kw what are the good for

[-Scott-]

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

That's as I remember it. Something to do with velocity of the incoming air charge. At any given engine speed, a cylinder has a fixed time in which to fill. If the valve opening is large the incoming air doesn't need to flow as fast as if the valve opening is small.

The high velocity through the small valve creates more turbulence in the cyinder, which results in better mixing, better flame propagation and more efficient combustion.

Cheers,

Scott

[Strange Rover]

There are lots of weird theorys getting thrown around here so here is a few more......

If you assume a motor is perfectly efficient then two motors with identical capacity will produce the same power and torque no matter what the individual bore and stroke. If the engines are the same capacity this is all that matters.

Now when you start to look at why longer stroke motors produce more torque and shorter stroke motors produce more power you have to start to look efficiencies and what limits things.

Shorter stroke motors have lower piston velocities and therefore you can make them operate at higher RPM. By developing the torque at higher RPM you produce more outright power. Now because you tune the engine to produce torque at higher RPM the motor generally wont produce as much torque at lower RPM and therefore the motor isnt as "grunty". Variable cam timing or running two seperate cam profiles (one for low RPM and one for high RPM) allows the engine to work well at low revs (like a grunty engine) ang also high RPM (like a peaky engine). Also shorter stroke engines also have larger bores (to retain the same capacity) ad therefore have larger valves which also lets them breath better which is also good for high RPM performance.

The reason why having a low conrod length to stroke ratio is good for producing power and torque is because a low ratio makes the piston dwell (or hang around) at the bottom of the stroke longer than a motor with a high ratio. This then gives the motor more time to suck in more air and fuel abd therefore produces more power and torque.

Sam

[Strange Rover]

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

That's as I remember it. Something to do with velocity of the incoming air charge. At any given engine speed, a cylinder has a fixed time in which to fill. If the valve opening is large the incoming air doesn't need to flow as fast as if the valve opening is small.

The high velocity through the small valve creates more turbulence in the cyinder, which results in better mixing, better flame propagation and more efficient combustion.

Cheers,

Scott

I think its more to do with small valves limiting how high the engine can rev. So you therefore have to set up the engine to produce power at lower revs - by tuning an engine to perfore at lower revs you produce more torque that the same engine tuned to rev higher.

Take any motor and throw in a set of smaller valves and it will produce less torque bacause it wont breath as well.

Sam

[HotFourOk]

Small valves dont limit how high an enigne can rev... it only lowers how much volume can enter and exit the cylinder per cycle. This means less fuel and air will go in, and less exhaust that is allowed to be expelled.
This is only per cycle though, the size of the valves does not effect how quickly it can do this...
When you rev too fast, it is often the valve springs which cannot keep up and you get 'valve float', where the valves are remaining open when they are not meant to. This allows for example, intake air to go out of the exhuast valve before the combustion stroke.
Often, when you change the cam to allow the motor to rev to a higher rpm, the valve springs are changed to compensate for the higher rpm. You can make the valves bigger to accomodate a higher flow of gas into/out of the cylinder, but this doesnt really affect how high the engine can rev, just how much power is produced on each stroke.

[J Top]

Long rods allow the piston to dwell at the top of the stroke longer, which allows the flame front to expand and apply more force to the piston instead of just running out of puff as the piston moves away too quick.
This is from Smokey Yunick, a famous US engine builder.
J Top

[RUFF]

Small valves dont limit how high an enigne can rev...

Yes they do.

it only lowers how much volume can enter and exit the cylinder per cycle. This means less fuel and air will go in, and less exhaust that is allowed to be expelled.

And here you explained why. Less volume entering and exiting will limit the amount of revs an engine can do. You can only flow so much air through a hole. Once it gets to maximum flow its not going to flow any more.

[F'n_Rover]

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

That's as I remember it. Something to do with velocity of the incoming air charge. At any given engine speed, a cylinder has a fixed time in which to fill. If the valve opening is large the incoming air doesn't need to flow as fast as if the valve opening is small.

