very basic car question

[Arnold27]

Ok, please bare with me here, I had a thought come up in my head about this and its probably 1+1 to you guys(simple), but I dont know...

could someone explain... why a 1.6 engine can go faster than a 1.2/1.4 etc. Has it got more cylinders or whatever they are called? my last car(1.2), suddered when I toped 100, and my 1.6 I have now... doesnt. Just curious why that is.. and what makes a 1.6 and 1.4 and 1.2 so diferent, because I feel a MASSIVE power diference between 1.2 and 1.6!

I actually like learning about cars, but I feel daft if i ask such questions on here cos you are all talking about stuff ive no idea about

Sorry

 

[fastwunz]

lol - thats what we are all here for! feel free to ask questions - but also feel free to give those who return with a stupid answer a good kick in the gearbox.

Funnily enough - i would like to know an answer to that question too.........

 

[Ex-User (19928)]

Me too !!!:quiet:

 

[tim_foster23]

i believe its to do wid the engine size how much fuel is gettin pumped into the engine cos its run on explosions n all that

 

[Matt_Pleece]

1.2,1.4,1.6 refers to the cc of your engine Cubic Capacity, the bigger this is the more fuel and air is put into the engine which means a bigger bang in each cylinder = more performance (rule of thumb, just cos a car has a big engine doesn't always make it fast).

 

[Matt_Pleece]

so to recap a 1.2 has a small amount of space in which to cram fuel and air = little bang = little speed whereas a 2.0 in the 172 for example has more space in which to put more fuel and air = bigger bang = alot more speed, this is a very rough guide lol

 

[fastwunz]

so to recap a 1.2 has a small amount of space in which to cram fuel and air = little bang = little speed whereas a 2.0 in the 172 for example has more space in which to put more fuel and air = bigger bang = alot more speed, this is a very rough guide lol

lol - well put my friend

 

[Matt_Pleece]

Bump

 

[Ex-User (19928)]

Basically, although they both have 4 cylinders, the 1.6 will have a bigger bore and stroke. The bore is the diametre of the piston, and the stroke is how far it moves in a complete motion.

Thus more fuel can be injected and a greater force exerted (more power).

The top speed is governed by a few things. Essentially power and drag. You'll hear people talking about power to weight a lot with Clios (that's all they have going for them:rasp, and this is essentially a good way to compare how well it will accelerate compared to other cars.

Once you get to high speed though, and the wind resistance becomes a greater value than the weight, then power is the limiting factor which is why in weaker cars you will reach your max speed before hitting max power or even the rev limiter.

 

[KingTrophy]

spud

 

[Sib]

my take is the bigger the engine capacity (cc) the more fuel and air can be mixed to create your output (bhp etc.). Obviously the larger the engine get the more cylinders you need as the bore can only be so big before we get a wenkle engine. Hence the reason we have v6's etc.

The real trick is the whole cycle and amount of revs you can get an engine to perform by getting air and fuel in quick and the gasses out just as fast. this is where turbo/super chargers come in. Finnally there is the cooling aspect especially on turbo'd cars.

Displacement is the best way to get gains initially but not the only way.

 

[Munson]

It's not an explosion or a bang - it's a controlled very rapid combustion

 

[sonic_2k_uk]

As already explained the figure your talking about is the engine displacement...

Read up at http://en.wikipedia.org/wiki/Engine_displacement for more info

Increasing the engine displacement (e.g 1.2 -> 1.6) is not the only way to increase performance as Sib explained, for example a 1.2 16v is pretty equal to a standard 1.6 8v in terms of acceleration up to ~95mph.

More info at http://en.wikipedia.org/wiki/16-valve

 

[Matt_Pleece]

^^so what u mean in other words is a controlled explosion or bang then lol

 

[Munson]

^^so what u mean in other words is a controlled explosion or bang then lol

No, it's a rapid combustion. Where the gases expand in a controlled manner. Pinking/detting (detonation) is an uncontrolled explosion or bang, and will f**k your engine quick time.

 

[Matt_Pleece]

pedantic arn't we just call u brainiac LOL jokes

 

[Munson]

pedantic arn't we just call u brainiac LOL jokes

:rasp:

 

[Arnold27]

ahhh cool, when I went to college for the day back in school(ohhh longtime ago xD), It was on car mechanics, and I took an engine apart, sadly i forget what it looks like inside but.. I remember the guy showing us a car one, compared to a bus... and the bus had 6 cylinders and the car had 4 (i think)? which makes sense now, because a bus needs much more power

another quick question, whats BHP?

 

[pturner3]

There are also many other factors that influence the speed, when measured in acceleration terms.

