Cylinder deactivation discussion

[Frank Lee]

Low CR = low efficiency.

Low rpm isn't magic- most low rpm engines are really long stroke so the piston speed ends up comparable to high rpm, short stroke engines.

[yoyoyoda]

Originally Posted by Frank Lee

Low CR = low efficiency.

Low rpm isn't magic- most low rpm engines are really long stroke so the piston speed ends up comparable to high rpm, short stroke engines.

Yep. and never said it was magic.

The problem however with doing a stroker engine is that then you have additional torque which the transmission can barely handle, so you then get spinning tyres at low speed which lose traction, and you guessed it, continue to spin.

Its not a very high RPM that the wheels are spinning at, its just slipping like crazy because of the additional torque. Which can probably be fixed by increasing the diameter of the wheels, to very large ones.

Thats what I've heard happens anyway.

Increasing the mass of the flywheel can then be used to counteract the lack of a power stroke during the times that cylinders 3 and 4 would be firing.

A definitely tempting modification to do, but on a carburetted engine its a lot easier to do.

[Frank Lee]

Well then what was that artificial 1200 rpm redline all about?

[yoyoyoda]

Originally Posted by Frank Lee

Well then what was that artificial 1200 rpm redline all about?

I would ideally like to see all engines kept under 1,200 rpm for longevity reasons alone. The longer you can keep a car and its engine the better it is for the environment.

A car that lasts the rest of your life would be nice in my book. Just get a new body every few years if people are fussy, one made from biodegradable plastics or hemp.

If people manage to do this anyway, add on a heftier flywheel, drop a cylinder or two, then car engines can double as stationary engines for use on an offgrid power system once we're done with them on the roads, or just plain make it dual use.

Adjusting the compression ratio would then enable use of 5+ year old petrol and/or 100% ethanol.

There are quite a few uses of old engines actually:
http://www.mtfca.com/discus/messages...tml?1199713339

[Frank Lee]

And that number came from where?

[yoyoyoda]

Originally Posted by Frank Lee

And that number came from where?

You are very intimidating so I'm just going to stop talking to you.

But fyi it came from my head.

[oldtamiyaphile]

Originally Posted by yoyoyoda

Other traffic is what prevents me from driving at <40km/h speeds (25mph), I've been known to even tell my neighbours that I want the residential speed limit reduced to 25-30km/h.

Driving too slow can be as ineffcient as driving too fast. You need high as possible road speed for the slowest possible engine speed. With the current residential limit of 50km/h, none of my cars are really happy in top gear. It's also too slow for DFCO to kick in for many vehicles (eg my Van 60km/h [2000rpm] in fifth, the Jeep needs about 100km/h [2000rpm] to DFCO in sixth).

My Fiat is already a 2 cylinder :P

[Cobb]

I hate to break it to you yoda, but the honda and toyota hybrids use the valve timing technology to delay closing of the intake valve to reduce the displacement and cr for increased efficiency by reducing pumping losses. They also switch over to a more normal mode for power, warming up faster and as needed. Honda retains the power mode in its hybrid civic. The redline is reduced in these cars vs what you see in the si, type r, etc.