Why can't today's cars have magnetos?

[GeorgeC]

Huh, I didn't know about those. I was thinking about the kind where they rectify and regulate the output of a BLDC motor hooked up to the output shaft of an engine.

There are. Big trucks have been using them for a long time. They're bigger, so they wouldn't fit a lot of airplane engine compartments. They have a second section behind the generating section that has a stator coil to which the field current is fed. A second rotor section picks it up, on-board diodes rectify it and feed it to the main rotor.

 

[Dan Thomas]

mags@30hp/liter vs ECU@90hp/liter? I think I'll take the ECU.

I'll miss being able to drive without an electrical system once every 15 years. I'll miss the lost performance every day multiple times per day.

Since when does an ECU triple an engine's hp?

 

[AggieMike88]

Well there's your problem. The Cadillac part, not the 2004 part.

But can't knock an almost free car. Got it at auction 6 years ago for $600 and less than 70k on odometer. Body work and engine good, but engine subframe and rh front suspension had to be replaced. Less than $800 in parts and labor got that done. Been working good up till now.

I think I'll get this electrical issue sorted, and start setting aside a sizable amount each month for next 10-12 months to build a replacement fund. Life needs are changing and focus is changing toward commuting gas mileage versus cargo space. Might start researching current gen hybrids.

 

[Juliet Hotel]

My bosses wife has had a few Cadillacs. The company founder has one now. Between the two of them, the horror stories of $500 headlight changes and $1200 battery changes seem endless. Any discussion of me owning a Cadillac has to start with how much you're going to pay me to take it.

 

[weilke]

I believe the ignition on the Rotax has its own built in generator.

Whoever came up with the ignition system on my Toro lawnmower is who I want in charge of designing the next aircraft ignition system. Never done anything to that thing, never gapped a plug or adjusted the timing. Yet come rain or snow or native attack, that thing starts on the second pull.

 

[John221us]

My bosses wife has had a few Cadillacs. The company founder has one now. Between the two of them, the horror stories of $500 headlight changes and $1200 battery changes seem endless. Any discussion of me owning a Cadillac has to start with how much you're going to pay me to take it.

GM junk. I have owned a couple of them, but won’t do it again. Everything from the whole dash going out to infant mortality on the brakes (Chevy Baretta). My Dad had a ‘72 Suburban with the 350 when I was young. The first engine barely made 70k and the second engine much less.

Edit: I understand Mike’s situation where he picked it up at auction, but personally, I would have gotten something else.

 

[Ted]

Well, Mike, I'll make a few points that (surprisingly) haven't been made yet.

First off, a magneto wouldn't have helped you. The ECU would've quit, or else the fuel pump (I suspect what actually caused the engine to stop running). Ignition does you no good without fuel delivery. So, you would've needed a magneto as well as mechanical fuel injection or else a carburetor.

There are two real reasons why modern cars can't have magnetos. First is cost, and second is emissions. Distributorless ignitions (originally coil packs and then in the late 90s/early 2000s moving to coil-on plug) actually cost significantly less for the OEMs to produce than distributors. The components are much simpler, just electrical coils. When Ford went to COPs from the coil packs, the cost savings from eliminating spark plug wires alone paid for the entire program the first years. Ultimately the electronic ignition is far more reliable than distributors or magnetos.

As previously pointed out, you can buy magnetos still and they're the preferred ignition system for some real high end dragsters where the internal cylinder pressures are extremely high and the mixtures are very hard to light off because they're able to produce a higher powered spark the way they're designed. Last I checked one of those magnetos costs upwards of $2k, just for the single magneto. That's a hard sell in my opinion, and even higher than it costs for our aircraft.

I'd have no interest in putting a magneto on a car and I'll take the rare failure like you had for it. In an airplane, the equation is different and I'm fine with magnetos because the failure modes work well. If I was building an experimental might do like @Ravioli and go with dual electronic ignitions, but I would also design the electrical system such that there was redundancy and different busses there such that an electrical failure wouldn't turn into an engine failure like you had.

 

[asicer]

Since when does an ECU triple an engine's hp?

Since you're able to design a combustion chamber that operates to very precise air/fuel metering, cam/crank phasing, ignition timing and output feedback. Granted there's a lot more that goes into the increased HP, but precision control is a significant part of it.

 

[Dan Thomas]

Since you're able to design a combustion chamber that operates to very precise air/fuel metering, cam/crank phasing, ignition timing and output feedback. Granted there's a lot more that goes into the increased HP, but precision control is a significant part of it.

Yes, but the implication was that an ECU would enormously jack the HP over a magneto. That's the way I read it, anyway. There's a lot more to it, as you say, but the biggest reason by far that you can get more power out of a litre is the redline RPM. Torque times RPM give HP, and running an engine to 6000 RPM will give a lot more power than running one to only 2700, no matter what sort of ignition you put on either of them. Raising compression adds as well. And now carmakers often use turbos, too.