13B Rotary Engine Update – April 2001
Ed Anderson

This is an update on my rotary engine powered RV-6A over the past two years.The good, the bad, and the ugly.  The past year, in particular, has been one of a number of disappointments regarding the project, but it ended on an upbeat note. I managed to attend my first Sun & Fun Fly-In with my Rotary Powered RV-6A and came home with the “Best Auto Engine” Sun & Fun 2001 award. What a great feeling to also have three other rotary powered RVs in the same row and then to win this award. However, as you will read, it was not an easy road getting to that point.

Rotary Row Sun & Fun 2001
(Four Rotary Powered RVs)

Since my retirement move to North Carolina in July 1999, shortly after flying off my 40 test hours, I have made the following changes to my Rotary powered RV-6A:

· Change of Oil Cooler type and Location
· Modification of Cowling to accommodate new Oil Cooler Location
· Painting the Aircraft
· Designing and Installing New Intake Manifold
· Replacing PSRU Rear Oil Seal with New High Performance Seal
· Replacing Failed HALTECH EFI Unit
· New Oil Pan and Header Tank
· Replacing Original 86 NA13B block with 91 Turbo II Block with High Compression Rotors

This article summarizes those changes.

Change of Oil Cooler Type and Location

After flying the aircraft down to North Carolina from Virginia on one of the hottest days with oil temp pressing the red line, I decided that I had to fix that problem once and for all. I had originally installed a large 8x11 EARLS oil cooler back near the firewall and had enlarge the air intake, duct and plenum several times. These modifications each incrementally increased the cooling ability of the oil cooler. These fixes were adequate except for two situations. First, the oil temp always rose above 220F on take off no matter what the OAT. It would slowly cool down to an acceptable range once airspeed built up. The oil temp would also edge up near the red-line on the hottest days, 90F+. So after the flight down I committed to fixing the problem.

Jim Mosur, a Canadian friend and fellow rotary powered RV-6 pilot, moved a stock RX-7 oil cooler up under the bottom of the cowl and constructed an opening of approx 3x11”. Jim reported that his oil temp was 180F even on the hottest days. However, this modification would require a considerable fiberglass modification of the cowl, one thing that I had attempted to avoid, as I have no love for fiberglass work. So after reconfirming his success with Jim, I bit the bullet. I ended up using the bottom of radiator mounts to hold the ends of the 21” long stock Mazda Oil Cooler. It just so happened they were approx 18” apart, which permitted me to fashion two hanging brackets and attach the oil cooler. Only had to change the length of one oil line to reach the cooler in the new location.  That was the easy part. The modification of the cowl for the air duct opening and to accommodate the oil cooler beneath the PSRU took a bit more work. I am happy to report having the same results that Jim found – oil temperatures dropped by 40F.  Oil temperature on take-off remains at 190F or below and also does so on the hottest days. So finally, after a year of flying with marginal oil temperatures and with Jim’s help the oil temp problem is fixed.

Here is a photo of the original oil cooler set up with the large fiberglass plenum. I could fly with this set up but oil temp on hot days was still a problem.

Old Oil Cooler

Header and Overflow Tanks

Ross Oil


Original Oil Cooler and Plenum (After 4 modifications)

Here is the new position of the oil cooler.

Have you ever seen so many cooling fins? Note: Cooler mounted to radiator cooler brackets (small white rectangular squares under each radiator with bolt heads visible)

Lower Parts of Radiator Mounting Brackets

Last modification of Oil system – Oil Temps Dropped 40F

Modification of Cowling to accommodate new Oil Cooler Location

This was how the mod of the cowling to accommodate the new oil cooler position started out with foam insulation glued to achieve the gross shape of the needed fiberglass work.

Foam Foundation for new Oil Cooler Air Duct

After much rasping and sanding and with the fiberglass application,it looked like this:

>Finished Oil Cooler Duct

Aircraft Paint Job

After getting the aircraft painted in November 1999, the cowl mod did not look too bad. I used PPG paint, which turned out excellent using a color base coat and clear coating that. Only one problem, apparently no hardener was mixed with the last clear coat. Not quite certain how this happened as we painted all through the night in order to meet the commitment to return the hangar to its normal use. The lack of hardener left the clear coat tacky for months during which I could do nothing but try to keep the dust and birds off it. As the PPG folks stated, it did eventually harden after the sun of the summer months cooked it. So the aircraft had to sit for months. I guess I could have stripped it and started over, but that was just too hard and expensive to think about for long. In any case, the $2500 paint job did not turn out all that bad.

Finally Painted!