The high velocity through the small valve creates more turbulence in the cyinder, which results in better mixing, better flame propagation and more efficient combustion.

Cheers,

Scott

The intake charge on a small valved / small ported mtr will have more speed / momentum , thus it can fill the cylinder past 100% ve.
(or more than an equivelant larger valve / ported head). only at low revs though. This is why long intake runners are good for low down torque.

I call BS on the turbulance been a good thing though - intake air turbulance is a loss in efficientcy. piston squish should be the only thing creating turbulance.

[-Scott-]

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

That's as I remember it. Something to do with velocity of the incoming air charge. At any given engine speed, a cylinder has a fixed time in which to fill. If the valve opening is large the incoming air doesn't need to flow as fast as if the valve opening is small.

The high velocity through the small valve creates more turbulence in the cyinder, which results in better mixing, better flame propagation and more efficient combustion.

Cheers,

Scott

I think its more to do with small valves limiting how high the engine can rev. So you therefore have to set up the engine to produce power at lower revs - by tuning an engine to perfore at lower revs you produce more torque that the same engine tuned to rev higher.

Take any motor and throw in a set of smaller valves and it will produce less torque bacause it wont breath as well.

Sam

One of the first 4 valve Celica motors to arrive in Australia had an extra set of butterfly valves, to close off one intake runner per cylinder at low revs. Road tests at the time seemed impressed with the size of the "power band."

Why would they do this?

[-Scott-]

I call BS on the turbulance been a good thing though - intake air turbulance is a loss in efficientcy. piston squish should be the only thing creating turbulance.

Intake air turbulence in the manifold is a bad thing - no argument. It effectively reduces the diameter of the runners, which is where your loss of efficiency comes in.

Turbulence in the cylinder (at low revs, at least) is a good thing.

YMMV

Scott

[jeep97tj]

I was told about the small valves giving u more power at low rpm buy a performance engine shop. The didn’t say u should install smaller valves into your engine but when u go larger than stock the air will no longer flow into the engine properly, the air will just flop in. With the stock valves at low rpm the air will continue to flow into the cylinder while the piston is at the bottom of its stroke, with the larger valves as soon as the piston stops moving down that’s it for air flow. But at higher revs it will continue to flow again when the piston stops moving.

It was more about if u just port your heads and put larger valves in your engine with no other mods u were more than likely going to loose bottom end power, but u would gain a little up top, but not worth the $$.

[cloughy]

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

That's as I remember it. Something to do with velocity of the incoming air charge. At any given engine speed, a cylinder has a fixed time in which to fill. If the valve opening is large the incoming air doesn't need to flow as fast as if the valve opening is small.

The high velocity through the small valve creates more turbulence in the cyinder, which results in better mixing, better flame propagation and more efficient combustion.

Cheers,

Scott

I think its more to do with small valves limiting how high the engine can rev. So you therefore have to set up the engine to produce power at lower revs - by tuning an engine to perfore at lower revs you produce more torque that the same engine tuned to rev higher.

Take any motor and throw in a set of smaller valves and it will produce less torque bacause it wont breath as well.

Sam

One of the first 4 valve Celica motors to arrive in Australia had an extra set of butterfly valves, to close off one intake runner per cylinder at low revs. Road tests at the time seemed impressed with the size of the "power band."

Why would they do this?

So do 4l falcons EF onwards, its to use longer runners at low revs for greater torque and the falcons would open at approx. 3000rpm to use the short runners, and iv'e seen it dyno proven there is a power loss either way if you only use long or short (manually operate butterfly diaphragm)

[Beastmavster]

Small valves - people seem to have different ideas as to what "small valves" are and are arguing at cross purposes.


Lets get the 2 Valve versus 4 Valve thing straight:

Any 4V per cylinder head uses smaller valves than a 2V per cylinder.

