IO-360 to O-540 Engine Upgrade Tips

[Baloo]

About 7 months ago I bought a beautiful plans built Bearhawk from builder Gavin Chester. His attention to detail is second to none and needless to say he built a magnificent aircraft.it has the 200hp io-360 and since I bought it I have been struggling to get anywhere near the performance numbers listed in the BH Specs even those for the 180hp variant.

After speaking with several other builders (4 to be exact) that have similar setups to mine it appears that the performance numbers that I am seeing are fairly consistent with the other aircraft and are on average at least 25 - 30% less than the published sales sheet specs for the 180hp Bearhawk specifically when it comes to climb performance.

Before I go any further I want to publically apologize to Gavin for a rude and unfair accusatory email that I sent to him last week. I let my frustration in finding where the performance had gone get the better of me. I am not a builder and have nowhere near the skills or knowledge that Gavin does and was out of line in sending him the email that I did. I am learning as we go here and enjoy harvesting knowledge from the likes of all of you!

So here we are, I have a beautifully built aircraft but need some more jam for the kind of flying I do. More specifically I need more climb performance and would like to have some reserve power for cruising in the mountains.

I have ordered a Barrows O-540 which won't be ready for the better part of 10 months. In the meantime I would like to start getting the necessary parts and pieces in play to minimize downtime when the engine comes. I will be going from an injected 360 to a carbureted 540.

I am planning to utilize my existing electric fuel pump as the priming tool and for the time being will use my Hartzell 80" CS Prop.

Please help me build a list of parts that I will need to complete the conversion and any tips on modifications that will need to be made to my airframe.

So far the list includes:
- O540 Dynofocal 1 Mount
- RV10 Baffel Kit
- Baffel Material
- Exhaust System (Recommendations?)

I'd appreciate any relevant tips or advice.

Respectfully,
Ryan

[AZBearhawk272]

Ryan

Not completely understanding the comment on needing more " jam" for the type of flying
you do.
All flying is a mission compromise proposition. The Bearhawk is a very capable
Aircraft, that said,all of my experience has been in 540 powered aircraft.

I want to clearly state that in numerous backcountry operations a 540 often has too much power!

Personally I think the IO-360 would be an ideal platform.

I would look at shedding some weight, adding VG, an efficient exhaust system and
possibly a different prop. And turbo normalize? Clean up airframe and cooling drag.

The 540 will increase weight, burn more fuel,
Harder to see over the longer nose. Longer landing roll and higher approach speeds.
And tend to be nose heavy........
Most back country ops cannot utilize full power on takeoff.

And that 80 In prop on most, is not enough to absorb the engine power. So $$$$$$

Interesting situation to contemplate.

Kevin D. # 272

[Baloo]

Kevin,
Thanks for taking the time. I guess it really depends what your definition of backcountry is and in what environment you are operating in.

In my case it's large mountains and short landing areas. My biggest issue with the 360 is my limited obstacle clearance climb capability and lack of reserve power at any altitude needed to operate in the mountains. When I talk about mountains I mean the Rockies.

Having spoken to numerous other 360 owners our numbers are fairly similar and that is sub 800fpm initial climb especially on warmish days which in my application just doesn't cut it. I'm not so worried about cruise speed as I am tired of clenching my ass cheeks trying to clear the trees.

Having only flown behind the 540 you have no idea how good you have it! I've flown both power plants and they are not event in the same universe.

If my mission was leisurely cross country flights for a burger the 360 would be fantastic but in using the aircraft to the edge of its STOL abilities the 540 seems like the way to go.

That said I do fly in and out of 600ft gravel bars but only if there are no obstacles.

Again, the question was not should I do the conversion but how best to do it.

[marcusofcotton]

I'd go with Vetterman exhaust, Clint is on this site.
1/2" fuel lines, but I'd consider getting rid of the electric fuel pump to save weight and complexity.

Gavin made a beautiful plane with lots of nice features, but it is on the heavy side for STOL ops - probably smooth in turbulence though. For STOL I'd look very critically for where weight can be saved.

[Baloo]

It is a little heavy. I have thought quite a bit about how to lighten it up and would take any ideas that you might have. Some things I have considered are:

Interior: He did a magnificent job finishing the interior. I took out all the interior finishing aft of the main doors and it weighed 13.8lbs. For the 14lbs it gives it a nice finished look and is staying in.

Back Seat: Weighs 30lbs and is removed for STOL trips

Prop: Hartzell aluminum prop 53lbs + 10lbs for dampning ring. Could be reduced to 44lbs by spending the $$ and going with a MT or Whirlwind prop.


Other ideas??

[Gash]

What battery are you using? I had the Odyssey PC680 in my RV-8 and saved 11 pounds by switching to an EarthX ETX680. Same size, better cranking, and super light. I did a lot of research on the EarthX batteries for experimental aviation before I made the switch, and I'm really glad that I did it.

Another way that I cut 20 pound was off my own body weight. The only way I could muster the will power to lose weight was to think of the aviation benefits. Crazy huh?

[Battson]

I still haven't been convinced that an EarthX can crank a -540 well enough. They are a lot different to a -360. Do you know of anyone using one in a -540 or -550?

[N942VT]

You're heavy and that must make a hell of a difference. If I was seeing sub 800 fpm something would be wrong, double that normally, hot days are at least 1000. Look, more power is better but I don't want people thinking a 360 Bearhawk is an underpowered machine good for only cross country, come fly with me sometime. Hot, high heavy, 50 more hp will always be better but if you could lighten that bird up either way you would be happier.