There was a down side to getting aircraft painted as perhaps all my trouble started from that point.  Not nice to make your project look too pretty else the gremlins may make your life miserable. However, while the aircraft was down due to tacky paint, I decided to replace the induction system.

Designing and Installing New Intake Manifold

The original induction system was designed based on information obtained from the folks who raced or otherwise hopped up rotary engines. I ended up with a fairly short intake manifold, with a Weber Throttle body with two 2” diameter throats and four injectors. While this is probably the thing for a rotary engine turning 10,000 rpm, it turns out it was not optimum for an aircraft installation where the engine is limited to slightly over 6000 rpm due to the gearbox and propeller tip speed limitations.

The unsuitability of this set up was apparent in the lack of power at operating RPM ranges. Based on fuel flow measurements with this induction system, it appears that the best HP produced was around 120-130 HP. Even with this, the aircraft attained a top speed of 186 MPH, but take-off roll was long and rate of climb was only around 900 FPM at gross weight.  All this induced me to take a second look at the induction system. After doing some calculations on the spreadsheet, it was clear that the airflow velocity through the induction system was only around 80 fps (assuming full airflow at 6000 rpm, which I was not getting) when conventional wisdom calls for over 250 fps.  Also Tracy Crook had reported much improved power with longer and smaller diameter tubes of a length designed to take advantage of the Dynamic Induction Charging interaction between the two rotors at around 6000 rpm.

So again using the spreadsheet, I calculated the required manifold path length to take advantages of this supercharging effect and proceeded to construct a new induction system. I used a stock lower naturally aspired (NA) 86 manifold and then used tubes for the upper part of the manifold.

Here is a photo of the complete induction system. Note that I use the stock 13B throttle body, which Tracy Crook cut down considerably leaving only the lower two throats and removing considerable weight. However, I decided to leave the primary (single throat) to feed the primary (inner) ports and the two lower throats to feed the larger secondary tubes (outer). I also reversed the throttle plate springs so that the throttle body would be wide open in the event of the throttle cable breaking. This was done for safety assuring that you would have power to make it back, controlling it with the ignition like the early old WW I biplanes.

New Intake Manifold tuned for Lower RPM Power

I modified the lower manifold by removing the variable induction cans and their shafts that control the variable intake port on the NA 13B.  I drilled the shaft holes larger to accommodate the secondary injectors and the built a fuel rail (cover by the red fire resistant hose) for the fuel distribution. As you can see from the photo, there are two sizes of tubes. The upper tubes slide over the smaller lower tubes. This was done to be able to see what effects varying the induction path would have on the dynamic charging effect. I actually toyed with the ideal of installing a small DC motor and having two switch positions for “Take-Off” and “Cruise” with the motor moving the tube further apart for low rpm effect and reducing the total length for higher RPM cruise. However, I have not gotten around to that project as yet and it may not be necessary.

Note: I had to place my secondary injectors in the bottom of the lower manifold. However, if you look at the 90 deg bend the outer tubes take into the lower manifold, you can see two small rectangular plates which hold two aluminum rods (plugs) in the secondary injector holes found in the upper manifold of the automobile. I had planned on using these ready-made holes for my secondary injectors, but could not as a motor mount brace interfered. I would suggest using these ready make injector holes and simply plugging the variable port can shaft holes, as it is the easier route to go.

Behind the throttle body are two fiberglass plenums one for the inner primary tubes and one for the outer secondary tubes.  The sizes of the lower primary tubes are 1.25” OD and the secondary are 1.5” OD. The upper tubes ID are 0.009” bigger than the OD of the lower tubes. For the Dynamic Charging effect the pulse wave should have a separate path for the primary ports and a separate path for the secondary ports. For that reason two plenums are used. Also for my design, the primary plenum must match up to the single opening in the throttle body and the inner primary tubes. The secondary plenum must match up to the double openings of the throttle body and the outer secondary tubes.

Here is a photo of what I came up with to accomplish this.

Primary Intake Plenum

Secondary Intake Plenum

The wide short form is the secondary plenum and the tall narrow form is the primary plenum. The shapes were formed out of (what else) foam insulation. The bottom of the primary plenum slides under and between the legs of the secondary plenum.

Here the fiberglass plenums are installed and covered with JB Weld epoxy to seal them. A ¼” metal plate screws (note tapped screw holes in edge of plate at bottom of plenum chamber) to the front providing a mounting place for the throttle body. The plenums are sandwiched between the ¼” front plate and a 0.063 rear plate with long bolts holding the two plates against the plenums.

