Today's Message Index:
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1. 04:40 AM - Re: 320-E2G sump question (Stucklen, Frederic W UTPWR)
2. 05:03 AM - Re: 320-E2G sump question (Gary Casey)
3. 05:21 AM - Re: Re: 320-E2G sump question (Stucklen, Frederic W UTPWR)
4. 07:21 PM - Re: Re: 320-E2G sump question (Dww0708@aol.com)
Message 1
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Cc: "'jlbaker@telepath.com'" <jlbaker@telepath.com>
| Subject: | RE: 320-E2G sump question |
--> Engines-List message posted by: "Stucklen, Frederic W UTPWR" <Fred.Stucklen@UTCFuelCells.com>
Jim,
My RV-6A does use the Vetterman crossover exhaust system.....
Fred Stucklen
RV-6A N926RV
--> Engines-List message posted by: "Jim Baker" < jlbaker@telepath.com
<mailto:jlbaker@telepath.com> >
> I've tried rejetting it, even sent the Carb back to Aero
> Sport Power. Nothing seems to correct the situation. I did read on
the
> Lycoming web site last week that this is a common occurrence
with
> Carb'ed engines.
Not that you may be able to do anything about it, but this sure
sounds like an exhaust scavenging problem. If all the intake runners
are approximately the same length, what is the situation with your
exhaust systems? Is it an issue that a crossover system might cure?
Just a thought.....
Jim Baker
580.788.2779
'71 SV, 492TC
Elmore City, OK
Message 2
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| Subject: | RE: 320-E2G sump question |
--> Engines-List message posted by: Gary Casey <glcasey@adelphia.net>
>
> Nothing seems to correct the situation. I did read on the Lycoming
> web site last week that this is a common occurrence with Carb'ed
> engines.
> Iv I run the engine at different power settings, I get different
> EGT's &
> CHT's. At 2350 RPM (fixed pitch prop) in cold air (less than 25*F)
> # 4 CHT
> goes so low it will start skipping, especially if I have leaned at
> all. All
> temps are fine at full throttle and at something like 2150 RPM. In
> warm air
> the situation is much less pronounced....
> So I've gotten to the point where I ether fly slow in cold air,
> (especially down low) or at full throttle, leaned, at high altitudes
> (11,000' or more). Sure makes me want to reconsider a fuel injection
> system....
> I do have all EGT's and CHT's, and have talked to Bart at Aero
> Sport Power
> extensively about this situation. He doesn't have too much to add....
>
>
> Fred Stucklen
One thing that we learned on car engines way back when was that the
carb inlet condition makes a big difference. I've seen some aircraft
installations that were well done except for the carb inlet. Ideally
the inlet should be a bell-mouth (elliptical is a good approximation)
or at least radiused with equal air flow from all directions. Not
easy to do with the tight space constraints that usually exist. One
way to do it that I have looked at (not done as I don't have a carb'd
engine) is to bolt a radius - no duct - to the carb inlet and then
surround the carb with inlet air by building a dam well above the
inlet that extends outward from the carb to the lower cowl. Air can
then flow past the carb and enter the inlet from the rear, balancing
the flow that comes from the front. The lower restriction will give
more power as well. Remember, a sharp-edge inlet will have a Cd of
about 0.6 compared to a radiused inlet that will have a Cd of almost
1.0, meaning the pressure drop at the inlet will be 60% of what it is
with a sharp edge. Might be worth a try.
Another thing we tried was a "dip tube", which is a tube that extends
down (oops, up) into the manifold slightly past where the individual
runners come off the manifold. This creates a sharp edge that
prevents the fuel and/or air from clinging to one side and not the
other. Made a definite improvement and carefully done didn't impede
the air flow too much.
Gary Casey
Message 3
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Cc: "'Dww0708@aol.com'" <Dww0708@AOL.COM>
| Subject: | Re: RE: 320-E2G sump question |
--> Engines-List message posted by: "Stucklen, Frederic W UTPWR" <Fred.Stucklen@UTCFuelCells.com>
David,
I've calibrated all probes (with a certified calibrations device). All are
within 1% accuracy. The idle cuttoff RPM rise is present (but this should
have no effect on the cruise RPM or cruise mixture problem). I've also tried
a new set of plugs, with exactly the same results.
