BTW Having said all that Tom Parkes is getting away with NO

intercooler

on his turbo three rotor in his Lancair ES. Go figure :)

Paul Lamar

Paul, I'm sure Tom is super low boost right now. His application is like
turbo normalizing. Bill Jepson

"Brian D. Cain" wrote:

I've been reading this thread a bit guys and I think I may be able to shed
a little more like on the subject.

This is a big, big, big concern of mine for what I do with the higher
powered
rotaries that we build for racing and the like.  As the application varies
(road
racing, aircraft use, street driving, drag racing, etc.), some of these can
change somewhat, but here's a list of the things that are commonly the
culprits that I've found in my own personal experience:

)  HEAT -- Combustion chamber heat is probably the single biggest cause
of engine knock.  This is the root that exacerbates all other problems,
namely auto-ignition of the intake charge at odd times.

)  Type of spark plug -- Depending on the application, and the loads placed
on the engine over a given period of time (i.e. constant heat generation),
the
right heat-range plug must be used.  For our drag racing uses, we use either
the NGK BUR9EQ plugs in both the leading and trailing spots or we'll use
the NGK R26 racing series 10.5's all around.  I'm sure you guys doing
aircraft
use can get away with the stock plug recommendation (NGK BUR7EQ in
the leading and BUR9EQ in the trailing), especially in normally aspirated
form,
as long as everything is setup well. Having too hot a range of spark plug
can be
disastrous as the ceramic 'body' of the plug can chip and explode from heat
and
send pieces flying into the combustion chamber. It can also lead to
auto-ignition
of the mixture.  I believe this is why it's commonly advised to run a colder
trailing
plug to help prevent this from occuring.  From what I understand, if the
charge ignites
too early in the compression stage, it can misapply combustion force and
attempt to
stop and reverse the motion of the crank.  I have no clue what happens with
the physics
behind this.

)  Hot spots - Hot spots in the combustion chamber that act as "glow plugs",
tending
towards auto-ignition of the intake charge at any given time during , due to
imperfections
in casting or machining (allegedly)

)  Spark advance -- Knock created by pre-igniting the mixture too early in
the
compression stage due to faulty tuning (firing the trailing plugs too
closely or ahead
of the leading plugs and/or firing the leading advance far too early) or
without
respect to the burn-rate of fuel used

)  Trigger problems -- RF interference caused by faulty trigger wiring for
electronic ignition (not an issue on distributor setups) that give erroneous
RPM
readings to the FI computer, firing fuel injectors and spark plugs wildly

)  Air/Fuel Ratio -- Running too lean of an air-to-fuel ratio, under heavier
loads, where fuel is used as a combustion chamber coolant

)  Poor fuel -- Auto-ignition of too volatile (or too low octane) of fuel
especially
with higher effective compression ratios

I think Paul pretty much nailed it when he said to keep charge temperatures
down assuming that the rest of the above-said conditions are prevented or
alleviated by setting up and tuning the powerplant properly.  I've seen
engines
fail from just about every one of those listed above.  In the automotive
world, it's not uncommon to run into this.  There's so few standards when it
comes to doing things "right" that it's more ambigious and left up to the
user
entirely.  It, then, unfortunately falls on the shoulders of the pragmatist
who goes
out and tries things, unknowing and ignorant of the technical ramifications,
and
blows the thing up.

One of the things I've found is these engines seem to be pretty
susceptible to changes in charge air temperature, moreso than boingers.  In
some
of my experiments with turbocharger intercooling, the engine has had both
much
more power as well as greater tolerances to air/fuel mixtures under heavy
loads with
low charge temperatures.  I play around quite a bit with water as a heat
exchanger for turbocharged applications for charge cooling.  I've seen both
more of a
"window of tolerance" in preventing engine knock as well as substantial
power gains.

I think someone brought up the use of alcohol as a fuel in this thread
earlier on.
The reason why some of these drag cars can get away with running gobs
of manifold pressure and not using any kind of charge after/intercooling,
all the while preventing deadly engine knock, is because alcohol is *terrific*
at keeping combustion chamber temperatures down.

Hope this helps.  I'd like to open the subject up more on the issues
concerning the after-effects of substantial engine knock and the differences between
the types of apex seals that are available (in particular 2mm 2-piece vs. 2mm
3-piece).

B

Brian D. Cain -/- Grand Prairie, TX -/- bdc196@comcast.net
BDC Motorsports - Performance Rx-7 13B Rebuilds, EFI tuning, etc.
MSN bdc196@hotmail.com, Yahoo! bdc196, AOL Symajhi, ICQ# 1733105
http://bdc.cyberosity.com -/- http://groups.yahoo.com/group/HaltechSupport

 
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