# Auto Engine to Air Craft

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#### blainepga

##### Well-Known Member
Many of us that consider building our own airplane hear about why we should not even think about using an auto engine in our project. It’s about the same argument as “if man were supposed to fly, he’d have been given wings”. I began by examining what was available in the certified market. It left me with a feeling that there was a lot to be desired. These engines were designed in the 1930’s and have remained relatively unchanged. Not many positives by the standards of a modern engine. Big cubic inches, low horse power, inefficient.

I began with of my understanding of the auto engine from 15 years of experience in drag racing. My first choice was a Mazda 13B rotary engine. Fewer moving parts, low weight, just not very complicated. But in order to get the horse power I wanted there would have to be many internal modifications to get the engine flight ready. I also looked at many other combinations, but I couldn’t seem to find one that didn’t have me making some sort of compromise.

I met Bud Warren at my first Copper State Flyin in 2006. His display interested me because of his PSRU he had on display. This was something I was going to need no matter what engine I decided to go with. He told about the GM Ecotec line of engines and in particular the LSJ motor with the supercharger. This combination had 205 Hp and 200 Ft Lbs of torque. There will always be some modifications to an engine, but there are no internal mods necessary with this line. Also, they ranged in horse power from 142 to 260. The cost of a crate engine (these are very complete crate engines) is from just under $2k to just over$4K for an LSJ motor. The Ecotec was available in a variety of GM products such as the Cobalt, Saturn, Saab, and the HHR to name just a few. The LSJ motors were in the Cobalt SS and the Saturn Redline.The LSJ engine or the similar turbocharged version will weigh 314 lbs. Firewall forward package should come in right at the same weight as an IO-360 certified engine or about 425 lbs.

The motor is an all aluminum engine with a seven quart oil pan, forged crank, rods, and pistons. The advantage of a forged crank in an auto conversion is that they are designed to have a certain amount of flexibility and are less prone to cracking or breaking. A cast crank is rigid and that could be a problem. When you’re swinging a prop and shut the engine off, that’s a great deal of inertia to stop. No matter what PSRU interface you are using (with the exception of the Bud Warren designed centrifugal clutch), a certain amount of that energy has to be absorbed by the crank. The supercharger has a built in intercooler. To get more boost at the rpm range for flight, you can change the front pulley on the supercharger to a smaller diameter unit. On the turbocharged unit just adjust the waste gate. I have checked with people in the know and they have indicated that stock injectors and fuel rails should be sufficient at those lower rpm ranges. The engine will never see over 5000 rpm.

Each project has its’ own set of requirements and engine selection should be based on those requirements. A firewall forward option will cost less than a similar certified package. I am going to go the other route by acquiring my engine through an outside source, build my own motor mount, an adaptor to interface my PSRU to the engine and all of the associated pieces for this build.The first order of business will be to create a cradle to support the engine. The cradle will be attached to a mockup of the firewall so as to get the proper reference attach points based on the prop shaft centerline and the cowell positioning. This will reduce the costs of this conversion even more. This total should be between $15k and$20 for a firewall forward build. A running total of the costs will be posted as I go. To date, I have spent about $3800 for the engine and the associated components and$2100 for my PSRU. I am lucky that I found an engine with 391 actual miles on it;

(kid 0, curve 1)

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The cradle is based on a small furniture dolly. This dolly is rated at 300 lbs. I reinforced it with the angle iron and two additional wheels. You will notice that I bolted everything together rather than welding. Eventually the engine will come off the jig. Welding will leave a very large unmanageable chunk of metal.

The engine is totally square in the jig. Angle iron works well for this purpose. It’s strong and inexpensive.

It doesn’t look pretty, but it is pretty stout. Also this is something anyone can build who doesn’t have welding skills. Having it on wheels means it can be moved around if necessary. It can be separated from the firewall when needed.

The plywood represents the firewall. There is a small circle located toward the center that was transferred from the firewall blue print. This is the prop shaft centerline. The jig was built to locate the engine on this centerline with the use of a lazar mounted on a tripod.

