BHP vs PS

Balfa

JHMEG wrote:

A fairly accurate approximation. Torque, due to the increased load from wind resistance, comes more into play at higher speeds.

Altho, it's all relative. A Civic Type R will have no problem overtaking at motorway speeds. And will do so quicker than a Transit because of better aerodynamics and a lot more power.

A completely inaccurate approximation, by both yourself and E92. Seriously, power is what gets you from 0-60, and torque is what gets you from 0-60, and power is what lets you overtake at motorway speed, and torque is what lets you overtake at motorway speed. They're just two different ways of looking at the same thing.

And engine doesn't discard one rule of physics and adopt another above a certain speed.

colm_mcm

looking at a dyno readout of power and torque curves can be helpful

crazylady333

hey thanks colm_mn, finally got it..an hour later..dnt think this site likes me

JHMEG

Balfa wrote:

And engine doesn't discard one rule of physics and adopt another above a certain speed.

If running in a vacuum, or on a bench.

Powering a vehicle introduces wind resistance into the equation which changes things. A torquey transit will not overtake a low torque CTR at any speed.

Stick the transit engine in the CTR and I doubt it will be able to overtake a real CTR either. Power matters at all speeds.

Plug

Balfa wrote:

A completely inaccurate approximation, by both yourself and E92. Seriously, power is what gets you from 0-60, and torque is what gets you from 0-60, and power is what lets you overtake at motorway speed, and torque is what lets you overtake at motorway speed. They're just two different ways of looking at the same thing.

And engine doesn't discard one rule of physics and adopt another above a certain speed.

Thank you sir! That sounds about right.

maidhc

JHMEG wrote:

If running in a vacuum, or on a bench.

Powering a vehicle introduces wind resistance into the equation which changes things. A torquey transit will not overtake a low torque CTR at any speed.

Stick the transit engine in the CTR and I doubt it will be able to overtake a real CTR either. Power matters at all speeds.

And try putting a CTR engine into a fully loaded transit...

I am a lawyer, not a physicist, but:

Torque is force

Power is force x speed

A CTR will develop maximum power and probably torque at (say) 10000rpm, if the engine was pulling a load of pallets up a hill the speed would fall and the torque drop off would be so significant the engine would stall. (unless the shortcoming was overcome with gearing... but you still have the issue of the longevity of an engine that buzzes at 10000rpm etc)

A transit however will develop maximum power at 4000rpm, and maximum torque at 1800 rpm. As it looses speed going up a hill this will be counteracted by an increase in torque so it will just stay lugging.

More torque means the engine can develop more force at the crankshaft. An engine with more torque will thus generally be much heavier and stronger. That is why the 7.5L cast iron lump in my tractor probably weighs more than a small car but only develops 130hp at 2000rpm.

Altreab

maidhc wrote:

And try putting a CTR engine into a fully loaded transit...

I am a lawyer, not a physicist, but:

Torque is force

Power is force x speed

A CTR will develop maximum power and probably torque at (say) 10000rpm, if the engine was pulling a load of pallets up a hill the speed would fall and the torque drop off would be so significant the engine would stall. (unless the shortcoming was overcome with gearing... but you still have the issue of the longevity of an engine that buzzes at 10000rpm etc)

A transit however will develop maximum power at 4000rpm, and maximum torque at 1800 rpm. As it looses speed going up a hill this will be counteracted by an increase in torque so it will just stay lugging.

More torque means the engine can develop more force at the crankshaft. An engine with more torque will thus generally be much heavier and stronger. That is why the 7.5L cast iron lump in my tractor probably weighs more than a small car but only develops 130hp at 2000rpm.

But how much torque and at what engine speed?

*grabs me coat

Balfa

JHMEG wrote:

If running in a vacuum, or on a bench.

Powering a vehicle introduces wind resistance into the equation which changes things. A torquey transit will not overtake a low torque CTR at any speed.

Stick the transit engine in the CTR and I doubt it will be able to overtake a real CTR either. Power matters at all speeds.

Okay, so by completely ignoring my point earlier about the AREA of a torque curve, you win. Or not...
You say a Transit is torqueier (let's not say that word again) than a CTR, and that's because you (and everyone else) looks at the PEAK torque number. That's understandable, because it's the only number the marketing bods give you, because they don't know any better, either.

I propose that the Civic actually has more torque, and here's why:

If you google image for type-r dyno, you'll see that a typical civic type-r engine produces, let's say an average of about 105ft.lb (142Nm) from 2,500rpm to about 8,000rpm. That's a total width of 5,500rpm. If you multiply the height by the width to get the area, you end up with 781,000.

I couldn't find a dyno graph for a transit (I suppose nobody cares ), but the top level diesel gives 375Nm @1900rpm, so let's suggest that it produces an average of 370Nm from 1000 to 3000rpm (a "powerband" width of only 2000rpm). Multiplying again, we get only 740,000.

