TORQUE not BHP

[disco-v8]

ok nearly every one out that who wants more power out of there car always asks how can they get more BHP out of there engine, when down to it its torque thats the thing you realy want...... basicaly BHP is a made up number and doesnt make any differnce what  they say an engines BHP is to me, as BHP is worked out from the torque figure anyway!!!!!!

every 1 i hear or everything i read tells you how to get more BHP from an engine, but who the hell wants BHP in a landrover?????  :? dont no about you lot but when im offroading i dont want to push my engine to 5000RPM to get the so called BHP figure out of it, i want low down grunt!!!!!

some placies that ive seen uprated cams from, show that they do torque cams and then high BHP cams, but what differences in the cam make more torque?????

i konw to have more BHP alot of ignition timing is done and the inlet and outlet valves are usualy over lapped so the exhaust pulls in the inlet....

BUT HOW DO YOU GET MORE TORQUE, and what things are done to engines to get this I.E. what fueling set up, ignition timing, cams exhaust ETC

[lambert]

Two ideas.
 
One. Tubular exhaust manifold with long equal length primary's. Each engine has an optimum.
 
Two. Heavier or more mass on the fly wheel. No more torque as such but it will keep spinning better at low engine speed. Again there is an upper limit to keep run on acceptable.

[disco-v8]

missinng the point with that one there mate.... im not trying to get more torque or power, and not trying to find out whats the best way of dog it!!!!

im merrly trying to find out what is done to an engine to get higher torque instaead of higher BHP, basicaly wot factors are diffenent between the two????

[lambert]

Ok.
 
Power is not a metric parameter it is merely a function of torque. The difference is where they occur in the rev range. At 5225 rpm or there abouts they are equal. More torque is found lower down power higher up the rev band.
 There for it is a matter of where the max revs are found.
 
That is probably no help as i have now confused my self. But then it is a tad complicated to explain.

[rollazuki]

Torque is a measure of work done, ie 1 pound foot is the ability to lift 1 pound with a leverage of 1 foot.
BHP (power) is a measurement of the speed that the work is done. Ie an engine that lifts the pound in half a second is more powerful than one which takes 1 second, but technically the torque produced is the same.

The two engines you describe are like chalk and cheese, there are major differences. to take two examples, use a buss engine and a race car engine. Bus engine produces all its torque at low revs, so lasts for ever, its designed for maximum air flow to be at low revs etc, and will be highly inefficient at higher revs. Its likely to have a low compression ratio, big heavy(reliable) pistons, large valves(only two) and a cam with a very mild open/close curve, and little overlap to make it efficient.
The inlet passages will be narrow, and probably poorly finished., no real need to spend cash in this area.

The race engine will be the opposite, light valves, and many of em, a high lift cam with long overlap(who cares about fuel wastage, its a race engine), lightweight pistons and rings(short life), an immaculately finished inlet and exhaust tract, and a very high compression, neccesitating the use of higher octane fuel, with good anti knock properties.

The two are miles apart.

[lambert]

Wot e sed. :D

[L90OOK]

Wot e sed. :D

 :(biglaugh): ROFPMSL :(biglaugh):

[thermidorthelobster]

They're actually two sides of the same thing, and they're directly related by a formula.

1 HP is 550 ft lb per second.

What does this mean?  It means that 1 HP has the ability to move something 550 ft per second against a force of 1lb.  So if you had a 1lb bag of sugar on the end of a string, and you had a 1HP winch, the winch would be able to move the bag 550 feet vertically (against the force of gravity) in one second.

Alternatively it could move 550lbs of sugar 1 foot, or 1100lbs of sugar 6 inches, etc.  (You can also substitute other things for sugar - flour, salt or other cooking ingredients all work :) )

In a rotating engine, the engine also turning a certain number of revolutions per second (or minute).  This means that power can also be related to torque and the rpm of the engine.

Specifically, power is torque x the engine speed in rpm, but we also have to multiply by a constant to convert from seconds to minutes, and allow for 1HP being 550 ft lb, not 1 ft lb.  If you do the math (this describes it quite well) you find that power is torque x rpm divided by 5,252.

So say your engine outputs 200 ft lb of torque at 2,000 rpm, you can say that the POWER of the engine at 1,000rpm is
(200 x 1000) / 5252 = 76hp.  But this only holds AT 2,000 rpm.  When you see HP quoted for an engine, it's always the MAXIMUM HP across the whole rev range.

