# What engine would YOU build

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#### wsimpso1

##### Super Moderator
Staff member
Log Member
If I could take an off the shelf motor and throw money at it I would get a small alloy block 4 cylinder motor and make an aviation specific head for it.
2 spark plug holes per cylinder.
2 valves per cylinder.
Reduction drive shaft running at 2 to 1 with bearings at front and rear to carry prop loads.
Secondary function of shaft is to activate valves.
For a 3 cylinder engine some balance factor built into shaft.
Now for the hard part.There has to be a drive system either belt or gear with some cushioning to drive the secondary shaft.
Two sparkplugs per cylinder with these small combustion chambers and EI is probably excess;
Two valves per cylinder when the base engine came with four means lots of custom parts. Now if you could get a SOHC four valve per cylinder engine, you would lose some weight while keeping most of the breathing advantages and not having to design and build a new head;
Reduction drive at 2:1 is scary, with all sorts of resonance interactions that you DO NOT WANT;
Balance shaft for a three is usually at engine speed, not the one-half engine speed that camshafts run at;
You will definitely have to build a vibration isolation system into the prop shaft as the big inertia of the prop will not play well with the firing vibrations - resonant frequency of the prop on one end and the whole engine on the other will require a soft enough spring system to drag 1st resonant order down near or below ground idle of this system.

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#### Dana LaBounty

##### Member
It's not what I would build rather what I am building. Brodix aluminum small block chevy. Bowtie head casting are at Valley Head Service being set up with twin plugs and enlarging the combustion chamber so I can get down to 8:1. I have a billet reverse rotation crank being built and displacement will be 421 cu.in. Vortex blower. Should make about 650hp at 4800. Twin mags and mechanical Bendix injection so no silly computers. EPI Mark 15 PRSU. The exhaust pulses from a V-8 at 4800 will sound like a V-12 at 3200.
It's going in a 3/4 scale XP-40Q-2. Power to weight ratio same as original. Back to the welding after lunch.

#### proppastie

##### Well-Known Member
Log Member
I thought today of a re-worked McCullough 2 stroke 4 cylinder drone engine from WWII...with computer manifold and controls like a modern car. I wounder how reasonable that would work.

#### revkev6

##### Well-Known Member
the drone motors made somewhere in the 50-60hp range at 4100rpm if I remember correctly. they swung a pretty small prop on a drone setup to fly at 200mph but also weighed less than 250lbs. I don't see them being a great engine for a plane unless you could swing something a little larger. if I was going two stroke I would want to look at the new snowmobile engines. efi with direct injection. something like the 600cc rotax motors in the newer sleds are very reliable and use much less gas and minuscule amounts of oil compared to the older carbed models. or the 800cc arctic cat engines that make 140-160hp... I wouldn't want to ever use that full power in the aircraft even at takeoff, but keeping it down to say 120hp for takeoff power would be interesting.

#### Geraldc

##### Well-Known Member

Any thoughts on this?Free valve head on a small alloy block with direct drive.

#### pelitox

##### New Member
Being realistic, a Fiat Twinair 105bhp should be powerful and really light. Worth a look.
Dreaming... Kawasaki H2R engine should break some records!

#### AJLiberatore

##### Well-Known Member
This thread is for everyone else but me to describe what conversion engine they would build if they had a clean slate and a reasonable amount of money to build it. T
Ok, I'll bite.

This is a bit different. VW 1791cc aka the Late Bob Hoover's orphan engine w/ his Hoover HVX Mods w/ rear drive. Now the kicker. Instead of running 1/2 VW's on UL's run this combo aka a full VW and try to get close to a live-able weight for UL applications, which means a big weight reduction program. Crazy? Probably, but a lot smoother and a chugger w/ a longer prop than we'd normally seem direct drive, aircooled, old-school, and not far off from what an old Ford Tractor engine was. I have a number of ideas in terms of the parts involved, and for weight reduction. Can I do it, not now, 2 kids in school etc etc. What has me thinking this is possible is the Gent w/ the Electric Belite, his total power-plant weight was not far off from that of a 4 cylinder VW conversion. Can a light UL air-frame be a match for a really light 4 cylinder VW, that is the question/challenge.

#### BBerson

##### Light Plane Philosopher
HBA Supporter
Yes, I am looking at a super light full VW option. It would be low rpm and low power. The challenge is cutting the weight off.

##### Well-Known Member
Log Member
When I lived in Colombia we had a lot of Fiat 500 and 600 cars around. They had two cylinder air cooled inline engines. There was a sport model called the Abarth that was 600cc and put out 35 hp. The 700cc Abarth puts out 50 hp. I’m
Not sure how many rpms they operate at. I’ve always wondered if one of these engines could accept a PSRU. There is a company in ‘Merica called Mr Fiat that sells the complete new engines. The 35hp is $3950 and the 50hp is$6600. Wonder if anyone has experimented with or has any experience with these engines.