The supercharger is the reason I chose this engine for my project. The pulley on the snout of the supercharger will be changed to a smaller diameter one to provide more boost in the rpm range that engine will operate in for airplane use.

This tangle of hoses and wire harness is what you are going to start with. This will eventually be replaced by a new harness and stainless steel hoses.

Click any of the attached pictures below to get an enlarged view.

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#### cheapracer

##### Well-Known Member
Log Member
An opinion...

Superchargers are what's known as positive air displacement devices, they turn at a given speed and each revolution displace 'X' amount of air. That's fine when at sea level but when you go up into thinner air then the volume that is displaced is reduced accordingly (because the air's thinner) so you might have say 8psi of boost at sea level but that might be reduced to 2 psi of boost at 5000 feet (whatever). Also note under load a supercharger can not produce more psi than the driven speed allows.

A Turbocharger relies on exhaust pressure that is usually in excess of what's needed to spin the turbines so if you have 8psi at sea level, the exhaust has enough excess energy to continue to speed up the turbo's turbine to continue to maintain that 8psi at 5000 feet (whatever).

Also under load and even at low rpm, the exhaust pressure is still increased by greater cylinder pressures to provide high levels of boost that a supercharger can not as it's limited by the driven rpm.

Just a suggestion but for these reasons you might consider changing to a turbocharged version that is far more suited for flying, possibly the supercharged's internals are the same.

If at all possible could you weigh and display?

#### timberwolf8199

##### Well-Known Member
If at all possible could you weigh and display?
Indeed. Would love to have a good number to fit to it. Before (as received/current) and after (as installed) numbers are also useful. So, if you're not to a point where you believe the weight is representative of installation weight...a current weight is still useful, and may prove invaluable later, once you post a final number.

#### rv6ejguy

##### Well-Known Member
The advantage of a forged crank in an auto conversion is that they are designed to have a certain amount of flexibility and are less prone to cracking or breaking. A cast crank is rigid and that could be a problem. When you’re swinging a prop and shut the engine off, that’s a great deal of inertia to stop. No matter what PSRU interface you are using (with the exception of the Bud Warren designed centrifugal clutch), a certain amount of that energy has to be absorbed by the crank.

I have checked with people in the know and they have indicated that stock injectors and fuel rails should be sufficient at those lower rpm ranges. The engine will never see over 5000 rpm.
Interesting project. We helped Bud with one of these a number of years back and it seemed to perform well.

The forged crank is simply stronger and has much higher fatigue resistance. The loads on shutdown are likely nowhere near what the crank sees at max power. The clutch arrangement only reduces torsional vibration concerns on the F1 range which is typically in the 850-1100 range on most 4 cylinder engines with lightweight props.

The stock injectors have sufficient flow rate on any engine for the maximum rated hp. Generally we de-rate automotive engines when used in aircraft as well.

The supercharger is relatively inefficient and hard to control in an aviation application. Turbos are much better suited I think you'll find but be sure to chose a proper turbo for aircraft use, stock ones will not be well matched due the different operating conditions.

Will be interesting to see what the final weight numbers are.

#### stol

##### Well-Known Member
If the supercharger drive belt breaks and there is no intake air bypass, or it has been modified.... This could happen......

Don't be that guy....:ermm:

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#### ekimneirbo

Thats a well written and informative topic lead in. I'm sure for all the logic and forethought you put into this, it will like most projects still require some reformulation and change along the way. My suggestion is to not get totally locked in to the path you chose and not think that some suggestions are worth consideration.....even if it means major change in what you have. The turbo idea, in my opinion is worth a little more consideration as for effectiveness in an airplane.....but the supercharger has been used successfully before. I was wondering about the PSRU that you plan to use. Is it your own design? The engine looks like its nicely packaged. If you stay with the supercharger, will you test it at the elevated rpms to insure that it can live thru the higher stress level? What hp do you expect from the package? I'm glad to see another builder step up and take a bite at the apple with their own ideas. I'm sure you can expect some setbacks along the way, but I wish you much success with your project.

#### Brian Clayton

##### Well-Known Member
Probably the biggest reason auto engines are not used in aircraft use, is weight to HP. For their output, aircraft engines are very light. You biggest enemy is weight. Parts breakage can be overcome with a generous application of cash, but "built in" weight is hard to reduce.

