August 13, 2010 at 5:04 am #83350
I am a new owner of a ’75 340 with Ram II 310hp 520N engines. I have installed a JPI 760 and GAMI’s to help me manage running LOP.
At LOP the engines run a bit rougher than ROP but acceptable. My engines peak at roughly 16 GPH at 33″ and 2300 RPM flying in the low teens but settle in at roughly 13.5 GPH LOP. This is the only fuel flow that keeps my hotest cylinders at/below 400 on each side in cruise. If I reduce any further than 12.8 GPH my engines start balking.
Problem is I seem to lose 20 KTS indicated and 30 KTS true flying in the low teens LOP…. Is this normal? Also I can not fly LOP any higher than 15K ft. because my speed decreases to close to 115 Kts indicated. I was under the understanding that running LOP would affect TAS by 5% roughly 5-10kts…not 30!!! And why can’t I run LOP higher up?
Secondly when running ROP my fuel flows for 33″ 2300rpm in the low teens are generally around 22-23 GPH again to keep my highest CHT’s at/below 400 deg in cruise. The cessna POH performance section shows I should be getting fuel flows in the 17-18 GPH range. Is this normal?
Any feedback would be greatly appreciated.
I have been battling high CHT issues for the last 9 months and the final solution after dealing with baffling and timing was to just crank the fuel flows way up from 26-28 GPH in climb to 31 GPH….
It’s really hard to keep the heat demons at bay….. Are AA intercoolers the only remedy?
Thanks.August 13, 2010 at 6:16 am #94335
Derek, you are running waaaaay to LOP which is why you are losing so much TAS and IAS. Normally most of us run the 340s with 310 HP at 34 inches and 2300 to 2450 depending on altitide LOP. At the higher altitudes, you need more RPM to keep the mass air flow high enough to keep the turbochargers from bootstraping. Bootstraping means the turbos run out of MP.
Your normal fuel flow LOP in the teens should be around 16 to 16.5 GPH and give you 178 to 190 KTAS depending on altitude with 190 KTAS around FL190. AT FL250 on a very cold day, you should see 205 to 208 at 15.5 GPH, but it must be an ISA day or colder which is rare. If it is not cold, FL230 will be the highest you can get.; maybe even FL210 if ISA plus 25.
I never climb with less then 27 GPH at 2550 RPM and 32 inches MP. Takeoff should be 34 GPH plus for the 310 HP and higher if you have the 325 or 335 HP engines. Your mag timing has to be dead on the numbers. Your baffles and innercylinder baffles have to be perfect with no light visible from the back with a 100 watt bulb in the back and in a dark hangar. All the gaps and holes on the innercylinder baffles should be sealed dead tight with red high temp silicon. The rear and side baffle seals should face forward and inward with the top cowling in place with no waves visible. Getting this right takes some effort but is easy to do right the first time.
The rear baffle on the #2 cylinder should have a roll of baffle seal stuffed in between the baffle and the rear cylinder fins so you have at least a 5/16 inch gap between the fins and the baffle (the rear baffle is springy enought o allow this stretch). The rear of the TCM cylinders have a fin stiffener cast into the fins that extends out to the rear edge of the fins thereby blocking cooling air flow to the rear of the #2 cylinder if the rear baffle rides tight against the back of the fins.
Pay attention to the baffle seal that extends underneath the prop shaft from one side to the other. If that is sloppy or missing, then gobs of cooling air escape and add pressure to the lower cowl which is not what you want for cooling airflow. There should be a slightly negative pressure in the lower and rear cowl so the pressure cooling air coming in the front holes does not meet resistance in trying to get out the cowl flap area and the louvers.
Most A&Ps do not understand the necessity of exact baffle seal placement and plugging holes so you have to educate them if that is possible. They have it in their heads that the CHT temp redline is 450 dF so what’s the big deal if you run 420 or 430! I have been wrenching on these things and flying them since 1962 and seen the downside of running the CHTs over 380 consistently.
PM me if you need other advice.
Dick WelshAugust 13, 2010 at 6:14 pm #94336
I operate a 340A with Ram IV engines and AA intercoolers, my experience with this configuration is that the AA intercoolers are magic. About four weeks ago I was at FL230, ISA +25, 2400rpm, 29″, (220 hp) 35gph(75 deg ROP), 218kts true, left was 405 CHT, right was 395 CHT with the cowl flaps closed. Take a look at flightaware N340GK
I have flown in 340s with the standard arrangement and the CHT’s under similar conditions are 30 to 40 degrees hotter at a similar power setting.
The power charts for the Ram IV w AA intercoolers is interesting to say the least. At 2700 rpm and 41″ at ISA the engine produces around 360 hp therefore the MP is limited to 39″ to maintain warranty. Even then the chart shows that the engine is producing 339 hp. This was done by Ram using a torque meter to determine output. RAM, to their credit has produced a power chart for this combination, the bottom line is that the AA intercoolers change the landscape. I’m sure the RAM VII configuration does the same and perhaps better.
I have operated turbo charged aircraft since 1984 and have found that even with perfect baffling and fuel management the engines get hot in the flight levels if power production is anything above 65% of rated power. The larger 140 cu. in. intercoolers change the game.August 13, 2010 at 9:54 pm #94337
Thanks for the replies.
