Outer Limits 4x4 Board

this may seem like a dumb question but what do kilowats actualy do and are they of any use when 4wd'ing compared to torqe

kilowatts sells cars and torque wins races.

It's all about the torque.

Simmo

Torque is the pulling strength of an engine - trucks want torque for towing.

Power is a measure of how quickly a motor can pull.

For low speed work, climbing etc torque is the important thing - and the lower the rpms the better.

Power is good for speed and acceleration - but only if you can get your revs up to peak power. Torque is what gets you the revs. Confused yet?

Racers want power, because that's what's required for speed, and they don't mind using a few revs. For lazy highway cruising a good torquey engine (like a V8 ) is better - to allow easy overtaking in a higher gear, without using high revs.

Hope this helps,

Scott

kw has a place in offroading......

Ask a suzuki driver who has bugger all torque....... they still seem to get through places bigger rigs may fail to.


If you have a high revving car for offroad it's not all bad - so long as you can get/have got appropriate reduction gear. Obviously the goal is to have a different final drive ratio applied to a sierra than a 4.2 turbo diesel.



High rpm power is great for flinging mud out of the trads of your tyres, allowing additional traction

Too much torque applied will generate wheelspin - whether it's torque at 1500 rpm or 5000rpm makes no difference, its the net effective force.

Obviously this changes based on gearing, and to generate similar torque at the ground you might find a patrol in 3rd low 2000rpm and a sierra in 1st low at 5000rpm.

The difference is down to how much ability you have to control the effective torque, and whether or not the vehicle has the torque to still accelerate in heavy drag situations (eg mud). This would be where the bigger vehicles get their biggest advantage - in mud not on rocks or loose stuff.

ok then that was helpfull but i'm still a lil confused

This is a easy way of thinking about.

Put a car trailer with a 2t 4x4 on it behind a 5.7L commodore, tows with out any trouble (heaps of torque)

Put that same trailer behind a turbo skyline, suxs, usless (Heaps of Kw)

T = F x d or Torque = Force x Distance

To simplify what torque and power are here is a very crude and basic discription.

Torque of the engine is the force of combustion acting on the pistion rod times the distance from the longitudinal axis of the crankshaft.

Power = Torque x Angular speed

Here power (Kw) is the torque multiplied by the rotational speed. The usual units for rotational speed is radians/sec, we can simply say that the rotational speed is rev's/min to simplify the explanation.

So power is a product of torque and engine speed and torque is the force which rotates the crankshaft.

OK, we'll try a slightly different approach. Are you mathematically minded? I'm making this up as I drink along, so if I'm wandering a little I hope you'll understand.

Force = mass x acceleration. To accelerate the mass of your 4by you need your tyres to apply force to the ground (no conveyors, please. )

Force = torque/distance. The force required (above) comes from the torque at the axle, divided by the radius of your tyre. More torque = more acceleration (Smaller tyres = more acceleration too, but smaller tyres = less fun for us. )

That's why we use gears. As you step down your engine revs you step up the available torque. So a low gear puts more torque at your axle than a high gear. More torque in a lower gear = more drive force = more acceleration. This is why you accelerate more in 1st gear than in 2nd (or 3rd etc.)

Power = torque x revs. For most engines peak torque is developed at lower revs than peak power. Above peak torque, although torque is reducing the revs are climbing at a faster rate, so the (torque x revs) figure continues to increase. Once torque drops faster than revs climb, power drops too. Note that although a gearbox will increase torque by reducing revs, it doesn't affect the power - because you've reduced your revs by the same factor used to increase your torque. (Let's not confuse the issue with frictional losses in the gearbox. )

So what does power do? Good question. Power is how fast energy is delivered. When you're driving your 4by it's losing energy through friction - at speed, air drag is the largest contributor, probably followed by losses in the drive train. If your engine can deliver energy faster than it's being lost, the vehicle can go faster. Once energy is lost as fast as your engine can supply it, you've hit your max speed - which isn't necessarily your maximum power, but let's not go there right now. If you're cruising flat out at max speed (say 115 in a diesel Hilux ) and the head wind increases, guess what? Extra air drag means you're losing energy faster than the mighty diesel can deliver it, so you'll slow down.

