# Wild West of Four Stroke Engines

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#### ToddK

##### Well-Known Member
HBA Supporter
After spending a lot of time looking into 582 replacements I have been amazed how many people are out there developing their own aero engines from the ever expanding 4 stroke market. It seems that 4 stroke is taking over nearly every market segment, and providing us with new engines to tinker with.

In many ways, it seems like we are sort in the "wildwest" area of 4 stroke conversions now that they are replacing small 2 stroke engines.

Yamaha 3 and 4 cylinder sled engines are getting a lot of traction, with builders offering them for sale as turn key engines, or selling parts.

The Mosquito Helicopter is using an arctic cat 800HO engine. I think there is a lot promise in that one for a 582 replacement.

There is a guy on FB who has very clean and very small Honda outboard motor that is nearly ready to run.

It just goes on and on. Who knows what the UAV and industrial engine markets will yield in the future.

Modern low volume manufacturing technology and cad programs have made engines like the upcoming O-100 a possibility.

For heavier airplanes Viking (all E... baggage aside) and Aeromomentum seem to be offering quality turn key engines at very affordable prices (half of a 912), both with the latest technology.

Add to that the number of guys out there with their buddies converting engines in the garage and not making a big deal out of it online.

Are we entering a golden age of 4 stroke engines? Maybe so.

What are you guys doing, seen, or heard about?

#### pictsidhe

##### Well-Known Member
My project will likely have 2x 10hp. A pair of GX200 clones slightly hopped up is my current plan. The Horror Fright 60363 212cc predators are supposed to be strong engines. I'd prefer a pair of GY6 or C70 based flat twins, but that would be far more effort. Maybe later.

#### Vigilant1

##### Well-Known Member
Are we entering a golden age of 4 stroke engines?
I >want< to believe that a bunch of inexpensive 4-strokes are soon going to make their way into the EAB and ultralight aviation world, but I'm not seeing it yet. Lots of experimentation continues, but as far as a turnkey option or even a build-it yourself kit, we aren't there yet--quite.

Anything that depends on used engines will be fighting the odds. For a one-off homebuilder who is not a gearhead (fewer and fewer of those out there), it can be hard to evaluate a used engine, finding and buying one isn't as easy as ordering something from a company, hard to know what is "okay" and what is "not okay" once you are inside, etc. For a company doing conversions as a business, accessing, evaluating, and transporting used engines adds costs--and then they have to market a used product.

The most successful auto conversion to date (the VW Type 1) was and is popular because it can be built from inexpensive new parts. And because they are simple and have remained the same for decades. They aren't perfect airplane engines, but they are darn good and if the new parts are good and the builder just follows the instructions/videos carefully, he'll/she'll have a good engine at the end of the process.

The offerings from Aeromomentum look very good: New parts, purpose-engineered PSRU (with lots of real running time on airboats), good HP/weight, and an attractive price. Lack of redundancy (ignition, fuel delivery) is an issue for many people, regardless of the reliability of the single EFI/EI on these engines. The most significant downside for a US customer may be the relative scarcity of Suzuki automotive expertise and parts in this country (it's a very different situation in Asia). The cars were never super popular here, and they have been orphans since Suzuki pulled out of the US car market 5 years ago. Maybe that's not a significant thing: the engines are still being made (a LOT of them are still being made . . .), they have been in production for along time, they are popular elsewhere, and parts can still be gotten online. But if I lived in Australia, would I buy a Corvair-based airplane engine?

If some car or motorcycle company offers an appropriate, light, and inexpensive crate engine and a conversion company can figure out how to buy them without the lawyers coming down on them, then maybe there is hope. I suppose they could let the customers buy the engines and send them to the converter. . . .

The small industrial engine arena could be an area where a standardized conversion (or conversion kit) might work very well.

By some measures, the road to "simple" four stroke conversions has gotten harder, not easier. With Tracy Crook's departure, the Mazda Wankel builders lost their one-stop shop for everything aero. VIJA has gone under, along with their GSXR1100 motorcycle engine conversions. Raven redrives has gone dark, and even before that they had stopped doing Suzukis and instead started doing Honda Fit/Jazz engines. Everything else in the conversion space remains fairly static: Vassili at AirTrikes has a web site and has done many conversions. Great Plains is still around, but in a different form since Steve Bennett passed away (I sure miss him (a great guy) and their catalog--both were tremendous resources). Aeroconversions (i.e. Sonex), Scott Cassler, and Revmaster are still supporting VW-based engines. Jan E is still out there (FWIW. No further comment). There are several active businesses helping with Corvair conversions (or selling complete engines). As stated above, I do think Aeromomentum may just hit a home run--I wonder why there aren't more flying? Maybe one of the sled engine conversions will hit the big time, or something based on motorcycle engines. So far, the sled guys seem to spend a lot of time posting on various boards online, and it is very hard for a prospective customer to tease apart all the old-vs-new ideas in their postings, to see any testing, and to avoid feeling that, as a buyer, they are right on the bleeding edge of somebody's latest "this should work" idea.