I have a hard time understanding what my problem might be if my engines peak at 16 GPH at 33″ 2300….how am I suppose to be getting LOP figures at 16GPH or ROP at 17.5 GPH…..If I kept my engines at these FF settings they would melt…. I have to reduce my FF to the 13.5 to 13.8 GPH range to keep the CHT’s below 400 and the TIT’s below 1650 for LOP…..and above 22 GPH ROP at the same power settings to keep CHT’s cool….TIT’s not an issue ROP.
Am I missing something? I can’t believe this is just a baffling issue of which I spent a day with my Tech tweeking all my baffles and sealing all the holes only to see some improvement but nothing enough to improve my problem….
Can there be any other issues at play?August 14, 2010 at 12:56 am #94338quote DEREK:
Have you talked to RAM?August 14, 2010 at 2:55 am #94339
Not yet…. Is there anybody in particular you can suggest I talk to?August 14, 2010 at 1:51 pm #94341quote DEREK:
Not in particular, but here’s their customer service page:
If you decide to call them, you should also be aware of this, from their website this AM:
Please don’t “shoot the messenger”! 🙂August 14, 2010 at 10:52 pm #94343
Thanks for the links….I have read them before. I am aware RAM is anti LOP…. I wouldn’t bring that aspect up with them only my ROP dilema of being perfectly leaned for CHT at cruise and showing 5-6 GPH over what I should be….
I have read both sides of LOP issue and I am a firm believer in LOP. I understand RAM’s position….LOP is not for the Sunday flyer. It’s for pro pilots who have the means and ability to manage LOP….mistreat it and you WILL fry your engine.
That’s why I am trying to see if my LOP problem is normal or not…..Am I doing damage to my engines being at 13.5 GPH instead of 16 GPH LOP as Dick mentions above. My CHT’s are cool (400 and less). My EGT’s are 1530 to 1600. My TIT’s are at 1625….is damage being done?
I have been in touch with GAMI and they have sent me somebody else’s 340 JPI data LOP. He as well was burning 13.5 GPH LOP….. I was unable to get that pilots info to confirm but I would sure like to hear from other owners running LOP to get their feedback.
I am guessing I may have “ignition” issues at play that may be the cause…..not sure yet. Should I try new spark plugs? Mags? Wiring harness?August 14, 2010 at 11:36 pm #94344quote DEREK:
I’m no expert, but, I’d be sure my mags and timing are “Perfect”. Go from there. Also, calibration of FF. Is your FF confirmed at the gas pump? Are you actually burning what your FF says?
Good luck!August 15, 2010 at 1:58 am #94345
I’ll look into it.
Thanks.August 15, 2010 at 5:19 am #94349
Derek, from the tone of your posts, it appears you do not have a CHT and EGT engine monitor, only the factory gauges. LOP should not be tried without an engine monitor. The factory gauges can be 50-100 degrees off depending on what type of CHT probes you have. By the way, our engines do not have TIT limits like a 210 has. If you are using the factory fuel flow meter, you could also be way off there as they are pressure guages instead of real fuel flow gagues. How are you timing the engine; do you use the timing mark in the plug hole on the left front nose case or are you using some other antique method?
Also the E gap of each mag should be checked; especially if you have 400+ hours on the mags. If you have over 500 hours on the mags, then they should be overhauled. I am hoping you have the Bendix 1200 mags instead of those cheap Unison/Slick monsters–basically throw away mags. I understand that RAM is still in the dark ages when it comes to the proper mags for our high flying planes. They want you to use the worthless pressurized Unison/Slick when a non-pressurized Bendix 1200 does not flash over due to their large distance between the distributor posts.
Besides the pressurized mags cam introduce water/moisture into your mags because of their construction and the chinsy moistur filter supplied.
You definitely have something going on in your engines or your gauges.
Where are you located so I can give you some names of qualified A&Ps that understand these engines.
Dick WelshAugust 15, 2010 at 5:17 pm #94351
I have a JPI 760 installed….wouldn’t dream of operationg LOP without it.
I am in Montreal, Canada but I spend the winter based in FXE so anywhere in South Florida would be great.
It seems I need to go over my baffles with a fine tooth comb. Somebody suggested it could be the root of my problem.
I had a TOP overhaul last Nov. just before I purchased the aircraft and suspect the A&P messed up my baffling.
Thanks for the info and I will check on my mag/plug situation….
Are Fine wire plugs worth the price?August 16, 2010 at 4:34 am #94353
Derek, I use the massive Autolites or whatever they are called now, but I have no heartburn with fine wire plugs. I pull the plugs at about 100 hour intervals and probably would if I had fine wires also. I check the timing and baffle condition when I do the 50 hour turbo exhaust check for AD 00-01-16 so mine gets lots of look see.August 24, 2010 at 2:25 am #94369quote RWELSH:
Sorry, Dick, I’ve got Slick pressurized mags on my RAM 1 TSIO-520’s. They’ve served me well and there is a repair station nearby that recently did a 500-hr inspection/repair — works for me 🙂
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