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Jabiru temps
I'm having a really bad time getting my CHT and EGT temps down in my Jabiru 3300. I did a lot of work on adding an extension to the lower cowl lip and adding a "fence" above various cylinders to move air back toward the rear of the ram air ducts. I had moderate success prior to early April, but then went to Ireland for 2 weeks and returned to outside air temps that were 40 degrees warmer than when I flew last.
Naturally, now my CHT and EGT temps are way too high. CHT's are high on #3 and #5 and EGT's are high on #5 and #6.
Today, I enlarged the Needle Jet from 2.85 to 2.90 mm and go some better numbers, but only could stay in the air for @ 5 minutes before the CHT's got dangerous, so I don't know how high the EGT's would have gone if I had flown longer?
I was turning 3160 rpm at 70 mph climb-out.
Replies to This Discussion
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Permalink Reply by Ian McClelland on
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Your argument is convincing. I have not and can't get access to the Yahoo Jabiru engine group.
What was Pete from Jab USA's comments about this?
I see Jabiru have published another Jabba chat.
Some interesting reading regarding a new efficient ground adjustable fiberglass prop design.
They are now recommending W100 oil if you are running on Avgas and to change the oil every 25 hours.
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Permalink Reply by Dr. Edward L. Olds III on
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Adrian,
Thanks for the interesting take on the Jabiru. I am still messing with fixes and trying extensions and baffles. Had some progress today.
Ed
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Permalink Reply by John Austin on
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Ian,
Sorry if I wasn't clear, but in response to your Wednesday forum post, the portion of my reply in italics is a direct quote from Pete at Jabiru USA. On the Jabiruengines Yahoo forum, in response to a query from a member, there is another response from Jabiru USA and this is a direct quote:
That is also in the manual. See the Overhaul manual JEM-001-3 which is on
line at www.jabiru.net.au . The arrow points to the propeller end of the
engine.
Jabiru USA Technical Support Team
931-680-2800There is a long discussion on that forum about this with very strong opinions on both sides and even references to papers from MIT! I'm not expressing an opinion contrary to Adrian's - I don't have an opinion at all! - I just wanted to let you know what Jab USA says since you can't access that information on Yahoo.
John
N750A
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Thanks John.
I was hoping Jabiru had a technical reason to explain why they install their pistons against engineering convention. Or is it that they can't admit they got it wrong now due to the consequences - warranty claims, loss of pride etc.
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Hi Ian,
There are contrary arguments ... I have no earthly idea who is correct! This may boil down to "how many angels can dance on the head of a pin!" I've got 140 hrs on a 3300A that is purring like a kitten (and cool!), so I guess I'm just fat, dumb, and happy! LOL!
Regards,
John
N750A
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Permalink Reply by adrian dines on
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Hi Ian,
your right about warranty etc. nearly 7000 engines ,all with pistons reversed [fitted wrong way] against all engineering convention. Under our consumer laws they would be required to fix all of those engines, imagine the cost. I have asked the question ,why back the front, no answer and i doubt there will be any answer under the circumstances. people have died behind these engines,with such things as props coming off, flywheels coming off & i'm fairly certain it's probably down to the pistons, From experience i have found auto engines with pistons reversed ,present with sim problems i.e. harmonic ballancers separating, blown head gaskets, running hotter than usual, we even had a holden 202 blue engine that broke all flywheel bolts, because of damage to crank flywheel face we had to dissmantle the engine, where it became appparent that the pistons were reversed, prior to this the engine broke the end of the cam shaft right on the end next to the drive gear twice. After reassembling the engine there were no more problems with regard to the above.
This engine was usual driven fairly fast for long periods.
They say the proof of the pudding is in the eating, well we have changed a couple of engines[ and i have heard of other's that have done so as well], were very happy with the results so far with over 200 hrs on one of them mostly in high amb. temps up to 42degc, usualy you would have halt flying after 35 degc .
cht are down 50 deg f on average 50 rpm gain static small drop in fuel burn, very smooth engine. a six pures like a kitten , but will pure even better w/ pistons turned arrow to flywheel.
engine research center has some good info on this subject , will try and find site and get back with it later today or tomorow
REGARD'S,
Adrian Dines
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OK. I wonder why Subaru don't follow this convention with their EA82? horizontally opposed engine?
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EA 81/82 has no offset, pin in center, not opposite off set like jab. subaru allso has longer con rods and a heavy flywheel. long enough rods provides same benifits as off set. jab has the smallest s/r ratio i have seen and light flywheel ,hence the need for offset in the right direction
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Permalink Reply by John Edwards on
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There has always,always,always been cooling issues with Jabiru when mounted on a 701/750.
Yet, a small minority(including Zenith) seem to have figured it out.
Cant they pass this information along to those who have not?