[MattS]

New member here. I am looking at purchasing a 4 place BH here in Brazil that has a Continental IO360 with a CS. I flew it last week and was a little disappointed with the fpm. Ryan, what is "a little heavy"? The W&B they showed me was 1520 lbs empty. What is a realistic EW for a BH with this motor? Thanks! Matt

[Baloo]

A little heavy is 1562lbs with unusable fuel and the backseat in. I am running the small odyssey battery bolted to the firewall.

All 4 other 360 owners saw sub 800fpm climb rates consistently. I haven't scratched 1000fpm off the ground not even on the coolest of winter days.

Don't get me wrong I use the 360 off strip and it does a pretty good job in and out of 600ft but forget it if there are any obstacles even at the end of 1000ft.

At first I thought it was just my engine but after speaking with some others perhaps it is just the combination of airframe, motor, prop and weight.

I'm my case I'm a bit heavy so perhaps the extra 60hp will overcome the weight and get me back in the game with respectable obstacle climb.

By my estimation after the engine swap and if I change the prop I should end up with the same weight.

[Battson]

Do you mean 50 hp, if you are going with a carb?

A better way to think of it is this, it takes about 100hp to get a plane that heavy into the air. Every hp after that is added performance.
So you are going from 100 to 150 spare hp. So about a 50% increase in spare power.

Despite what has been said, I believe you can't have too much power in a backcountry situation. Power = safety margin, and too much safety margin is not a common complaint.

[Baloo]

Typical mission weight is around 2000lbs so all things being equal empty weight really shouldn't matter if the mission weight remains the same.

[Baloo]

I don't want anyone to get the wrong idea here. The Bearhawk especially the one Gavin build is a first class aircraft and the 360 engine is a great power plant. All I am saying is that in my application and mission profile I am converting to go with the 540. That is the beauty of experimental aircraft every ship is slightly different and every pilot's needs are different.

The 360 is great but it really depends on your mission profile. Much how your selection of tires will depend on your mission needs 8" tires vs 31" tires both do the job and both have their downsides but each suits a different mission much like engines.

[Bcone1381]

Baloo, I am guessing, is Taking Off at some very high density altitudes which the majority of us never see. An airport elevation of 6800' in the afternoon with 85 degrees, the engine will behave like its about 10,500'. My college Aerodynamics Course told me that Aircraft climb due to Excess Horsepower. So, 60 extra horse power will make a lot of difference in climb. I am sure a takeoff/climb with an IO-360 making only 20 inches of manifold pressure would be disappointing. I doubt he is making 150 horsepower in those conditions.

I might also add that Baloo did not desire a discussion about the suitability of the IO-360, rather it was a request to help him develop a parts list, tips and advice for the swap to the O-540.

Would you save 50+ pounds off the nose by going with a Cato fixed pitch climb prop?

[whee]

I hesitate to say anything but since only a couple people have actually answered your question I'll chime in. I researched engines extensively and the O540 was a very close second choice for me. I actually almost bought a core 540 and would have if it hadn't been a unique model.

If I were doing the swap:
Engine mount from Bearhawk aircraft.
RV baffle kit.
Vetterman exhaust
I'm partial to McCauley props and I think there is a 2 blade 84" version approved on the 540 but if you can afford a MT...
If Gavin followed the recommended crank flange distance recommendation the cowl modifications should be minor.
I'd ditch the fuel pump and install a regular primer.
Are 1/2" fuel lines really necessary? Thought I read in the Beartracks that Bob recommends 3/8" lines for both the O360 and the O540.
Really pay attention to the baffling. From what I was able to study out the 540 Bearhawks can run pretty hot. One Bearhawker told me his oil temp would be close to redline if he shot 5 touch and goes in a row.
The silicon baffle seal material from spruce works good but it is ugly orange. I can't remember where but there is a place that sells the same material but in different colors.

Good luck with the swap.

[Battson]

The 1/2 lines idea is a pipe-dream I had too. But.... it would be so hard to implement, and then the engine fittings choke it to 3/8 anyway.
The 3/8 is heaps, provided you use the right design and avoid restrictions like too small a fuel transducer, standby fuel pump, unnecessary bends / fittings.

[Baloo]

Bcone,
Thanks for taking the time to post and for clarifying that I am looking for engine swap tips not opinions on my decision to swap which is a personal one and a decision that has not been made lightly given the expense. While my home base is near sea level I do operate in the mountains where density altitude for take off and cruise are serious considerations.

I haven't considered going to a fixed pitch prop. Despite the weight I like the flexibility that constant speed gives me. Once you go CS it's tough to go back. Regardless of prop choice I'll be able to shed 10lbs off the nose with the 540 by getting rid of the dampener required for the 360 and 80" Hartzel.

Whee,
Thanks for your post, keep the tips coming.

[N942VT]

Baloo, I am guessing, is Taking Off at some very high density altitudes which the majority of us never see. An airport elevation of 6800' in the afternoon with 85 degrees, the engine will behave like its about 10,500'. My college Aerodynamics Course told me that Aircraft climb due to Excess Horsepower. So, 60 extra horse power will make a lot of difference in climb. I am sure a takeoff/climb with an IO-360 making only 20 inches of manifold pressure would be disappointing. I doubt he is making 150 horsepower in those conditions.

I might also add that Baloo did not desire a discussion about the suitability of the IO-360, rather it was a request to help him develop a parts list, tips and advice for the swap to the O-540.

Would you save 50+ pounds off the nose by going with a Cato fixed pitch climb prop?

He was making some general comments comparing one to the other, I was simply trying to say that's not what all of us see. Don't get so sensitive.
Good luck to you Baloo