[Isaac Zachary]

Originally Posted by JSH

Safety: It you cut fuel and turn of the engine anytime you lift of the throttle you go to full engine braking. This is braking separate from the hydraulic braking system and the ABS system can't control it. In low traction situations engine braking alone can be enough to lock the wheels and cause the vehicle to lose control. (RWD truck, unloaded, downhill, on snow)

This is one of the reasons that you don't find high speed automatic emergency braking on manual transmission cars.

Are there ABS systems that increase the throttle when the tires start to skid from engine braking so as to eliminate engine braking from the equasion?

If not, I still don't see the point. In the cars I've driven with a kill switch of some sort I've never felt a difference in engine braking between fuel on and fuel off, with the exception of putting around in 1st gear at idle speed. If your gearing is low enough to cause your tires to slide from engine braking with fuel off they will do the same with the fuel on, except in that 1st gear scenario.

Now is elimiating the chances of sliding at 5mph worth it? Maybe. But at those speeds I don't see engine-braking-sliding as being a problem that one couldn't easily control.

Originally Posted by JSH

You also wouldn't want to car to lurch forward if someone hit the throttle with the car at a stop, in gear, with the clutch engaged. A manual car should only start when in neutral or when the clutch is disengaged.

And what would be the difference between that and an automatic with or without stop start, or in an EV? In an automatic or an EV, if the car is in gear and you hit the throttle the car will lurch forwards. Why would the same thing in a manual transmission car be less safe?

Originally Posted by JSH

Convenience. Shifting into neutral to turn off the engine gives the driver control of when it happens. There can be plenty of cases where the driver might not want the engine to turn off. A 95 degree day in humid Alabama stop and go traffic comes to mind from personal experience. (I didn't buy a Civic Hybrid because it didn't have an electric AC compressor and the AC turned off at stops)

This is why a switch could be added. Obviously the driving style would have to change. But we are talking about a DIY project here, right? and not a car designed for the masses?

Originally Posted by JSH

Longevity: For long life you want your engine to come up to operating temperature quickly. Turn your engine off every time you lift the throttle could cause the engine never to come to operating temperature. (This is why hybrids don't turn off the engine until it comes up to temperature)

I can agree with this principle. But again, the reason why a simple switch could be added for the feature? A simple switch would be much easier than to make a complicated system that tracks engine temperature, engine speed, car speed, neutral position on the transmission, maybe catalytic converter efficiency, etc. so it can electronically decide when and when not to turn off th engine. Not that such a system wouldn't be nice in a way, but I don't see it as necessary when all you really need is just a switch on the dash.

I mean, ya, you could make a system that tracks thinks like if your AC is on or a system that tracks engine temperatures so it won't kill the engine during those moments. But then you also have to guess when the system is going to decide to do what it wants to do. For an example, you come up to a stop and the engine isn't warm enough, so it keeps idling. You come up to another and it decides it's warm enough so it shuts off. Then, of course, now you do need the system to only make those on and off transitions when the car is in neutral so it won't be doing it when you're doing something that an unexpected shut off could mess you up.

But that brings up another problem. What if you suddenly need to take off? Now you have to start the engine in neutral, then shift into gear and then release the clutch. Sure, we who like to hypermile have done that. But the nice thing of starting the car in gear, especially with an electric motor and clutch engaged, is that you can hit the accelerator and go just like in a typical hybrid or automatic or EV.