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Lufthans 06-02-2020 03:10 PM

Hans' RV3 - O-320 with a twist
Hi guys,

After a hiatus of about a year, the withdrawal symptoms from selling my share in the RV-4 became too much. And so I have bought myself a -3. The plane is in need of a fair dose of TLC, which I plan to give it.

Coming from a number of Subaru powered aircraft projects that are still racking up trouble-free hours and outperforming all expectations, the knee-jerk reaction was to lose the O-320 and put one of my Subaru conversions on. But I really think I'll pass this time and go with Lycoming. With a twist.

My plans thus far - and comments VERY welcome. These Lycomings are new to me ;-)

1: The plane comes with a mid-time O-320 C3B. I believe it to be somewhat of an oddball, only used on a twin (can't remember which one) in the mid-1950's. Old style parallel mounting points. 7.0:1 compression. Hollow shaft. Carburetted. I don't fancy buying a new engine and then try to get this one off my hands. So the plan is to keep this engine as the starting point.

2: As much as I'd love to go all-out, paying 13K for a C/S prop is not in the books for this plane.

3: I want to run mogas in it. 100LL costs upward of $12 per gallon here, even in this economy. Mogas is still $7-ish per gallon, but gets things within the realm of affordability. Mogas here is 98 RON, which is about 93 in US measurements.

So, the plan for the engine:
Take the cylinders off, do a valve job, check the valve guides.

Change the pistons for 8.5:1 items. I was thinking of the ASC75089F from Combustion Technologies. (what's the word on their products?). I believe 8.5 is about as far as I can go with Mogas, right?

Do I need thick piston pins for these?

Then - Can I fit new rings, or should I then also hone the cylinders?

Injection and ignition will come from two Link ECUs:
Each tank will have its own high pressure fuel pump (preferably IN the tank to eliminate all vapour lock issues) and fuel return line. Each side will have its own fuel rails and fuel injectors. And its own ECU.
Each ECU will also run its own set of ignition coils and (automotive) plugs.

Since you don't want both ECUs injecting fuel at the same time, two externally connected switches (to eliminate any single point of failure) will kill the power to the injector drivers of one ECU at a time.

There will be no more fuel selector valve. The ECU that is at play for injection determines from which tank fuel is used.

Each ECU has its own battery en bus. Batteries are fed from the alternator through a FET coupler.

So basically the only thing that is not redundant is the alternator. I can live with this. If it fails, I'll have two batteries to run things until I land.

If anything else fails, it will be on one site. I then also lose the availability of the fuel in that fuel tank. My flying is not between Iceland and Greenland, so I can live with that.

So, to continue:
Now that the carburettor is no longer needed, and carb icing no longer is an issue, I might as well get those intake runners out of the sump and get some cold air into the engine, rather than lukewarm. So I'll weld up a new oil sump and new intake manifold, with one big throttle body, and some ram air.

And yes, I know. There are vendors out there who deliver excellent products for what I am thinking of here. A few of them are even RV pilots. It's just that after half a dozen engines (including a 600 hp Ferrari V12 in a car project), I feel up to the challenge of developing my own mouse trap.

So... What do you guys think?

Oh, and what power output can I expect? I figure coming from 150 hp, the 8.5:1 will give me 160. The fuel injection and more accurate and stronger ignition 5, the cold air induction another 5 and maybe a handful for better flowing of the intake? So between 170 and 175? Or would that be overly optimistic? It would be somewhat important when ordering a prop from Catto...

Michael White 06-02-2020 04:18 PM

A lot of people will tell you that as long as the engine is making good power, not making metal and not burning huge amounts of oil, leave it alone and fly it until it needs an overhaul, then do the re-build. This is something well worth thinking about.

If/when you do the rebuild...if you're going to replace the pistons, new rings and a hone job are not options. The new pistons should come with new rings, so use them, and a hone job will help the new rings seat properly, reducing oil consumption, so it's best to do it while you have the pistons out. It would also be a good idea to check the connecting rods or even replace them as well. Cheap insurance...

Not sure, but you may be right about the 8.5:1 pistons being the the most you can go for mogas. I did a quick wiki-check and all the mogas rated variants they listed were 7:1 or 8.5:1.

I think 160 - 170 HP would be a realistic expectation for what you've got listed. To get much more you'd need 9.5:1 pistons and 100LL.

Good luck with the -3,and let us know how it turns out!


sf3543 06-02-2020 07:14 PM

I think I would just upgrade the pistons, hone the barrels and get new rings.
You could do that easily, run MoGas and in the future, if you want to do all those other things you won't have to redo anything.
You just might be satisfied with how it flies.
Possibly get a better performing prop.
All that other stuff sounds heavy to me.

Does your MoGas have ethanol in it? If so you might want to look at anything in the fuel system that may not be compatible with it.