Now, you'll notice that for the same torque, the higher the rpm, the higher the HP.  If you had 200 ft lb of torque at 4,000 rpm, ie the same torque, the power would be 152HP.  This is why peak power is high up the rev band.

This is also why people talk about torque as 'low-end grunt', and power as high-revving power.  Because power only becomes significant at higher engine revs.  If you had a totally flat torque curve, the max power would always be at the high end of the rev range.

If you're sufficiently bored, you can take a tuner's torque curve and do the maths, and work out what the power curve for the same engine is.  Do this and you'll actually invariably find that below 1,000rpm they exaggerate the power!  If you plot torque against (power / revs) you should get a straight line...  but you never do, because they fix the graphs.

You can also see that if you do something which changes the TORQUE of the engine, by definition you also change the POWER, but only the power in that part of the rev range where you've changed the torque - which isn't necessarily the max power.  If you change the torque at higher revs, then you're boosting the power much more strongly that if you change the torque at lower revs, so high-end torque boosts will mean the max power is likely to go up, whereas low end torque boosts won't unless the torque curve is affected quite noticeably.

Does this make any sense?

[jjsaul]

As someone about to start automotive engineering at uni i find this very interesting!
Thank you for all the explanations so far  :D

[rollazuki]

Good luck jjsaul, I wish Id done auto eng instead of electronic eng. Its pants!

[Hobnailkelly]

There aint no substitute for CC's ...

[extreme90]

or as ive said before  :P
get a diesel aka a tractor engine
no bhp
but a kin massive flywheel to store a load of energy and give u zillions of ft lb's of torque
all at idle
now 6000rpm and coughing and spluttering like your v8   :tongue:  :tongue:

ps u upsilverdale sunday ad ?
dan

[Xtremeteam]

2 secs



let me find the link to a small diesel engine thats quite torquey

[Xtremeteam]

http://people.bath.ac.uk/ccsshb/12cyl/


5,608,312 lb/ft at 102rpm   :twisted:

[disco-v8]

They're actually two sides of the same thing, and they're directly related by a formula.

1 HP is 550 ft lb per second.

What does this mean?  It means that 1 HP has the ability to move something 550 ft per second against a force of 1lb.  So if you had a 1lb bag of sugar on the end of a string, and you had a 1HP winch, the winch would be able to move the bag 550 feet vertically (against the force of gravity) in one second.

Alternatively it could move 550lbs of sugar 1 foot, or 1100lbs of sugar 6 inches, etc.  (You can also substitute other things for sugar - flour, salt or other cooking ingredients all work :) )

In a rotating engine, the engine also turning a certain number of revolutions per second (or minute).  This means that power can also be related to torque and the rpm of the engine.

Specifically, power is torque x the engine speed in rpm, but we also have to multiply by a constant to convert from seconds to minutes, and allow for 1HP being 550 ft lb, not 1 ft lb.  If you do the math (this describes it quite well) you find that power is torque x rpm divided by 5,252.

So say your engine outputs 200 ft lb of torque at 2,000 rpm, you can say that the POWER of the engine at 1,000rpm is
(200 x 1000) / 5252 = 76hp.  But this only holds AT 2,000 rpm.  When you see HP quoted for an engine, it's always the MAXIMUM HP across the whole rev range.

Now, you'll notice that for the same torque, the higher the rpm, the higher the HP.  If you had 200 ft lb of torque at 4,000 rpm, ie the same torque, the power would be 152HP.  This is why peak power is high up the rev band.

This is also why people talk about torque as 'low-end grunt', and power as high-revving power.  Because power only becomes significant at higher engine revs.  If you had a totally flat torque curve, the max power would always be at the high end of the rev range.

If you're sufficiently bored, you can take a tuner's torque curve and do the maths, and work out what the power curve for the same engine is.  Do this and you'll actually invariably find that below 1,000rpm they exaggerate the power!  If you plot torque against (power / revs) you should get a straight line...  but you never do, because they fix the graphs.

You can also see that if you do something which changes the TORQUE of the engine, by definition you also change the POWER, but only the power in that part of the rev range where you've changed the torque - which isn't necessarily the max power.  If you change the torque at higher revs, then you're boosting the power much more strongly that if you change the torque at lower revs, so high-end torque boosts will mean the max power is likely to go up, whereas low end torque boosts won't unless the torque curve is affected quite noticeably.