- Gearing
- Tyre resistance, and inertia from mass and diameter.
- Aerodynamics (including Drag, Slipstreams, wind speed and direction,air density)
- Fuel quality
- Lubrication
- Friction of moving parts (condition, build quality and lubricant in use)
- Quality of the engine build (blueprinting, possibly)
- Incline
- Road surface material
- Mass of vehicle, including towing, passengers, effects, fuel
- Air density
- Engine condition
- Inertia of all moving parts (due to different designs)
- Driver
- Traction
- Large electrical load on the alternator will consume more power
- Air conditioning, power steering, auxilliary consumers onload.

End of the day you can never judge a cars acceleration from the engine capacity, number of cylinders, aspiration or even BHP for that matter. Yes, admittedly some of the above factors have minimal impact, but they all count.

Simply speaking though, its all about power to weight and friction.

Cheers
Phil

 

[MarkCup]

My take on this (and it's mostly been said above) is;

To get more power you need to burn more fuel.
To burn more fuel you need more air (hence why so many people go for induction kits to let the engine breathe more freely).

Without getting into all the engine intracacies, there are basically 4 ways to get more air into an engine so it can burn more fuel;

Bigger cylinders
Forced induction (a la turbo or supercharger)
Higher revs (that's why 180bhp from a 1,100cc bike engine is possible)
Nitrous oxide injection (which I think is basically super dense oxygen?)

 

[rory182]

for example a 1.2 16v is pretty equal to a standard 1.6 8v in terms of acceleration up to ~95mph.

so a 1.2 16v clio / corsa etc is as quick as a 205gti?! me no think so

 

[Clio_V6_255]

ahhh cool, when I went to college for the day back in school(ohhh longtime ago xD), It was on car mechanics, and I took an engine apart, sadly i forget what it looks like inside but.. I remember the guy showing us a car one, compared to a bus... and the bus had 6 cylinders and the car had 4 (i think)? which makes sense now, because a bus needs much more power

another quick question, whats BHP?

More cylinders does not give more power. More cubic capacity (for the same efficiency) gives more power or forced induction (turbo's / superchargers) or different fuels etc.

Specifically BHP is a calculated value derived from torque measured at a certain engine speed. The engine speed is measured in revolutions per mins (RPM)

BHP = [(torque, in lb/ft) * (RPM)] / 5250

lb/ft is "foot ponds" and old imperial but still widely used measure.

Torque is the turning force the engine can exert. The higher the better.

BHP is the amount of work the engine can do. The higher the better. But really only a calculation from the torque.

To be honest lots of people mis-understand the relationship. You see high RPM is good because you can run lower gears, which make the wheels easier to turn, so increase acceleration. Which is why diesels with monster torque at low revs still accelerate relatively slowly (due to high gearing).

Peter

 

[Sib]

my wife gets the controlled explosion,
bit on the side is the rapid bang...

 

[DebV6]

Well, you learn something new everyday!

 

[edde]

To be honest lots of people mis-understand the relationship. You see high RPM is good because you can run lower gears, which make the wheels easier to turn, so increase acceleration. Which is why diesels with monster torque at low revs still accelerate relatively slowly (due to high gearing).

Peter

200hp at the wheel is 200hp at the wheel regardless of rpm of the engine they will both accelerate as quick.

A golf tdi at 2k might make 120hp at the wheels will accerate as quick as a Honda etc 1.6 which is scremeing at 8k if it is still making the same hp.

 

[Clio_V6_255]

200hp at the wheel is 200hp at the wheel regardless of rpm of the engine they will both accelerate as quick.

A golf tdi at 2k might make 120hp at the wheels will accerate as quick as a Honda etc 1.6 which is scremeing at 8k if it is still making the same hp.

I read this a few times and it confused me...

Are you agreeing or not...

Oh well..

Peter

 

[jiminy]

200hp at the wheel is 200hp at the wheel regardless of rpm of the engine they will both accelerate as quick.

A golf tdi at 2k might make 120hp at the wheels will accerate as quick as a Honda etc 1.6 which is scremeing at 8k if it is still making the same hp.

gearing has a huge effect on acceleration, otherwise you could accelerate as quickly in 3rd as opposed to 2nd gear

 

[edde]

gearing has a huge effect on acceleration, otherwise you could accelerate as quickly in 3rd as opposed to 2nd gear

Hp at the wheel is Hp at the wheels there no getting away from it. Nothing else matters.

3rd doesn't accelerate as quick as you've got drag slowing you down more. You get 200hp at the wheels in 1/2/3/4/5 gear a car won't accelerate as qucik as drag is lower.

 

[jiminy]

so does it not matter which gear im in from standstill, 1st and 5th will accelerate at the same rate if i drop the clutch at 2000rpm

 

[edde]

so does it not matter which gear im in from standstill, 1st and 5th will accelerate at the same rate if i drop the clutch at 2000rpm

If you drop the clucth in 5th then the problem is your wheels are wanting to spin at high speed but have very little torque. Gearing meana that when you drop the clutch in 1st the wheels have more torque but spin so much slower.

