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Date: Tue, 25 Aug 2009 15:49:09 -0400
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From: mmcmanus@grandecom.net
Subject: Re: [LML] Re: Plenum pressure and Injector performance LOP
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I have a similar problem on my 360.  It is the angled valve, IO 360,  
10:1 pistons, 2 standard mags, EI cylinder monitoring, spread is .3,  
and NO plenum.  But the very same issue.  I can lean to LOP, for a  
couple of cyls, but before all of them hit LOP, the engine starts  
running (too) rough.

GAMI installed my injectors about 5 months ago, and we test flew the  
airplane, we were not able to get the engine to run smoothly LOP even  
though they did change out one injector to get the spread to .3.  GAMI  
told me that no matter how balanced the injectors, they could not make  
up for ignition deficiencies.

My engine and the ignition system have about 450 hours.  GAMI said  
that the life expectancy for mags is about 600 hours.  They suggested  
I start with changing the plugs.  I did and that did not help.  So I  
can change out the wires and mags or live with it.

I generally cruise around 10,500 which puts me below 65% power.   
According to John at GAMI, at LT 65%, there is no danger of hurting  
anything even if some cyls are right at peak, that is, there should be  
no pressure issues doing damage to a cylinder due to high peak  
pressures.  So I can lean down to about 7.9 to 8.2 with the engine  
running smoothly (but not LOP for all cyls).  And that's good by me.   
180 knots at about 8gph works just fine.

So in summary, GAMI blames my issue on my "old" ignigtion system.

Matt McManus
LNC2 360


Quoting Tim Olson <Tim@5000feet.com>:

> That is all good stuff.  I just did all that on my own plane.  We're
> all talking Fuel Injected engines, that's for sure.  I just did this
> write-up of my own experience doing the lean test and all:
> http://www.myrv10.com/N104CD/upgrades/20090822/index.html
>
> The problem is, there is one guy in particular who's a friend
> of mine and I flew his plane, and analyzed his GAMI curves
> and his are probably better than mine (and mine are < .2)
> and yet he still can't get even all the way TO peak without
> it stumbling.  So I'm trying to learn what other effects
> to worry about.  Timing, Compression, Exhaust, and whatever
> else.  My compression is 8.5:1, his is 10:1.  We have different
> exhaust, but both are supposed to be good at exhaust scavenging
> and good flowing.  Timing he's got to check and verify yet.
> The interesting thing is, there are a few other people I'm
> talking to who have plenums and circular inlets by
> coincidence and they're all having the same problem...stumbling
> as they get to 13gph or so...and considering I know the one
> guys injectors are flowed well and peak together, I'm getting
> curious as to how much of an effect things like Plenum air
> pressures and the like will have on injector performance.
> Looking for the things OTHER than the gph spread in the
> EGT peaks that could cause things not to run at peak EGT or
> leaner.
>
> I sure hear you though....LOP can definitely be faster than
> ROP when you start dropping off extra fuel stops from the
> equation!!!
> Tim
>
> Sky2high@aol.com wrote:
>> Listen up Grasshopper,
>> 1.  If the engine is carbureted, you may be out of luck as there is  
>> no way to control the F/A ratio in each cylinder.  However, you can  
>> try step 3 for informational purposes if you have the equipment  
>> listed in step 2.  2. You must have an engine monitor and sensors  
>> that display (or record) EGT for each Cyl and the fuel flow.
>> 3.  Injected engines must perform the GAMI lean test before a "next  
>> step."  At 75% power (that means at or above 6500 MSL, 7500 if  
>> using ram air and KIAS is less than 190, or higher), WOT (necessary  
>> to control air distribution when running LOP) .     a. Starting  
>> sufficiently ROP, lean in small steps (less than .3 gph) and record  
>> the EGT for each step for Cyl 1.  Continue past peak EGT for that  
>> Cyl for about 50F degrees LOP or until ugly roughness.
>>    b. repeat "a" for each cylinder.
>>    c. Check the gph for each cyl peak EGT.  If the spread in .3 gph  
>> or less, you are done and you should be able to run LOP 20F, 30F,  
>> 40F depending on the spread).
>> 4.  If the spread is GT .3 gph,  you must fix the A/F ratio.  A  
>> cheap way to start is to provide equal air pressure to each  
>> injector - a wee plenum distribution to each shrouded injector) and  
>> repeat the Lean Test.
>> 5.  if the lean test shows the proper spread, go fly LOP (less than  
>> 75% power)...................
>> 6. If the lean test fails (GT .3 gph spread), consider different  
>> sized injector nozzles (either GAMI or others) for the rich/lean  
>> cyls.
>> Grayhawk can fly a 320 at 8500 MSL, ROP, 9.5 gph and see 195 KTAS  
>> or LOP, 7.5 gph and 186 KTAS (all things being equal) thus  
>> eliminating a fuel stop at 3.5 hours cause he could go another  
>> hour. 195 x 3.5 = 683, 186 x 4.5 = 837, 837/195 = 4.3 + 1 (re-fuel  
>> stop time) = 5.3  Duh!
>> Grayhawk
>> In a message dated 8/24/2009 2:40:57 P.M. Central Daylight Time,  
>> Tim@5000feet.com writes:
>>
>>    Hey guys, I am remembering a long time ago reading about
>>    how the air pressure surrounding the injector can affect how
>>    well the injector works.  If I'm not mistaken, turbocharged
>>    engines even use some pressure manifold around the injector
>>    to accommodate for the increased Manifold Pressure.
>>
>>    What gets me curious is that I'm having a discussion with some
>>    folks right now who are all having problems running Lean of Peak
>>    and their engines stumble before they get to peak EGT. Between
>>    the group, there are a variety of ignitions such as 2 mags
>>    or 1 lightspeed and one mag, and varieties such as 8.5:1,
>>    9:1, and 10:1 compression ratios, but the one constant is that
>>    they all have what is purported to be a more effective cowl...
>>    the Sam James cowl with a plenum.  So I'm wondering if the
>>    knowledge base some of you have would provide any insight
>>    to the issue. I originally was worried that the 10:1 pistons
>>    might make LOP operation harder to accomplish, but perhaps
>>    there is just too much air pressure on the outside of the
>>    injector?  The cowl is known to often have too little exit
>>    area, so it could be that the pressure differential is
>>    even too high between the top and bottom half of the
>>    cowl.
>>
>>    Any insight you can give?
>>    Thanks,
>>    Tim
>>
>>    --
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