Does this make any sense?

thanks with that one i think thats the best answer ive got so far BUT!!!!!! its not exsactly what im asking......

with the answer you've just put im more sure ill get a proper answer from you...... everything you just wrote there i already knew, even though it took a while for me to understand at first when i first founds out about it....

i know what i want to say and ask but its hard to put down when your on a computer and its seems thats its coming out wrong!!!!! basicaly i know what TORQUE is and BHP is, and like i said at first i dont believe in BHP as its just a figure made up from TORQUE


ill try a bit harder this time to get my question out properly.... ok forget its a V8 like mine just imagine its any engine, petrol or diesel i dont realy care.  like you just said racing engines usualy have loads of cam over lap to increase the air flow, so wot sort of cam would a torquey engine have???? BUT dont forget im not just asking about cams, i want to no everything that differ from a high BHP engine and a high TORQUE engine and please please dont come up with the usual stuff that kids already no of.....

im the sort of person who understands all about MAPS, batch injection firing, ignition timing, that you need 1 cubic meter of air per minute to abtain 1BHP (yeah work that out in a high powered engine), injection spray pattern, why sraying fuel on the back of a valve is good, compression ratio's, pinking, air flow, longer and shorter inlet manifold vary power, differnt size tummpets give different air ressornacies which vary air flow ETC..... all that simple and very understandable to me....

BUT i just dont understand what factors including some of them from above change an engine from a high BHP 1 or a TORQUEY 1


ok just thought of another exsample.... a 3.5 disco/RR V8 produces more torque than power, but in an SD1 theres more power than torque, so even tho there the same engine what differences are there in the air and fueling????? ...... oh please dont say its cuz of the shorter inlet trumpets and shorter exhaust manifold system i already no that, this will only increase BHP by abit, but mainly helps with the air flow...... mainly i want to know what does the ECU tell all the electrical components to do differently from each engine, like how long each pulse width is, wot fuel pressure do they use cuz its all got to be different....... also works the same on my 3.9 and a TVR

anyone understand my question abit better and can help me understand abit more?????



oh by the way dan it didnt go close to 6000 RPM it was spluttering at 4300 RPM got home that day and found out it was a bit of damp in the dizzy.  wipped it out and hey presto boy racer killer again and sounding even better 8)

i know ur a stubern arse but put it this way dan, its got enough torque at low end RPM to break 2 long half shafts, and a brand new diff, plus im sure its nakered my front diff aswell, but its still going :o

wont be at silverdale its off the road while i get an MOT

[thermidorthelobster]

I understand the question, but I don't know the answer, sorry!  I'm OK with the theory side but I have very little idea about actual engines  :(

But I'm going to keep watching this thread, because I've often wondered the same thing.

[Bulli]

i dont believe in BHP

what about the tooth fairy?

Right Rolla answered your question and if you understand all the above as you say then you should have more knowledge than the rest of us.

The main differences between the Rover SD1 and the v8 as fitted to the same year LR's were the cams and the pistons. Cams are the heart of the engine and really do play such an important role.
In that year there is no pulse width as they are both Carb engines!! so no fuel injection so there is little difference in the way they were fueled.
The cams in the SD1 are higher lift and longer duration. This is less fuel efficient but allows a larger charge to be drawn into the combustion chamber...hence a bigger bang.
The compression ratio was much higher in the SD1 engine which means the mixture is burnt more efficiently as this forces the flame front across the piston. Im also 'guessing' that the SD1 engine will run a little more advance.
The higher revving the engine the more advance is required, my bike runs upto 40 degrees advance at the redline of 11k , v8's are around 5.

The cams and high comp pistons combine to more the torque curve up the rev range, lowering bottom end torque but freeing up bhp a the top end.
You gain more bhp by allowing the engine to breate more efficiently. Thats why stock v8's run out of puff quite quickly.Well that and the hydraulic tappets....

[Terranosaurus]

As far as I've grasped over the years it's down to what revs the engine is optimised as, all the things already mentioned, inlet and exhaust tract lengths, cam profiles etc all change the optimum revs of a particular engine.

Using different combinations of cams and lengths etc it is possible to produce engines that mange to get greater than 100% filling of the pistons at precise revs by using the harmonics of the inlet track to pulse air in when required.

High reving engines just haven't got the time to fully fill the cylinder but they make up for it by having more combustion cycles instead. This is one of the reasons for high compression ratios on these engines - the dynamic cylinder pressures aren't what they should be cos the cylinder wasn't full anyway.Also the long duration race cams mean that the pressure from the combustion is only being used to push the pistons for a relatively small l% of the cycle.