It is exciting to see a new engine project though, I hope it works very well. I look forward to seeing some weights and your progress!

When re-inventing the wheel, you still end up with a wheel.

#### BoKu

##### Pundit
...These engines were designed in the 1930’s and have remained relatively unchanged. Not many positives by the standards of a modern engine. Big cubic inches, low horse power, inefficient...
Well, no. Yes, the foundation engineering of most of the opposed air-cooled engines dates to the 1930s. However, there has been a lot of development and refinement on top of that.

Also, don't assume that their relatively low power/displacement ratio means that conventional aircraft engines are inefficient. That kind of thinking is a trap. They are quite deliberately so designed because it allows for good power at relatively low RPMs. And that allows for direct drive, eliminating the need for a PSRU with its attendant weight, parts count, reliability, and durability issues. If you want to discuss effeciency, I think that metrics such as pounds of fuel per HP per hour would be a better unit of measure. And when you do that, you see that conventional airplane engines are actually pretty good.

Thanks, Bob K.

#### Brian Clayton

##### Well-Known Member
The future is probably going to be down to fuel burn. A airframe can be designed and wrapped around most any weight engine (realistic weight), but you have to be able to afford to feed it. To make a engine viable, it needs to get the same or better fuel economy at close to the same weight (including equal power) as a comparable dedicated aircraft engine. Its not that a automotive engine will not work in a aircraft, its just in most applications purpose built aircraft engines outperform automotive engines. I will give a example. I am fooling with a honda engine for aircraft use. The very first obstacle I know I have to meet or beat is weight. Since it will fall in the 60-80 hp range, it has to weigh in at least close to comparable aircraft/vw engines. Doesnt matter how cheap they are or how cheap parts to rebuild are, weight is king. Power is easy to make (not always cheap) and reliability can be achieved.....

As far as "modern" engine tech. It boils down to making more hp per lb of fuel. Thats what the modern cam profiles, combustion chambers, intake/exhaust runners, efi, ignition, etc will gain. And those gains are usually small. The DD engines are usually big displacement in order to make high torque (and a flat torque curve) at low rpms to swing a large diameter prop, not because they are "1930's tech". The saying "no replacement for displacement" holds very true in this case. Well, forced induction helps too....

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#### ekimneirbo

I look at it from a slightly different perspective. While we generally consider engine weight to be "King", we should not get lost in that assumption. The deciding factor should be how the weight of the engine combination you choose will affect the particular airplane you adapt it to. Kinda the same thing, but a little more inclusive. If the airplane someone builds can accept the additional weight of a water cooled engine, then what effect will it have on the flying qualities? Are those changes acceptable for the type of flying you plan to do? An example is the popular 4 place Bearhawk. It can fly with anything from an O-320 to an O-540. Yes it flys differently with the O-540, but the designer says it an acceptable choice and there are several examples currently flying.
This airplane will easily accept the weight of a PSRU V8 or a non PSRU V8.
On the other hand, as you move to smaller and lighter airplanes, the choice may become more difficult. One must accept the fact that the additional weight of water and the components to move it about and exchange heat are going to make the combination heavier than an air cooled engine. If the airplane and engine combo will work sufficiently to not compromise the flying qualities where the airplane becomes dangerous or uncontrollable, then you can often make alterations that will allow the weight/balance of the airplane to be optimised. Things like relocating the battery or radiator and the use of a wood or composite prop can go a long way. I think (just my opinion) that a PSRU should be a last choice option, but unfortunately it has become somewhat accepted as a first choice by many builders. I say this because it puts weight right on the nose, increases complexity, and are expensive. But I do admit that there are some fine examples where this works well for certain combinations. The point is that when deciding what engine to use, you have to consider what the weight of the whole combination will weigh, and what it all will cost. If someone uses a heavier engine with no PSRU and produces similar power, I would choose that as my first choice. As I said, this is difficult to do with smaller airplanes. If a builder can get past this hurdle in building, then they should enjoy increased economy in fuel and maintainance for the life of their airplane. So while I agree that weight is the first thing that must be considered, putting a somewhat heavier engine in place is not always a problem that can't be overcome by relocation and parts selectivity. Further, with the injection on todays engines you have better economy which means less fuel needs to be carried, and virtually no chance of any iceing problems. The big question seems to be, not how much your engine will weigh vs an aero engine, but how much will ALL the selected components weigh. Most of the aero engines have metal props so quite a bit of weight savings can be had there. Lightening a flywheel, replacing a heavy cast aluminum oil pan,using a lite weight crankshaft,lite starter,headers can help also.

