Q.  Dear Q&A - The question by Bob Whittier regarding changing the camshaft profile to move automotive horsepower down to usable propeller rpm is interesting, but tough to accomplish. First of all, I don’t want to come off negative in my response because I know how an acid reply can kill an experimenter’s desire to share what he is learning.

I operate an automotive machine shop. This has given me some 22 years of seeing what makes engines work and break. Fifteen years of building and driving race cars gave me reason to build a variety of different bore and stroke combination engines looking for a perfect or trick combo. I don’t know that I ever found one, but I did learn that the engines can have a distinctly different character or behavior.

After recently becoming a pilot, the powerplants in aircraft are a great point of interest. At first I thought they were crude or primitive, antique designs. I soon realized most of these designs and the engines themselves have stood a test of time that may never be equaled. Wanting to have something of my own to fly gets me back to the original question, how to go flying without the cost and often time-consuming constraints of aircraft engines?

Upon reviewing a lot of engine specifications and dyno reports, I came to a sobering realization, and Mr. Whittier’s question is most of the answer. If we take an engine that makes great power around 5000 rpm and slow it down to usable propeller speed, 2500 or so, despite what we do with the camshaft or anything else, we have taken away half of the power strokes and these engines do not do their best loaded hard at slow speeds. I know 50 to 70 horsepower does not sound like much, but in direct drive you need more displacement to get it. For a direct drive set up, a greater amount of displacement needs to be achieved with stroke. Not necessarily greater than the bore, just more than most motors have in stock form. Pretty much all of the four and six cylinder engines fell short of what I saw as necessary stroke. By mixing some parts from some older V-8’s, horsepower and weight more in line with say an O-470 Continental may be accomplished.

I am currently building a direct drive engine to do some dyno testing and I will pass the results along if you would like - good, bad or otherwise. It should be about 220 horsepower. As designs like the Skytruck and Murphy Super Rebel emerge, I need to hurry. I hope to have numbers on the new powerplant by early summer.

Sincerely - Jim Woodbury, Perry, Michigan

Q.  Dear Don - I enjoy reading the Engine Q&A in EXPERIMENTER.

I am building a SkyStar Vixen and flew the O-240 powered Vixen at Oshkosh in 1995 and was really impressed with the performance, but the price of an O-240 in New Zealand is $30,000. So, to my mind the alternative is the Subaru ER-27 six-cylinder engine. I believe this will give similar performance to the O-240.

I have purchased an ER-27 from AAA Engines, Fort Worth, Texas as advertised in EXPERIMENTER. The reason I purchased the ER-27 is the similar weight to the O-240, the Continental being 240 pounds dry. With a reduction drive, I believe I would achieve the horsepower necessary under 4,000 revs. I don’t feel comfortable at all flying aeroplanes that have to run at very high revs. My adage is, "if you are not comfortable in it, you don’t fly in it because you won’t enjoy it."

My question is - I have seen the ER-27 mentioned in earlier issues of EXPERIMENTER and would like to communicate with anybody using the ER-27 regarding engine mounts, reduction drives, the power curve, the availability of a manual for the ER-27 (the Subaru XT6 was never exported to New Zealand hence the reason I imported one), suggestions on weight reduction and reduction ratios.

Yours sincerely - A. G. Colquhoun, R.D.4 Cambridge, New Zealand

A. Dear AG - It’s nice hearing from someone so far away. If I am reading correctly, your letter states the SkyStar Vixen requires 80-100 hp and you want to use an ER-27 Subaru. That with a redrive would probably be the way to go. Then you could use a longer prop. It would give you over 600 lbs. of thrust to accomplish your project.

On the redrive information, tell the manufacturer the horsepower and required rpms needed to run the engine and length of the prop, and he’ll select the proper gear reduction. I am enclosing information on a redrive from the company called New Horizons who makes planetary redrives. If you want a belt-type redrive, Rotary Air Force out of Canada makes a nice redrive also (P.O. Box 1236-A, 1107 9th St. West, Kindersley, Saskatchewan, Canada S0l 1S0, phone 306/463-6030, FAX 306/463-6032).

I know it’s hard to purchase different types of Subaru engines in your area; I’d probably have chosen a 2.2 Legacy because it’s lighter and with four valve per cylinder, breathes better. The one you have is fine. I do not have a manual available. You could probably purchase one from a Subaru dealer or auto parts store. I hope this works for you. - Don

Q.  Dear Don - The section that I always turn to first is Engine Q&A followed by Hints for Homebuilders. Your section is fascinating and I hope you will consider collecting all the information you have gathered over the years and put it into a book.

My question has to do with calculating horsepower with a redrive. When people ask you about which Subaru engine to use for a certain horsepower, you always have an answer. Would you please tell me how you calculate it?

My next project is going to be an RV-4 and I plan to use a Subaru engine and would like to have the horsepower at the propeller be around 180 or similar to a Lycoming O-360. If I use a Legacy engine, what is the redrive ratio, prop size and pitch (guesstimates) to yield approximately 180 hp and how do you calculate it?