Edit: Torque is what accelerates a vehicle. Power determines the maximum speed (at which acceleration stops.)

Does that help?

Scott

Someone once explained it to me as simply as a boxer:

Torque is how hard the punch is, Kw is how fast the punches come.

It made sense to me anyways...

jeep97tj wrote:This is a easy way of thinking about.

Put a car trailer with a 2t 4x4 on it behind a 5.7L commodore, tows with out any trouble (heaps of torque)

Put that same trailer behind a turbo skyline, suxs, usless (Heaps of Kw)

Says someone who's never even seen the torque curve of a GTR and completely blinded themselves to how incredibly easily they pulled away from the big v8's up the hill at bathurst.

Torque is dependant on the amount of air/fuel combustion, not how many cylinders you have.

About the Commo vs Skyline thing...

An Twin Tuboed R33 makes 280Nm..

A 5.7L Commodore makes around 480Nm...

You do the math

No.....

A commodore claims 480Nm...... A skyline claims 280ft-lb. That's actually about 375 Nm.


However an R34 MEASURES more than claimed at the wheels. Dont think you'll ever see that on a Commodore.

Check the web you'll find a lot of people getting way way way below holden's claimed figures when they stick them on a dyno.




However, lets look at apples and apples, say a VT Clubsport versus an R33 GTR.

Both are already lightly modified. All mods are listed.

What does the Commodore actually measure when tested??
http://users.senet.com.au/~dtech/vtclub ... nedyno.htm

Hmmm... is that a max of 200 Nm I see? Ohh yeah I believe it is.


Here's some from an R33 from stock through all his mods. Remember R33 = over 10 years old.

http://www.planetkingsley.com/skyline/#stage0

Now where does that start? About 275ft-lb.... meaning about 372 Nm.

No torque at all... only about double the VT Clubby....

while on the torque topic - can someone explain why this is....

all things been equal - the less cylinders a mtr has the more torque it will produce. IE a 4 cyl will have more torque than a six, a six will produce more than a V8.

Thats to do with reciprocating weight. 2 litre 4cyl has heavier pistons than a 2 litre 6 cyl thus more leverage on the crank for every stroke. It also means that the the 4cyl won't rev as hard as it is too hard for the engine to stop the pistons and start them again at TDC and BDC.

Uh-oh. This is a can of worms!

"All things being equal" is the key here. What's equal, and what isn't?

Heavier pistons may be an issue, but I think that will affect maximum revs more than torque.

Torque is force x distance. To keep things equal, let's presume both engines have the same stroke, so the crank has the same throw, and the "distance" component is the same.

So which engine has more force? All things being equal, both will generate the same Brake Mean Effective Pressure - i.e. both exert the same pressure on the piston crown. But because they both have the same capacity, with the same stroke, the four cylinder must have a larger bore, so the pressure must generate more force (on the larger area) and hence higher peak torque from each firing stroke.

However, the four cylinder has fewer firing strokes per rev than the six cylinder, I suspect there will be some averaging occurring, so I'm not sure the difference will be as marked as the above rationale would suggest. Or I could be wrong - again.

Scott

of4x4 wrote:Someone once explained it to me as simply as a boxer:

Torque is how hard the punch is, Kw is how fast the punches come.

It made sense to me anyways...

I reckon this sums it up perfectly.....

About the V8 vs boost thing, it's all dependent on the application. Boost is an amazing thing, afterall the F6 Typhoon is (was?) the most powerful Australian built production car (torque) and it's a turbo 6. Even the XR6 turbo's have incredible amounts of torque down low compared to the 8's of any new breed and will walk away from any of them from low to mid range acceleration.

