Great discussion, to which I'd like to add a couple questions for Walt, Ross, Michael, Dan and anyone that may have data/experience to add, plus some experience from my ROP/LOP testing. No intent to hijack, and hope this is value added.
- Walt, do you have MP numbers for the test? I know you said WOT at about 8,000' in response to Dan's query, but knowing the MP would be a good data point. Seeing the trend and rate of increase in CHT vs Fuel Flow would be good too.
- Does a max increase of 9 on a base of 20 in the P-mag mean 29 is the max advance? (I know that may sound like a dumb question, but I also know the P-mag curves are proprietary, and we may not know where his timing actually was...that's not a shot at P-mags at all, just a data question).
- Does your friend by any chance have an O2 sensor installed, with a lambda or AFR readout? More good data if available.
- What type of spark plugs is your friend running, auto or aircraft? Is the heat range of the plugs correct?
- What type of fuel was he running? 100LL hopefully, but want to be sure it wasn't MoGas.
- Walt, Ross and Michael, you guys indicate this was almost an expected result. Is that because it's an angle valve engine with 10:1? Or because it's an AV/10:1 with Pmags? Interested in why you feel this way, and if it has applicability to parallel valve motors with 10:1.
Here's my semi-selfish reasons for asking all this (along with trying to add to the discussion here, and help find root causes of a damaged engine)
Background: I have a Lycon IO-540 CB45 (narrow deck, parallel valve) with 10:1 CR. One mag (I've had both Bendix and Slick over the years), one Electroair EI. I run REM37BY massive electrode plugs on all cylinders, gapped for the mag on the bottom, and the EI on the top. Much of my testing was done with the mag timed at 25 and the EI at stock delivery setting (which is about 23). I have an EI timing readout and an AFR readout. My engine monitor is an older VM-1000, with no data logging, so LOP testing and injector balancing is quite the 20th century analog/slide-rule-ish process, with lot's of hand-written log sheets transferred into spreadsheets along the way.
I've done quite a bit of LOP testing and injector balancing over the past 10 years, most of which was done on X-C flights up at 10.5K to 13.5K. I've always been concerned about detonation "red zone", especially with my 10:1 engine, so higher altitude testing has been my norm (its where I like to cruise on X-C's too). Typical power settings have been WOT/2100 to WOT/2300 (2200-2300 is where most of my data is). WOT at those altitudes has been 19-21 or 22" MAP. With the mag at 25 and the EI MAP sensor on, and EI advance reading in the mid to high 30's, I'd never seen runaways or CHTs over 400 during any of the tests. I've felt that I had safe margins from detonation. Cylinders 2 and 5 used to peak first, and run a bit hotter than the rest (CHT), but over time, I made injector restrictor body changes that balanced things out nicely.
Flash forward to now, after an upgrade from a Bendix RSA-5 to an AFP FM300B fuel injection servo (a couple years ago). I hadn't done any recent LOP tests, and Steve Smith and I discussed that at Reno this year, as we chased cylinder cooling with a new nitrous system and water spray system installed. Our goal was to adjust external water spray to keep 1, 2, 5 and 6 cool, and bring up 3 and 4, while I slowly leaned towards best power for racing with nitrous (about 11.8 to 12.0 AFR). We just about had it nailed when my fuel pressure transducer failed on Sunday taxiing out...didn't get to test our last adjustment. 2 was the last cylinder to stay hot, and we didn't know if it was the governor blocking air, another airflow issue, a water issue, or a leaning issue. So Steve encouraged me to do some LOP testing on the way home to check that aspect, which I did.
While I was looking to see how 2 was acting on those recent post-Reno '21 tests, it seemed to fall back into line, and 5 became my hot spot. On one test, at 11,500/21.5"/2300RPM, it slowly crept to 425-430, but cooled right back to 380 on the lean side. 6 got to 400, and the others were all 395 and below. Concerned about that 430, we did a compression check and borescoped the engine, and saw no indication of damage. In fact, my airpark neighbors (builders and mechanics) were impressed with the condition of my 2000 hour motor (and compressions were in the 73-77 range, 5 being the 73). I also cleaned all the plugs and injectors.
One thing I'll fess up to is that I found all of my plugs (top and bottom) gapped for the EI. Dammit...that's too much gap for my mag plugs! I messed that up, and must have raced that way...probably left some power on the table. Hopefully I've not damaged my brand new mag! So far no indication of that.
So after assessing the engine, cleaning (and re-gapping) my plugs and cleaning my injectors, I set out to do some more LOP/injector balance testing. After a discussion with Don at AFP and Steve about race CHT and my recent LOP testing, I did a cruise power leaning test (10.5K/22.1" MP/2300 RPM) on one day, and a 75% (ish) test (8.5K/24.2" MP/2400 RPM) on another day. Mag and EI had been set at 21 for racing (MAP sensor off for racing with nitrous), but I reset both to 22.5 for these tests, and had MAP sensor on. EI readout was 30 on the first test, and 29 on the second).
Test 1 showed #5 got to 396 CHT with all others in the 360's/370's. #6 has been trending slightly lean of the others, and is the first injector body swap that I will try next.
Test 2 showed #5 got to 405 CHT with all others in the 380's and 390's. Similar delta to #5 from the rest.
Don recommended this comparative test, to see if at higher power, the richest and leanest cylinders were changing. I see a clear trend that 6 is leaner than the rest, and a less clear trend that 5 richens at higher power.
I need more testing to establish more clear trends, but seeing this thread has my attention about doing LOP testing at 24 squared. That brings my post full circle, and thanks for bearing with me on all the above.
Is the experience of Walt's friend a "10:1 Angle Valve with P-Mag" issue?
Does his result translate to a 10:1 Parallel Valve engine with a mag and an EI?
Asking for a friend (my engine)!