#### Brian Clayton

##### Well-Known Member
I agree. But most airframes dont allow for that wide of a range of engine choices. Most have a weight range/hp range built in. I am sure that a airframe could be designed around any weight engine, but then the design would be married to that particular engine, unless you pay a weight penalty with a different engine. The idea I was trying to get across was that you need to end up with a "common" weight to HP range. There are some diesels that would make great DD aircraft engines, but they are 500lbs too heavy. I am interested in the OPs weight and HP ratio.... that will determine if the engine is practical for a variety of homebuilt uses. In my opinion anyway....

As far as weight savings. I cut every single extra, bracket and extra casting material (bellhousing mount too)off my honda block and head. It created about two 5 gallon buckets of chips. Removed about 9lbs. Modern castings are pretty thin. The only way I see to save any more on those two pieces is to re-trace the castings with a cnc machine, and i dont think you could save 1/3 of what I already removed. That leaves the crankshaft, cutting down the counterweights will remove 5-6 lbs, if you can get by with it. Valve cover is light cast alum (very thin) already, and a new oil pan will save about 1-2 lbs, if you can ditch the factory windage tray. Dry weight should be in the Low 140's. Pretty much the same engine as the OP's, so it should be close to what he can save.

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#### ekimneirbo

I agree. But most airframes dont allow for that wide of a range of engine choices. Most have a weight range/hp range built in. I am sure that a airframe could be designed around any weight engine, but then the design would be married to that particular engine, unless you pay a weight penalty with a different engine. The idea I was trying to get across was that you need to end up with a "common" weight to HP range. There are some diesels that would make great DD aircraft engines, but they are 500lbs too heavy. I am interested in the OPs weight and HP ratio.... that will determine if the engine is practical for a variety of homebuilt uses. In my opinion anyway....

As far as weight savings. I cut every single extra, bracket and extra casting material (bellhousing mount too)off my honda block and head. It created about two 5 gallon buckets of chips. Removed about 9lbs. Modern castings are pretty thin. The only way I see to save any more on those two pieces is to re-trace the castings with a cnc machine, and i dont think you could save 1/3 of what I already removed. That leaves the crankshaft, cutting down the counterweights will remove 5-6 lbs, if you can get by with it. Valve cover is light cast alum (very thin) already, and a new oil pan will save about 1-2 lbs, if you can ditch the factory windage tray. Dry weight should be in the Low 140's. Pretty much the same engine as the OP's, so it should be close to what he can save.
I believe most of what you said is correct, but each item and circumstance will vary considerably with the type of engine chosen.Its hard to make blanket statements though that one engine type will always produce greater horsepower than the other per lb. While standard aircraft engines set the standard we strive to meet or exceed, there are a lot of varibles. As I have stated in the past, my interests lie in LS Chevy engines. I think that adding a PSRU to one of these engines is usually the wrong way to go. In my opinion, without essentially gaining any weight, one can go from a 346 cu in LS1 to an engine that has 415 cu in and much more hp at 2700 rpms. I think that 250 hp is easily attainable at that setting and most smaller aircraft won't need or be able to utilize much more than that. Weight wise, this engine can outperform a O-540 if proper parts are carefully selected. Dropping back to the 346 cu in LS1 and adding a PSRU will allow even more power per pound, but you end up with a setup that is too heavy for most small airplanes and produces more power than can be used. Complexity,parts count,and expense all rise substantially. Going with the larger cu in LS 415, selection of an undercut crankshaft with most weight concentrated at the extremes of the counterweights will allow appx 15 (if memory serves) pounds of both rotating and dead weight to be removed. The oil pan is cast aluminum and weighs 12.6 lbs. A sheet aluminum, or better yet, a composite pan could relieve most of this weight. There are composite valve covers available which would save another 2 lbs. I would have most of the extra money for these parts because I didn't buy a $5/$8K PSRU.The flywheel can be lightened somewhat with weight again concentrated near the extremity of the wheel to provide rotational mass. An undersize racing harmonic dampener would provide additional weight savings.....Gradually the combination becomes more and more viable. The work you have done on your Honda combination is pretty extreme by most standards, but you appear to be getting closer to fruition, and I really hope it works for you. The point is that each scenario is different and the results will be different.
Going to the aero engines, probably the most impressive combination I can think of is the Carbon Cub. With its O-390 and ultra liteweight parts, it is a superior performer. First, its engine produces lots of power for its weight, and would be hard to match in a hp per pound comparison. An average O-320 will weigh almost the same as a similar O-360 but make much less hp/lb. Kinda the same thing as the LS1/LS415 I mentioned above. Hp/lb ratios are all over the map,so its really hard to make generalized statements that an aero engine will always outperform an auto engine per lb. For those people who wish to press forward with a conversion, they should also throw into the equation that much of the heavier engines weight can be offset not only by lightening their engine, but lightening their aircraft with the use of composite components like the Carbon Cub does.

