Bhp Levels

[Rom 0]

Fun fun

 

Im not overly bothered by bhp figures, for all the reasons outlined. Bhp is top end screaming, torque is low down grunt. Hence diesels have a fair bit of pull mid range, but lack up top.

Both are valid measurments, but in my opinion, bhp is more for kids who just 'got 10 bhp from this backbox'

[Anulfo 22]

Fun fun

 

Im not overly bothered by bhp figures, for all the reasons outlined. Bhp is top end screaming, torque is low down grunt. Hence diesels have a fair bit of pull mid range, but lack up top.

Both are valid measurments, but in my opinion, bhp is more for kids who just 'got 10 bhp from this backbox'

 

Ooooh yeah baby!! That fantastic Peco big bore back box that gave me another 40bhp on my E-reg SR Nova!!!Hehe

[Jakob 1]

on the road is seems supurb no dips in power or anything and it pulls like hell but that could be down to the gearing i am running.

 

the ingnition was adgjusted on the rollers

 

dont get me wrong i was happy the the job the the rolling road company did, as they increased the power by 30bhp and it does run good

 

i was just expecting a little more bhp out of a 1900 as there are 1600 running more power

 

 

1600 will always make more power (hp) than 1900 if you have the same head-flow and everything else equal.

 

You need a lot more to understand your graf and your engine output. What seems like a disapointment could turn out to be quite interesting.

As mentioned tourge is what matters AND where you have it in your rpm!!!! Same tourghe will give you more hp when peak at high rpm than if peak at lower rpm.

 

What are the figures of your cam in regards to lift @0.1mm and duration. That will tell you a lot.

AND the big valve head - would that be the XU10 head on a XU9 bore??? (valve shrouding...) I doubt with that tourge figure.

 

Anyway your engine is running somewhat 85% of it potential. If you are seing 145hp at 5800 rpm, then you are to have a happy surprise going into the 6000 rpm scale and with the right cam going into the 7000 rpm. You have lots of potential with your tourge that high in the rpm and with that figures. Try a aggressive came ...

[DrSarty 90 1 Cars]

GLP> Yes master...so sorry, aka ram it!

 

And Vicki: you had a concern about some results concerning someone measuring the performance of your engine, so you got some answers. You can't really criticise what you've got as it's become very interesting, and some of the best threads have started like this.

 

It pains a lot of people on this forum, and elsewhere I guess, that some people get so hung up on horse power. You had a concern as it was - rightly or wrongly - important to you, so we helped and you should now know quite a lot more than when you originally posted.

 

So a bit more info for you is that what is actually important, is that from your graph we can see HOW your engine spreads and delivers the torque. This is supreme info because it truly shows how well your engine is working.

 

What I mean is, say you or anyone buys one of these super duper Peco back boxes for their car, and then takes it to a rolling road and it really does 'on paper' make 10bhp more, then the rest of the engine's rev range outside of where the new higher WOW 10extra BHP shows itself might be complete dogs*it and the car's a bitch to drive. That's an extreme example, because you could take your car to 5 rolling roads and get 5 different results. In that case, would the highest result make you the happiest?

 

So if we can see that graph then we as a forum, which includes people far far more clever than I, can offer some true insight and advice into perhaps how to make you happier and eek more performance HOW YOU LIKE IT from your engine.

 

Trust us, we're actually on your side. Rants and strong opinions voiced now and again actually does us all a favour, so please just let it happen. Thanks to you and WeeJimmy, we're where we are now.

 

Rich

 

P.S. And Jakob:

1600 will always make more power (hp) than 1900 if you have the same head-flow and everything else equal.

