In the November 1994 issue there were two very nice tables relating to engines. The problem is I have no idea which engine or engines they relate to. Since you are the Subaru Guru, I assume the listed engines are Subarus, but which model? EA81? EA82? Legacy?

Since I will probably need to refer to these charts in the future, I need to better understand them.

Thanks - Jim Remington, Richmond, Virginia

A.  Dear Jim - In the charts shown in the November 1994 issue, the OHV stands for overhead valve, which is 1800 cc engines built from 1980-1985 rated at 72 hp. The OHC stands for Overhead Cam, built from 1985 to present with 85 hp to 95 hp depending on the injection (fuel). The Legacy is 2.2 liter 130 hp and the 2.5 is 155 hp. The engine that you will be using on the Rebel will probably be the 2.2 liter with a redrive. It will fly very well. In that same issue of the magazine, all the vendors for the various special devices are also listed.

Hope this helps answer your questions. - Don

Q.  Dear Don - Thank you so much for your time in sharing your experience and knowledge with us. I am just about to start work on a Sonerai II "stretch" because it is a two place. I need horsepower, but weight is a consideration (1150 lbs. gross). The plans call for a 2180 cc VW engine (76 hp max @ 3600 rpm, 165 lbs.), but the reliability of a VW of this size has been questioned.

I was turned on to the Subaru engine by another member of EAA Chapter 14, and he loaned me his 1995 EXPERIMENTER magazines so that I could read your articles. This has caused me to subscribe! (Editor’s Note: YEAH!) My questions are these:

1) Is the 2180 cc VW unreliable enough to warrant changing to a Subaru.

2) I do not want to use a redrive (cost, weight, cost, complexity, cost). So should I use an EA-81 or 82. You gave a 325 lbs. thrust rating to the EA-81 without redrive. Do you know how this compares to the VW (52 x 44 prop)?

3) I know where a cheap EA-82 turbo (w/o the turbo) is. If I got this engine should I reinstall a turbo, put new (higher compression) pistons in, or live with less hp down here at sea level? (I also know where to get a cheap EA-81. Which is better for my needs at the same price?)

Thank you for your contributions to experimental aviation! - Kurt Muller, San Diego, California

A. Dear Kurt - Read your very interesting letter about your Sonerai II. I noticed most Sonerais are powered by VW 70 hp engines. The EA-81 is 72 hp and will probably fit the aircraft very well with a 52 x 26 prop. The rpms will be about 3800.

If you read the last few magazines there’s a few individuals flying different types of aircraft with the EA-81 and doing very well.

You asked about the EA-82, it’s a heavier engine; if I was to use a heavier engine to get more horsepower, I’d rather use an EA-81 with a redrive and accomplish more with less weight. Turbos are too heavy and cause too many problems.

Try an EA-81 with direct drive; if that does not give you enough performance, add a redrive and it will solve your problems with very little modification.

Thanks for your letter. - Don

Q.  Dear Don - I’ve been reading your column regarding Subaru engines in the EAA EXPERIMENTER.

I was wondering if anyone has adopted the Subaru Engine to an airboat operation or an airboat drive as this seems to be an excellent application for the Subaru engine.

If anyone has used this engine for airboat drive, is there any technical information available? On construction of the engine mount? Can an electric starter be used? Hope to hear from you at your convenience.

Respectfully - John Maxwell, New Gretna, New Jersey

A. Dear John - Yes, there are a few individuals in Louisiana and Florida using the Subaru with a redrive on airboats, and it’s working very well. For the motor mount, make a bed mount. There are redrives with electric start on the market, listed in the November 1994 issue.

Thanks for writing about your project. - Don

Q.  Dear Don - I have just started my subscription to EXPERIMENTER and have read a couple of Engine Q&A articles that have stories about converting Subaru engines for use in aircraft. I purchased Kitfox Model IV - 1200 in 1992 without an engine and the firewall forward kit. I have been constructing my kit very slowly in hopes that somehow I would be able to afford to purchase the remaining engine and firewall forward kit.