Torque is also proportional to the mass that is rotating. 4x4 engines generally have heavier flywheels than an equivalent CAR engine, to improve torque at the expense of acceleration (power).

Conversely, race cars and wannabe race cars generally have greatly lightened flywheels to increase acceleration.

For those who dont really understand boost here's how it works.

Engines dont know what shape they are, or how many cylinders they have. An engine is just basically a pump for air and fuel that's made solidly enough that it doesnt go boom when the fuel is ignited.

An engine can only suck in as much air as the engine itself can deal with and the air pressure. Air pressure at ground level is 1.0 bar by definitition (dont make me take it to hectopascals).


For a naturally aspirated engine, say your HSV V8, that is say a 5.7 LS1, that's the equivalent of 5.7 litres of air sucked in.

In fact it's a bit less - any 2 Valve per cylinder pushroad engine is not the worlds most efficient. You'd be lucky if you got the cylinders 80% flushed and filled - we'll use this as an estimated figure. (Actual engine efficiency due to heat and friction is much much lower - we'll just talk in terms of air pumping ability).

So say 4.56 litres equivalent.


The Skyline is only a 2.6 litre engine, but being turbocharged gets a little help. Say your skyline is running at 0.9 bar boost pressure - approximately stock (note this will vary based on air temperatures and densitys and the build spec - eg Japanese spec is different to UK spec is different to Aus spec).

OK. 1.0 bar + 0.9 bar = 1.9 * 2.6 litres = 4.94 litres.

Now the Nissan skyline GT-R engine is one of the more advanced engines going around - no VVT (not needed since it way exceeds Japan's maximum legislated power already) but otherwise it's state of the art DOHC 4V per cylinder.

It's maybe 90% airflow efficient, so equivalent pumping force of 4.46 litres.

Not much in it there really is there? 4.56 vs 4.46. Remember the engine only knows how much air can go into it, not how many cylinders it has.

Ok, down low say 2000 rpm when the turbos havent kicked in and are only providing say 0.3-0.4 bar boost, the LS1 has a clear advantage - the GTR is really only working with an effective engine of about 3 litres versus 4.5 litre.


Let me point out no-one in their right mind would drive around in a GTR at 2000 rpm, nor are they gonna tow a box trailer at 2000 rpm


At 3000rpm when the turbos are running near full boost it's pretty level, and they're both working with a pretty similar equivalent capacity of 4.5 litres.

By 5000rpm the v8's running out of puff and it's efficiency is dropping, but the GT-R still has another 2000 rpm to go. At this point the v8 is toast.


Well actually, the v8 was toast from the start... unless you'd agreed to idle off the line.... 3000+ rpm launch + 4wd...... remember godzilla?

Will it take off ?

Conrod lenght also plays a part.

Zute wrote:Conrod lenght also plays a part.

I've heard this! Stroke to rod length ratio is significant, and apparently the Nissan 3.0 in the skyline/VL commodore is close to perfect.

But what's "perfect?" Not something I've ever understood, and not interested enough to Google it. Yet.

Scott

Isnt the impact of conrod length more an aspect of the crank's throw than anything else? I dont know that the rod itself should be claiming responsibility....



Conrod length to bore diameter is critical in motorcycles for high rpm applications, and certainly if you looked at the GSXR range (a great example because they change just about everything on the bike every year) there was a "torque sweet spot" in bore/stroke ratio which was reached pretty early on, but quickly ignored in the quest for more horsepower.

Motorbikes generally are massively oversquare (bore > rod length) and that is suitable for high horsepower high rpm applications. It's undoubtedly more efficient in it's own way, but so too is a massively undersquare large semitrailer engine.

I think as far as a sweet spot goes, it's dependant on your application. There's not going to be any magic number that is optimum and suddenly gives you 20% more power and torque or anything like that.

Yeh i heard that the most torque is produced from any given engine when the stroke/bore ratio is closest to 1.