Just to recap the issue, CHT's & EGt's between cyclinders are diverging
under certainpower settings (10-5217 carbureted O-320-D1A engine with
Vetterman crossover exhaust). Running the engine at low power settings (2100
RPM and lower) and at full power setting results in CHT's & EGT's that are
very similar (CHT's within 5*-10*, EGT's within 50*). Runing the engine
between 2200 - 2440 RPMS (maybe around 90% throttle) results in diverging
CHT's & EGT's, with cylinders #3 & #4 (#4 being the coldest), especially in
cold air (< 25*F) and leaned. #4 CHT will go below 200*F and begin skipping.
The tests I have run seem to indicate that the CHT/EGT divergence is
directly related to the throttle plate position. Try this: pick an altitude
below 8000' where the OTA is 20* or less. Run at 1900 RPM cruise, full rich,
and note all CHT's & EGT's. Be sure to allow time for thermal stabalization.
Repeat the same test at 500 RPM increments, and then at different mixture
settings (witht he 1900 RPM mixture setting as the reference point.).
Normalize the numbers by showing only the differences in temps between the
1900 RPM full rich data, and all other data. Plot out curves of divergence
Vs Throttle position for different mixture settings. (Having a normalized
CHT/EGT gauge helps emmensly in visualizing the resulting divergences...)
What I saw was about the same CHT's/EGT's differences at 1900 RPM and
full throttle, with diverging temps at throttle positions in between those
settings. I have also noted that at higher Outside Air temps, there is a
lesser problem. This might suggest that the fuel atomization at the colder
OAT's is not as complete at is is with higher OAT's. This, coupled with the
throttle plate position, could cause more fuel to be routed into the front
cylinders, with more air going to the back cylinders. (Remember, the
throttle plate position [at less than full throttle] favors flow towards the
front cylinders.)
I would like to try other carburetors to see if there isn't a better
solution. I'm not sure that there are any other carbs out there that will
run OK on this engine.... Another solution might be to put a honey cone type
device between the carb and the sump. This should help straighten out the
air flow....
Fred Stucklen
RV-6A N926RV
430 Hrs
--> Engines-List message posted by: Dww0708@aol.com
<mailto:Dww0708@aol.com>
Just listening in here All carbureted engines should have the
distinct
slight rise in RPM just prior to fuel off at Idle RPM. That
establishes not
induction leaks and proper idle fuel to air ration. That said
better swap your
probe around to establish repeatability of you symptom. Use a remote
pyrometer and be sure that you guages are accurate. The spark plugs
are vital,
play musical sparkplug's. Keep a numbering system and vibe ech them
to keep
them straight. Plugs should be examined closely for indications as
to
combustion quality. Compressions should be with in 80 percent of each
other.
David
Message 4
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| Subject: | Re: RE: 320-E2G sump question |
--> Engines-List message posted by: Dww0708@aol.com
vetterman? The idle cut off check is kind of an induction tube integitidy
check,it proofs if you have vacuum leaky pipes. Vacuum is strongest at idle
RPMs and a sucking leak will inhibit the proper RPM rise ( lean out ) at Idle
cutoff indicating lean condition. I know Lyc uses an oil heated induction
manifold, Helps atomization. If the carb heat is leaking it can adversely affect
the fuel air ratio. Any way looks like you have been trial and erroring it.
The industry is like that. I am curious, Lyc operators manual? I have
one, the thing that comes to me is what is the manifold pressure doing? Is
there a curve trend that should/would mirror you other parameters? Manifold
pressure at pressure altitude and OAT. Manifold pressure is the power
indicator. Then there is the basic push rod clearance with dry tap it. Very
important to brake horses and volumetric effeciency.Selection of push rod lengths
are how to adjust dry tappet clearance. Some might say that that valve timing
issue would lead to engine roughness and it should but needs confirmed. Very
basic. If I was a Lyc tech rep I would verify all this before before
experimenting away from the basic engine design. Have read about the intake and
exhaust rocker arm movements and making sure consistent to other cylinders. Are
all the correct part number items include in proper engine build up. David
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