Bret Ludwig wrote:

I watched a CFI/CFII/ATP young stud at a FBO I work at lose a
O-235-L2C in the pattern and still wind up in a supermarket parking
lot. Would have been a beautiful rollout if not for those pesky parking
dividers! I also saw an ob/gyn with his wife and four rug rats in a
cabin class twin run an engine up and for some stupid reason pull the
prop ALL THE WAY BACK at full power. A cylinder on the right side of #2
came off and went through the cowling. If it had been a left hand jug
one or more people would have died for certain.

Sorry, I'd rather fly a Chevy.

So a ham-handed pilot couldn't bust the Chevy. And a good
CFI/CFII/ATP couldn't glide back to the airport unless the dead engine
under the cowl was a Chevy. Hmm.
I flew a Subaru that burned a valve when the mixture was
adjusted to lean for cruise. The 16-valve engines have really slender
valves, just about the same size as you'd find in your Briggs &
Stratton, and they heat up REALLY fast and will burn instantly if they
get a tiny bit too hot. It's one reason they had electronic fuel
injection in the car: to protect the engine. I had my son's Suzuki 1.6
Litre 16-valve apart last week, same problem: burned valve, and it had
the same tiny little valves. The stem was so small (0.215" ) that the
valve grinder chuck would barely close enough to hold onto it. Such
small stems don't transfer heat well at high power settings (like in an
airplane).
Therefore, many auto conversions may run well and smooth and
deliver decent power and get good mileage, but they have to be run much
more carefully than the old Lyc with it's massive sodium-filled valve
stems and thick valve heads. The pilot who blew the jug off his engine
likely treated it that way all the time for a long time and it finally
bit him. He was asking for detonation and got it, and NO engine would
stand for detonation for any length of time.
The Lyc or Continental will stand for more abuse, except for
shock cooling or persistent really rough power handling. Lycoming, for
instance, says that you can lean their normally-aspirated direct-drive
engines any way you want when at 75% or less; just try THAT with your
Soob or Suzuki.

Dan

A lot of good points, Dan, and I would like to add a little:

I think a lot of people run their conversions--or proposed conversions--much
too fast! That doesn't mean that I have ever completely withdrawn
automotive conversions from my consideration. Once you get away from the
LSA criteria, some candidates really stand out and some in GM's Vortec
series really stand out. However, before I actually undertake such a
project, I would very carefully review the portions of Part 23 that pertain
to VNE. There are portions of Part 23 where I would probably cut some
corners for my probable mission profiles, such as the propeller to ground
clearance for a tail wheel type aircraft, but I would not deviate from the
VNE definitions--because unusual an attitude recovery could be needed when I
least expect it. Obviously, this does not improve the power to weight
ration of the conversion.

I still like some of them; but it's not a "done deal" and, if it's supposed
to be a club project flown by several pilots to be determined later,
fuggeddaboudit!

Peter