That is a fascinating comment, and I'm not arguing with it one bit, but I'd like it explained please. Edited December 7, 2008 by DrSarty

[DrSarty 90 1 Cars]

Please excuse me for posting again, but I've borrowed the below from the extremely knowlegdable (and most importantly experienced) Sandy, from the last post in 'Big Valves...are they really needed' thread which is also in this topic category. This may help make my point, particularly the last bit:

 

Many experts will tell you that big valves = more flow and therefore less cam duration is needed to achieve the same cylinder filling, so the engine will work well over a wider rpm range; in theory that's true. My experience however, is that bigger valve engines are more sensitive to cam profile and timing and the undesirable side effects of a less than perfect cam profile with bigger valves are more pronounced than with smaller valves (mostly a boggy and unresponsive engine, that seem to make the numbers at the top, but feels horrible low down and thin in the mid range and at part throttle). Since most of the engines we're talking about on this forum are one offs, using off the shelf cams, without the facility or budget to experiment with a wide range of cam profiles and complementary inlet/head/exhaust designs; it makes more sense to me, to get to an ideal set up quicker and easier with standard valves.

 

I've achieved 97lbft/litre and 133bhp/litre from XU 16v engines I've built and set up so far, on standard valve sizes; with (if I say so myself ) immensely flexible power delivery and very sharp throttle response. To me, the way the power is delivered is more important than the numbers (but harder to convey!)

 

As for Jakob's interesting comment: these are specs (non cat) taken from CarFolio for me to try and get my head round what he's saying:

 

1.6 GTI Ex Works - 1580cc

 

Maximum power 115.0 bhp (85.8 kW) @ 6250 rpm

Specific output 72.8 bhp/litre

Maximum torque 98 ft·lb (133.0 Nm) @ 4000 rpm

Specific torque 62.1 ft.lb (84.18 Nm)/litre

bmep 1057.8 kPa (153.4 psi)

875-900kg 14" wheels: 0-60mph 8.9secs

 

1.9 GTI Ex Works - 1905cc

 

Maximum power 130.0 bhp (96.9 kW) @ 6000 rpm

Specific output 68.2 bhp/litre

Maximum torque 119 ft·lb (161.0 Nm) @ 4750 rpm

Specific torque 62.5 lb.ft (84.51 Nm)/litre

bmep 1062 kPa (154 psi)

875-900kg 15" wheels: 0-60mph 7.6secs

 

So is this an 'all things being equal' situation? The heads are the same aren't they? Same inlet but with different injectors. Only other difference being displacement due to longer stroke on 1.9, or have I missed something?

 

This does indeed show (unless there's an error) the specific output of the 1.6 being nearly 5bhp per litre greater than on the 1.9 engine. This to me matches what Jakob is saying, i.e. it is 'more powerful' per litre. But with larger wheels (and more torque) we have a much quicker 0-60mph from the 1.9. Note that there's only a gnat's cock in the specific torque measurement, which shows the 1.6 seems to be being as efficient as the 1.9.

 

So what happens if we put 15" Speedlines on a 1.6 acceleration wise? Whilst specific outputs are either in the 1.6's favour or matched, what difference if any if the wheels are also equal does 20lb/ft peak torque make?

 

And before anyone gets excited, this is NOT me saying 1.6 is better or worse than 1.9, I'm just exploring Jakob's comment further to play around with perceived POWER and how it translates into real world speed & fun, which surely is partly what this whole thread is about? Or is it purely about results on rolling roads, which aren't the most exciting places to drive?

Edited December 7, 2008 by DrSarty

[Rom 0]

Ive always thought smaller wheels = better acceleration. Bigger = slower , but higher top speed (negligable, sp?)

Something to do with the rolling radius.

 

Of course, i could be completely wrong. Or just mis read your post..im tired and cranky

[VisaGTi16v 1]

That is very strange that the 1.6 has more bhp/litre, never noticed that before. Smaller wheels will help acceleration if you dont have the power to pull long gears. 0-60/62 figures are often pointless as lots of cars need 3rd to hit 60 like my zx 16v for example. A Xsara vts also needs 3rd for 60 whereas a Gti6 can hit it in 2nd iirc giving it a lower 0-60 time but slower to 55 than a Xsara.

 

On a different note and back vaguely on the original subject. I agree Torque is good as ive been in my friends 350bhp/600kg Seight, unsure of torque figure but it has something silly like 180ft at idle and 300 odd peak but diesels are all about torque and I hate diesels so therefore bhp is the winner!

[Batfink 201]

the engines would be more similar in relative bhp/litre if they were different bores to change the capacity, but there is always going to be a difference when the stroke is different.