There's a number of really good reasons for this:

Flatter piston crown absorbs less heat for same compression ratio than a domed 2V one. As heat loss is the main reasson of inefficiency in an engine that's a big thing.

Less likely to have hotspots on the flatter piston crown allowing higher compression ratios on same quality of fuel.

The extra weight of the dome makes for lower safe piston speeds due to the extra strain on rods (even a few grams weight can have the euqivalent of a couple of tons of force on the conrod at high rpm).

Less valvetrain load and frictional losses from lighter parts.Lighter valves are less likely to be a limiting factor in high rpm situations and are less likely to suffer valve bounce.

Hence higher revs from 4V engines, (unless you put no effort into improving the bottom end to suit).



Smaller valves generally allow for a more direct intake port shape, and better gas flow.


2 smaller valves replacing one can easily supply more surface area, especially in part opened/part closed situations.

You can also slightly stagger the valve opening by slighly altered cam profiles between intake valve A and B (and also exhaust valve C and D) to create a better swirl effect. This will help fill the cylinder and empty the cylinder more effectively.



About the only situation I can see where a 2 Valve engine will outperform a 4 Valve engine is in prostock motorbikes, where the 2 Valve engine is given a large capacity advantage.

While 2 Valve engines may "feel" more torquey in some circumstances, it's generally because the most efficient part of the engine's power curve is nearer idle speed than peak power - because the engine just can't rev anywhere near as high.

However, the peak torque will fall well short, and the peak power will fall even shorter.



Put the power and torque curves up back to back, and CC for CC (or Cube for cube for the V8 dudes) you'll see every time the 4 Valve will blitz the 2 valve.

[crankycruiser]

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...

Now that makes sence!!!!!!

[rockcrawler31]

in the V8 vs ricer skyline debate, has anyone considered longevity?

someone (a bevan) once suggested to me V8's and old tech pushrod engines were better due to longevity. A litre of fuel in each car both contain the same amount of energy units or BTU's whatever. The ricer might go as fast on a smaller capacity engine, but at the cost of engine longevity due to the tolerances needed and being run at the edge of engineering limits. essentially it's using technology to harness or limit energy losses. His arguement was that the clunky V8 will still be pulling well when it done several hundred thousand kays.

Not that any of this matters to you traffic light heroes.

Besides, i drive a diesel, so i gave up on any kind of speed a looooong time ago and rode fast bikes instead.

[Beastmavster]

in the V8 vs ricer skyline debate, has anyone considered longevity?

someone (a bevan) once suggested to me V8's and old tech pushrod engines were better due to longevity. A litre of fuel in each car both contain the same amount of energy units or BTU's whatever. The ricer might go as fast on a smaller capacity engine, but at the cost of engine longevity due to the tolerances needed and being run at the edge of engineering limits. essentially it's using technology to harness or limit energy losses. His arguement was that the clunky V8 will still be pulling well when it done several hundred thousand kays.

Not that any of this matters to you traffic light heroes.

Besides, i drive a diesel, so i gave up on any kind of speed a looooong time ago and rode fast bikes instead.

Depends on build quality and build tolerances too.


Japanese engines - even the cheaper ones - are built to much higher standards than most american built or australian built engines. And the flagship cars are given a little extra care.

I'd lay good money out that without overboosting a skyline GTR, and with proper warm up before thrashing it would last as long as a LS1 V8.

And let's face it - Holden is not exactly known for the build tolerance quality of it's engines.

Dont believe me, then go and ask about the Lexus warranty... then ask for the same deal down at Holden on a SS commodore.

[1MadEngineer]

ok it is a well known and widely published fact (every turbo mag) that a skyline with a blow-off valve and 20" wheels will have 600kw.

but once they are at the drags there is always excuses such as "we have too much wheelspin cus there is too much power" or "the track is crap" or " i was playing the wrong 50cent album".

yet the lowly 450-600HP v8 just rolled through for a mid to low 10 at 125-135mph. most rear wheel 450kw v8s have no prob doing ~1.3 60ft, yet it is very rare to see a mighty 4wd (ultimate traction) nissan match it.

killerwatts arent they like reaaaaly small asian horses, you know bonzai style

[bazzle]

Taken from one of my forums...

