CHT's and timing (e-mag / p-mag)
 

First my e-mag/p-mag ignited RV-9A seems to be running well (just over 10 hours). Just for the info, I have a carbureted 9:1 O-320 with FP prop. I "think" that my baffle job is good and I see signs of sealing all around the top of the cowl and everything is tight and every hole I can get too is RTV'ed to prevent leaking. I have the timing in the low advance setting and have backed the initial timing an extra 2.5ish degrees ATDC (per their manual, and also they did go back about a month ago to be re-mapped or whatever the change was). I really saw no difference in CHT between the 2.5 degrees after and at TDC (perhaps I should go more??). Anyways I run just barely under 400 degrees on 1-2-4 and just under 425 on number 3 while cruising in the 2000-4500 foot range at 2500 rpm and ~25 inches MP (FP but I do have a MP gauge). I am not surprised that 3 is the high one since 4 has the oil cooler there which probably allows better flow around that cylinder. These numbers are with no leaning and do not seem to have changed at all in the 9.5 hours of flight. Engine is using little to no oil so I am guessing it is broken in by now.

After all that, my question is should I continue to retard the timing, or should I leave it alone? The numbers are okay right now according to the Lycoming manual, but when I go from 40-50 degrees to 90+ in the summer I am afraid that will help bring them up to a little too much. I understand that numbers will be somewhat higher with EI than non, but I am unsure how much "higher" means. Any advise would be appreciated. Also I would guess my cooling will be just a little bit better with fairings to pick up more speed, but I would imagine that change to be slight.

Thanks,
Scott
#90598 - N598SD Flying (~10hrs)

Hi Scott.

I have about 110 hours on an (early) Emag and have had cool CHTs from day one. My baffles are good, and my cowl outlet is maybe a little bigger than stock.

The EI will raise CHTs a little, but generally not much, especially on the lower advance setting. You can also set the Emag/Pmag to fixed timing like a magneto an d that should eliminate that effect (and eliminate a little power too)

Others will disagree (and do), but I don't like seeing CHTs over 400 if it can be avoided. Your CHTs may drop as the engine breaks in, but I would at least fashion a temporary "extractor" lip for your cowl outlet to improve airflow through the cowl. It will cost you a little speed, but I think the tradeoff is worth it in cylinder life.

Also, make sure the CHTs are accurate, I have seen people chase erroneous readings.

James Freeman

Also, note that a number of people have been able to lower the #3 CHT's on Lycomings to about the same as the other cylinders by a nice baffle mod discovered by someone over on the RV-list.

The mod is to space the rear baffle about 1/8" off the rear of #3 cylinder head by using a 1/8" washer between the rear baffle and the cylinder at the baffle mounting hole on the rear of the head.

Several RV's in this area have done this with good results. When I studied the head fin design, it is apparent that a small space would allow airflow whereas when the rear baffle is tight to the outter cyl head, no flow can occur.

Again, this is only at the outer end of the cylinder head. The baffles should still be tightly fitted to the barrel portion of cylinder.

Deene
EAA Tech Counselor

Excellent, thanks!!! Something I will DEFINITELY try.

Scott

Scott, There may have been another remap since the one you are mentioning. You might call the folks at emag and see if you have the latest map.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at you own risk."

Mixture more than timing?
 

Scott,

I have an early e-mag on an O-320 and have always run max advance. My CHTs were high to start with. With baffling work they started to come down, but I think there is more to be done - I'm now looking at how the upper lips seal and thinking of blanking off the edges of the lips. My O-320 came from a 172. Their airboxes are very restrictive, meaning that in an RV the motors almost always run lean (how well can you lean off - do you always get an EGT rise when you start to lean?). I have increased my main jet diameter by 0.003" and saw an immediate reduction in climb out CHTs, and am now able to lean normally at altitude. I am considering a further 0.002 or 3" increase to get my climb out CHTs down to around 380 - now around 410. They used to be over 430, I was never brave enough to find out how much over. I seem to remember my original main jet diameter was 0.098", so I would estimate something around 0.103-5" would be optimal for a 160hp O-320 with Van's airbox.

Yours, Pete

I have suspected possibly being lean. When I checked the plugs, they looked great, maybe too great considering I was running full rich. I will test next time I fly. I have been running full rich for the first 10 hours and the next flight will include leaning to see that I get a 150-200 degree rise from full rich to peak on the EGT's (as best I could tell from some RV-list archive searches that is what I want to see).

I did space off the screw going into the back of the #3 cylinder head 1/8" last night so i'll see if that helps #3 to even out with the rest. Does not seem like much, but it makes sense that it would help and ~20 degrees is not that much. Also I realized I only had about 1 degree ATDC on my timing and moved that to ~5 (per the e-mag guys). An email from them indicates that yes I probably have to send them in for a newer firmware which it didn't sound like will change the mapping, but it will then make them able to be programmed via laptop and the software that should be out within a week or so. Then no more having to send them back.

As far as drilling out the jet I suppose it might be obvious when I mess with the carb but what all do I have to take off and/or apart to get the jet out (i.e. does carb have to come off or can I get to it on the plane)?

Thanks,
Scott
#90598 - N598SD Flying - 10hrs

You have to take the carb off the airplane, then split it apart - its obvious how to do it. When you pull it apart be careful about the accelerator pump plunger. "Drilling" out the main jet is not really the right term. Find out the size of your main jet by using a number drill set, then take it out of the carb and carefully open it out 0.002 or 3" at a time. Don't use a drill motor - the metal is quite soft (brass I think), may be chuck the drill bit up and spin it by hand. Again, be careful of the plundger when putting it back together. It should only take a couple of hours. The worst bit is getting the carb bolts undone (on the bottom of the sump).

Pete

To keep up to date, I flew last night and did some leaning.

First, spacing the #3 baffle about 1/8" (two washers) brought #3 CHT closer to the others. On a rainy day I will add one more washer to test and see if it gets even better or not. I had also moved my timing to 5 degrees ATDC.

Impressions, right away are (it was 80+ degrees yesterday and until then the hottest I had flown in was low 50s so that would certainly be part of it) that it did not run as smooth or feel as powerful. I flew out and leveled around 4500 feet rpm ~2400 rpm. #3 EGT read around 1250 and I started leaning. It got to maybe 1300 and the rpm was decreasing. Mixture back in and the rpm came back up. To me, that says I am on the lean side, or rather "leaned" when running full rich. As per many hundreds of hits on the rv-list archives, I took the carb off last night and will "jet up" (i.e. #38 drill bit). The flight was short as my oil temps were 220-230 as it was hot and I had not removed some of the foil tape blocking part of my oil cooler needed previously to get the temp up. I will test again and post the results. Hopefully I can get the timing back in too. Finally I did not climb hard at all but once level all CHT's were 375+ with #3 right at or below 400. I have Van's CHT and EGT gauges with the EI dial to change between them so I cannot see all at once.

Scott
#90598 - N598SD Flying - ~11hrs

Scott--

If RPM is decreasing as you lean, then at least one cylinder is already lean of peak. I think you are exactly right that you are running too lean.

The EGT needs to be at least 200 degrees cooler than peak in each cylinder when running high power settings rich (e.g. takeoff and climb). If the highest EGT you see on a given cylinder is 1300, then you need to be below 1100 at WOT on takeoff. Then you can lean in the climb to keep the EGT at or below the takeoff number.

I agree with the advice to pull the carb and open the jet.

James Freeman