So on a race engine each small push from the piston means there isn't an awful lot of torque but the fact you have so many of them means that there is plenty of power there.

On the torque optimised engine the high % cylinder filling means compression ratios don't need to be high to get a good burn, and the short duration cam and low revs means each combustion can be used to it's max, this gives good torque but the small number of cycles means lower torque, as there is simply less fuel being used so less energy input.

Personnally I (fly in the face of convention) see no reason why a higher reving powerful engine can't be used off road provided the gearing is low enough. Low gearing multiplies torque, it does not multiply power though

[Eeyore]

Also, at greater spark advance you need to run quite rich (up to 25% in some cases) otherwise you end up spitting combustion into the exhaust and melting stuff. The exhaust products'll hit 1100+degC - which isn't healthy! The solution to overheat is to over fuel and use the fuel itself to lower the temperature and pressure in the cyclinder (you'd be trying to run at about 850degC in a road engine)

Optimal torque is made when the moment of highest cyclinder pressure corresponds with the sector of the crank being horizontal - quite literally the force is pushing down on the longest effective lever. Flame propogation in the cyclinder happens at a fairly constant speed, so inorder to optimise the pressure in the piston with the crank as the speed of crank rotation increases, the spark has to be produced earlier and earlier- the higher the revs, the earlier the spark is required otherswise you still get maximum combustion when the crank has exceeded bottom dead centre, which drops the power somewhat.

Engines - seemingly so simple yet, so darn complex!  :shock:

It's one o' them subjects that needs someoen with a pad and pen and a lot of knowledge - and that ain't me!!  :lol:

This won't have helped!

Cheers
 8)
Eeyore

[rollazuki]

A high revving motor with lots of gearing will work fine(try a zuki) but is annoying, and hard on the engine. Believe me, the difference between a stock zook motor(1.3 l, revs to 6000) and a diesel(peak torque at mebbe 2000) is sooooooo much nicer to drive off road. Easier on the ear as well!

[glaggs]

If your driving off road; trials, laning, which challenge or just pay n play then torque is more inmportant than ultimate power. Peak power is only realy important for speed type events ie. comp safari. The down side is that the torquier engins tend to be Diesel and there fore theres a weight penaltiy. I'll keep reving  the whatsits off my Zuk, sounds better than any burbbling chip fat burner any day.....


......Hi Ian how you doing.

[Eeyore]

I would argue and say that torque is better for comp motors too, especially in the clag!

I've seen too many lightweight, really revvy cars just spin the wheels instead of making good progress.

But as rightly said, it's gotta be torque for challenge motors, which is where diesels win out, but heck, they put a hammering on the drive train!

Cheers
 8)
Eeyore

[Henry Webster]

I would argue and say that torque is better for comp motors too, especially in the clag!

I've seen too many lightweight, really revvy cars just spin the wheels instead of making good progress.

But as rightly said, it's gotta be torque for challenge motors, which is where diesels win out, but heck, they put a hammering on the drive train!

Cheers
 8)
Eeyore

Although it is fair to say that the current crop at the front end of the British Off Road Championship may disagree.

Kershaw and torgue no-longer go together in the same sentence.

I, however, am still convinced of the need for torque.

H

[Eeyore]

Although it is fair to say that the current crop at the front end of the British Off Road Championship may disagree.

Kershaw and torgue no-longer go together in the same sentence.

Ain't that the truth!

But whilst his car is blindingly quick, it was struggling for traction at the weekend. Same of the cars without 'lectronic managment kept hitting the rev limiters as the wheels span out. Must play havoc with the drive train!

Quite spectacular it was!

Cheers
 8)
Eeyore

[extreme90]

ill keep my tractor engine for the challenges
shows any v8 up on the rough stuff
just not blistering on road

[extreme90]

ad, does snapping a half shaft at idle rpm count for me  :P  :P
ok mate,
you heard about weston coyney tho  :shock: there filling it in soon  :shock:
dan

[Xtremeteam]

ill keep my tractor engine for the challenges
shows any v8 up on the rough stuff
just not blistering on road

i love my TDi cos i can plant it,take it to 20psi o boost & it spools up & <edit> off,  8)

[Hobnailkelly]

Just to digress a bit and as we have some experts on.  
Why do diesel engines make such a knocking noise ?
Mine makes a hell of a racket at tickover (Diahatsu 2.8 td) When it's moving I can't hear anything above the whine from the turbo, rumble from the tyres and droning noise from the snorkle so I don't know if it gets better or worse!

