# What engine would YOU build

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

### Help Support HomeBuiltAirplanes Forum by donating:

1. May 22, 2019

### wsimpso1

#### Super ModeratorStaff Member

Joined:
Oct 19, 2003
Messages:
6,156
3,462
Location:
Saline Michigan
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.

Last edited: May 22, 2019
sotaro likes this.
2. May 30, 2019

### Dana LaBounty

#### Member

Joined:
Mar 29, 2019
Messages:
16
5
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.

Winchester, pictsidhe and spaschke like this.
3. May 31, 2019

### proppastie

#### Well-Known Member

Joined:
Feb 19, 2012
Messages:
4,041
1,187
Location:
NJ
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.

4. Jun 6, 2019

### revkev6

#### Well-Known Member

Joined:
Mar 9, 2010
Messages:
425
91
Location:
massachusetts
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.

litespeed, sotaro and proppastie like this.
5. Jun 13, 2019

### Geraldc

#### Well-Known Member

Joined:
Nov 12, 2011
Messages:
187
99
Location:
nz

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

sotaro likes this.
6. Jul 9, 2019

### pelitox

#### New Member

Joined:
Jul 9, 2019
Messages:
1
0
Being realistic, a Fiat Twinair 105bhp should be powerful and really light. Worth a look.
Dreaming... Kawasaki H2R engine should break some records!

7. Jul 9, 2019

### AJLiberatore

#### Well-Known Member

Joined:
Nov 27, 2011
Messages:
108
22
Location:
Canton MI
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.

8. Jul 9, 2019

### BBerson

#### Well-Known MemberHBA Supporter

Joined:
Dec 16, 2007
Messages:
12,642
2,581
Location:
Port Townsend WA
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.

Pops likes this.
9. Jul 9, 2019

#### Well-Known Member

Joined:
May 27, 2019
Messages:
204
251
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.

Derswede likes this.
10. Jul 9, 2019

### Vigilant1

Joined:
Jan 24, 2011
Messages:
4,384
2,059
Location:
US
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.

11. Jul 9, 2019

#### Well-Known Member

Joined:
May 27, 2019
Messages:
204
251
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.

Last edited: Jul 9, 2019
12. Jul 9, 2019

### GTX_Engines

#### Member

Joined:
May 17, 2013
Messages:
14
8
Location:
Atlanta, GA
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. 13. Jul 9, 2019 ### Vigilant1 ### Vigilant1 #### Well-Known MemberLifetime Supporter Joined: Jan 24, 2011 Messages: 4,384 Likes Received: 2,059 Location: US 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: Jul 9, 2019
14. Jul 9, 2019

### wsimpso1

#### Super ModeratorStaff Member

Joined:
Oct 19, 2003
Messages:
6,156
3,462
Location:
Saline Michigan
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

15. Jul 9, 2019

### pictsidhe

#### Well-Known Member

Joined:
Jul 15, 2014
Messages:
7,339
2,115
Location:
North Carolina
Shouldn't that be in supplier announcements?

16. Jul 9, 2019

### pictsidhe

#### Well-Known Member

Joined:
Jul 15, 2014
Messages:
7,339
2,115
Location:
North Carolina
I had a 1989 fiat for over 10 years. It was great. The dreaded rust bug eventually got it.

17. Jul 9, 2019

### TFF

#### Well-Known Member

Joined:
Apr 28, 2010
Messages:
12,049
3,474
Location:
Memphis, TN
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.

18. Jul 9, 2019

### Derswede

#### Well-Known Member

Joined:
Jan 7, 2016
Messages:
887
275
Location:
Central North Carolina
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

19. Jul 9, 2019

### Pops

#### Well-Known Member

Joined:
Jan 1, 2013
Messages:
7,482
6,457
Location:
USA.
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.

20. Jul 9, 2019

Joined:
Dec 16, 2007
Messages:
12,642