In sum, I think it still >is< the Wild West of four-stroke engines. What we don't have yet are a wide range of simple-to-buy-or-build, inexpensive, standardized offerings.

Just my two cents.

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#### Topaz

##### Super Moderator
Staff member
Log Member
The various explorations into the single-cylinder and V-twin industrial engines intrigue me. I do have a question that I haven't heard addressed, however. Most of these engines have fixed mixture settings, especially the ones rated for sale in my state of California. For example, the Predator 670cc V-twin is set up for operation below 3,000'MSL. There is a "high altitude kit" (a different set of jets) that allows operation from 3,000'MSL to 8,000'MSL, but there is no other way provided of adjusting the mixture.

How are people addressing a mixture control on these conversions? Replacing the carb altogether with one that has a mixture control? Or, are they simply not doing any mixture control? The engine won't just stop at 3,001'MSL, but it will start running increasingly rich as altitude increases. For an ultralight, probably not a major issue, but for more of a "regular" sportplane, it's likely to make a difference.

#### Toobuilder

##### Well-Known Member
HBA Supporter
Log Member
My Taylorcraft has no mixture control of any kind. Not optimal by any stretch, but it does OK.

#### Victor Bravo

##### Well-Known Member
HBA Supporter
My Taylorcraft has no mixture control of any kind. Not optimal by any stretch, but it does OK.
+1 on three of the four Taylorcrafts that I've owned. No mixture originally, and when I hooked the mixtures up later there was very little difference.

#### Armilite

##### Well-Known Member
After spending a lot of time looking into 582 replacements I have been amazed how many people are out there developing their own aero engines from the ever expanding 4 stroke market. It seems that 4 stroke is taking over nearly every market segment, and providing us with new engines to tinker with.

In many ways, it seems like we are sort in the "wildwest" area of 4 stroke conversions now that they are replacing small 2 stroke engines.

Yamaha 3 and 4 cylinder sled engines are getting a lot of traction, with builders offering them for sale as turn key engines, or selling parts.

The Mosquito Helicopter is using an arctic cat 800HO engine. I think there is a lot promise in that one for a 582 replacement.

There is a guy on FB who has very clean and very small Honda outboard motor that is nearly ready to run.

It just goes on and on. Who knows what the UAV and industrial engine markets will yield in the future.

Modern low volume manufacturing technology and cad programs have made engines like the upcoming O-100 a possibility.

For heavier airplanes Viking (all E... baggage aside) and Aeromomentum seem to be offering quality turn key engines at very affordable prices (half of a 912), both with the latest technology.

Add to that the number of guys out there with their buddies converting engines in the garage and not making a big deal out of it online.

Are we entering a golden age of 4 stroke engines? Maybe so.

What are you guys doing, seen, or heard about?
=====================================================

So what Engine did you come up with for the 582UL replacement? The Skidoo/Rotax 670(92hp) built by Rotax Rick is the best I have seen.

4 Strokes have always dominated all aspects of Flying, Commerical and Large Kitplanes, except Part 103 Ultralights and Smaller Kitplanes! When someone produces a 1500cc - 2000cc 2 Stroke with a Turbo, they will Blow most of these Smaller 4 Strokes out of the water. Most Small Kitplanes use less than 100hp! A 670 Twin can make that. With 2 Strokes at 6500rpms it takes on Average 7cc to make 1hp. So that Skidoo/Arctic Cat/Yamaha, 800cc/7cc = 114.3hp, 1000cc/7cc = 142.9hp. PSI makes a 1800cc/7cc = 257.1hp. That's without a Turbo.