An additional question is in reference to different types of redrives. Has anyone done any research on friction losses on the different types of redrives. I have noticed that it takes considerably more effort to hand turn a redrive that uses a cog belt than it does to turn a planetary drive. Does this make a difference on engine output? What about heat generated by friction in the cog-belt systems?

Thank you for your help. Keep up the great work! - Jonathan Tibbets, Kaysville, Utah

A.  Dear Jonathan - With the RV-4 and the horsepower you want to achieve, the Legacy engine with redrive will in reality be about 150 hp. If you use the 2.5 liter engine from a Subaru Outback. Its 165 hp with redrive would give you 170 horsepower or more to the prop.

You asked how I arrive at answers to all the questions about Subarus? From years of experience working with Rotary Air Force and lots of research that I’ve accomplished myself and with people working with their projects, getting feedback. It’s all about people sharing their ideas and experiences.

If you want to get 180 hp, the 2.5 liter Subaru would be the answer. The horsepower of the Outback is 165 hp at 5600 rpm, which would give you torque of 162 lbs. at 4000 rpm. Now running that through a redrive, say at 2.1:1 would give you around 340 lbs. of torque to the prop, at about 195 - 600 lbs. of thrust.

Rotary Air Force is working with a 2.5 at this time and we’ll be publishing the results of the testing. They’re also building redrives for the 2.5 and low profile intake manifolds.

Cranking an aircraft when using a redrive will be harder to start, and dangerous. Electric start is preferred and safer.

The cog belt drive does not create too much friction, according to some manufacturers. Some people like belt drives because they’re easy to inspect before preflight. - Don

Q.  Dear Don - Thank you for your prompt response to my original letter and the information on the gear reduction unit from New Horizons Components.

I have purchased a 2.2 Legacy engine out of a totaled station wagon. Except for some cosmetic damage from battery acid, the engine is in excellent shape with only 11,000 miles on it.

The questions I have at this time are:

1. In the original article of the September ‘94 EXPERIMENTER, it mentions an adaptor plate for a cut down 009 VW distributor. Would you send me one of these C.O.D. or let me know the price and I’ll send a money order for it?

2. In my latest J.C. Whitney catalog, p. 134, there is a high performance electronic ignition system for Volkswagens. Is this the Mentor ignition system, or would it be comparable to the Mentor?

3. Lastly, on p. 28, the upper picture shows an intake manifold you designed. Could you give me some insight for fabrication of this manifold? Could I adapt the stock injection manifold or would it be as simple to buy a manifold from Curtis Patton?

Thank you very much for your help. - Don Harrop, Anaconda, Montana

A.  Dear Don - On the VW distributor problem we discussed, I’d recommend using the Ford Escort distributor, 1983-85. It will work. The #1 plug will be at 6 o’clock.

An intake manifold is being made for the Legacy by Rotary Air Force (see address above) using a 350 Harley model #2300. - Don

Q.  Dear Don - I need advice from your column. I am building a Sonerai I, single seat. Gross weight will be 775 lbs. and I want a cruise of 150 mph.

I can build a 2234 cc VW (94 x 82) or use an EA-81, which I have. The Subaru must be direct drive. My questions are:

1. Which engine do you think will do what I ask best?

2. What prop and rpm do you recommend. I don’t mind short TBO’s. (Three-blade Warp Drive?)

3. Can you suggest an EA-81 direct drive kit and are electric start kits available?

4. Can I remove the EA-81 intake manifold, build tubing going to an aircraft carb underneath the engine. Is the flow in balance. I read about bypassing by going down to an a/c carb.

5. Who makes a crankfire ignition for the EA-81?

Any other comments would be appreciated. I’ve enclosed a stamped SASE.

Thanks - Mike Criddle, Lafayette, Louisiana

A.  Dear Mike - On the Sonerai I which calls for 60 hp, you can go direct drive with an EA-81. Max rpm would be 3800 with a 52-54 inch prop. Max tip speed would be 320-330 lbs. of thrust. This is the first Sonerai project I’ve had experience with, so if someone reads this letter with a similar project and can give us some feedback, it would be appreciated.

If direct drive does not work, maybe a planetary drive would be another option. The reason I recommend the planetary drive over a belt drive is because of the straight lines on the design.

On the direct drive, it’s easy to hand start Subarus. On a redrive, most come with electric start. Tennessee Props (125 Deerfield Drive, Normandy, TN 37360, phone 615/455-4516) makes a good two-blade prop.

On the updraft manifold, I haven’t heard of anyone experimenting with that type of set up. On the Subaru, anything is possible.

Here’s a contact for an ignition system - NSI Propulsion Systems Inc., 206/435-1055, FAX 206/435-4554).

Thanks for your letter. - Don

 
^__________ engine q&a ^__________