Gearing just changes the rpm and torque at the wheels lower gears mean more torque and less rpm. 200hp is still hp ATW.

The best way to see this is to go to a rolling road. and get your car tested as 2nd and 5th gear the power is exactly the same but in 2nd the car wheel won't be going as fast but have more torque which means theat power exactle the same.

 

[edde]

I read this a few times and it confused me...

Are you agreeing or not...

Oh well..

Peter

Disagreeing your suggesting from how I read it

You see high RPM is good because you can run lower gears, which make the wheels easier to turn, so increase acceleration.

In your example a 50000rpm engine making 200hp would accelrate faster than a 500rpm engine making 200hp it wouldn't thouhg it would make 100 time the torque but accelerate the same.

Diesels don't accelerate slowly they just chnage up more due to the way there gearing and power bands are a 200hp tdi at its peak power vs a 200hp petrol at peak power are exactly the same acceleration wise.

The big problem is diesel feel quicker as they make loads more power than an equivalent petrol at low rpm so they fell quicker at low revs at high res they arn't equal to a petrol Hp wise usually so when the revs get up the petrol is quicker as it does have more hp which is what you need to accelerate. The diesel also well you've got a load of HP anwway so the rise in HP is smaller.

 

[GordonD]

Hp at the wheel is Hp at the wheels there no getting away from it. Nothing else matters.

3rd doesn't accelerate as quick as you've got drag slowing you down more. You get 200hp at the wheels in 1/2/3/4/5 gear a car won't accelerate as qucik as drag is lower.

Sorry Edde, you know more about what you are talking about than anyone else in this thread, but you are wrong that aero drag is the only reason acceleration is lower in higher gears than in lower gears.

Speed is acceleration times time.
Acceleration is proportional to force applied.
Power is the rate you can change a given mass's kinetic energy.
But kinetic energy increases with the SQUARE of speed.

So you have to gain energy faster to accelerate at the same rate at high speed than you do to accelerate at that rate at a lower speed. So if you have a given amount of power even without aero drag your rate of acceleration will decrease with speed. To get the same rate of acceleration as speed went up you'd have to keep applying the same amount of force, and since power is force times speed the power required to do that would also have to go up in proportion.

The easier to understand application of that basic physics principle is brakes. They don't work through a gearbox, they act directly on the wheels. The force they apply is the same at all speeds. So they do achieve the same rate of acceleration (in their case negative acceleration) at all speeds. To do the same when accelerating you'd need a motor that could apply constant force at all speeds. But they can't, they apply constant power, but they can't because when you change up into the next gear you are still applying the same power, but because power = force x speed, the force is reduced by the gearbox ratio. So the acceleration is less. What remains the same as you go up through the gears is not the rate the speed increases but the rate kinetic energy increases.

Edde think about it as a dyno curve. An engine that produced the same power from 2000 rpm through to 6000 rpm would only be producing a third as much torque at 6K than it was at 2K. So at 6K it would only be producing a third as much pushing force at the wheels to accelerate the vehicle, and the rate of acceleration would only be a third as much. However if it had a flat torque curve from 2K right through to 6K it would produce constant acceleration, but that'd require it producing three times as much power at 6K than at 2K.

 

[Clio_V6_255]

Disagreeing your suggesting from how I read it

You see high RPM is good because you can run lower gears, which make the wheels easier to turn, so increase acceleration.

In your example a 50000rpm engine making 200hp would accelrate faster than a 500rpm engine making 200hp it wouldn't thouhg it would make 100 time the torque but accelerate the same.

Diesels don't accelerate slowly they just chnage up more due to the way there gearing and power bands are a 200hp tdi at its peak power vs a 200hp petrol at peak power are exactly the same acceleration wise.

The big problem is diesel feel quicker as they make loads more power than an equivalent petrol at low rpm so they fell quicker at low revs at high res they arn't equal to a petrol Hp wise usually so when the revs get up the petrol is quicker as it does have more hp which is what you need to accelerate. The diesel also well you've got a load of HP anwway so the rise in HP is smaller.

My earlier post which I quickly edited..:clown: was incorrect as you noted.

Its 10 years since I studied this stuff at university and it pains me to admit i confused myself.:dapprove:

The reason for the BHP measure is specifically to take into considerstion the torque and rpm. There are 2 ways to make a quick car, increase the torque or make it run at higher revs (or both). You can get the same acceleration from a high torque low rpm diesel as a low torque high rpm petrol engine.