[DrSarty 90 1 Cars]

On a different note and back vaguely on the original subject. I agree Torque is good as ive been in my friends 350bhp/600kg Seight, unsure of torque figure but it has something silly like 180ft at idle and 300 odd peak but diesels are all about torque and I hate diesels so therefore bhp is the winner!

 

This is kind of what I'm saying though. BHP is frankly meaningless. An engine, diesel or petrol only makes torque, that's all it does. Diesels, particularly diesel turbos make sh1te loads of torque, which some find sexy, others, you and I included don't. I know Maturin loves it. But it arrives in only a small area of the usable rev range which makes it a killer for acceleration if they're in the sweet spot, occasionally I suppose making us look silly.

 

As a result I guess diesels don't normally display large BHP figures, because a lot of that oomph (peak torque) has gone as they approach the red line, whereas petrol engines seem to deliver that spread of true power, i.e. torque, over a much more usable rev range. Petrol turbos are a half way house I guess, where they make masses of boost enhanced torque at a certain rev range which tends to be higher up the rev range to still deliver the sexy, high BHP figures.

 

If someone can prove me wrong about BHP, I mean about me saying it doesn't really exist and only torque does, then I will gladly eat humble pie with custard and learn. But I feel confident that BHP is just torque looked at through rose tinted glasses and is a rate of doing work rather than a measure of an engine's capability to rotate a crank.

 

I have mentioned many times on this forum that a far more realistic rating for an engine would be something like this:

 

'Using 80% of the rev range (between 0rpm & rev limit), 95%+ of peak torque can be delivered over what percentage of this band?'

 

EXAMPLE:

Let's say we have an Mi16 with PeterT's stage I road cam & his chip mod.

A PeterT chip on an Mi16 gives a rev limit of 7,500rpm. This means we have the 6,000rpm band of 1,500-7,500rpm to look at (i.e. 80% of the rev range)

Peak torque is perhaps 140lb.ft, so 95%+ is anywhere on the torque curve equal to or higher than 133lb.ft.

If the engine produces 133lb.ft for a band of 750rpm, then that is 12.5% of the 80% band in question.

 

> This means that engine would have a 133 / 12.5 rating, meaning it generates at least 133lb.ft over 12.5% of the practical rev range.

> This means a peak figure could be shown (or worked out)

> And this means this true power is accessible for 12.5% of the usable rev range, which in comparison to a 133/10 motor would be 'better', and provable so.

 

This really only compares engines and not cars, as I appreciate that there are so many other contributing factors in grading performance. But this method could be used on an engine dyno or on a rolling road, where I think with the latter it should be done using only ATW figures. In a shoot out however i.e. a rolling road day, providing the calculation back to fly was consistent it would still produce comparitive results.

 

But realistic ain't sexy, although I think for example a 120 / 40 engine would be mega impressive. It may produce less peak torque (which is where skewed figures come in - like horse power I'm afraid) but the top 5% of true engine power would be on tap for nearly half the rev range from tick over to red line. Now that's SEXY!!

Edited December 8, 2008 by DrSarty

[VisaGTi16v 1]

I think I need another cup of tea before reading your post a few more times to understand it

 

A friend has a remapped Bora TDi thats 197bhp and 292 ft/lb, the kick in the back when he accelerates is just mad and for normal every day driving and overtaking its all you ever need but then it only has 2000rpm power band. Diesels were marketed back in the day as being torquemiesters (er) where you never needed to change gear but these days thats just not true. They bump the turbos up so much that most quickish ones dont get power until almost 2k then run out of steam just over 4k. I much prefer a smooth power delivery from idle even if I have less outright power, rather have a much wider power band. Ive never driven a fast petrol turbo but in the wet they must be awful unless absolutely on it and correct gearing, at least when sprinting the Visa I know whats going to happen when i touch the pedal. Clearly super chargers are the way forward

 

Back to the original post. If the car feels quick and you are happy then the figures are not that relevant. All rolling roads read differently. I see people on here claiming well over 180bhp for the spec of my Visa yet I only had 168 on the rolling road where I took it. You could go somewhere else and see 160 odd from your 8v. I think you said you have 40's, they should be fine for your power, take a look here 35mm chokes which I presume they can take are good for 169bhp so more than enough. People fiting 40's to 16v's however always baffle me as its almost impossible to get any more power out of them compared to the standard injection!