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John E.,
It's obviously challenging to cool the Jab in a high-drag, low-speed airplane! To further complicate the issue, the Jab 3300 (that's what I have so I can't speak to the 2200) has been in a constant state of evolution. I've made this point before, but after serial #2331 with the reworked plenum, runners, and diffusers for more even mixture distribution, hollow push rods, deletion of external oil lines with consequent change in cylinder heads to increase cooling fin area, I think it's an "apple-to-oranges" comparison of difficulty cooling the engine. My engine, #2427, typically runs low-to-mid-range 200'sF in winter and mid-to-upper 200'sF in summer. On a long, continuous climbout, I might see one cylinder pop up to 305F or so, but it falls right back in line in cruise.
My oil temps were marginal after break-in (211F is continuous limit), even with a 10-row cooler. (The standard FWF kit from Jab USA has a 7-row.) The front of the sump is heavily finned and a very effective cooling surface. Zenith has a kit to duct high-pressure air from a hole in the cowl to the finned sump which is very effective and lowers oil temps immediately 10-15F. HOWEVER, it's also pumping additional high pressure air into the lower cowl which can aggravate cylinder cooling. You need the most negative pressure you can get to aid flow through the cowl. I designed an oil sump cooler that bleeds ram-air off the left ram-air duct in front of the inlet dam. It gives the same 10-15F immediate drop in oil temps, but doesn't aggravate CHT's, in fact, my CHT's went down! (About 20-25% of an "air-cooled engine" cooling is actually done by oil cooling!) My theory is since I'm "borrowing" high-pressure air that's already in the ram-air duct, I'm probably not adding additional high pressure to the lower cowl ... it was going to ultimately wind up there, anyway. For whatever reason, it works and works well! Going from the 7-row to the 10-row cooler didn't help much - my gut feeling is that if I had gone to the oil sump cooler duct first, the 7-row would have been fine.
So, here's my opinion on how to approach it for the 750, but with the caution that engines earlier than #2331 may be more challenging:
(1) Extend the cowl lip 2" for a total of 3" to increase lower cowl negative pressure and protect cowl outlet from ram-air effect in extended climb at steep attitudes. (This is recommended and covered in the Jabiru installation manual.)
(2) Ensure that ram-air ducts are tightly sealed to cowl inlets and are tight against the cylinders. I made little "fences" of aluminum strap to hold the fiberglass tabs of the ram-air duct against the cylinder heads.
(3) Install an oil sump cooler but do NOT put another hole in the cowl! Duct air off the left ram air duct in front of the dam (there's a convenient flat spot just in front of the dam beside the "bump" that clearances the oil filter.) Spruce sells a flanged 2" adapter for the SCAT.
(4) Consider using the wood Sensenich prop. I've seen it reported several times that this prop cools better than any other. The theory is that because it is wood, it still has a relatively wide blade near the hub that moves more air into the inlets. A lot of adjustable and composite blades are relatively "skinny" near the hub.
That's the four most effective things to do to cool the engine. Now, to "tweak" it further,
(5) #5 is infamous for being the "hot" cylinder and mine was, too. I extended the ram-air duct (with aluminum) down the backside of #5 to keep the cooling air on the fins as long as possible. It is no longer the hottest cylinder!
(6) I fabricated end-plates that block the gap between the cylinder fins and cover some of the access holes in the fins for the cyl. head bolts. This keeps cooling air from spilling out laterally between the cylinders and forces it down between the fins to do more cooling. Helped a few degrees on the right bank. Although the left bank was already cool, I installed them anyway just so it wouldn't "look funny" (HAHA!), but it really didn't do much for the already normal temps on that side.
(7) I fabricated extensions of the dams at the ram-air inlets to block some of the airflow to #1 and #2 (they're always the coolest and this forces the air further back in the ram-air duct instead of dumping around #1 and #2). I also made a ramp that curves up over the barrel of #1 and #2 and terminates at the apex of the curve of the barrel to further direct air further back.
(8) I had a tiny bit of stumble at WOT, so Pete at Jab USA gave me a vaned inlet tube that installs just before the carb to straighten the airflow and reduce turbulence. It cured the stumble, and made my already-tight EGT spread even tighter! Also, the engine seemed to run a few degrees cooler!
The end result at 140 hrs is an extremely smooth, powerful engine. I started oil analysis at 100 hrs and Blackstone Labs said at 100 and 133 hrs that there was "less wear than average" and "it looks like this relatively new engine is getting off to a good start." Can't argue with that!
So, that's my story and I'm sticking with it!
John A
N750
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Permalink Reply by Tim Treat on
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... The Jab is an awesome engine and if one will take the time to do a proper installation including jetting and prop pitch, the heat issues are non existent. I fly in the mountains and see temp changes of 40 degrees or more and altitude changes of 5000 ft every flight. Sadly, some of you go cheap and don't have mixture control. Install mixture control (I run a rotec carb) and go fly!
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Permalink Reply by Peter Autenried on
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Did anyone install the Rotec liquid cooled cylinder heads? And if so what was the experience?
http://www.rotecaerosport.com/products/lch/
How about the Rotec Throttle Body Injector?
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