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  • #83370

    I was wondering if anyone has a standard 310hp RAM II 340 with some JPI data so I can compare flight info. I am still tweaking some warm CHT issues and would like too see what I should expect in reference to CHT vs. fuel flows in climb and in cruise.

    Thanks

    #94401
    rwelsh
    Participant

      Derek, I don’t have a JPI, but I do have a pair of 610 Insight GEM engine monitors. I can’t download mine due to the goofy way Insight made thse thing in past years. But I have over 900 hours and six years of experience and 45 years of flying and wrenching.

      I have the RAM IIs and 310 HP like you. Takeoff FFs should be in excess of 34 GPH each. Climb power of 2500 or 2600 and 32 inches should have a FF of 27.5 GPH and a speed of 120 to 130 KIAS. The CHT should come in around 340 dF low and climb to 390 dF in the 20s with the cowl flaps wide open. I never lean in climb as fuel is cheap compared to cylinders. If your FFs aren’t set this high, you will run considerably hotter.

      I cruise LOP at 31 (15.5 each) GPH total in the 20s and get 204 KIAS; usually 34 inches and 2350 RPM. If the OAT is more then 10 dC above ISA, then it is hard to get above FL220 due to the boost running out of steam.

      My CHTs at cruise are 370 and 380 dF with the cowl flaps closed tight. To get these speeds and temps a lot has to be right like super tight baffles and seals with absolutely no holes or light showing in a darkened hangar from front to back. The plane has to be rigged correctly so the control surface don’t produce drag for being out of rig. Although the 340 has a good CG range, some speed can be had for loading correctly–not too much in the back and at least 100 pounds up front. This is assuming you have a current W&B that is known to be correct.

      You will find most A&Ps don’t know squat about how the baffles should be because to them the temp limit is 490 dF so what are you worrying about at 430 dF. The aluminum in the cylinder heads changes molecular shape above about 420 dF which is why hot cylinders get about 700 hours if they are lucky. I believe I made a write up earlier on the baffle issue on this forum.

      Now if you are running ROP, I can’t help you much in cruise although I have done it a few times to see what speed and fuel flow I got. At a minumum of 125 dF ROP, I burn 18.1 GPH a side and maybe get 2 more KTAS, but the CHTs are running close to 395 dF. I say a minimum of 125 dF ROP because the engine gurus at Ada, Oklahoma say 125 dF is the least lean you want to run ROP due to what they call the RedBox which is where the cylinder internal pressures are the highest and most detrimental to cylinders– from 125 dF ROP to peak EGT. John Deakins has a write up on this issue on his Pelican Perch website.

      In your earlier post you said you and teh mechanic spent time with the baffles, but that leaves me cold as I don’t thin he followed through completely with the baffle seals. Also you did not mention if he checked the timing and how he checked it. 2 degrees off can give you a 40 dF difference, particularly if it is advanced. You didn’t mention if the mechanic looked at the baffle seal across the lower part of the engine under the prop shaft as this is an important tweek to have it there and tight. Also you didn’t mention if he put the baffle roll between the baffle and cylinder fins on the #2 engine. If you mechanic doesn’t want to do these things, then you will never get it right. Too bad you are a planet away from the west coast.

      LOP with super tight baffles, EXACT correct mag timing (I use the plug in teh nose case for timming) and correct rigging will get you the best that is available. I might mention I have AA innercoolers installed which allows me a little more boost as the innercoolers cool the boost air more.
      Dick Welsh

      #94403

      Dick,

      Thanks very much for your detailed responses. They are most informative.

      We just finished inner baffle adjustments and sealing. 3 of the 4 baffles on one side were misaligned. I also replaced all lower and front rubber baffles… Upper baffles to be tackled next week…. Busy time of the year for my shop. We did also gap #2 cylinders as you mentioned.

      Quick question for you…. On the right front intake where #6 cylinder is exposed I have noticed quite a few 340 owners use sealant to seal along the metal baffle and the cylinder fins that face the slipstream of the intake. Should I do this as well? Not sure if it improves anything or not.

      I did a test Flt with the changes I have already done and did notice a slight improvement. I am able to run LOP with 14.8 gph per side an improvement over 13.5…. With only a 20kt TAS loss….better than the 30kt loss I had before running LOP.

      I am planning to ovhl my 4 slick mags as well as finishing the top baffle replacement. Hopefully that cures the rest of my problems

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