Edited December 8, 2008 by VisaGTi16v

[Batfink 201]

I think all peak figures are pretty meaningless, especially when looking at the engine in isolation. At the end of the day its what is outputted after the gearbox that matters.

Different engines will be better in different situations, A big flat torque curve is great for a car with less than optimum gearing and may overcome certain disadvantages, though a car with a peaky power band, a good gearbox can keep the car on the powerband better and just as effectively.

[DrSarty 90 1 Cars]

Very true Kev, hence me mentioning that the peak torque, or even worse BHP figure would only momentarily describe an engine in isolation.

 

It goes zero distance to explain the car and its performance in the real world. The engine should very much be matched to the application, and in non-track, non-strip work, i.e. road & rally, I suspect that my sort of 'availability of true engine power' rating would reflect quite clearly how drivable the engine/car was.

Edited December 8, 2008 by DrSarty

[weejimmy 1]

"If someone can prove me wrong about BHP, I mean about me saying it doesn't really exist and only torque does, then I will gladly eat humble pie with custard and learn. But I feel confident that BHP is just torque looked at through rose tinted glasses and is a rate of doing work rather than a measure of an engine's capability to rotate a crank."

 

that is what bhp is, the rate that the torque is produced, thats the point.

ok imagine a boxer he can have 400lb/ft punch, but if he only punches at 1mph its not going to mater.

but if a boxer that can only punch 200lb/ft punches at 200mph its gona hurt.

 

so a high torque car may be able to tow a tractor etc which is great but not what your after.

a lower torque higher bhp car may not be able to pull much but it can make the torque faster so can accelarate the car faster.

 

theres a milion difrent arguments/ angles to look at this.

this is just my atemt to explain how i see things.

 

torque = tractor bhp = f1 kinda thing

 

ill say no more on this thread.

[DrSarty 90 1 Cars]

ok imagine a boxer he can have 400lb/ft punch, but if he only punches at 1mph its not going to mater.

but if a boxer that can only punch 200lb/ft punches at 200mph its gona hurt.

 

The punch IS the torque. A boxer who can't punch at all isn't a boxer.

 

You said that torque is irrelevant earlier. Do you still think this?

 

BHP (in horse power) = Torque (in lb.ft) x RPM / 5252

 

As Alex said, the 5252 is just a conversion constant, which means BHP doesn't even exist without torque. It is just a function or factor or description derived from it, and explains absolutely nothing.

 

Back on topic again (and sorry Vicki if you think we/I've trashed your thread; but I actually think it's very interesting) this is why I'm saying don't 'worry' about the horse-power reading. Get the graph up so we can see the torque curve which shows how the engine is truly performing. If the rolling road guys also have shown you your AFR (air to fuel ratio) graph too that will help us help you. And don't forget, if you're loving the car, then spend more time hooning it.

 

Yes, there will be a BHP curve, but that's just a mathematical function of the torque curve, it's IMHO not actually a measurement. Still waits to be shot down in flames...which I'm sure will happen, but I simply cannot see now what else an engine produces.

Edited December 8, 2008 by DrSarty

[B1ack_Mi16 67]

BHP is what counts really.

 

For example, what would be fastest?

Either a 205 with 400lbft and 150bhp, or a 205 with 200lbft and 200bhp?

 

As long as you are gearing the cars in such a way that both will reach the same top speed at the maximum revs for it's engine, the one with most power would always be fastest, at least as long as you can assume both cars have a more or less flat torque curve.

 

Power counts, torque isolated does not.

[danpug 1]

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

[B1ack_Mi16 67]

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.

[weejimmy 1]

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-rover.org/showthread.php?p=2506850

 

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

 

thi

[danpug 1]

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.

[Batfink 201]

no - you just need more gears to keep it in the peak powerband

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.

[DrSarty 90 1 Cars]

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 December 8, 2008 by DrSarty

[DrSarty 90 1 Cars]

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.

 

[casanova2007 0]

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.

[Moz_Goodwood 0]

your all torque you are sarty

[DrSarty 90 1 Cars]

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.