If money was no object, the Rotax 912 would be installed in the plane. Money is tight and slow coming. The cost of the Rotax engine has increased to where there is no way I could afford one. Thus I went looking at the Subaru.

I chose the EA-81 Turbo. I live in the mountain area east of Fresno and will be doing some flying in and over the mountains. One of the articles I read was from A. L. Sutphin of Oak Hill, West Virginia. The pictures clearly show his Kitfox with a direct drive prop. I thought that maybe direct drive would be in an inexpensive way to go. I managed to contact him about his installation, and he gave me the results of his attempts at direct drive. I picked his brain of what works and what didn’t.

I still have many questions about the best way to use the engine I have with what equipment came with the engine - starter, alternator, fuel injection and distributor.

What are the disadvantages of using stock systems? This engine seems to work well in the cars; if it’s not broken, why change it. If there are sound reasons to modify then I need to know why, what needs modifying and where I can get what will be needed to modify.

Mr. Sutphin indicated that direct drive did not work well for him, that performance was not sufficient to get his plane to fly the way he thought it should. He has since put a reduction unit on his engine and performance increased, along with the cost of the unit.

What is a good, reliable inexpensive propeller reduction unit that will work on my engine application? Also, I need information on radiator applications. Engine mounts and ideas on fuel system changes. I would also like your thoughts on propellers.

Thank you. - P. Michael O’Kelly, Prather,

California

A.  Dear Mike - Concerning your letter on the Subaru Turbo engine, using all the components and computers you’ll have a handful of wires; I believe, like you do, to keep it simple. I haven’t had much experience with turbo’s because of all the extra weight, oil coolers, etc. I believe the regular aspirated EA-81 with a redrive would work very well, even in high altitude areas, using fuel injection aftermarket, because the new type smaller computers and carburetors work very well also. You might want to get some back issues of EXPERIMENTER to review some of the other columns as well.

Using stick computers and fuel injection might be a little complicated if you have not had any experience and don’t have the Subaru manuals to go by. The regular carburetor-type engine will work very well and be light weight.

Warp Drive has a three-blade, ground adjustable prop available (see Classified Ads in the back of EXPERIMENTER).

I hope I’ve been of some help to you. Have fun building your airplane! - Don

Q.  Dear Bill (Bronson) - In the February EXPERIMENTER I read with interest the letter to you from Richard Chapple of Laurel, Montana, in particular his reference to a "rumor" that Warp Drive propellers are breaking VW cranks.

First of all, I do not like dealing with rumors. Facts are much better to work with. I called Richard in Montana, Ben Owen at EAA and Daryl Heinemann of Warp Drive. Richard and Ben had no first-hand information on VW crank failures. Daryl said he was aware of two VW crank failures by an individual in Tennessee with Warp Drive propellers but did not have specific information. I asked him to investigate these failures and advise us of the results so we can put the rumors to bed.

I have built several VW conversions and have been flying behind VW engines for over 20 years. I have never had any basic engine failures. These have included 1835 cc engines using original VW forged high carbon steel cranks and 2074 cc engine using 4130 chromoly forged cranks. I am currently flying a Cygnet with the 2073 cc engine and a 58 inch three-blade Warp Drive propeller with about 75 hours on the engine.

I am a past president of EAA Chapter 113 and am personally aware of three VW crank failures. The first was in a Volksplane with a Revmaster 2100 cc engine with a light-weight, stamped aluminum blade, ground adjustable propeller. The crank broke at the center main on take off and was a cast aftermarket crank. The other two happened on a Sonerai, both to the same pilot builder and were in-flight failures. Both broke at the center main and both were CAST aftermarket cranks. I personally inspected the last failure and it was clearly an instantaneous, overstress fracture. Fortunately, all three resulted in safe landings with no injuries and little damage.