A longer stroke will produce more torque, a square engine ( stroke x bore are the same) will help produce more kw's, an over square ( shorter stroke larger bore) more again, an under square ( long stroke short bore) will help produce more torque. Of course there are a lot of factors to this, lc and patrol 6's are a long stroke design and help to give them good lazy pulling power (torque) where as something like a rover 3.5 which has stroke smaller than its bore lacks torque but can be made to produce reasonable kw's although still underpowered for the weight it is required to move.

I think the "long stroke" design is good for torque because the throw of the crank is longer - when compared with a "short stroke" engine of same capacity. The longer throw applies the piston's force at a greater radial distance. Torque = force x distance.

But (for the same capacity) the piston area is smaller, so for a given BMEP the piston doesn't generate as much force. And longer stroke requires higher piston speeds to cover the longer distances. I understand F1 engines (and probably many bike engines?) have very short strokes to allow for the extremely high revs.

With rod-stroke length, the rod obviously needs to be long enough for the piston to clear the crank counterweights at BDC. If I imagine an engine with ridiculously long rods (say 10x stroke) then the rod and crank aren't near right angles for very long, which I'm guessing isn't good for efficiency. Perhaps the aim is to get the rod as short as possible? As close to 1:1 as possible?

I think I'll have to Google this.

Scott

The Rod Ratio is a measure of the rod length divided by the stroke. Basically it is telling you about the rod's angularity. A high rod angle (low rod ratio) generally means faster wear to the rings, pistons and bore. As the rod length increases the rod angle decreases. The problem with low rod ratios is that the piston tends to need to be shorter. From what I have come across the max ratio for reliability seems to be around the 1.5 and generally prefered to be around 1.6 to 1.8 unless you are going racing.

Ask a suzuki driver who has bugger all torque....... they still seem to get through places bigger rigs may fail to.

thats because all sook drivers have the ability to drive AROUND all those places bigger rigs may fail..... AROUND!!! and yes i gess thats a skill.

known 2 wrote:this may seem like a dumb question but what do kilowats actualy do and are they of any use when 4wd'ing compared to torqe

Just to add to the discussion (or add confusion )

Damn kilowatts, should've been a term kept with electric motors
What's wrong with the old "bhp"?

Yes, KW or bhp is a by-product of torque (turning effort)
Higher rev's usually = more KW = more power (or momentum)
A short stroke motor will usually rev higher and more freely than a longer stroke than bore motor.

Lets say you have 2 engines of the same size (displacement) but one has a longer stroke than the bore, and the other has a shorter stroke than the bore.
You put them in identical vehicles and chuck a caravan on each of the tow balls.
The long stroke engine should pull the van with less effort at lower rev's than the short stroke engine. The short stroke engine will need higher rev's/lower gear to keep momentum going.
It doesn't necessarily mean the short stroke engine has less torque than the long stroker, it just means that it's peak torque is usually at higher rpm's in a short stroke engine.

Another important thing is the "torque curve" i.e: the revs at where the torque really starts to pull things along and the point at which it peaks.
This is where you will get your quickest acceleration in any given gear and in a perfect world a healthy flat torque curve would be magic.
Most manufacturers work to achieve a near result to this but usually design engines according to costs, market demands, EPA reg's etc.
Some good results have come from variable valve timing.

My Rodeo's peak torque is at 4200rpm (in the book) and it starts making really good torque at about 2500rpm so rev's are kept around there in the really soft stuff.

NJ SWB wrote:I think the "long stroke" design is good for torque because the throw of the crank is longer - when compared with a "short stroke" engine of same capacity. The longer throw applies the piston's force at a greater radial distance. Torque = force x distance.

I think you may be onto something here Scott. Having a long stroke must give more torque because the crank throw is proportionally longer.
Oh no, we are getting back into momentum discussions...

Another conflicting factor is that engines with smaller valves apparently produce more torque??? Or do I remember that wrong...

gudgeon(sp) pin offset will also affect torque, some builders of race engines reverse the pistons to get more torque, at the cost of engine life.