Q The Engineer

I talked to KS Avionics yesterday and it looks like they have a TIT probe available for at a reasonable price point. If I can dig up the specs for the CDT it sounds like they can make them too. Anyone have the print for the CDT? I hear it's a thermistor and not a thermocouple.

Thanks for the feedback gentlemen.

Throw pressure to the cylinder you're checking with closed valves and listen into the intake and exhaust. It will tell you everything you need to know.

Based on my experience it is. You have to manage IMP, TIT, and CDT. Yep, to get a 6 cylinder the burbles at idle, it's definitely worth it.

LOL I have a bad keyboard that misses stuff as well. Reall recognizes real!

That makes sense, just like on my LB, it gets richer as it goes rearward. Fair enough, I appreciate you clarifying and for my lack of experience. I thought you were talking injector flow, not fuel flow. I realize what needs to happen. However, I won't compromise what makes sense to satisfy anyone. It's my ass in the seat and I'll do what's right for me and my airplane. You'd be wise to do the same.

No they won't, no engine will foul a plug based on being lean, none. They will foul a plug being rich or in oil. I'm not sure who you are but you lost me with this incorrect information.

Thanks man, I appreciate it. .5 gph is not very good, it's really bad actually, and it all depends on the feed pressure that changes the flow. I'll work my own injectors. It's really interesting how aviation does it's deal.

He is clearly a diamond in the rough. I consider myself capable in the engine, engineering field. Bob is capable and as real as it gets! Not trying to spell check but its Minnis. Names matter.

Likely truth. Just gotta watch engine weight and CG.

He's agreed if I'm willing to take it on. One thing is clear, it's my ass in the airplane, I'll be doing the work and engineering on all of it. I'm extremely fortunate to have a great A&P and IA I can work with. Bob is good and a wild man!

Thanks for the feedback. I won't be going that way. Finding some salvage hardware would be my preferred approach.

The tuned exhaust is only used if the cam is set up for it. You need the low pressure wave hitting the cylinder when both the intake and exhaust valves are open using the exhaust energy to pull in air from the intake on overlap. I think you're talking average pressure versus dynamic pressures in both systems. The average is the average, the dynamic is the result of blow down and tuning lengths on both the intake and exhaust. I have no idea what a GAMI is? Can you share some info? It sounds like you have a great machine! Cheers!

Good post. Do you know what are the differences are between the MB and SB hardware? My understanding is it's nothing, just changing operating speeds.

I can talk to you about DLC coatings in general. If you'd like to chat PM me. Thanks

FYI, our TIT limit with inconel turbines/housings is 1562 deg F continuous. I don't believe any better production materials were available back in the 80's to mid 90's for turbines. Our TBO expectations are 20,000 hours using that TIT limit.

I'm learning in mine so I'll deal with the consequences. I just don't see training in a 172 for 70 hours that I'm never going to fly again. They are traveling machines for sure. It sounds like the race shop had the A/F ratio way rich causing the issue. It was common on engines with high overlap cams. It takes a bit of carb work but it can be resolved, you just need more airflow at idle without feeding it more fuel. I understand and will deal with it. Fuel dilution is fine, the biggest issue is fouling the plugs. It shouldn't be too much of a problem as long as it gets leaned out to clean the plugs up frequently. Thanks for the feedback.

Good post and the numbers are fuel flow for ROP and LOP. Thanks and cancel my request.

Just getting caught up, thanks for your feedback. If you're looking for best fuel economy, yes, max allowed continuous TIT should do it.

I checked the 252 POH Bob gave me. Normal is 1300-1650 deg F, 1650 deg F redline maximum limit*. * = do not exceed 1650 deg F for more than 30 seconds, do not exceed 1700 deg F under any circumstance. Yep the GB and LB's have a short runner to the head with a long log. The MB and SB's have a tuned, longer runner. MB and SB's also have a Garret turbo and an aftercooler where the GB/LB doesn't, it's a straight turbo, no aftercooler. On the short drop runner GB and LB's, the standing wave under lower speed conditions pushes injected fuel back into the long log. The air is fed front to back on the engine so as air is moved to feed the middle and back cylinders the mixture gets richer and richer causing over rich conditions on the back cylinders. The MB and SB intake runners are 4x longer than the GB/LB (haven't measured my parts yet, much longer) so the standing wave pushes the injected fuel up the runner the same amount however, since the runner is much longer, the blown back fuel never hits the common log/plenum so the fuel doesn't get pushed to the middle and back cylinders. That is the idea in theory. Bob says he proved it during 231 development which is what drove the new intake manifold on the 252. He sent me the data but I haven't had a chance to look at it yet. What are you referencing on 13.3-14.5 when Rich Of Peak and around 11 on Lean Of Peak? That is new to me. The burble on decent is definitely there! I'm not ready for TIT tuning in the pattern yet, I'm not that good. And I kinda like the burble being a race car guy. Thanks for your feedback.

I'm with you on the TIT, I'm thinking 1650 deg F for continuous is a bit high. I'll check with my guys for a check on TIT limits using inconel.

Great post, thanks for your feedback. I've not been using TIT to tune for a couple of reasons, my instructor is not good with anything not full rich until reaching pattern altitude and that coupled with me not being that good yet keeps me at full rich. I'll add the TIT tuning when everything is automatic, it's clearly not yet. I'll ask Bob about the box numbers and check the POH. Running the engine lean of peak on the run up and doing a run up lean every 3 pattern runs has solved the problem so far as Bob suggested. I wouldn't want to go 1650 deg F even with an inconel turbine/casing. No engine monitor here other than TIT, CDT, oil temp and head temp as from Mooney. We definitely got shake but no bang so it must not have been too bad. I can't tell you if it's the same plugs or not without exh port temp measurements. Bob's thought was full rich with extended rich idle times and the poor intake design on the MB loading the back cylinders is causing the issue. I've been helping my CFI with the engine management but I'm still learning stuff. I've been doing engine development/design for 32 years so I get the fundamentals. Good thoughts sir, thanks for your feedback.

I wanted to share some info on the M20K engine I've become familiar with. The engine has an intake manifold design that is less than optimum. The standing wave pushes fuel to the rear cylinders causing misfire at low speed, light load. It causes the plugs to load up and misfire. I've flown the airplane training towards my private pilots license so we've run it full rich for about 10 hours. I did a mid field crossing, hit 500 AGL and pulled back to cruise power at 33" in Hg. The engine missed hard enough to shake the plane. My instructor called my airplane to give you an idea. I talked to Bob Minnis as he was the engineer on the J to K project for continental. Bob shared you shouldn't run the engine for that long full rich. I've been leaning the engine out on run up and every 3-4 pattern runs I'll do a run up to lean it out to clean the plugs off. It's worked good so far. FYI

It is if you're into engines and managing their complexities. If you don't like engines, likely not. A J would be a better machine IMO.

Yep, that's why I kick the gear down early. And to be honest, the gear warning horn and stall horn are so close it's hard to sort them. That's the only thing I've found I don't like about the Mooney. Speed brakes would be cool. Good post, thanks for that.