You cannot see them here, but the two primary injectors in the engine block are behind and hidden by the tubes.  Of course, when I installed used Mazda Injectors (required for the block injector ports) one of the four injectors (two primary behind tubes and two secondary injectors installed in the shaft holes in the lower manifold) was bad. After much fiddling around I finally figured out it was one of the inner injectors, which of course meant I had to remove the manifold to get to them –sigh!

New manifold installed on aircraft. Note the small clearance between the motor mount bolt (lower left of photo) and the left outer runner tube. I ended up turning the bolt around so that the smaller head was in this position to provide adequate clearance. So when you build your motor mount I suggest keeping mounting tubes as far away from the manifolds (intake and exhaust) as you reasonably can.

So naturally, you want to know what effect all this work on the new manifold had as well did I.  However, the gods (remember me mentioned them earlier in the Paint write up) intervened. On the first flight with the new manifold, the ROC was increased by 300 fpm, however, after approximately 1 hour of flight during which I was tuning the fuel injection system (I had to use different fuel injectors with different flow rates with the new manifold) I smelled oil.  Returning the to airpatch, I found the underside of the aircraft covered with oil. The oil was clearly leaking from the rear PSRU seal.

Replacing PSRU Rear Oil Seal with New High Performance Seal

The rear seal of the Ross PSRU had always had a small leak, just drops, but which did mess up the bottom inside of the cowling.  However, it had never been anything more than an irritant, but this was different. So I initially removed and replaced the national oil seal with another of the same type thinking that perhaps all the time the aircraft spent sitting during the winter out in the cold without the engine being run might have caused the seal to harden or set. So just before the planned trip to Sun and Fun, I hurriedly replaced the oil seal and took off for a test flight the day before I was scheduled to depart. After 30 minutes I returned with the canopy covered with oil (bottom of aircraft also). This was about the only time I was glad for a crosswind as with the aircraft crabbed into the wind, I could see the runway out the side of the canopy. Uneventful landing, but no trip to Sun & Fun this year.

I finally decided that I had it with the leaking rear seal, so I researched over the Internet and found a replacement seal that was suppose to hold against 300 psi of oil pressure and was suitable for the shaft speed. It cost about 5 times what the old seal did, but would be worth it if it stopped the leak. Now is the time I get to confess - as I am told it is good for you. Confession follows:

It now appears that the seal was probably not the root cause of the oil leak. Yes, the oil did flow from the seal, but later I found that the back of the throttle body plenum of the new induction system had crimped a thick venting hose I had coming out of the block to vent blow-by gas. The blocked hose prevented the crankcase/oilpan from venting though it.   Instead the blow-by gas found a path through the oil drain hose returning oil from the PSRU to the oil pan and pressurized the PSRU case causing the oil to be blown past the sea. However, I have left the High Performance seal installed (after all I paid $65 for the thing). Well, somewhat embarrassed but also relieved, I rerouted the hose to remove the crimp. So, I thought that even though I missed Sun & Fun it was probably just as well as I needed another flight or two to tune in the fuel injection timing with the different Mazda injectors I was now using.

Post Mortem on New Seal

Well, the high performance, high $$ seal did not cut the mustard. After two flights, oil was detected leaking from the rear PSRU shaft seal.  A fellow rotary flyer had installed the same seal and reported it leaking after 15 hours. Upon removing and examining the seal, it appears that the white Teflon insert in the center of the black sealing material was rotating.  The seal was removed and the regular seal ($12) installed.  Hopefully, the rerouting of the vent line will keep the PSRU from pressurizing. I later added a 1/8” vent fitting in the top of the gearbox, which appears to relieve the pressure buildup on the gearbox and vents any oil, pushed out the vent back to the oil sump.

Aborted Take Off –er- Flight -er – Emergency Landing

After inserting the new PSRU seal and fixing the crimped line, I decided to continue with tuning the injectors.  Since static RPM was limited to 5000 RPM on the ground, the only way to tune the fuel injectors for the range above 5000 rpm with the HALTECH (and laptop) was to do it in the air. Not too hard to do using the laptop, but I still would not recommend any EFI requiring a laptop in the air for tuning. In any case, I revved up the engine to its 5000 RPM and started the take off roll.  Airborne a little over halfway down the 2300 foot strip doing 80 mph and at about 30-40 ft altitude, the engine started to surge. RPM went from 5100 to 3500 or lower and then back in about 1 second intervals – really gets your attention.

