# What engine would YOU build

Discussion in 'General Auto Conversion Discussion' started by Winginitt, May 15, 2019.

1. Jul 9, 2019

### Hot Wings

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If you are going to spend that much time How about an all new engine. Start with a Subaru EA-81/81 crank, cam, lifters and rods. Stir in the Fiat 500 cylinders and heads mentioned above. The only major part left is a custom crankcase. Get chef Pete with his O-100 experience to mix and bake and have a 3/4 scale VW engine.

2. Jul 9, 2019

### Billrsv4

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IMHO I would avoid the new Kawasaki H2 like the plague. And I'm a motorcycle guy! It makes great power, but at high RPM and would require a very carefully designed reduction drive. I am trying to re-produce a drive that was excellent, and just getting that going is very difficult. I suggest anyone doing an alternate engine design should do the PSRU FIRST! If you are not able to do that you need to work directly with someone who has, and has flying examples. I am dissing myself here as I have been working on my project for several years as a sideline. Torsional vibration problems are no joke and with a major reduction 2.5:1 or higher there are multiple vibration orders to concern yourself with. Also do not expect to use the motorcycle transmission as a means of reduction. The input primary shaft (attached to the clutch directly) is really the only part designed to hold 100% of the engines power ALL the time. You guys talking about belt reductions, if you plan to make more than 50-60 HP just avoid belts altogether. The drive will end up weighing more than a gearbox before you are able to handle the bearing loads. Also the most capable belts, DO NOT, ABSOLUTELY DO NOT, ABSORB SHOCK LOADS! In fact they can make vibration problems even worse. All this and I am an alternate engine fan. I have chosen the wankel rotary myself (Mazda) but aI'm not kidding myself that it's an easy job. More than half of the alternate engine attempts fail, either to work at all, or worse in use. Just be very careful about what you are doing. There can be great satisfaction in going your own way and succeeding. You must just be sure to check all the boxes before you take that thing into the air.
Bill Jepson

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3. Jul 9, 2019

### Billrsv4

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The Freevalve engine is something that ICE engine manufacturers have been working on for 50 years. It is no surprise that one of the few successful examples is being built by a company who's cars start at nearly a million dollars and go UP from there. The design is very interesting but if you can't build an engine with no possibility of valve tangle you could really have problems in an aircraft. Biggest worry I would have is a lightning strike causing a computer foul-up. Since all those valves are computer controlled if your computer goes down so do you! That said the freevalve sytstem is quite interesting and I would love to try it out...in my CAR.
T.O. Bill

4. Jul 10, 2019 at 12:38 AM

### BBerson

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The liquid cooled Subaru is even heavier. The idea is to make the aircooled VW weight the same as the typical two pounds per hp of a normal direct drive aviation engine at 2700 rpm.
It shouldn't be as much trouble as machining from a solid block like a Jabiru engine.

5. Jul 10, 2019 at 1:02 AM

### N804RV

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If I had money to burn, it'd be something like the Falconer V12 with the Thunder Mustang PSRU. But then, it'd be on a Thunder Mustang so...

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6. Jul 10, 2019 at 1:10 AM

### Vigilant1

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But, in fairness, do purpose-built direct-drive 2700 RPM aviation engines of these small HPs/displacements weigh just 2 lbs per HP? Just due to scaling factors, engines generally weigh less per HP as they get bigger.

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7. Jul 10, 2019 at 1:17 AM

### BBerson

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I just figure if the engine is good for 80hp, it is too heavy for 40hp. Two pounds per hp is a nice goal, but three pounds per hp is my realistic goal. (120 pounds with 40hp)

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8. Jul 10, 2019 at 2:22 AM

### Hot Wings

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No liquid. The Fiat 500 mentioned above is air-cooled.

The VW is already pretty light. Post war German engineers didn't use any more material than they needed. That corporate culture remained pretty much intact up through the evolution of the 69mm stroke engines. The 1300cc blocks are about 2 pounds lighter than the 1500/1600. You have to wonder why VW would use more material unless they needed it with the larger displacement/power.

If you could find an old 40hp ('65 and older) engine and have the crank offset ground for Chevy sized rod bearings/rods then cut it for larger bore that would be the lightest base to work from. It wouldn't be a very reproducible engine since there aren't many 40hp motors left in circulation.

There just isn't any easy and cheap way to a light VW engine.

