auto stop going away?

Leadfoot J. McCoalroller · Jun 13, 2026 at 11:22 PM

futurist said: ↑

(to my knowledge, Mazda currently makes only conventional 180-degree flat-plane-crank inline-Fours)
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They recently launched a 3.3L turbocharged inline 6 in their biggest SUV. I don't know how it's pinned. Not clear whether the bang start was being developed for this or the older 2.5L 4-cylinder or both.

Trollbait · Jun 14, 2026 at 10:28 AM

futurist said: ↑

That Mazda system sounds good on skim... but what happens when you stop at a light for more than a minute, as many in big cities... or during rush hour parked on a clogged freeway?

The compression in that topped cylinder on comp stroke, leaks past ever-more-light-tension rings, as combustion pressure getting behind the rings, at idle rpm, is what seals gases in and prevents blowby. That blowby'd increase, meaning all the compression above the rings, would be in the crankcase and out the PCV system. So even if the PCU knew what cylinder was nearest TDC-C, it'd only have limited time to be effective, DI-ing fuel into it -- power requires 3 things: atomised air/fuel mixture, timed ignition, and compression. Any one lacking, and no-go.

Also remember... when none of the other cylinders are firing, any pistons on compression stroke suddenly have nothing to help them compress intake air, but perhaps crank flywheel effect, if any -- so that air will resist, meaning never reaching at full TDC anyway (air suspensions on trucks are well-capable of performing as well as steel springs off-road). Interested to know how Mazda engineers figured their way out of these initial misgivings I see, anyway.

Toyota's e-CVTs are pretty cool in that air leaving the cylinder on ICE startup, is designed in -- no decomp tricks needed, as starts with less comp stroke via late-closing intake valve, but a full-seal on the exhaust side -- so minimal catalyst contamination (still some chance on overlap, if any). But keeping full Otto-cycle compression and valve timing (and thus power and emissions control, as most ICE-only VVT systems for all mfrs use) with A.S.S., looks like it means owners will just have to get over their bucking, stumbling ICEs, esp with the industry's political shens in play
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Leadfoot J. McCoalroller said: ↑

Well, the point of the Mazda system was such that they would be able to delete the starter motor altogether, enjoy a less-complicated flywheel (no tooth ring needed) a much smaller 12v battery and maybe a few other little optimizations.

I think the general idea was to tolerate the terrible combustion conditions of a cold cylinder that had long since leaked down all compression. They'd still get enough shove out of that one bang to do better on the next and be up to normal by the 3rd. Or so the theory goes.
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What I recall from the last time I read about it.

Computer picks a cylinder that is near top dead center in approach.

The DI fires in some gas that gets ignited.

This drives the crankshaft in reverse.

The first cylinder to reach enough compression is fired. This happens within one backwards engine revolution.

That cylinder is fired to start normal operation.

I want to say Mazda was calling this system KISS, but my brain is fuzzy.

Isaac Zachary · Jun 14, 2026 at 10:35 AM

Start-stop makes a lot of sense if you're the kind of person who drives with your windows down. It's always nice coming up to a stop and being able to hear the birds instead of bpbpbpbpbpbpbppbpbpbpbppbpbpbppbpbpbpbpbpbppbpbpbpbpbpbpbpbp.

auto stop going away?

Leadfoot J. McCoalroller Senior Member

Trollbait It's a D&D thing

Isaac Zachary Senior Member

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auto stop going away?

Leadfoot J. McCoalroller Senior Member

Trollbait It's a D&D thing

Isaac Zachary Senior Member