Matt Lang wrote:
[snip]
Whats your background and your background with motors if I may ask?
When the DFI were released we (we is the blokes I work with) took a
who exaclty is "we" ?
I have a small group of old blokes who do stuff, "we" develop all sorts
of stuff, some for ourselves, some for others. They enjoy the tangles I
get myself into in the NG but every single time so far they've been
right on the money, even when "we" were definitely the odd ...... out in
the early DFI days:-)
[snip]
Ficht failed spectacularly as predicted because the impact pressure
rise was never going to supply enough pressure rise to give proper
atomisation, coupled with the lean mixtures it had a serious
failure rate & as I said was doomed from the beginning. Optimax faired a
little better but still had the problem of low injection pressure (they
use a normal injector pressure but unlike a normal injector into a
vehicle manifold (which is usually below atmospheric pressure) they
inject against the pressure of the output from the additional air pump,
so the atomisation problem remains, as does the question of lean mixture
heat buildup.
These days optimax motors seem to work pretty well ? I havent heard
recent failures..
I think that's probably right, however you don't see the endless
purchasing spree of new ones like you did in the boom & Brunswick have
all but given up on it & are going 4 stroke, not that the dealers trying
to sell something will admit it;-)
Both technologies are by now totally discredited, Brunswick are clearly
going 4 stroke throughout the range & Ficht brought OMC down, then Bomb
(who have some proper engineers) got rid of it, now in a last desperate
gasp E-tec will try to mitigate against the symptoms by using ever more
heat resistant oil & pistons that will not "melt" till a higher temp:-)
Sorry to smile but it's absurd!!! if petrol sees any temp around or
above 250C it auto ignites (detonates), even the lowliest of aluminium
is good to well over 600C. So their latest suck it & see try is as
doomed as the original Fichts & for the exact same reasons;
One hasnt heard of any bad news about HPDI ... doesnt this indicate
there is no general problem and this can work fine?
No that's true & I comment about that to Tom, there are definite
reasons they are more reliable (which tend to confirm the reasons why
the others aren't), but it must cost Yamaha lots (800psi petrol???) so
it seems they are also going 4 stroke.
[snip]
(v) It's long been known (mainly from aircraft engines, but also some
attempts with car engines Chrysler, Honda & Mitsubishi) that engine can
run on very lean mixtures, however the "abnormal" combustion leads to
heat buildup in the chamber surfaces. Usually an engine running very
lean will not detonate while still extremely lean (i.e. their latest
sensor will not sense anything), but this doesn't stop the chamber
surfaces getting overly hot.
These days some car manufacturers have 4 stroke DFI motors which work
well. Isnt that techinically the same as a 2 stroke DFI (in regards of
the problems)?
It is similar but as I said, other than dead idle, most of the time
that a 4 stroke can risk running lean are times a boat motor just never
sees. The comment about only half the ignition events is relevant to
heat buildup also.
(vi) In an OB 2 stroke the head can be kept very cool being alloy &
having an endless supply of cool water, but the piston/rings in a 2
stroke is almost totally uncooled. Once the piston temps gets over 250C
(not very hot really) then auto ignition is a certainty but while lean
probably no harm done, simply because there isn't enough fuel present.
(vii) The trouble starts when the power is quickly increased above the
lean burn mode, suddenly there is plenty of fuel available & this sudden
excess fuel rather than cool the piston just auto ignites but now it
will lead to full on detonation = more heat = more detonation etc etc bang...
Do I read correctly that the dabgerous behaviour is:
From idle to WOT? But lets say from 2000-3000 to WOT is no issue?
Yes after say 2000 (it varies) the engine is on normal mixtures so then
if the oiling system is working as intended it should be as good as any
non DFI 2 stroke. Opti does have a much better 7 into 7 (the extra is
for the air pump) oiling system than Ficht's 1 into 6.
[snip]
(b) The piston aircraft engines are also run lean although never
anything like as lean as Ficht & Optimax claim. Aircraft lean as
the air density lowers with altitude so they're not really very lean at
all & allowing that they're big slow turning essentially lazy
engines, even so they still run the risk of having heat buildup in the
chamber when operated too lean, so pilots are trained never to recover
from lean cruising by just giving the engine full rich mixture & more
throttle (exactly what happens when an OB is suddenly powered up after a
long run in the lean mode). Pilots are trained to richen the mixture
slowly as the power is slowly increased, this is to give the chamber
temps time to normalise as the extra fuel is added; just in case:-)
Now, what exactly is lean mode for a DFI outboard? Idle only or lets
say below 3000 rpm?
Idle up to about 1800 they put cyls back to full mixture mode at
different times so you don't "feel" it as the boat accelerates.
You are also welcome to email me. My email as posted is real.
Sorry to be so long again, but this subject has been a war since 98 &
it seems till Brunswick are all 4 stroke & E-tec has failed it will
continue.
No worries! I prefer detailed information and yes i run into some of
the older "discussions" about the subject 
Take care.
K
Matt