9. Jul 10, 2019 at 3:00 AM

### Vigilant1

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Then this:
?? By >aviation< standards, I'd say (as you did) that the 60 HP Type 1 is already pretty light, and I'd say it is cheap. A hand-start 60 HP, already built by somebody else and ready to have a prop mounted on it is $4350 and weighs 145 lbs, so$72.50 per HP and 2.4 lbs/HP. The cost is about double per HP what a new 27 HP industrial engine will cost, but then we still need to get a prop on that engine.
But I get your point--if you want a light, cheap 40 HP VW engine (that remains light and cheap per HP at that output), there's no easy way to get there with a Type 1 -- if we insist on using all 4 cylinders. A hand-start 37 HP 1/2 VW is light (85 lbs = 2.1 lb/HP), and still not crazy expensive ($100/HP) for an engine that is ready to mount. While we are talking about new cases and major surgery, where's that guy who was talking about linking two 540cc B&S singles (19 HP each) to make an approx 40 HP engine? Last edited: Jul 10, 2019 at 4:15 AM sotaro and John wadman like this. 10. Jul 10, 2019 at 4:58 AM ### BBerson ### BBerson #### Well-Known MemberHBA Supporter Joined: Dec 16, 2007 Messages: 11,401 Likes Received: 2,091 Location: Port Townsend WA Two Briggs coupled is about the same weight as a light VW. Either way I would run it mostly 2000 rpm with a big prop. Way below the original manufacturer design power. 11. Jul 10, 2019 at 8:42 PM ### mm4440 ### mm4440 #### Well-Known Member Joined: Jan 14, 2012 Messages: 94 Likes Received: 17 Location: LA area, CA A Vanguard 627 cc based engine with a belt drive can produce 35 hp and weigh less than 100# for about$4000 with all new parts. That is buying a "airboat engine" and bolting on a belt drive from known suppliers. Or search; Polini Thor 250, about the same money, power and only 50#. and ready to put a prop on but a two stroke. It is looking better all the time.

12. Jul 10, 2019 at 10:51 PM

### BBerson

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Murray, that 35hp is not at 2000 rpm. The essence of serene flight for me is a low powered motorglider "loitering" at low rpm and low noise/vibration. Almost gliding, but gliders are hardly practical. A motorglider can provide 20 minutes of motor on or motor off gliding for a few dollars.
Here is a link to your excellent EAA glider/motor glider webinar (EAA membership not required) https://eaa.org/Videos/Webinars/Aircraft-Building/5822929903001

13. Jul 11, 2019 at 4:32 PM

### mm4440

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Thanks. Electric is what you are looking for. for self launching sailplanes it is practical and available now. It is on the expensive side and duration is limited but adequate for a day of soaring on a charge if there is lift.

Back to B&S 627, Would need to turn close to 5000 rpm to get the 35hp which would be used for take off and to clear the trees and then pulled back for a normal climb. CHT will determine what continuous power level is achievable. In fan cooled engines such as the VW and industrial engines, running faster cools better because fan output goes up faster than power with rpm. As for cost, with so many parts replaced would it be cheaper to buy the needed B&S parts rather than a complete engine? A usable cheap engine would be great. Turbo or supercharging is a possible way to get the power with out high rpms. Cooling is again the critical limiting factor. It will be hard to beat modifying an existing paramotor engine for a fixed wing installation.

14. Jul 11, 2019 at 10:31 PM

### Victor Bravo

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If the aircraft is a powered sailplane, the glide ratio will be higher than a non-glider, so engine reliability is a little less critical

Last edited: Jul 12, 2019 at 1:41 AM
15. Jul 11, 2019 at 10:55 PM

### BBerson

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Yes, I but don't want the engine flying apart and shearing off my tailboom either. Other than cost, electric is fine for a pure self launching motorglider, but I want a dual use Airplane/Glider for occasional powered trips. (say 16-1 glide or so, not interested in soaring in thermals anymore.)

16. Jul 12, 2019 at 10:11 PM

### mm4440

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5000rpm in the Van 627 looks like 2300 fpm mean piston speed, a modest figure as engines go. Big aircraft engines are ~3000 fpm and car engines 4000 fpm and higher at rated power. Stress increases with square of rpm. I think that if B&S warranties the Vanguards for 3 years with cast rods, upgrading to billet or forged ones should last a reasonable time in a 5000 rpm peak engine. They could be replaced at overhaul, say 500 hr.
Getting enough power at a 2000rpm cruise would be difficult and might require a two speed psru and possibly a controllable pitch prop. Good headphones are simpler. Even electrics make prop and some motor noise.