800cc at 6500rpms with 4lbs of Boost = 156hp
1000cc at 6500rpms with 4lbs of Boost = 195hp
1800cc at 6500rpms with 4lbs of Boost = 350hp

Drop the Max Rpms to 5500rpms and use a Turbo. My Skidoo 670 [email protected] comes in at 93% efficient.
800cc at 93% efficient at 5500rpms = 96hp, with a Turbo at 4lbs of Boost = [email protected]
1000cc at 93% efficient at 5500rpms = 120hp, with a Turbo at 4lbs of Boost = [email protected]
1800cc at 93% efficient at 5500rpms = 217hp, with a Turbo at 4lbs of Boost = [email protected]

Don't be fooled by these Few People in this World of almost 8 Billion now, touting their New Converted Engine. Touting 1-50 Engines Sold with very few Flying Hours of use doesn't make them reliable! Unless you like being their Test pilot! Rotax 2 Strokes have Millions of hours on them. Rotax's 912 has been out since 1993 and is starting to have many hours on them. Out of 750+ Airframe Manufactures in the World at one time, NONE, that I know of, ever Adopted any Auto Engine for their Airframe in the last 50 years. People have been trying to convert them for 40+ Years, and very few have been very successful. Some of the Newest Auto Engines from Chevy, LS type are showing some promise if, you keep the rpms low.

Show me just 50 of the same Type Auto Engines making 1000hrs in the World, to match Hirths 1000hr TBO for it's 2 Strokes, even 600hrs for Simonini's 2 strokes? Is there a limited few People in the World that can Build, Fix, and maintain these Auto Engines for Airplane use, Yes, but very few.

BMW
Mazda 13B
VW
Corvair
Subaru
Ford
Chevy
Dodge
Yamaha
Arctic Cat
Polaris
etc.

Who is converting the Arctic Cat 800HO engine? Got a Link?

Bill

#### Turd Ferguson

##### Well-Known Member
HBA Supporter
My Taylorcraft has no mixture control of any kind. Not optimal by any stretch, but it does OK.
It probably had one but like all the Stromberg carbs with back suction mixture control it was not connected to a cockpit control and the mixture control arm was safetied to full rich at the carburetor. I flew my C-85 powered Cessna at 9500 ft on cross county flights with no mixture control. It puttered along quite well, but;

Eventually I found a solution, the suction arm needs a method to make very minute changes. The common practice today is lengthening the mixture arm and using a vernier control so the arm can be moved in ~.005-.010" increments at the carburetor. Then you have realistic mixture control.

#### blane.c

##### Well-Known Member
HBA Supporter
I have written Walbro a few times about there EFI or "EEM" as they call it. These are kits for small displacement engines. Following is the latest reply.

Yep, we ae working with Polairs, Kohler, Husqvarna, MTD, and several other OE's.
The 'retro fit" EFI kit we hope to have complete by the end of the summer will
contain a fuel pump as well.
At this time, this limited information is all I can offer.

Thank- you,

Luis J. Salas
Program Manager II- Aftermarket
Walbro
6242-A Garfield Avenue
Cass City, MI 48726
p. 989.872.7322
f. 989.872.1135
website : www.walbro.com

HBA Supporter

#### pictsidhe

##### Well-Known Member
I'm really interested in supercharging small engines to allow direct drive. Turbos don't work too well at ultralight size, though. I am working on an alternative.
The Comprex type superchargers would be good. Unfortunately, they haven't been made, much.

#### blane.c

##### Well-Known Member
HBA Supporter
The small supercharger should be of twin screw design and electrically driven. If electrically driven then all of the engines hp can be used for takeoff power, the supercharger draining the battery. After takeoff the climb power reduction will allow recharging of the battery.

#### blane.c

##### Well-Known Member
HBA Supporter
The engine should be of flathead design, the weight reduction of the valve mass being put into cubic inches. At the rpm's being used for direct drive of the propeller and in combination with supercharging it is a rational compromise. The engine should also be EFI or EEM whatever term you prefer as most of the real benefit of modern technology aside from supercharging is computer control of the engine. The crankcase should be magnesium alloy for lightest weight and the crankshaft sintered steel alloy to eliminate forge or billet stresses. Obviously EEM includes electronic ignition, magnetos are no longer viable for a progressive aircraft engine.

#### Topaz

##### Super Moderator
Staff member
Log Member
My Taylorcraft has no mixture control of any kind. Not optimal by any stretch, but it does OK.
Do you end up with any fouling from the engine running rich, or any other effects? How is it "not optimal"?

Re industrial engine carbs. Unbolt the carb. Drop it in the trash. Now, go find a CV carb (s) from an engine of about the same hp per cylinder. Make it fit and you have an altitude compensating carb.
Interesting. A (very) brief search didn't turn up a lot of vendors for constant velocity carbs in the size range of the Honda GX670 and Predator 670cc engines. I'm not really thinking of buying one, but would you happen to have a vendor that has a range of carbs like this?

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