Ed_Wischmeyer 06-02-2020 07:22 PM

You've undoubtedly got a narrow deck crankcase, and the engine gurus I've talked to got agitated when the topic of conversation got around to higher compression ratio because the crankcase could be more prone to cracking.

My suggestion is to live with the lower compression ratio and lower power. Do the math and figure out how much more cruise speed you'll get from a higher compression ratio (when I did that exercise on my RV-8, I think it was only a few knots) and how much more rate of climb you'll get.

If you've got an O-320 in a -3, you've got a rocket ship already. As for a constant speed prop, your plane is probably at a forward c.g. already, and the constant speed prop will likely take a little bit off the handling.

johnf_1 06-02-2020 11:33 PM

Mid-50s O-320
Hi Hans: I fly behind a 1955 O-320 150 hp from an Apache. It came to me with about 3200 hours TT and 7/1 pistons, thin wall pins, and 1/2 valve stems (they came initially with 7/16, so watch for this) I flew it from 1986 until 1990, and then rebuilt it with chrome barrels, thick piston pins, o-360 rods, and 8.5/1 pistons. With my old Pacesetter 200, it turns up to 2850 at 8500, so extending the hp curve in the manual from 2700 to 2850, it is making 170-175 hp
Confession: I did not install longer studs and did not use "B" cylinders with base plates. My rationale is that the engine see 160 hp for a pretty short period of time-sea level take off till the first power reduction or the altitude at which it makes 150 hp (around 3000) Part of that rationale is that I get to 500 feet pretty quickly, and can make a 210/30 turn back if one of the cylinders pop off.
I am told it is a common SuperCub/Pacer uncertified mod and no problem. I have about 700-800 hours on my set up with no trouble, and operate from a field elevation of 125 feet.
A 3 with a 160 engine will be fun. Back in the day, Jim Ewing had a Rocket 1 which was a 3 with an angle valve o-360 pumped by Lycon....I recall a Bakersfield Bunch lunch in the late 80s, and he pitched up to pretty close to vertical and climbed like a homesick angel...John N95JF

Lufthans 06-03-2020 02:55 AM

Thanks guys. Lots of good info here!

So basically it is either keep the pistons, rods, rings and cylinders together and be satisfied with 150 hp (or whatever it turns out with after the rest of the mods), or go all-out, but then be worried about the fact that it is a narrow deck engine.

Steve: the stuff that I am proposing isn?t all that heavy:
Add two EFI fuel pumps at 1 lbs each
Subtract a low pressure fuel pump
Add a fuel return line
Subtract the fuel valve
Add to ECUs (at 1 lbs each)
Add fuel pressure regulators, fuel rails and some piping.
Remove carb
Add (much lighter) throttle body
Swap out one sump for another.

All in all, I?d say I will not gain more than maybe 5 lbs.

We?ve got *some* ethanol in our mogas. Up to 5%. However after doing all this, my fuel system is 100% automotive. Could cope with much more ethanol than that.

Reason I want to go the EFI and electronic ignition route is 1: better starting, 2: smoother running, 3: reduced fuel burn (at $7 per gallon not something to sneeze at), 4: auto lean. After flying behind smooooooooth Subarus all the time, there is no way that I am going back to the 1930?s in fuel and spark.

Ed: good point about the higher compression ratio in combination with the narrow deck crankcase. I don?t care about the extra top speed (a theoretical 4.5 mph, so indeed almost negligible). The 250 fpm extra climb rate that 10 extra hp provides DOES matter to me though. My flying consist mostly of either formation flying, or dogfighting cumulus clouds. Quick dashes up to the cloud base, have my 15 minutes of fun and land again. 250 fpm matters. However, a cracked crankcase also matters.

Food for thought.

Rick RV-4 06-03-2020 10:05 AM

Hi Hans,

Just my humble opinion, but for your intended goals (high climb rate, quick and short hops, and no need to squeeze out a few extra knots of top speed), it seems like choosing the right prop may do just as much for you as doing all of the work on your engine.

I have an RV-4 w/ a stock O-360 and dual P-Mags. I had a metal Sensenich prop on there, and just switched to a new Sensenich ground adjustable prop. The change in acceleration and climb rate, and smoothness was awesome. I do have the prop set a little more towards the climb side, but still get very good top end speeds. Solo, I see initial sustained climb rates of 2,300 - 2,600 fpm for the first few thousand feet, and the angle is impressive. That?s in Netherlands type of conditions (sea level, 15c).

Rick RV-4 06-03-2020 10:09 AM

Follow up
And the EFIs will definitely help your fuel burn. Flew a 1,500 mile trip with three other RVs (two fours and an 8). I was always burning less than the other guys (1.0 - 1.5 gallons per hour) based on how much fuel we?d each get when we?d fill up. And I do run rich of peak since I?m not fuel injected.

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