The moral of the story is that cast cranks may work in VW cars, but they’re not worth a damn in airplanes. You cannot put a propeller (any kind) on the front of a cast crank and a flywheel on the other end, introduce firing impulse torsional loads and expect anything but failure. Unfortunately, homebuilders are great bargain hunters and cast aftermarket cranks are cheaper than forged cranks. A bargain is defined as something you can’t use at a price you can’t resist. I have a whole basement full of bargains, but not cast cranks.

I would urge your readers who may be building up their own VW engines to either stick with the original VW drop forged high carbon steel crank in the 69 mil stroke or, if going to an aftermarket crank of the 78 mil stroke, to pay the price and buy a SCAT 4130 chromoly drop forged crank. They are a lot cheaper in the long run.

Kindest regards - Joseph Hillebrand, Sun Lakes, Arizona

A.  Dear Joe - Sorry for the delay in writing. I also dislike rumors because they are usually bad science, and as such are very misleading. In my opinion - metallurgical or casting flaws aside - the thing(s) which break most crankshafts (in planes, cars or fixed-base engines) are: 1) The engine should have been align bored; 2) The crankshaft was improperly ground; and 3) The engine is improperly assembled.

Simple substitution of stronger metal in the crank will usually make the crank last longer than the service life of a given engine, but this is no substitute for doing things right. Among other things which I emphasized transferring the thrust load through the "flexing" crankshaft.

I now have 110 hours on my engine and the "end play" is still the .004 to .005 of an inch I started with. I am personally sure this is another area which is of great importance in an aircraft conversion of the VW.

On the Warp Drive prop - it is much smoother than any propeller I have seen, and its flawless airfoil couples up to the air throughout the rpm range. In the case of my "short stroke" engine, this prop’s ability to "couple" at lower rpm is so noticeable that my engine cannot rise to its take off value of 3200 rpm. I can see that if you had a "long stroke" crank in a badly aligned bored block or a typical rear mounted thrust washer system (okay when the clutch is on that end) the added flexing would tend to cause crank failures. No magic, mystery or defect in Warp Drive props, but rather just bad engine science. - Bill

Q.  Dear Mr. Bronson - When I read Richard Chapple’s letter in the February EXPERIMENTER I was shocked to hear that he had bolted a Warp Drive prop on a VW engine. At all of the various VW forums I’ve attended at Sun ‘n Fun and Oshkosh, the experts recommend using wood props only. Mr. Chapple seems to have reservations about propeller selection, too, though he has successfully flown with a Warp Drive on his Scamp. I expected a stern warning from you and was surprised that you also have air time on Warp Drives. As you point out, performance is significantly better as compared to standard wood props. Is the crank breakage problem an unfounded rumor, or have you and Mr. Chapple just been lucky so far?

Regarding Mr. Chapple’s questions about wrapping the intake manifold with oil lines to fight induction ice: The legendary Morry Hummel has been doing that for years on his excellent little 1/2 VW engines.

Thanks for an interesting and informative engine column. - Wayne Whitaker, Stone Mountain, Georgia

A.  Dear Wayne - I will refer you to my response above to Joe Hillebrand in regard to Warp Drive props on VW engines. I think the real culprit is not the prop but the above listed engine defects. The superior "coupling power" of the Warp loads the engine in a way which will tend to "ferret out" any hidden defects. Kinda like you or me going more than one round in the ring with a trained boxer - no legs!

If your engine has the kind of front-mounted thrust system I use and is perfect in all other ways,it will probably be okay. No luck to it. - Bill

Q.  Dear Bill - In the February ‘96 issue of EXPERIMENTER you mention "tuned length exhaust" and silencers for the 1/2 VW engines. Would you give more information on this please?

