IO-470K CHT and Baffles

[Curtis Weddle]

I figure this has been discussed a bit by the other stock early Debonair folks, but I wanted to see what people are observing and doing to cope with cooling, performance, and efficiency issues.

I have a 1961 35-A33 Debonair with the 225 hp IO-470K.  I routinely see CHT around 400 on takeoff and in climb with ambient temperature 90-100 degrees.  I have set the unmetered and metered fuel pressures within the recommended values, and fuel flow is set above the TCM value to 24 GPH as recommended by ABS and various sources.  It seems there is no simple way to get this engine to run efficiently in climb and not fight to keep CHT below 400.  I climb at 115 KTS until climb rate decreases below about 400 ft/min, then reduce by 5 KTS until and repeat until reaching cruise altitude of 9500' or 10500' on trips over 200 nm.  I usually find I need fuel flows of 19 GPH at initial cruise-climb of 2500 rpm and 25" Hg, and taper off to 15 GPH as manifold pressure decreases.  I have GAMI injectors and have attempted to run LOP, but this results in rough engine operation.  I have performed the GAMI lean test at various altitudes and all fuel flow spreads are within their limits.  I understand that the low-compression 470 series engines do not generally run well LOP.

Bottom line is that I feel something is wrong with the baffling or the way I am operating the engine based on what other folks are seeing.  I understand that the IO-470N has larger cooling fins and that may be why my friend with 260 hp sees significantly lower CHT indications with the stock baffling.  It appears that D'Shannon may only offer their baffle kits for the higher output engines, but I have an inquiry in to them about installing on the IO-470K.

If you have experience with a similar engine or aircraft, please let me know what kind of operating practices you are using and what kind of numbers you are seeing.  I usually see 144 KTAS at WOT and 2400 rpm at 10000' with a fuel flow of 11.5 GPH.  With the high fuel flow in climb, this gives me an overall fuel economy of 11-11.5 NMPG, which doesn't seem too great for the speeds I am seeing.  Any inputs would be appreciated.

[Bob Siegfried$comma$$ II]

Curtis-

I would try using full throttle during your cruise climb, which should give you some extra fuel over the 25" MP setting. That should increase the detonation margin and reduce your CHTs. Your efforts to ensure the baffles are in good shape are very important. Seal any detectable leaks with RTV silicone.

Regards,

Bob

[Mike Edwards]

In my C33 I find the original design but aftermarket baffles curl the wrong way on one side.  They curl down instead of up.  If I reach in (when the engine's cool!) and pull each one up so they lie on top of the cylinders and wiring, then the cooling is noticeably better.  I have tried to "train" them to curl the right way for years without success.

[Curtis Weddle]

It will definitely pump more fuel if I push everything forward.  I suppose I was just looking for more options than throwing more fuel into the engine, as it eats quite a lot as it is.  I know it's not a Toyota Prius, but I've been trying to get my fuel economy a little better.

I suppose I'll look more into the baffle issue - it seems they've been minimally maintained, and I could probably get some of the nice silicone material to replace the rubber stuff on there.

Still waiting for an answer from D'Shannon.  I am expecting them to say that the compatibility of their baffle kit with the A33 is predicated on installation of their IO-470N, IO-520, or IO-550 STC.

Will update when I hear from them.

Curtis

[Curtis Weddle]

Looking at the text of the STC on the FAA website, is reads "for aircraft as modified by STC...," so I believe the IO-470N installation is a prerequisite for the baffles.  

Curtis

[William Jones]

Did you get the D'Shannon baffles?  Did they improve cooling?

I have a B33 with the 470K engine and your original post reads like what I experience.  I have a JPI engine analyzer.  Cylinder #3 is about 20F above the others and cylinder #6 runs 30 to 40F above the others so I takeoff and climb with one eye on the JPI.  110 to 115kts indicated keeps #6 right at 400F with mixture full rich.  For short field takeoffs I have no choice then to let #6 go above 400F and once up and away I can then let the speed build and get it to cool down.  Going through 3000 feet I have to start leaning or the engine starts to run rough.  At cruse I can keep #6 at 400F with 12.5 to 13 gph with 22 to 23 inches and 2450RPM.  Even now with the cooler weather I have to keep a close watch on the JPI.

I also have the Gami injectors and each time I try to go LOP the engine quits so I gave up on that.

