Technical question for rev-heads

[Slytovhand]

Hey gang.

This one is for all those ppl heavily into cars.

I'm contemplating buying a new car (although, I'm also contemplating getting out of debt first ).

One thing I want to know, which no-one has given me sufficient answer for, is the technical reason why a more modern 1.6L 4cyl car has more power, acceleration etc than an earlier model car...

I've heard some fairly glib answers like 'technology', but I actually want to know how.

Anyone???

[It's me]

Here's a start:

1. Weight. Cars are a lot lighter than they used to be (smaller, thinner panels, aluminum replacing cast iron etc.)

2. Computer controlled fuel injection and ignition. The computer continually adjusts the fuel supply and ignition so as to extract the maximum amount of power of of the fuel yielding more power and less waste. The computer learns all the time, continually compensating for driving habits, temperature, sparkplug wear etc.

3. Transmission: New cars have more gear ratios, so the engine can run closer to it's optimal RPM more of the time

4. Reduction in parasitc losses. Use of electric steering pumps etc. mean less engine power used up by such things.

5. Variable valve timing, variable intake manifolds etc., also controlled by the car's engine computer.

6. Computer designed combustion chamber, intake manifold, exahaust, etc. Used to be engine designe was less science and more trial-and-error. Today computer simulations allow engineers to play with hundreds of designs before they fabricate them, and they also have much better sensors for testing what they do build.

[Spiffy McMoron]

Here's a start:

1. Weight. Cars are a lot lighter than they used to be (smaller, thinner panels, aluminum replacing cast iron etc.)

Well, yes and no: The days of the 20-foot long land barge are pretty much over, but cars are slowly getting heavier each time they get redesigned. This is due to cars getting stronger chassis, more standard luxury, performance, emissions, and safety equipment equipment (air conditioning, air bags, independant suspensions, satellite navigation, sound-deadening material, 7-speaker stereos, sway bars, power windows/locks/seats/steering, catalytic converters, larger wheels and tires, ABS, etc.) and becoming larger from generation to generation. As a point of comparison, I'm going to compare two Honda Civics: one from 1973, and one from 2009:

• Length: 139.8 inches (1973) 177.3 inches (2009)
• Width: 53.3 inches (1973) 69.0 inches (2009)
• Height: 53.0 inches (1973) 56.5 inches (2009)
• Weight: 1536 lbs (1973) 2630-2831 lbs (2009)
• Engine: 1.2 liter I-4 producing 50 hp (1973) 1.8 liter I-4 producing 140 hp (2009)

As you can see, the modern Civic is much larger (and more powerful) than it's bell-bottomed predecessor. So while it's true that modern cars use more plastic and aluminum to keep weight down, cars are getting larger and heavier when compared to cars from 10, 20, or 30 years ago.

2. Computer controlled fuel injection and ignition. The computer continually adjusts the fuel supply and ignition so as to extract the maximum amount of power of of the fuel yielding more power and less waste. The computer learns all the time, continually compensating for driving habits, temperature, sparkplug wear etc.

3. Transmission: New cars have more gear ratios, so the engine can run closer to it's optimal RPM more of the time

4. Reduction in parasitc losses. Use of electric steering pumps etc. mean less engine power used up by such things.

5. Variable valve timing, variable intake manifolds etc., also controlled by the car's engine computer.

6. Computer designed combustion chamber, intake manifold, exahaust, etc. Used to be engine designe was less science and more trial-and-error. Today computer simulations allow engineers to play with hundreds of designs before they fabricate them, and they also have much better sensors for testing what they do build.

Bingo!

Another reason is better general engine design. Most car engines are single or dual overhead cam engines, which--although they are more complex--better control the amount of air and fuel getting into the engine's combustion chamber, and the exhaust leaving it. This leads to more power, better fuel economy, and lower emissions.

