Many readers have asked me to comment on the 3 articles published in Kitplanes magazine (March, April, May 2001) on the EJ22 turbo powered RV4 by Tom Wyatt III. My comments are intended to help guide people down the right path and maybe save some time and money on your project, not to diminish the accomplishments of others. The Kitplanes article certainly covers many points of what to do and what not to do in a Subaru turbo conversion and we can all learn from Tom's experiences.
02/18/05 I was sad to hear of the passing of "Turbo" Tom Wyatt recently in an auto accident. Tom was a pioneer experimenter in the finest sense who freely passed his real world knowledge on to others. He wrote many fine articles for Kitplanes and the Alternative Engine books and had a real gift for writing in a readily understandable and engaging way. Although I did not know Tom personally, he had been a fixture in automotive turbocharged racing circles for many years and more recently involved with experimental aircraft. I had the honor of being contacted by Tom's sister shortly after his death asking me if she could get a copy of my tribute posted on this site about her brother. I was happy to help in this small way. Tom will be sadly missed in sport aviation and racing circles. His contributions should not and will not soon be forgotten and may he continue to "fly" elsewhere. R.F.
Redrive
Many people do not consider the repercussions of the choice of redrives for their aircraft and engine installations. Redrive offset describes the offset of the engine crankshaft vs. the propeller shaft. With the intake manifold located on the top of the engine vs. the bottom as on a Lycoming and most aircraft having much more room in the bottom half of the cowling vs. the top, it is very important to choose a redrive with enough offset to avoid doing time consuming mods to your cowling if possible. Planetary redrives such as the Ross have no offset. The Eggenfellner also has no offset. The Marcotte has a couple of inches on most models depending on ratio and most belt drives offer substantial offset. The airframe, cowling and thrust line will dictate your choices here.
Engine Mount
The attachment of the mount to the EJ22 has been done in many ways, some well thought out, others less so. It makes sense to use the original factory pickup points for major attachments as these are stiff and substantial. Tubes spanning long distances and those under compression need to be of larger diameter and/or supported midway by cross braces. Proper triangulation is a MUST both laterally and to handle bending loads. This is especially important with a heavy prop and when pulling major G due to the severe gyroscopic loads. Don't underestimate these. This is not a good place to save a couple of pounds! 3/4 by .049 4130 tubing should be the minimum used with this engine.
Propeller
Turbocharged engines need to have a variable pitch propeller or much of the advantage of the turbo is wasted. This also allows for easy adjustments to HP absorbtion if your targets are off. It is very difficult to choose the correct fixed pitch prop the first time with so little performance data available. Make your life easier. Even a ground adjustable prop is preferable to a fixed pitch one.
Cam Belt Cover
This serves no useful purpose on an aircraft engine. Discard it and save a couple of pounds.
Oiling System
The factory lubrication system is well proven and reliable. Messing with it can lead to disaster. An external dry sump system is a reliability liability, not to mention heavier, more time consuming to fit and more expensive. It is unclear if the final RV4 configuration was still dry sumped as the larger Subaru oil pump was apparently used with the new short block. Possibly they were only using an external scavenge pump.
Exhaust System
Don't even consider mild steel on a turbocharged engine. 321 stainless is usually the best choice unless you can afford and weld Inconel. Don't skimp on the wall thickness here to save a couple of pounds. .049 to .065 wall tubing should be used, not thinner gauges which will crack and are difficult to weld. Stainless tubing MUST be slip jointed in all run planes due to its higher coefficient of expansion or it WILL crack.
Intake Manifold
Your redrive choice will have a major impact on the intake manifold that you can use due to height restrictions under the cowling. The factory manifold can be turned 180 degrees so that the throttle body faces rearward. A short 30 degree bent tubing adapter can attach the throttle body to the manifold and save about 1.5 inches of height. The factory manifold is well designed but a bit on the heavy side and it is tall. Eggenfellner makes an excellent light, low profile intake for a reasonable price. If you like fabrication, you can make your own out of composite, steel or aluminum. If you make one, be prepared to spend many hours. This is exacting work. There are references on this site showing the steel one that I fabbed as well as the Eggenfellner one.EJ22 Intake Manifold and Subaru Powered Lancair 320
Engine Choice
The EJ22 turbo block is the superior choice for aircraft. The closed deck block design, stronger pistons and piston oil cooling jets make a big difference in reliability cruising under constant boost. New short blocks are available from Subaru for a reasonable price. I don't recommend using the atmo open deck designs for turbocharged applications.