The first thing to remember is that BHP is not measured on a dyno - only torque, BHP is a factor of torque and engine speed - its just a theoretical calculation

First, power, what do we mean by that?

Well, we usually express power in terms of the amount of time it takes to do a certain amount of work... for example, one horsepower is measured as the amount of work required to lift 33,000 lbs over 1 foot in 1 minute (huh -that's obvious, _). As this is such an obviously Scottish measurement (as James Watt first devised the calculation) , we have a metric equivalent... the metric horse could lift 4,500Kg a metre in a minute... 98.6% of a good British horse. The Europeans decided to call it a PS (Pferde Starke - German for Horse power!)instead of an HP to cover their shame. Also, in the newfangled metric system, 1hp is the equivalent of 746 Watts of electrical power. So, to recap briefly:

1 HP = Roughly the amount of work a horse can do lifting coal up a mineshaft, assuming his heart was really in it = 1.014 PS = 0.746 KW - easy huh _

Now we need a way to measure this output - so we use a defined force or "brake" to see how much energy we need to apply to stop it - Hence "Brake Horsepower" - and is defined as it's maximum performance at a certain rpm.


The other thing we babble on about is Torque... Torque is the amount of force applied to turn something multiplied by the distance from the axis of it's rotation... sounds all weird, until you realise that we use the engine to rotate the front wheel, so torque is something that would be nice to calculate. Something interesting is that 1hp is 550ft/lbs of torque per second.

Now, it's fairly easy to measure torque... this is where the dyno comes in, and we calculate horsepower from an engine's torque output multiplied by the revs...


A dynomometer is just a heavy drum (brake), an accelerometer and a computer... if you know the weight of the drum, and you know how fast it's being accelerated, you can calculate the torque that must be being applied to the drum. What you also want to take into account are the frictional losses on the drum, and the air temperature at the time (which is why you'll see air temperature, pressure and a correction factor calculated by the software... as air temperature goes up, so the effective power output goes down, so the correction factor has to go up to normalise this).

Taking a Dyno Run
( As used today at PTS - differs slightly if they use an inductive loop)

So, to measure torque, we strap the car to the dyno, start it up and run it up in the gears to 3000RPM the dyno operator holds the car at a steady 3000 for 6-7 seconds and the dyno learns the road speed for that car at 3k. ( Some dynos use an inductive loop to accurately measure RPM - but the rev counter method works fine for most modern cars) - now with a given road speed the RPM can be calculated.
... cars tend to do their power runs in 4th gear, as it's the best gear for acceleration at speed and less chance of the wheels slipping, as the calculation errors get smaller the bigger the numbers are. 4th is used because on cars these days 5th gear tend to be a bit of an overdrive.
The throttle is gently floored, and the dyno slowly allows the speed of the engine to increase - this measures the torque of the engine. When the engine reaches maximum RPM, the operator puts the car in neutral, and allows the wheels to decelerate of their own accord - this measures the losses of the transmission,driveshafts,bearings brakes (if they are sticking) and tyres

Now here comes the maths

BHP = Torque (lbft) x RPM
_ _ _ _ -------------------
_ _ _ _ _ _ _ _ 5252

This means that BHP is always equal to torque at 5252rpm _- if its not then there is something wrong!

Now using Pauls results from today we get max power of 169.3BHp @ 7869RPM but 115.0lbft of Torque. The important factor here is that it makes its maximum power at nearly 8000rpm!

