Question About Engine Capacity

[237SJ]

Right, I know this sounds like a silly question and I could google it but - when you bought a car in the 'old days' it would have (eg) an engine capacity of 1700 and could do 0 - 60 in 8.8 secs but now cars can do similar but they have 1000 capacity.  What have they done to the engines to make them more efficient?

[bhg481]

Engines have been made far more efficient - leaner mixture, improved gas flow etc and cars have become lighter and more strwamlined so more power, less drag gives more speed from the same size engine.

[237SJ]

My 1700cc Puma was much more streamlined that the current Puma though so it can't be anything to do with that

[bhg481]

What year was your 1700 Puma and what year is your current one? What is the BHP rating of th two engines?

Engines are producing a lot more BHP/cc than they were years ago - lighter pistons, lighter flywheels, better ignition systems, computer-designed gas flow, aluminium cylinder heads etc. Apart from the streamline car bodies are lighter and generally more gears to keep the engine closer to its peak efficiency RPM.

[237SJ]

I bought my Puma in 1997 from new.  God, I loved that car.  It was a dream to drive. I had it for 14 years, did 120K miles (I was out of the country a lot of the time) and it never broke down on me once.  Just looking at replacements (have had another car in the meantime)

[douglas9401]

The answer to getting more from less might lie in the world of Formula One.

[ToraToraTora]

the basic issue here is that CC and power output are not related. Classic rookie error.

[Rationalist]

Cars are lighter; engines are better designed and engine management software controls the combustion of the fuel more accurately.

Aerodynamics plays a part, but that's mostly about fuel economy at speeds above 60km/h or so

A lighter (lower mass) car needs less torque – and hence less power – to achieve a given acceleration. Sao a less powerful engine.

Replacing steel with aluminium and aluminium with plastics saves weight.

Engine management software squeezes more power from each stroke by ensuring the fuel is fully burned.

Your old Puma probably pumped unburned fuel out of the exhaust under hard acceleration

Shorter cylinders mean the engine displacement is less, for similar power output.

Multi-valves per cylinder permit better control of the fuel/air ratio and bettter modelling of flow patterns within the cylunders all mean more effgicient burn and more even force on the piston face. That translates to more even forces on the crankshaft.

Turbo charging the engine – which means pumping more fuel into the cylinders – makes for more force per stroke.

It's lots of small things adding up to very significant improvements in fuel efficiency, power output and performance.

But a lot of it is about weight/mass and better understanding of the fuel burn within the cylinder.

[237SJ]

Thank you.  Sounds like the A350 :)  Not sure what Rookie error is though.

[Hymie]

TTT’s talents seem wasted in IT - if he can design a 100cc engine producing 500bhp; after all he wouldn’t make the classic rookie error of thinking engine capacity is in some way related to output power.

[Hopkirk]

I think the biggest difference is the turbochargers used on these little three cylinder engines.

They are not without problems though. Our little Fiesta 1 litre has six gears, and you have to work quite hard keeping the engine spinning fast enough to produce the power.

[Hopkirk]

That's five years too many for me.

[Hopkirk]

Gears, not years.

[jno]

which one are you going to keep, Hopkirk, forward or reverse?

[Hopkirk]

Actually my car doesn't have a gearbox so it has no gears.

It's an EV.

The Fiesta is the wife's.

[ToraToraTora]

21:10 ok what I should have said is they are not corellated. An F1 car has 1600cc yet it gets around 1000bhp. I have a 4200cc engine and I get around 420bhp. Various techniques can be used to get more power, forced induction of course but many other things too.