Thank you. - Ed Fultz

A.  Dear Ed - The layout for my tuned exhaust is part of my narrative advertised for sale in the Classified Ads section. I do sell a narrative with drawings on the exhaust system separately, but the rear support bracket must be of your own design as mine is integrated into my head system. - Bill

Q.  Dear Bill - I noticed your name as a volunteer for technical counsel in EXPERIMENTER magazine with experience in VW conversions. I am sending you this letter since I am currently designing a VW motor mount and would appreciate your comment. I have enclosed a SASE for your convenience.

I am building a Sonerai II and am on a budget so I couldn’t afford a Diehl case, but I’d like to have the provision to add a starter and accessory case at a later time. For this reason, it makes sense to design a motor mount out of 4130 tubing and use the same attach dimensions that a Diehl case would use.

I decided to design a conical mount similar to the one described in Tony Bingelis’ book Firewall Forward but when I did the layout, I found that due to the small distance between the firewall and the VW case in a Sonerai, all of the tubes were almost in plane. For this reason, I went ahead and placed the tubes in plane.

I have included for your review two drawings: One with just the mount details and one with some of the VW engine details overlaid just for info. If you know of a better way to do this or if you see some obvious flaw with the way that I have designed the mount, please let me know.

I had a couple of other questions. What carburetor should I use? The carburetor that I am thinking about using is a Zenith since I have heard good things about it and since I understand that the Posa is no longer available (I got mixed reviews on the performance of the Posa even if I could find one.) I understand that there is more than one version of the Zenith and I am not sure which one to buy, and I also am concerned about its ability to function using just gravity feed. Additionally, since the Sonerai has very short runs of exhaust pipes, it would be very hard to mount a heat muff for carburetor heating. What do you recommend in this application?

I was given a stock crank and a good case and was thinking about just putting in oversize cylinders. I have been cautioned to go on larger than 90.5 mm rather than the 92 mm to get the full 1835 displacement. The reason stated was that there has been a history of cracking on thin cylinder walls of the 92 mm cylinders. What is your opinion?

Lastly, I was wanting to put good connecting rods in since I have heard that that is a weakness in the engine in such a high load application as an aircraft. Can you recommend a source for good rods?

- Gene Cook, Friendswood, Texas

A. Dear Gene - I like good triangular design in tube structures, and in particular around the engine area. My friend has a miniMAX with a 1/2 VW (firewall mount) and the tubes are almost in plane, with cross braces. I didn’t like the design, and it was been rewelded three times. Your design "looks better," and if you proceed with it, just make motor mount inspection a part of your preflight. Put a dollar in a jar each time you land, and soon you can buy a new Diehl case for your peace of mind (unless a ballistic chute is cheaper and lighter).

On carburetors, I always like gravity feed (it never fails to pull fuel down), old fashioned under-engine mounting (can’t leak gas on "hot stuff), and simplicity. The Zenith carburetor works, and its shortcomings are well known. I don’t want a slight increase in performance if I must give up a drop of dependability.

I am not convinced that a tuned exhaust system (mine gave me 50 more rpm, and less noise) wouldn’t work on a Sonerai. Then you could have carb and cabin heat. Think about this idea.

I noticed a difference in case weights on VW engines, and selected a "heavier" one for my conversion. I’m using 92 mm cylinders with no trouble. Most problems in engines are traceable to the builder, or preexisting defects. My narrative is a good primer on many of these pitfalls.

Since there are only four rods in this engine, you can buy racing items, but I used stock reconditioned rods with no problems. In a car the VW will go 150,000 miles or more. Airplane conversions usually do not turn more than 3200 rpm, operate in clean air, we can’t "pop the clutch," or lug around in a "tall gear," so in many ways our application is gentler. My 25-hour oil change interval is equal to a 1250 mile interval on a car, and I inspect the engine before each flight. I also hand prop the engine, so I get a good feel of compression and smooth operation as I pull it through on choke. No, I think in many ways our little airplane conversions are easier on this engine than when it lived in a car. - Bill
    

^__________ engine q&a ^__________