It was definitely those pesky PSIs. 1.5 of them will cause this!!!111

Sounds like they need a timing adjustment :P

I'm familiar with Helmholtz resonators (having designed a few myself for various projects), but I wouldn't say a 2-stroke is *exactly* a Helmholtz resonator... At least not a simple one! From Frits Overmars (if you're not familiar with him, I highly encourage you to look him up!):

I'm quite familiar with Helmholtz resonators, no need for me to look them up. I'll concede on crankcase Helmholtz resonance, my memory didn't serve me as well as I thought.

Thanks for the kind words! I'd love to have a transparent 2-stroke motor!

Awesome!!

Oh and regarding acoustics... the idea is similar but the pressure levels are far too high to be considered "acoustic." Using acoustics as an analogy is okay though I think.

Crankcase impact is a discussion for another day, but simply put the exhaust impact is much, much more important than the crankcase. You can change crankcase volume wildly without much impact on the torque curve (compared to changing the exhaust volume/length/etc wildly). It's a common misconception in the world of…

Basic idea is correct. More specifically, there's pretty much always two things happening at the same time.

On your first point: :X

I'm not sure if you're referring to the John Mulaney routine or not, but posted for extreme relevance:

:slowclap:

First of all, it's not "now" just because your memory of anecdotes says its true.

Look, you obviously know more about embedded systems than I do, but I don't think you're very familiar with how ECUs are implemented in modern cars. There's not "the ECU" but rather "an ECU." I can tell you for a fact that in the cars I work on (at the cutting edge of the technology, i.e. prototype vehicles for a…

Wow, Ray. This post makes me miss your presence here. As someone who is perhaps more qualified to be considered in the "automotive industry," it surprised me and hurt me that I haven't been invited to this invite-only Facebook group... then I read the rest of the article and realized that names don't mean much. So,…

I don't think it's entirely unlikely that BMW — and most other car companies — will eventually abandon the ICE for something more efficient. Let's face it, all of the low-hanging efficiency fruit has been plucked from the old Otto four-cycle engine, and while they get better and better, they're still not all that…

I was thinking along the same lines, but pulling timing gives more exhaust heat, so I don't think this is quite it. I would put my money on issues with pistons/rings/etc. that won't necessarily show up in water or intake temp, but will definitely cause durability issues, so the countermeasure is to cool the combustion…

My slightly-educated guess would be that it is tuned for good fuel efficiency and low emissions. That tuning causes durability issues when running with high power for extended periods of time. So, after some time, to prevent damage, they simply limit the power. The EPA regulations are not something they can break, so…

I had one of these as a rental over Thanksgiving. I put over 1000 miles on it, mostly back roads and highway (50-80mph). I averaged no more than 24mpg... pretty bad for something rated at 30mpg, when my GF's Passat TDI gets roughly 48mpg driven at 75-80mph while being rated at 42mpg highway.

I love this comment