#### Vigilant1

##### Well-Known Member
Yes, I am looking at a super light full VW option. It would be low rpm and low power. The challenge is cutting the weight off.
This is a bit different. VW 1791cc aka the Late Bob Hoover's orphan engine w/ his Hoover HVX Mods w/ rear drive. Now the kicker. Instead of running 1/2 VW's on UL's run this combo aka a full VW and try to get close to a live-able weight for UL applications, which means a big weight reduction program. Crazy? Probably, but a lot smoother and a chugger w/ a longer prop than we'd normally seem direct drive, aircooled, old-school, and not far off from what an old Ford Tractor engine was. I have a number of ideas in terms of the parts involved, and for weight reduction. Can I do it, not now, 2 kids in school etc etc. What has me thinking this is possible is the Gent w/ the Electric Belite, his total power-plant weight was not far off from that of a 4 cylinder VW conversion. Can a light UL air-frame be a match for a really light 4 cylinder VW, that is the question/challenge.
I'd be interested to see the weight saving ideas. It is always a struggle to do it at reasonable cost and effort.
As far as applying the specs of an electric motor, cables, battery, etc to a gasoline engine:. IMO, devotees of electric power are willing to make a lot of performance sacrifices that would suddenly become unacceptable if we were talking about a gasoline engine.

##### Well-Known Member
Log Member
The other interesting engine I’ve been researching is the 1/2 Chevy 350 block. SCAT enterprises made a V4, as did Ford. Saab ended up using the Ford V4. They became hotrod engines as well as race engines. A guy named Wilson from the Midwest modified the Chevy 350 for Midget race cars back in the day by cutting a V8 in half. Being that it’s fairly easy to build a dependable 350hp 350, I’d think a half of a 350 could easily produce 125-150 hp. Having a hard time finding people who have done this and Mr Wilson has long since passed away. There are PSRUs already made to bolt to this engine though they are for the full V8 but maybe a PSRU for a Chevy V6 motor would fit. All kinds of performance parts are available. Aluminum heads, rocker covers, pans, billet aluminum pulleys, rockers, etc. Betting you could build a 150 hp motor weighing in at under 275 before PSRU. Who knows.

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#### GTX_Engines

##### Active Member
I started down this road 15 years ago thinking, "Hey, all these guys using VW engines, let's go with a 914 Porsche." My reasoning: Porsche uses a far better aluminum alloy than VW, the internal webbing and shuffle pin arrangement is far better, which allows less crankshaft displacement under far heavier loading, and the whole package lends itself to using larger jugs and greater displacement, and even turbo charging w/o over stressing the block. In other words, a basic 2.0L Porsche 914 boxer is twice the motor the VW bus engine is to begin with, so why not start with that instead of a stressed out, punched out, already over-priced after market modified VW?

Then a buddy installed a 118 lbs, 120HP, 4-stroke 3-cyl Yamaha snowmobile on his Air Command gyrocopter in 2007 and we were all blown away. I have been converting the Yamaha Genesis 150HP RX1 and Apex snowmobile engines for aircraft use ever since 2011. One of my Apex kits walked away with every STOL competition it entered and the Grand Champion prize at Oshkosh 2018. Money talks, BS walks. 172 lbs installed, including everything except the battery and NOS boost kit. WHen he hit the boost he figured it was producing 195 hp at TO. Who gives a rat's patootie if it uses a PSRU? It takes up the same space under the cowl as a Rotax 912, burns 4-5 GPH with one soul and 6 GPH with two up at cruise speeds.

With 150-200 Yamahas flying for 12 years w/ no known forced landings, there is little point in looking any further for a great conversion engine. Price is about $7000 for everything, installed. These are the available Mohawk Aero Yamaha conversion 4-stroke, water cooled, NA-EFI engines today, with installed weights: 80hp 2-cyl 120-125 lbs; 135 HP 3-cyl 160-165 lbs; 150-165 4-cyl 170-175 lbs. There is no engine - certified or experimental/conversion - which is comparable in any combination of power, weight, cost, reliability and fuel burn. Stop dreaming, wake up, and realize that what you want and need is both affordable and available right here, right now. #### Vigilant1 ##### Well-Known Member Lifetime Supporter I have been converting the Yamaha Genesis 150HP RX1 and Apex snowmobile engines for aircraft use ever since 2011. One of my Apex kits walked away with every STOL competition it entered and the Grand Champion prize at Oshkosh 2018. Money talks, BS walks. 172 lbs installed, including everything except the battery and NOS boost kit. WHen he hit the boost he figured it was producing 195 hp at TO. Who gives a rat's patootie if it uses a PSRU? It takes up the same space under the cowl as a Rotax 912, burns 4-5 GPH with one soul and 6 GPH with two up at cruise speeds. With 150-200 Yamahas flying for 12 years w/ no known forced landings, there is little point in looking any further for a great conversion engine. Price is about$7000 for everything, installed. These are the available Mohawk Aero Yamaha conversion 4-stroke, water cooled, NA-EFI engines today, with installed weights: 80hp 2-cyl 120-125 lbs; 135 HP 3-cyl 160-165 lbs; 150-165 4-cyl 170-175 lbs.