My mechanic is suggesting new baffling but I am wondering if that will really help.

[Mike Edwards]

I talked to D'Shannon at the ABS convention last weekend, and they said they have no plans to build a baffle kit for the IO470K.  They said because the cylinders are different it would have to be a separate design and build, and the market is not big enough.

[Ronald Roberts]

We had a similar problem with our Debonair (IO-470J) and the OEM baffles. They were cracked,patched and in poor condition. We replaced the large rear aluminum baffle with one from SRS Aviation (they advertise in ABS)and have had lower CHT with better cooling. One caution, ours didn't fit exactly and needed some field modification. Suggest ordering the parts separately and match drilling for you aircraft. Dave at SRS was very helpful and the baffle is .050 aluminum very stout.

[D. W. Brown]

In 2002 we upgraded our BE35-C33 fm IO-470K to -470N w/BD'S baffle kit. Just pulled -N @ 1917 hrs for Ly-Con O/H.  W/fixed cowl flaps, we're lucky to get CHT's above 300F, & need to lean in climb to obtain EGT's up to 1420F. All OP's are 100F+ ROP during Climb, Level & Descent, w/CHT's @ best reaching 350F in climb. Gami's & JPI EDM-711.

[Earl Pounds]

Same problem on my 470K. Crummy flexible baffles and lotsa leaks around the aluminium bits. Replaced the flex with new blue rubber and patched and filled all the other openings. Number 6 CHT seems to have dropped 40-50 degrees and the others have gone down, but not as dramatically.   

[Marcelo Cunill]

Curtis,

same problem also on my Debonair 35-A33 with IO-470K. Also had asked DA?Shannon for making baffle kit and they told me not to be interested.

Had some post about the same problem with member Robert Willms, topic "IO 470K Baffling" started on April 01 by John Judson. Robert sent me some pictures about the job he did sealing all around the engine to improve air flow through the cylinder fins. I am waiting my anual for working on that.

Using full throttle will help you not only by adding more fuel but going faster for better cooling.

Ronald, while looking at SRS Aviation website I saw that they not only sell the rear aluminium baffle but also 470 Series Silicone Baffle Kit; what do you think about it? Why didnA?t you choose to install it?

Did anyone installed this Silicone Baffle kit from SRS ?

[Eric Iversen]

I'm with you, guys.  My '62 Deb has the same issue on climb-out.  

I often see temps just above 410, but only on #6, and only until I can get her to pattern altitude and nose her down to pick up some speed. If I climb out below 120 knots... back up it goes.

Has anyone here seen or performed the airflow mod on the CSOBeech site (http://csobeech.com/Bo-Flow.html).  This seems to make a lot of sense, especially once you look down there and see the labyrinth that is the nosebowl structure.  This mod cleans that up.  

I can confirm the claim on the CSOBeech page that the air flows back out the front of the cowl.  When I had a pushrod tube leak, the oil would mist and get on the windscreen.  There was no streaking on the cowl hinges, but the back of the prop close to the spinner also had a misting of oil on it.  When we replaced the pushrod tube grommets that problem went away.

I also wonder if the little "lip" on the bottom of the cowl, where the cowl flaps would be, isn't also messing up the airflow, especially at high angles of attach that we see at takeoff.  I can't help but think that between the high angle and the sharp edge, the air isn't practically being pushed up from the bottom as it burbles over that hard edge ().

For now, I just get to an altitude where I can reduce my AOA as quickly as possible and proceed to cruise/climb to keep things below 400, even if just barely below.

[Blair Simpkins]

I had my baffle seals replaced with rubber and my fuel flow bumped up to max. With full bag of gas and me (165 lbs) I climb out at Vy (102 mph) WOT for the first 500 feet and my digital CHT gauge reads 390-415 depending on OAT. At 500 feet I back off to 25" x 2500" until I reach 1000 agl. I then hold 1000 agl until I accelerate to 120 mph and reduce power to 23" x 2300 and resume climb. By now (1-2 min) my CHT is about 390. A 200-400 fpm climb keeps my CHT under 380. Cruise CHT is around 360 and I lean to 1400 EGT on hottest exhaust.

The point I'm trying to make is, the Debonair is a hot running engine. 100 mph is just not fast enough to cool the engine at full power (take off).     

1963 B33