[roflwaffle]

Originally Posted by theunchosen

Cylinder deactivation is not really a good solution.

Even if those cylinders don't have any vacuum. . .have you tried to push a piston in a cylinder? Its not bad if you are just moving one piston through the cylinder, but even then. . .it requires a hammer and a block of wood. To turn the crank with no vacuum on a 4 cylinder I have to have a 2 footer and still pull hard enough that working out later would be a mistake. The engine is fighting that same force about once a second in a v8 if you disengage half the cylinders(by disengage lock the valves open during compression, intake, exhaust and expansion, shut off sparks and injectors).

Compressing the trapped air and the extra friction from the shut off cylinders certainly isn't as good in terms of overall FE as going w/ a properly geared 4cyl, but it's still way better than an improperly geared V8.

My 2008 Chevy Tahoe has the Eaton Active Fuel Management system (internally called "Displacement on Demand"). After 24k miles, and using the ecm provided instant fuel economy, I can see the change from 18 to 26 mpg on a flat road at 55 mph very day, both directions. This includes trailer towing(boat and hay delivery). The ratio is the same when using 85% ethanol.

Originally Posted by theunchosen

If you really wanted to make a vehicle sporty but FE friendly as well you have pretty much 2 options. Forced induction from a supercharger that you can switch on and off with a secondary air intake that doesn't have to flow through the pre-cooler, compressor and extra piping or two small engines with the ability to completely disconnect either from the drivetrain completely and deactivate it.

Option one is obviously more simple. Its also obviously cheaper(especially if you do it yourself).

Option two is much more complicated. Its most likely 3-4x more expensive and you have to do it yourself.

Most people chose the charger and an on off switch, but those who chose the secondary engine have something thats really honestly worth bragging about. If you for example took 2 H22A redtops and dropped one in front one in the rear you'd have more hp than the 08 corvette(430 for the corvette and 437 for the twin engine). IT also still leaves you the option of integrating forced induction on whichever motor you won't be using for the FE runs(or both if you go with a supercharger-switchoff). Another large advantage to this over the standard corvette block. . .they have 2 valves per cylinder whereas the h22 has 4.

It also buys you awd that doesn't get bogged down at launch like every other awd system ever made. The problem with AWD arises with the differentials to split the power. Even the GTR's enormously expensive drivetrain bogs down as it switches power over from RWD at launch to AWD pull, given its much better than anything else but it still happens. The only expensive linkage to make sure each engine is sharing the load equally. . .is the billions of dollars of. . .asphalt.

Theoretically I am a fan of the twin engine idea, but practically. . .its not feasible. The advantages two engines buys couldn't be outweighed by the difficulties in manufacturing it. Yes if something goes wrong you could limp home on one engine without further damaging the other at all, but you would need to build a rear engine mount, move the fuel tank, and build a shift linkage that mated up to the transmission in the front as well.

Iono, both those sound really complex compared to shutting off a couple cylinders and increasing mileage by a good ~50% at low loads. Granted, they might be good for a ~60% increase instead of a ~50% increase since there isn't as much cylinder friction and no heat loss from compressing/expanding air in the close cylinders, but I don't think the extra couple mpg is worth all the effort/complexity.