#### blainepga

##### Well-Known Member
I understand how a supercharger works. WWII fighters were equipped with various supercharger/turbo-superchargers. Some had some type of mechanical drive while some were exhaust driven. As I said, I am going to change the front pulley on the supercharger to get better performance at the lower end of the rpm range.

Blaine

#### blainepga

##### Well-Known Member
Firewall forward with all components comes in around 425lbs to 430lbs. Compare that to a fwf io-360 and it's about same. Using the normally aspirated engines, subtract 35lbs for the blower. The stock LSJ engine is 314lbs.

Blaine

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#### blainepga

##### Well-Known Member
The PSRU was intended for airboat use. It comes in at around 55lbs. There have been no failures in 25 years of use. It has a 2.0 ratio and it has a reverse rotation. It has a Visco/elastic coupler and uses a stock flex plate from an HHR Ecotec application. Depending on the pulley I end up with, I expect about 260hp at WOT. The stock number for the supercharger is 12psi at 6500. I intend to get to at least that number at the lower rpm range.

Blaine

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#### blainepga

##### Well-Known Member
This supercharger does have an intake bypass valve in the event of a belt failure.

Blaine

#### blainepga

##### Well-Known Member
I am not looking to an alternative to my combination. This post will follow what will it take to get it ready for the Mustang II I am building. The combination I have chosen for my specific application Is based on a IO-360 for hp and weight.

Blaine

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#### blainepga

##### Well-Known Member
Everyone,

Please don't make the assumption that I haven't done my home work. I am writing with the assumption that my audience is also well informed about the subject of certified aircraft engines vs auto conversions. There are some omissions I will cover in upcoming posts; such as, dual ECU's with a custom harness with an A/B switch to select one or the other. Once the engine and mount, etc., are complete the whole combination will be run on a test stand then taken to a shop for dyno testing. The numbers we have calculated are very promising. The GPH difference should be amazing. Particularly when you are not using avgas as a cooling agent for the cylindar heads. But application sometimes doesn't fall inline with those numbers.

Blaine

#### Brian Clayton

##### Well-Known Member
based on a IO-360 for hp and weight.
This is going to be very exciting to see. I wish you the best of luck and I am anxious to hear and see more.....

#### blainepga

##### Well-Known Member
Any replies not directly related to the combination I am building serves no purpose on this thread. The debate about auto vs certified engine for me has been completed because I am going to use an auto conversion. The size and type of engine is done. PSRU vs no PSRU has also been decided. Any comments or suggestions about this combination are extremely appreciated and welcome. I don't believe I have all of the answers and maybe together we can come up with a combination that will be applicable across many different airframes. The purpose is to come up with something that is safe, long lasting, efficient, and cost effective.

Blaine