Turbocharger/Wastegate
The article goes through many turbo part changes in the quest for the correct match. The original choice was obviously not successful. Compressors are matched for mass flow or airflow which is directly related to hp and operating altitude. The standard T3 -60 or Super 60 are the best choices for EJ22s from 160 to 180 hp and operating below oxygen altitudes. For higher hp and/ or altitudes, the TO4 E50 compressor has been shown to work well. A smaller compressor may sometimes be required at very high altitudes to avoid compressor surge at the higher pressure ratios involved. If you are matching for high altitude use, either work the math or consult someone who really understands the issues. This is not a place to be guessing when solid data is available.
The five turbine end changes done could have been avoided by installing a wastegate to begin with. All modern applications use wastegates. It is unclear in what the final turbine housing/wheel combination was on the RV4 as the article contradicts itself. The photo on page 83 in the May issue says that an N wheel was used in a P housing. These are TO4 parts and the photo plainly shows a T3 housing with the integral wastegate hole. TO4s do not have these. Also the author states that a .83 A/R housing is the largest available for the TO4. This is incorrect. TO4 turbine housings are available in A/Rs up to 1.71 in the tangental series. The largest housing available for the T3 is .82. Had the author simply chosen a .82 housing with a Stage 3 or Stage 4 wheel in the T3 series and used the integral wastegate, he would have been able to cockpit set whatever boost desired, without changing so many turbines parts. This would be very expensive for the average person. The wastegate also prevents overboosting and damaging the engine. Not using a wastegate simply does make make much sense. Despite the statement on Page 88 in the May article, the final combination of parts DOES make sense for the RV4s application- a properly sized compressor for the low hp and a very large turbine and housing to prevent overboosting when not using a wastegate.
Intercooler
Although the factory EJ22 turbo does not use an intercooler, it probably should have and and so should your aircraft. As the author discovered, very high induction temperatures were being generated which is no surprise if you run the calculations. A proper intercooler installation should reduce the charge temperatures down within 30-50F of ambient. This would lead one to believe that the author's installation was not well designed with temperatures still around 160F. Spearco Intercoolers offers complete engineering data for matching their cores. These cores tend to be much more efficient than most OE designs and are an excellent choice. Many people underestimate the core massflow required in aircraft applications. www.spearcointercoolers.com
HP
An EJ22 turbo fitted with a well matched turbocharger, intercooler and induction system should easily generate in excess of 200hp at 5500 rpm and less than 50 inches MP. Any less than this and you are not doing something correctly.
Cooling
This is generally the biggest problem. Make sure that your rads are big enough, an efficient design, tightly ducted with sufficient exit area. Adjustable exit flaps are recommended as you need more exit area at low airspeed at high climb power and less at high speed and lower cruise power settings. Fixed cowl exits are a poor compromise at high speeds. Adjustable ones go along with adjustable wastegates and propellers. They allow you to vary things without making time consuming and expensive hardware changes and they are more efficient in the long run. Guide vanes to efficiently turn the inlet flow and spread it over the whole rad surface are often required and just as often overlooked.
Conclusion
Be aware that you are doing an engine development program and that you will have to change some things. If you think that you will bolt this on and go flying with no problems or changes, you are being unrealistic. If you only need 160 hp, consider installing a naturally aspirated EJ25. It will be far less work. Study any enginering data that you can obtain on the components that you plan to use in your conversion. Someone has probably done something similar in the past and can offer informed advice and save you time and money. A certain amount of trial and error will likely be involved in your engine program but you can save much frustration and money by applying science rather than speculation to your problems. Happy flying.