Andy Blower made more torque 123.5lb/ft - therefore it must be quite a bit more powerful right? - WRONG ! - he made his max figure at 7309rpm - and as BHP is proportional to speed and his engine was making its torque at a lower RPM value - he gets 169.4 BHP - a whole 0.1bhp more _

Shirish made 129.8lb/ft at 7466rpm - which equates to 170.4BHP

So now we have 115, 123.5 and 129lb/ft of torque - all at different engine speeds - All giving an output of 170BHP give or take a little bit

The moral of this essay is - it is better to make torque at high RPM for a screamer! - and thats why beause Hondas rev so high they produce the power!

I realise I've forgotten an important part of the calculation _

Where did the 5252 figure come from ?

As discussed what we actually measure is torque, expressed in ft/lb, and then we calculate actual horsepower by converting the twisting force of torque into the work units of horsepower.

Visualize a one pound weight, one foot from a fulcrum on an "invisible weightless" bar. If we rotate that weight for one full revolution against a one pound resistance, we have moved it a total of 6.2832 feet (pi times a two foot circle), and, we have done 6.2832 foot pounds of work.

OK. Remember Watt? He said that 33,000 foot pounds of work per minute was equivalent to one horsepower. If we divide the 6.2832 foot pounds of work we've done per revolution of the weight into 33,000 foot pounds, we come up with the fact that we have to rotate that weight at the rate of 5,252 revolutions per minute in order to do 33,000 foot pounds per minute of work, and thus do work at the equivalent rate of one horsepower.
Therefore, the following formula applies for calculating horsepower from a torque measurement:

Horsepower = ( Torque * RPM ) / 5252

Thats where the 5252 comes from


Torque is only half the story. While torque is the force created, it doesn't account for the importance of revs.
Imagine trying to remove a wheel nut from a car with a standard wheelbrace and all the torque you could produce can't loosen the "Kwik fit special" airgunned super tightened wheel bolts. You apply lots of force, i.e. torque, but you still can't generate any rpm. Therefore nothing is accomplished, no power generated despite your cursing and kicking. So - Without rpm, torque is useless!

Two engines may make 125 foot/pounds of torque, but if one is a FixOrRepairDaily turning at 5,000 rpm and another is a Honda turning at 10,000 rpm, the Honda is doing more work than the FixOrRepairDaily, therefore generating more power.

HP = Torque x RPM / 5252

so the FixOrRepairDaily makes 125*5000 / 5252 = 119HP,
but the Honda makes 125*10000 / 5252 = 238HP - must have been an S2000 _


Love the F.O.R.D swear filter

If anyone got this far - class dismissed


Bazzle

[Patroler]

Sounds pretty good to me... Was going to say a similar thing with less typing, but you did it for me

Also find it funny when people say 'my car has 120 hp with 35" tyres' Would still have 120hp with 31" tyres - dyno rollers would be spun slightly slower but more torrque would be applied to the rollers - rolling resistance could make a difference though.

Also Big tanks can be powered by big high tourque low revving diesels or gas turbines which rev really high and have not much torque - lots of gear reduction achieves a similar result (power and speed) at the tracks though.

Torque power and revs are all linked and all something to consider.

[chunderlicious]

i had a civic with 325000 on the clock not much smoke till the revs got high (6500-8000RPM) and it only started to blow any smoke after myself my sister and brother learned to drive in the car. and most of all i being 18 at the time drove it like i stole it. ive seen v8s do the same. engineering is engineering.

as for the ricers doing shit times and complaining about wheelspin;

1. ricers are too proud to admit they cant drive a car.
2. they think that because theyve got a turbo they need a brass button clutch to drive it anywhere without "clutch slip" more commonly known to most as riding the clutch. (for those who dont know, brass button is on or off)
3. they try to do a good 60ft in a MANUAL, while smart people in V8s use AUTOMATIC transmissions suited to their engine and usage.
4. they fully sic burn out pulls chics
5. they are like children in trouble, unless you can blame someone else you just cry and itll all be forgiven and forgotten.


BAM!!! thats all folks


RICE RULES (im putting a 302 in a rocky)

Ev