So, actually less torque. Not a huge difference, but the point remains. Everything else can be controlled by gearing. Give the Transit 8 very short gears with f1-speed gearshifting, and it'll blow past a civic all the way up to its 8th gear redline at 80km/h

Let's not forget that a transit, with maybe twice the frontal area of a civic, will require twice the torque to overcome wind resistance at speed. And with 1.5 times the mass (is that all? I was surprised!), will require 1.5 times the torque to accelerate its own weight.

If you put the transit engine into the civic with the appropriate gearbox, it'll make the civic a little heavier and, as we've seen above, will have a little less torque and, therefore, will be slower than a stock civic.

if, on the other hand, you put the civic engine with the appropriate gearbox into the transit, the transit will be a little lighter, and have a little more torque, and will outrun a stock transit. And the engine won't really snot itself any more than if it was run flat out in the civic, thanks to the short gearing giving it a break in the heavy transit.


Notice the way I didn't mention power anywhere?

JHMEG

Ok, I'll put it to ya this way:

Transit engine in CTR with CVT gearbox that keeps it at peak torque (1900rpm).

CTR with CTR engine, CVT gearbox that keeps it at peak power (7800rpm).

Which will be quicker to 100 mph?

Balfa

JHMEG wrote:

Ok, I'll put it to ya this way:

Transit engine in CTR with CVT gearbox that keeps it at peak torque (1900rpm).

CTR with CTR engine, CVT gearbox that keeps it at peak power (7800rpm).

Which will be quicker to 100 mph?

Sorry, re-reading my earlier post now, I probably missed your point when I was writing it...

First of all, the answer: the CTR engine.

For a constant speed (with constant wheel size, that means constant wheel speed), you can divide the engine speed (and hence multiply the torque) much more at 7800rpm than you can at 1900rpm. When the gearbox multiplies the torque of the engine, the effective torque at the wheels goes up. Let's pretend, to make it easy, that the wheels are spinning at 1900rpm (134mph with my mazda's 14" wheels!). The 1900rpm engine is going through a 1:1 gear ratio, so its torque is multiplied by one. Because the engine turning at 7800rpm is turning four times faster than the engine turning at 1900rpm, you get to divide its speed (multiply its torque) by 4. When you multiply a CTR's torque at 7800rpm (156Nm) by four, you get 624Nm laid onto the road... Much higher than the transit engine's 375Nm at the road.

That's why peak horsepower is so popularly quoted... it's a combination of torque and rpm... in effect, it's the point after which torque drops off too rapidly to benefit from longer gearing and before which the rpm is too low to allow sufficient torque multiplication.

JHMEG

Very informative!

So if I can get my engine to spin to 17,000 rpm (twice the current max), I'll be putting down 2x the torque. I feel a project coming on!

I get the impression from your explanation that you may have dispelled the theory from the diesel advocates that diesel engines have "better overtaking ability due to mid range torque"? ie a diesel spinning at 4,000 rpm (ie close to the upper limit) is putting down significantly less torque than a petrol spinnning at 7,000 or 8,000 rpm, owing to the multiplier effect of the gearing?

Balfa

JHMEG wrote:

Very informative!

So if I can get my engine to spin to 17,000 rpm (twice the current max), I'll be putting down 2x the torque. I feel a project coming on!

Assuming you can keep the torque curve flat up that high, AND you modify the gears appropriately, sure
People often don't pay much attention to gear ratios (again, it's not something that marketing bods care about), but they are, of course, quite significant. After I test-drove, but before I bought my Mazda, I tried a 2001 Geo Prizm (rebadged Corolla) and despite having a very high-tech 1.6 litre, 123hp engine, it felt awfully sluggish compared to the 105hp, similarly-sized Mazda. Before long I realised the automatic transmission was a freakin 3-speed!

That said, if performance was the only reason people bought cars, we'd all be driving 7-speed close-ratio semi-automatics. Usually, the manufacturer tries to set up the ratios so that at about 65mph, the engine is at its best efficiency (usually around 2,000rpm, depending on per-cylinder size among others - my poor Mazda buzzes at over 3,000 at that speed ), and then they fit all the other gears around that.
On second thought, it wouldn't surprise me if they tried to have the engine running most efficiently at 55mph, at least over here, because that's the speed that the govt. tests the highway fuel economy at, so the old marketing fellas get to publish marginally higher figures at the expense of ACTUAL fuel economy that you'd get if you drove at a more realistic 65mph

I get the impression from your explanation that you may have dispelled the theory from the diesel advocates that diesel engines have "better overtaking ability due to mid range torque"? ie a diesel spinning at 4,000 rpm (ie close to the upper limit) is putting down significantly less torque than a petrol spinnning at 7,000 or 8,000 rpm, owing to the multiplier effect of the gearing?