What I was saying is (and I still believe this to be true) that many people miss-understand these points. Thats why a diesel engine with the same torque as a 4ltr petrol engine (common for a modern 2ltr turbo diesel) is not necessarily faster than a much smaller but higher reving petrol engine.

And they way you work out the relationship is using the formula as given.

Hopefully we can both agree thats correct.

I'm not knocking diesels just trying to answer the question, and realising how much of this simple stuff i've forgotten.

Peter

 

[GordonD]

There are 2 ways to make a quick car, increase the torque or make it run at higher revs (or both). You can get the same acceleration from a high torque low rpm diesel as a low torque high rpm petrol engine.

The problem is "quick" can mean different things.

You can mean "responsive", ie, torquey, that is you're cruising along and you put you foot on the throttle and you get immediate strong acceleration to pull out and quickly and safely pass the car in front of you. Big American V8s and diesels are like that because at the revs you're normally driving at the torque is at its peak. So you've got lots of it available just by pressing the throttle. High revving 4s are usually not like that. With them when you're cruising along normally the engine might only be turning over at 2-3,000 rpm, which is well below the 4-5,000 rpm speed the engine produces maximum torque at. So they don't feel instantly responsive like a diesel does. You have to either wait for the revs to build up a bit before you get that surge of power. On the street the thing that makes a car feel quick is having plenty of torque at fairly low revs.

The other meaning of "quick" is getting good acceleration times on the drag strip. That's where high revving 4s excel. You keep them revving up in their peak torque and power ranges and they're fast. And that's where diesels and big petrol V8s don't excel. You put your foot down and you get a surge of torque that spins the tyres, but almost immediately the revs increase to the point where the torque falls off, or the rev limit is reached, and you have to change up into ther next gear. On the track the thing that makes a car quick is having lots of power, and it doesn't matter how its obtained, whether by having a high revving small engine with short gearing that lets it rev, or a big lazy engine or a turbo diesel.

 

[Saner]

Okay guys keep this coming.

Very interesting stuff. I am trying to design an Induction kit for a Uni project and so I need to learn as much as possible about power curves and how everything works together.

Can anyone recomend some reading?

 

[Clio_V6_255]

The problem is "quick" can mean different things.

You can mean "responsive", ie, torquey, that is you're cruising along and you put you foot on the throttle and you get immediate strong acceleration to pull out and quickly and safely pass the car in front of you. Big American V8s and diesels are like that because at the revs you're normally driving at the torque is at its peak. So you've got lots of it available just by pressing the throttle. High revving 4s are usually not like that. With them when you're cruising along normally the engine might only be turning over at 2-3,000 rpm, which is well below the 4-5,000 rpm speed the engine produces maximum torque at. So they don't feel instantly responsive like a diesel does. You have to either wait for the revs to build up a bit before you get that surge of power. On the street the thing that makes a car feel quick is having plenty of torque at fairly low revs.

The other meaning of "quick" is getting good acceleration times on the drag strip. That's where high revving 4s excel. You keep them revving up in their peak torque and power ranges and they're fast. And that's where diesels and big petrol V8s don't excel. You put your foot down and you get a surge of torque that spins the tyres, but almost immediately the revs increase to the point where the torque falls off, or the rev limit is reached, and you have to change up into ther next gear. On the track the thing that makes a car quick is having lots of power, and it doesn't matter how its obtained, whether by having a high revving small engine with short gearing that lets it rev, or a big lazy engine or a turbo diesel.

I quite agree. You can't beat a high revving petrol engine on track, but in the real world a big lazy v8 or diesel engine is great for relaxed performance due to the low down torque available.

Thats one of the reason I bought the Vee. Nice 'n' torquey (due to relatively large cubic capacity)! BUT also get upto high revs and she delivers there too.:approve:

Peter

 

[McBunny]

i think you shouldn’t be allowed to drive till you at least know how and why a car moves !!
im quite shocked at the level of knowledge of some people on this forum i always wondered why those resistors on ebay get sold now i know most people know f**k all about cars !

 

[sonic_2k_uk]

so a 1.2 16v clio / corsa etc is as quick as a 205gti?! me no think so

Indeed.. i was trying to give a direct comparrison.. the 205 GTi has ~110bhp from a 1580cc engine due to a larger bore and valves if i remember correctley.

 

[McBunny]

the mistake people always make is trying to compare 2 engines from 2 completely different cars you simply cant even if you take them out of the car and mount them on at test bed and measure the speed at the prop/driveshaft on the gearbox they wont perform the same even with exactly the same gear ratios. its just not that simple

 

[edde]

I quite agree. You can't beat a high revving petrol engine on track, but in the real world a big lazy v8 or diesel engine is great for relaxed performance due to the low down torque available.

I'd disagree an engine wich give Hp accross a big power band ie a diesel or a V8 etc is great on track much better out of bends than a petrol IMO.