[disco-v8]

As far as I've grasped over the years it's down to what revs the engine is optimised as, all the things already mentioned, inlet and exhaust tract lengths, cam profiles etc all change the optimum revs of a particular engine.

Using different combinations of cams and lengths etc it is possible to produce engines that mange to get greater than 100% filling of the pistons at precise revs by using the harmonics of the inlet track to pulse air in when required.

High reving engines just haven't got the time to fully fill the cylinder but they make up for it by having more combustion cycles instead. This is one of the reasons for high compression ratios on these engines - the dynamic cylinder pressures aren't what they should be cos the cylinder wasn't full anyway.Also the long duration race cams mean that the pressure from the combustion is only being used to push the pistons for a relatively small l% of the cycle.

So on a race engine each small push from the piston means there isn't an awful lot of torque but the fact you have so many of them means that there is plenty of power there.

On the torque optimised engine the high % cylinder filling means compression ratios don't need to be high to get a good burn, and the short duration cam and low revs means each combustion can be used to it's max, this gives good torque but the small number of cycles means lower torque, as there is simply less fuel being used so less energy input.

Personnally I (fly in the face of convention) see no reason why a higher reving powerful engine can't be used off road provided the gearing is low enough. Low gearing multiplies torque, it does not multiply power though

Also, at greater spark advance you need to run quite rich (up to 25% in some cases) otherwise you end up spitting combustion into the exhaust and melting stuff. The exhaust products'll hit 1100+degC - which isn't healthy! The solution to overheat is to over fuel and use the fuel itself to lower the temperature and pressure in the cyclinder (you'd be trying to run at about 850degC in a road engine)

Optimal torque is made when the moment of highest cyclinder pressure corresponds with the sector of the crank being horizontal - quite literally the force is pushing down on the longest effective lever. Flame propogation in the cyclinder happens at a fairly constant speed, so inorder to optimise the pressure in the piston with the crank as the speed of crank rotation increases, the spark has to be produced earlier and earlier- the higher the revs, the earlier the spark is required otherswise you still get maximum combustion when the crank has exceeded bottom dead centre, which drops the power somewhat.

Engines - seemingly so simple yet, so darn complex!  

It's one o' them subjects that needs someoen with a pad and pen and a lot of knowledge - and that ain't me!!  

This won't have helped!

Cheers
 
Eeyore

now this is the stuff i enjoy to read, the stuff that takes a few times of reading to actualy understand, anything thats very technical i love......

so basicaly what im starting to understand with torque is, that its all down to compression really!!!! as with a racing high BHP engine your losing some compression through the cam overlap.  plus as petrol has a certain way of burning, it has less room to ignite to full combution so has more force on the piston pushing it down relating in more torque.  but as petrol has a lower igniting point its hard to get high compresion ratios with out preignition, without changing the fuel to a higher RON/EON rating......

      so as silly as it sounds but would adding more fuel help to lower the preignition of petrol by trying to keep the combution chamber cooler, or wud it make the hole thing even worse as theres more substance in the chamber that cant be compressed (a liquid) making it even high comp ratio and preigniting it even sooner???????

or is it alot more of a timing thing where they would leave the ignition timing alot later so its not trying to push on the piston BTDC and and slowing the piston down and losing power, and make it so that it ignites just ATDC so all the power is on the down stroke, but then again the fuel might not have enough time to fully burn, but then again torque happens at lower engine RPM so mite be better


ok ok bit late at night now and think im confusing myself and cotradicting everything ive ever learnt about engine fueling and timing!!!!!!

[Eeyore]

Higher cycliner pressures usually result in more pushing force. In short throw engines this translates as lots of speed. In engines with a longer throw on the crack it translates as more torque (same force working with longer leverage).

So yeah, upping the cylinder pressures helps - but it depends on what end result you want out!

Anyone remember the good old 1.5ltr turbo F1 engines? They used to generate a cylinder pressure that exceeded the yield limit of aluminium , therefore everytime the cycle went pop it would have bent the conrod. So, they couldn't use aluminium as it would have bent or fatigued to death . Steel can have an infinate fatigue life if loaded properly, but it was too heavy, so they went for titanium instead. Mind you in qualifying trim the engine was out-putting about 1500bhp!!  :shock:

I beleive they had very short throw cranks.

...and just don't get started on dragsters! :lol:

Again, more ramblings!

Cheers
 8)
Eeyore