Yeah, even though I'm a diesel advocate (because of fuel economy per hp!). Because of the higher torque across the rev range, they can get away with longer gearing, which more significantly multiplies the wheel speed and divides the torque at the wheels than petrol.
I think the misconception may come from the fact that at cruising speeds, diesels are already at the start of their power band, so just mash the pedal and off you go... It's a satisfying experience.
Petrols are usually well below their powerband (too highly geared) at cruising speeds, so unless they downshift, they're not going anywhere fast. But if you do drop to 3rd in a Type-R, you're going to snot past most diesels. Not a 123d, though. Mmmmm... 123d....

That said, it may have been different in the past when cars really did have peak torque at some particular rpm. Most modern engines, especially with cvvt and stuff, achieve close to peak torque throughout the revs.

JHMEG

Balfa wrote:

65mph, the engine is at its best efficiency (usually around 2,000rpm, depending on per-cylinder size among others - my poor Mazda buzzes at over 3,000 at that speed

LOL. My DA6 would be at 4,500 rpm at that speed, in 5th! All 5 gears very short, max theoretical speed in 5th being about 120mph @ 8,000rpm (Jap speed limited cuts in slighty before that tho).

Yeah, downshifting is all part of the fun of driving a petrol. Not into downshifting to overtake, well maybe time to start thinking about what kind of slippers would be comfy...

maidhc

JHMEG wrote:

Yeah, downshifting is all part of the fun of driving a petrol. Not into downshifting to overtake, well maybe time to start thinking about what kind of slippers would be comfy...

You don't like diesels or cars that are not made by honda, which is fine, but diesels do have their advantages... there are certainly no petrol cars on the road that can return 55mpg + over a full tank and still have reasonable power for real world (non racetrack) driving.

(cue the hybrid argument.... )

JHMEG

maidhc wrote:

You don't like diesels

Understatement! The work of satan...

maidhc wrote:

or cars that are not made by honda

True, I would consider myself a Honda fan, but there are many non-Honda cars that I wouldn't mind owning.. GTR-R34, Z06, certain Mustangs and American muscle cars in general...

maidhc wrote:

there are certainly no petrol cars on the road that can return 55mpg + over a full tank and still have reasonable power for real world (non racetrack) driving.

A diesel that does over 55mpg would be what, a 1.8 or so. That's awful small for a diesel, and would be zero fun to drive. Slippers time again...

Balfa

JHMEG wrote:

A diesel that does over 55mpg would be what, a 1.8 or so. That's awful small for a diesel, and would be zero fun to drive. Slippers time again...

Did I not just say 123d? 54.3mpg and more hp than a Civic Type-R.

JHMEG

Balfa wrote:

Did I not just say 123d?

...which doesn't actually exist.

It'd be cool if they did pull it off tho.

Balfa

JHMEG wrote:

...which doesn't actually exist.

It'd be cool if they did pull it off tho.

It exists, they did pull it off, you'll be able to drive one in November. They're probably already taking orders.

JHMEG

By pull it off, I mean that it's actually a good, usable engine. If massive boost comes in high up in the rev range, well they can say it's 200 odd bhp, but it won't be usable.

It wouldn't be the first time a car didn't live up to the pre-launch hype spun out by the manufacturer.

Having said that, I hope they do actually do a good job of it. It will be a fair achievement.

(How does a 30mpg 5.0 litre 500bhp V10 normally aspirated petrol engine compare?)

maidhc

JHMEG wrote:

If massive boost comes in high up in the rev range, well they can say it's 200 odd bhp, but it won't be usable.

Like a type R....?

OKenora

I can offer you a 50mpg car with 300lb/ft torque at 1800 rpm and max power of a nads over 200bhp @ 5200 rpm. Well driveable and will leave any type R dead, best of both worlds car

unkel

JHMEG wrote:

time to start thinking about what kind of slippers would be comfy...

JHMEG wrote:

certain Mustangs and American muscle cars in general...

You are so ready for a petrol V8. Auto.

JHMEG

maidhc wrote:

Like a type R....?

No boost (no turbo). Power builds progressively.

OKenora wrote:

I can offer you a 50mpg car with 300lb/ft torque at 1800 rpm and max power of a nads over 200bhp @ 5200 rpm. Well driveable and will leave any type R dead, best of both worlds car

What car would this be? (Wouldn't be a 42mpg 175bhp 2.4jtd 156, that does 60 in 8.0?)

unkel wrote:

You are so ready for a petrol V8. Auto.

Only if it has leaf springs in the rear suspension. Leaf springs are soooo cool.

unkel

JHMEG wrote:

Only if it has leaf springs in the rear suspension. Leaf springs are soooo cool.

Damn - you seem to age fast! From a (probably too old) boy racer adept to middle aged connoisseur of mighty engines to a "leaf spring" suspension fool? I've never seen Alzheimers progressed like that in a single day :eek:

Balfa

JHMEG wrote:

No boost (no turbo). Power builds progressively.

