Abby Normal

[PilotjohnS]

So here is my plane running lean of peak at 10500.

Is this egt spread normal when running lean of peak, or do i need to balance injectors to make the spreads more even? In general, the most lean of peak was the first one to go lean of peak.

My apologies to Mel Brooks for the title.

Oh ya, here is a view out the window, 9500 over heartland of California.

 

[sailvi767]

Your EGT’s are fine and your CHT’s look good also. The important item is not the actual EGT value but when they each peak relative to fuel flow. The lean assist is essentially showing you that item. Your number 4 might be peaking a bit late but if the engine was happy it would not bother me. The injectors can be balanced to try and get them all very close.

 

[D-Dubya]

Gotta Love Young Frankenstein

Your EGT’s are fine and your CHT’s look good also. The important item is not the actual EGT value but when they each peak relative to fuel flow. The lean assist is essentially showing you that item. Your number 4 might be peaking a bit late but if the engine was happy it would not bother me. The injectors can be balanced to try and get them all very close.

Abby Normal...who can forget some of those classic scenes? Anyway, back on topic, if you want to look up what he's referencing above, look up the GAMI Lean Test or the Mixture Distribution Test. Mike Busch says the goal is to get the fuel flow spread (a.k.a. GAMI Spread) equal to or less than 0.5 GPH. Some people say that figure should ideally be 0.2 GPH, but that's pretty tight. Keep in mind that if you make the #4 injector smaller to tighten up the spread, the CHT on that cylinder may creep up just a bit. You'll have to decide what compromises to make. Not sure what your CHTs look like on takeoff at WOT, but if they're not crazy hot, optimize as you see fit. It looks like you've got a pretty good setup there.

 

[BillL]

0.2 is a good target, beware the double EGT peak.

<snip > Some people say that figure should ideally be 0.2 GPH, but that's pretty tight.

Not so extreme - my M1B stock ran this way at 50 hrs. My engine is easier to run the GAMI at 2500 rpm and 8000 ft DA. WOT. YMMV

Turning the mixture knob - just a tiny amount (0.1 GPH) at a time and allow 20 sec stabilization time.

Also, since spark plugs don't misfire equally This means that as you approach the peak you can skip the first peak and get to a second peak if too coarse on the mixture adjustments. When one plug is misfiring enough to increase the peak higher than the first peak. A misfiring plug increases EGT like retarding timing.

If one is way off - - I would not make nozzle changes before ensuring all plugs are gapped and firing properly.

 

[PilotjohnS]

Good to go

Seems like my gph spread was less than 0.2 gph; so i guess I am good.

I also noticed after 20 minutes or so, sometimes the egt, or delta egt, would wonder off a little. A miniscle turn of mixture would bring it back..

If I dont see a gph delta of more than 0.2 gph, I wont mess with it.

Thanks all.