There is no engine - certified or experimental/conversion - which is comparable in any combination of power, weight, cost, reliability and fuel burn. Stop dreaming, wake up, and realize that what you want and need is both affordable and available right here, right now.
Yes, you've mentioned this before. You say "available right here, right now." Do you have a web page, pdf file, or a scanned scrap of an index card that shows how a person with $7000 in hand would convert that to a usable aircraft powerplant? There are many photos on your site and mentions of the HIghlander at Oshkosh, but is there a roadmap/itemized lists for example packages, etc? Thanks. Last edited: #### wsimpso1 ##### Super Moderator Staff member Log Member When I lived in Colombia we had a lot of Fiat 500 and 600 cars around. They had two cylinder air cooled inline engines. There was a sport model called the Abarth that was 600cc and put out 35 hp. The 700cc Abarth puts out 50 hp. I’m Not sure how many rpms they operate at. I’ve always wondered if one of these engines could accept a PSRU. There is a company in ‘Merica called Mr Fiat that sells the complete new engines. The 35hp is$3950 and the 50hp is \$6600. Wonder if anyone has experimented with or has any experience with these engines.
I thought that everyone who had owned a FIAT from the 1960's and 1970's would have to have died before FIAT could hope to sell a meaningful number of cars in the US again. I had an 850 Sport Coupe that used parts the way most cars use gasoline.

If these engines have reliability even an order of magnitude better than the one in my 850, I would not dream of using it in an airplane.

Billski

#### pictsidhe

##### Well-Known Member
Shouldn't that be in supplier announcements?

#### pictsidhe

##### Well-Known Member
I thought that everyone who had owned a FIAT from the 1960's and 1970's would have to have died before FIAT could hope to sell a meaningful number of cars in the US again. I had an 850 Sport Coupe that used parts the way most cars use gasoline.

If these engines have reliability even an order of magnitude better than the one in my 850, I would not dream of using it in an airplane.

Billski
I had a 1989 fiat for over 10 years. It was great. The dreaded rust bug eventually got it.

#### TFF

##### Well-Known Member
89 is too new for the original Fiat experience. I only messed with duel cam ones. Always wanted a 128 for autocross. Or a Yugo dressed up in Gulf Porsche blue. There is a ratty X19 I see on the way to work every day.

#### Derswede

##### Well-Known Member
A friend had a REAL Abarth Fiat 500 we ran in local races...sounded like an angry hornet. I learned how to shift VERY fast to keep that engine in the powerband...think it was around 7K most of the times, but it could twist up motorcycle rev ranges. Only thing I could not keep up with was a VERY modded MiniCooper Radcliffe (the REAL Mini, not the BMW thing....).

Derswede

#### Pops

##### Well-Known Member
HBA Supporter
Log Member
Yes, I am looking at a super light full VW option. It would be low rpm and low power. The challenge is cutting the weight off.
Getting rid of weigh in the Type 1 VW is not easy. A long block is 116 lbs, add a stroker crank for a bigger cc engine than 1915 cc and you added 2 lbs. Use the not so cheap aluminum cylinders and save 5 lbs. I hear different stories on the life of the alum cylinders.
Builders have made flywheel drive engine and cut all the round bellhousing part off the flywheel end of the engine but I don't know how much it saved in weight. Use aluminum oil pump cover, aluminum oil sump cover on bottom of engine, aluminum fuel pump cover plate. Auto distributor and coil and a small light weight battery for the run time that you can live with. The shrunk fit prop hub is the lightest weight with an aluminum prop crush plate. The 1835 cc engine is the most bang for the buck and weight. Aluminum 1 1/4" dia aluminum intakes manifold with single port heads, (Lighter than the dual port heads and more torque with a straight drive engine below 3000 rpm). Short 1 1/2" dia ( about 9") SS x .032" exhaust stacks. Also need to make a light weight bed engine mount. My Culver 60"x 26" prop weighed 3 lbs.

#### BBerson

##### Light Plane Philosopher
HBA Supporter
I am talking about chem-milling or machining the parts to make them thinner like a Briggs engine. For 40hp at 2500 rpm they don't need the thickness of a 80hp VW.