Homebuilder BS

[Colonel]

So I get the EAA magazine in the mail. Flipping through it, there's a guy with a Skybolt
bragging about his 370hp engine, which sure looks to me like an angle-valve Lyc 540.

I can see it's direct-drive so it's limited to something less than 3000 RPM (past that,
the prop tips are supersonic and thrust reduces).

The cylinder BMEP required to produce that much torque at that low an RPM in that
engine exceeds the capability of 100LL. Is he running purple 115/145? And how is
is getting that BMEP? You can't do it naturally aspirated so he's either running nitrous
or a turbocharger or a supercharger on his Lyc 540.

No, he isn't. Just more homebuilder BS.

[Scudrunner]

He probably got the K&N cold air filter kit installed we all know that add 100HP

[Slick Goodlin]

Not discounting someone lying (it’s easy, fun, AND cheap!) is there anything that could drag a 540 kicking and screaming up to that power? I feel like I’ve seen people talking lately about Lycomings in displacements I’d never heard of, like 380s and whatnot; could they have bigger bore jugs that would fit a 540 case?

IIRC the Reno guys are claiming north of 700hp from some 540s though they’re probably flirting with rapid unplanned disassembly. Me, I’d probably try and hunt down one of those Orenda V8s that were almost popular years ago. They just seem like they should have a much higher ceiling on what they can do.

[Colonel]

I think it’s one of the clone experimental engine companies makes a Lyc four 390 or something like that.

Lycoming made an AEIO-580 for a while but oddly it’s not very popular.

Ok. To get really big horsepower out of a Lyc 540 you either have to spin up the RPM and add a gear reduction unit, or up the torque below 3000 RPM with direct drive to the prop.

No one except me likes gear reduction so we have to insanely up the torque and we do that with BMEP

We need to get a lot more oxygen and very very high octane fuel in the cylinder to do that. We can either do that with positive displacement or nitrous.

I don’t know of any add-on superchargers for Lycomings.

People have added turbochargers to aircraft engines but they are not as popular as you might imagine. I know a guy added a turbocharger to his Pitts but the gyroscopic precession of aerobatics destroyed his bearings in short order. Probably lost oil pressure, too. I’m sure he didn’t have an accumulator which is essential with a wet sump.

Which brings us to nitrous which is the way to go. High octane fuel, back off the timing and a kevlar tank to save weight. I might suggest wet vs dry for these power levels as well as a vibration sensor strapped to the heads.

Another great thing about nitrous is no intercooler which is essential for positive displacement because of adiabatic compression heating. Methanol injection can help with this.

Nitrous is perfect for a race aircraft application. Didn’t the Luftwaffe use it in WWII?

https://en.m.wikipedia.org/wiki/GM-1

Pro tip: if you’re going to wildly increase the BMEP of your Lycoming, the existing cylinder base studs and through bolts just aren’t going to cut it.

Add external straps that go all the way around the engine, tying pairs of cylinders together. Personally I would design a girdle that bolted on underneath that valve covers.

[Colonel]

Fun fact: the GTSIO-520 engines I used to fly with in the C421 produced 375hp on low octane 100LL by spinning up to 3400 RPM with a 3:2 gear reduction to the prop, and a turbocharger with a little (but not a lot of) boost. Maybe 10 inches for a few seconds during takeoff?

Everyone except me hated those engines. I loved them. Smooth, powerful and reliable. At least with my hand on the engine controls.

[Colonel]

Back of the envelope: if you really want to go turbo, as a rough rule of thumb you double the intake manifold pressure from ambient sea level with an additional 15 lbs of boost, you might be able to double your stock angle valve IO-540 from 300hp to 600hp …. if you have ridiculously high octane fuel and an intercooler which you really don’t want on an airplane, so it’s time for methanol injection.

Alcohol is really good for positive displacement.

Now, all of this assumes that the bottom end can take this.

The top end makes the horsepower, but the bottom end has to take it.

Pro tip: increase your piston ring gap as the BMEP increases. This is because the additional heat causes the top ring to expand and when the gap goes negative and the ring buckles, it will break a chunk off the top of the piston ring land and grenade your engine.

Too much heat on the piston rings - either from one second of high BMEP or simple overheating from loss of coolant- will cause your piston rings to soften and they will not seal any more. Low compression and low power and terrible gas mileage and high oil consumption results from this.

[TundraTire]

Doesn't adding turbos to homebuilt aircraft bring a whole new set of issues, ie aircraft flutter?

I recall Van's putting something out a while ago explaining why they didn't use turbos in the RV's.

[Colonel]

That’s a very good point but let me explain one tiny detail….

Flutter is based on TAS not IAS - look it up.

A turbo and oxygen for the pilot allows a pilot to fly very high where the IAS is very low but the TAS is very high.

This means you are operating very close to flutter speed and that is death.

A guy in the hangar next to me at my old home airport is dead now. Andy Phillips. Had an RV-7A with an awesome paint job from a car guy that used bondo on the rudder to smooth over the rivets.

But that bondo weight ahead of the hinge line dropped the rudder flutter speed from 300 KTAS to around 250KTAS and one day, doing aerobatics Andy blew through Vne and his rudder fluttered. It looked like a stick of dynamite went off in the tail.



Anyways Andy is dead now. We gave him a nice funeral and I hope people learned about operating with a reduced flutter margin.



Also IMHO don’t do aerobatics in an RV unless you’re a pro and don’t make mistakes which doesn't exactly describe the people you meet at aerobatic contests.

People have pulled wings off them and it holds the dubious distinction of ever being the only aircraft type banned from IAC aerobatic contests. It is not a structurally strong aircraft.

Life member, EAA IAC NRA

[Jamesel]

The Forced Air Systems are STC’ed for Lycomings, but only for “Turbo-normalising”.
G3Ignition.com pulls a claimed 404 hp (they’ve got 2 graphs & everything, so it MUST be true) out of a 260 hp base O-540 with their bolt-on Supercharger.

One of the locals has a belt-driven Vortech supercharger belt on his Harmon Rocket. The engine tuner figured he was pulling over 400 hp with water/meth. He, also, decided that this airframe was at it’s design speed limit, so isn’t going for any more power.

Where did you hear that RV’s are banned from IAC contest? A couple RV4s & a RV8 flew in contests in 2022, & as a sometimes competitor (who has flown RVs in Sportsman in the past) and a current IAC judge, this is news to me. I thought the only “blanket” prohibition IAC had was against Ultralights.

[Colonel]

I didn’t say they were banned now. That was in the past, before your time.

As someone who has removed the no-aerobatic restriction from several RV’s (-6, -7, -8) it is my opinion that they are terrible contest airplanes. But don’t take my word for it, ask the people who were killed flying aerobatics in them.

Terribly unforgiving. Not structurally up to mistakes.



As a pilot and engineer, I strongly recommend that if you want to keep living, don’t do anything in an RV that you wouldn’t do in a 172.

A 172 will do very nice rolls, loops and hammerheads within the structural limits of the Utility category, but there is no room for mistakes. RV is the same. If your last name is Hoover or Holland, you don't need to be told this.

Feel free to kill yourself to prove me wrong. You won’t be the first or last. Maybe let us know anything you'd like for your funeral?



I flew the missing man when we buried Freddy at sea. Would you like that?