As well, better evolutionary changes made to engines--instead of designing a whole new engine which new problems, a lot of car companies will revamp engines and make a bunch of smaller improvements to it. This includes things like changing the design of the intake manifold for better airflow, using one single serpentine belt instead of 3 or 4 V-belts, altering size of the piston skirt to reduce friction, making the cylinder heads out of aluminum instead of iron, and a 1001 things that I couldn't even begin to realize are important to an engine.

Compare the past 25 years of engine development to the past 5 years of computer chip technology. There have been enough incremental advances in design that you couldn't put your finger on one particular advance as being key to the increase in power, but to try and compare the power of the two eras would be a lop-sided battle.

[protege]

Spiffy summed it up nicely

Engines are more powerful and more efficient than years ago. Nothing illustrates that point more than my fleet.

Both my '69 MGB GT and my '07 Toyota Corolla have identical engine sizes. They're both 1.8-liter fours. Where the MG's B-Series is all-iron and uses pushrods, the Toyota's engine is aluminum and has twin cams. The older engine only has two valves per cylinder, while the new one has four. The MG has twin carbs (which can be a bitch to tune, since it's all mechanical--the slightest bit of wear screws up the fuel/air mixture), while the Corolla uses fuel injection. Oh, and the Toyota has an additional gear to play with. That's why it gets 40-45+ miles per gallon, and the older car only gets about 25-30.

But, the one area where the Toyota is let down...is by its handling. The Corolla's a nice car, but a bit boring on back roads. The suspension is simply not designed for spirited driving...which the MG excels at

[Slytovhand]

Hmmm - thanks! It's given me a better idea!!

I've been toying with the idea of buying something that actually has a bit more grunt - like a V6 or something. But, on further research, I'm actually thinking of a 2003 MG TF (not sure which in the series - there's a 120, 135 and 160 - will depend on what the actual differences are in the builds and performance... and $$$ - though I reckon I can afford any of them - unless it's the 80th anniversary edition ) but their engines are all pretty much the same - 1.8L 4cyl. And I'm currently on a 94 Nissan Pulsar 1.6 4cyl... hence my question.

Oh - one last question - how do I compare Power and Torque measurements, given they all seem variable?


Should I even bother asking how much difference there'd be between modern 4cyls and modern 6cyls??? Cos I've always wondered this about the WRX and other hotted up cars - why they seem to match the V6's in acceleration (or am I seriously wrong with that??)

[protege]

The WRX has a turbo--that's why it puts out 260+ horsepower. Of course, that causes the economy to plummet--18/25 isn't all that good. Plus, at least in the US, that car starts out at roughly $28 grand!

Here's something that might help you out. Especially this item right here:

Torque- Turning or twisting effort, usually measured in pound-feet. A measure of the angular moment or rotating effort exerted on the crank shaft inside an engine. Torque is responsible for the vehicle's acceleration. Horsepower sells cars, but torque wins races.

About the last point--I was always told that if you tune an engine for torque, horsepower will take care of itself

[Spiffy McMoron]

Here's something that might help you out. Especially this item right here:

Torque- Turning or twisting effort, usually measured in pound-feet. A measure of the angular moment or rotating effort exerted on the crank shaft inside an engine. Torque is responsible for the vehicle's acceleration. Horsepower sells cars, but torque wins races.

About the last point--I was always told that if you tune an engine for torque, horsepower will take care of itself

I heard of a formula in Car and Driver that gives a rough estimation of horsepower:

Horsepower = Torque X RPM / 5252

I don't know what's so magical about 5252, but that's what it is. That's why there are main two ways to increase the horsepower in a car: make the size bigger (which increases torque) or make the car easier to rev (which increases the RPM). Both NASCAR and F1 racing engines put out about 800 horsepower, and they use a different way to do this: NASCAR engines are big, 5.8 liter engines that have a alot of torque, but F1 engines are limited in size to 2.4 liter engines. In order for an F1 engine to put out that kind of power, they can rev to 19,000 rpm!

My car can rev to about 6,000 rpm. Anything more than that and I'm on the market for a new engine.