Naturally aspirated diesels run out of air very early on... the whole point of the turbo is to keep them going a bit longer, not provide a surge at high revs. And this one's a twin turbo, so it should be even smoother.

Besides, we've already discussed that you need to rev the clappers out of a type-r to go anywhere... What was it about downshifting being part of the fun of petrol?

(How does a 30mpg 5.0 litre 500bhp V10 normally aspirated petrol engine compare?)

Uhh, it has a bit over half the fuel economy, less horsepower per litre (!!!), no turbocharger and uses a different kind of fuel. But what has an M5 got to do with anything?

JHMEG

Balfa wrote:

Naturally aspirated diesels run out of air very early on... the whole point of the turbo is to keep them going a bit longer, not provide a surge at high revs. And this one's a twin turbo, so it should be even smoother.

I didn't explain myself right. A few years ago I drove a Seat TDi of some sort (maybe Cordoba, tho could be wrong). Boost, which was noticeable arrived late. Change up gear high up in the rev range, and the damn thing dropped out of boost. Then repeat all over again: building, building, boost, redline (or near), up gear, boost gone.

Short gears are required for late boost like that. But short gears give cr@p economy. So I'm thinking BMW will do late big boost and short 1, 2 & 3 so that it can be kept on boost. 4, 5 and 6 will be much longer for economy, but changing from 3 to 4 will drop out of boost, as will 4-5 etc.

So you might never really see boost in 4th onwards. But for legal driving that shouldn't be a problem.

Balfa wrote:

Besides, we've already discussed that you need to rev the clappers out of a type-r to go anywhere... What was it about downshifting being part of the fun of petrol?

Max power is in the 6,000+ range. So ya, maybe BMW will (as outlined above) make the 123d more like a petrol to drive (ie downshifting a requirement).

Look, either way, I hope they pull it off. That Golf 1.4 super turbo hasn't set the world on fire, despite all the hype. I haven't driven one myself so I can't say anything about it tho.

Balfa wrote:

Uhh, it has a bit over half the fuel economy, less horsepower per litre (!!!), no turbocharger and uses a different kind of fuel. But what has an M5 got to do with anything?

Who said anything about the 19mpg M5?:D

JHMEG

unkel wrote:

Damn - you seem to age fast! From a (probably too old) boy racer adept to middle aged connoisseur of mighty engines to a "leaf spring" suspension fool? I've never seen Alzheimers progressed like that in a single day :eek:

LOL. It really depends on what you're into.

Gotta respect cars that can do wheelies(!), and have parts that sound like weapons, big weapons, like "Holley Double Pumper". I had a carb once, but it had a very boring name (and the car couldn't do wheelies either). Ok, so coutesy leaf springs they don't do corners, but who cares...

Skyline, well you gotta respect a car that's nicknamed Godzilla. And for a 10th the price (incl mods) will outrun a Veyron.

I'm reminded every time I drive behind a diesel car of what's not to like about diesel cars. The air-recirculate button on the dash has been nicknamed the "diesel in front" button. They smell brutal and burn the lining of my nose with their acid fumes... when the don't then I might reconsider!:D

bushy...

JHMEG wrote:

I didn't explain myself right. A few years ago I drove a Seat TDi of some sort (maybe Cordoba, tho could be wrong). Boost, which was noticeable arrived late. Change up gear high up in the rev range, and the damn thing dropped out of boost. Then repeat all over again: building, building, boost, redline (or near), up gear, boost gone.

That was maybe (badly) done on purpose ,more than likely inspired by marketing bods, to try and make it feel sporty,peaky whatever. Kinda sounds like wrong turbo for the engine.

maidhc

JHMEG wrote:

I'm reminded every time I drive behind a diesel car of what's not to like about diesel cars. The air-recirculate button on the dash has been nicknamed the "diesel in front" button. They smell brutal and burn the lining of my nose with their acid fumes... when the don't then I might reconsider!:D

You have a very closed mind.

I also love cars with Carbs and leaf springs. Not being able to afford anything wilder I have a '74 Ford Capri with a 2.0 overbored pinto engine and a few other mods here and there (AP racing clutch, maniford, camshaft, Essex Carb).

Diesels are just a better proposition for a daily driver though. My 1.8 Focus TDCI has plenty power for overtaking, corners fantastically well, and does the aforementioned 55mpg. It is also a lot quieter than the Capri!

JHMEG

maidhc wrote:

You have a very closed mind.

maidhc, there's nothing closed minded about not liking diesels! My dislike starts with my nose, and continues on with my ears and then my right foot.

BTW, a lad I know has some sort of special edition Capri 2800. Dunno much about Capris but there were only something like 400 made. Mint condition, and worth a fair bit too.