17. Jul 12, 2019 at 11:32 PM

### BBerson

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I didn't mean to use a Briggs at 2000 rpm. It would need to be twice the displacement at 2000 rpm, such as a 1600 VW.
In the old days (early 1900's), the engines were very large displacement and light weight and low rpm (direct drive).
For example, the Manly-Balzer radial was 540cu.in., 52hp at 930 rpm and weighed 136 pounds!
Considered more reliable than the Wright chain drive system.

Last edited: Jul 13, 2019 at 12:23 AM
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18. Jul 13, 2019 at 12:14 AM

### AJLiberatore

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Vigilant, and too Pops and BBerson as well...

Here are some of the ideas, controversial yes, new skill sets needed to do them on a more reasonable budget, but I know some are gonna be pricey.

* Gun drill the Crank and Cam
* Stock Banjo clip valve cover Replicas made out of Carbon Fiber
* All bolt-ons possibly Carbon Fiber instead of AL.
* I have an idea for a mount, kind of an "X" that would go on pulley end w/ the Rear Drive
* Take off a great deal of the rear flange leave enough for a drill w/ a Bendix similar to the STC for the Conti's
* I have an idea for the bottom of the case but I hold on that.
* Carbon Fiber intake.
* On the intake system, I have stumbled upon some things that have me wonder about how hard it is to balance flow and some interesting folks that tackled it and won.
* A Sonex type ignition on the pulley end.

Someone mentioned it might be easier to scale a VW down, for that matter that concept applied to a Jab, would be not far off from when they showed up w/ a 45hp 4 cylinder eons ago @ OSH. Maybe my desire to make a smooth 4 cylinder UL is chasing windmills, perhaps smoothing the 2 or just going w/ the 3 Cylinder Verner and be done with it.

19. Jul 13, 2019 at 12:33 AM

### Vigilant1

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FWIW, some of the Vanguard engines come stock with forged conrods (it looks like the 810cc's have them, the B&S site makes no mention of the conrod construction fr the 627cc Vanguard engines)
The in-flight experience with the Vanguard 627cc engine operated at 4500 RPM or so (to make "about 35 HP" according to the builder) indicates that many parts need to be exchanged for any hope of keeping them airborne in that type of service. An aftermarket camshaft (the stock one broke at 120 hours), shaved head, valve spring packers, aftermarket exhaust valves, aftermarket rocker arms, a different carb, induction and exhaust work, 8 degrees advanced timing, etc. After doing this, the potential TBO of the engine still remained undetermined as that engine was shelved for a different one. More in this post, as well as additional helpful posts in that thread by Kevin Armstrong, a builder who used a Vanguard 627 and an Ace PSRU on his trike for several years.

IMO, unless there's a no-budge weight limit (Part 103, etc), if more than 23 HP is needed it makes a lot of sense to start with more cc's. The B&S 810cc engines are available at same/lower cost than the 627cc engines, put out up to 28 HP at their designed 3600 RPM (so a direct drive can be used--cha-CHING!).

Last edited: Jul 13, 2019 at 12:46 AM
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20. Jul 13, 2019 at 2:34 AM

### Victor Bravo

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This may spin itself off into a separate thread, and that's fine, but here goes-

IF there are in fact too many technical or cost issues with a small 4 stroke E-AB engine based on the little Briggs V-twins...

and if there is a niche for small engines in the 30-40HP range for airplanes that are too light for the VW, O-100 and HKS class....

Then exactly what upgrades, modifications, and rework do we need to do in order to genuinely improve the level of safety/reliability of the many modern 2-stroke paramotor and UL engines that are available now?

My friend Murry (mm4440 on this forum) has always told me that some sort of throttle body fuel injection and electronic ignition would resolve the overwhelming majority of the 2-stroke reliability issues. What does everyone else think about this?

If there was a workable, affordable, modern fuel and ignition system (something RV6EJGuy built for this market, or Micro-Squirt, or whatever else is out there), and it was adapted onto the Polini, Simonini, Vittorazzi and any other state of the art air-cooled 2 stroke.... would that finally yield the magic answer for making a 30-40 HP engine ultra-reliable enough to fly over downtown Los Angeles?

I know that the modern paramotors are a lot lot lot better than the previous generation of 2 stroke powerplants, but wht are the real-world, factual, remaining issues from a "fixed wing airplane" perspective?

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