see a physical explanation proving the opposite from those who really think torque is what matters.

#59
DrSarty

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I'm kind of at a loss after reading that.

You've baffled me as you're doing what I keep repeating in this thread is fundamentally wrong; you're separating BHP (which I believe you're calling 'power') from torque, and it simply cannot happen, as BHP is a product of torque.

An engine ROTATES a crankshaft. Whether you connect that to 23 gearboxes or none at all, the only force in the entire equation is the rotational one generated by the turning shaft. That force is explained and measured as torque, that is it, that is all there is.

Now before you rant, the derivation of horse power is to equate the amount of torque generated to the rotational speed of the shaft, which now includes the factor of time, which makes BHP a measure of work done, which is power. Therefore, torque cannot under any circumstances be irrelevant, cannot NOT be part of the equation, because it has to be part of every equation relating to the engine generating motion, as all it creates is a rotational force.

I'm not saying engine's don't produce power, I'm saying they make torque and that's all. Power is just a description of the way the torque is delivered.

Have I got this totally wrong, or are people winding me up now? :)

I'm hammering this out to clarify it in my head too BTW, so I really am prepared to be proven in idiot.

#60
B1ack_Mi16

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I'm not good at explaining things I can tell you, but at least I have a Master degree in mechanical design and been working with some systems transferring power through drivetrains etc. earlier.

The point I'm trying to prove for you is that the engine power is what will get you to accelerate or go fast.
You can see it from my formulas.. ?

Of course if you up the torque of the engine itself the power of it will also go up, but it really is not important what torque the engine makes to make this kind of power!

The power produced is what will get you accelerated in the end. As you can see the only "gear" ratio needed in the equation is the Radius of the wheel, and the rotational speed of the wheel (read speed of car).

So two cars independent of what gearbox or wheel sizes they have, (as long as they move at the same speed) when they floor the pedal, the car with the most power will start accelerating fastest.