Of course, my heart was pounding and mind was racing – “What now, Hot Shot??” There were only three choices, continue to attempt flight, attempt to land on golf course off end of runway or try to put it back on the runway with the runway remaining. Well by this time there was not much runway remaining, but beyond the golf course there were only trees and the golf course did not offer much as a power line went through the center of the only fairway that might have been suitable and that would have taken a 90 degree turn. I have always said I would rather go off the runway doing 20 mph that find myself airborne with no viable options.  So, putting my money where my mouth was, I closed the throttle and dove for the remaining run way. Touching down 300 ft from the end of the runway, I immediately getting on the binders HARD! I left black rubber marks for the next 300 ft. Boy!! Was the end of that runway coming up fast!! Steered between two end of runway reflectors and ended up about 12 Ft off in the grass. Heart pounding, nerves jangling, and engine still surging (at low idle RPM). I killed the engine as fellow airmen came running up to offer assistance. No damage to me, or the aircraft (other than my nerves).

I could only come up with two potential reasons for the engine surging. Either I had the injector timing too lean in the 5000 plus rpm range and as soon as the engine started to unload as airspeed picked up it increased in rpm into the lean mixture range where upon the rpm would decrease back to where there was adequate fuel and start up again, etc. The only other possibility was a one-time glitch in the EFI system. That was the one that bothered me the most and in the final analysis, I think was a symptom of impending EFI failure.

A few days later as I was running the engine up on the ground the EFI system failed completely.  The system failed with the injectors stuck in the wide-open mode causing liquid gasoline to pour through the rotor housings and out the tail pipes. I decided then to remove and replace the HALTECH with Tracy Crooks EFI, which has redundant processors and other nice features for airborne use.

Stuck Apex Rotor Seals

After ordering the new EFI from Tracy Crook, I had several weeks before it would be ready and shipped. But, since I had to remove and rewire the wiring harness, the delay would be of no consequence. Tracy was kind enough to send me the electrical plug that I would need with his unit so I could begin rewiring the hardness immediately. having completed the new wiring harness, the EFI unit arrived, so naturally I went to plug in the male plug on the wiring harness into the female plug on the EFI and – IT WON’T FIT! After examining and measuring the two plugs, it is clear that the male pins of the wiring harness plug are installed in a metal shell meant for the female part of the plug and is too large. I had never had that happen in all the years of wiring plugs! So Tracy (who I think suspects my wiring ability at this point) shipped me another plug.  This of-course meant clipping the 37 wires off the unsuitable plug and rewiring to the new plug. Do you know how tiny those pins are to solder wire to when your eyes are as old as mine?? But, the new plug worked just fine.

 It was not all that bad, just took another day to do so. It took several more days to get all the old wiring removed and the new harness placed in the aircraft. But, finally the wiring and EFI was installed. So naturally the next step was to start the engine. No luck. I noticed that as I cranked the engine (which had not been cranked since being severely flooded when the old EFI failed) that it was cranking much faster than normal. So I got out of the aircraft and pulled the prop through by hand a few times – NO COMPRESSION! On either of the rotors!!

Apparently (this is conjecture on my part) when the liquid gasoline flowed through the rotor housings it washed the oil off the seals and seal slots, which after 5 weeks of sitting there in very humid weather proceeded to develop light rust around the seals and slots.  After working though the exhaust port for about a week and trying every trick folks were kind enough to suggest, I was able to get 5 of the six apex seals (three per rotor) unstuck, but nothing would move the sixth seal. So I decided I would have to take the engine off and disassemble it to unstick the remaining stuck seal. Well, it turns out, I am glad I had to remove the engine.

Disassembling the engine I found that the sixth apex seal (rear rotor) was stuck so badly that it took a punch to finally remove it from its slot. Two of the side seals on the same rotor were stuck so badly that I had to take them out in pieces. Also, I notice that the triangular part of one of the apex seals on the rear rotor was cocked (apparently from the previous rebuild) and had cut a deep groove in the side of the center iron housing providing a path for combustion gases to flow back into the intake cycle and undoubtedly not helping performance.  In addition, the street porting of the intake ports had been minimal which also did not contribute to power production.

So, I decided to rebuild the 91 Turbo II block I had in the workshop and replace the 86 NA 13B.  Although this has all been aggravating from one viewpoint, from another viewpoint neither aircraft nor I were damaged and so could proceed to have fun tinkering.

New Oil Pan and Header Tank

While I was waiting on parts to rebuild the 91 block, I decided to redo my oil pan. The original one I purchased from Ross Aero. With my “Plugs Up” orientation of the block that put the oil pan on the side of the engine. The Ross oil pan was well made, but had a few design features that were undesirable from my viewpoint.  You could not maintain a very high oil level in the pan (approx 2”) before the oil level started to interfere with the cooling oil flowing back into the pan from the central housing.  The symptom was foaming oil being blown out the housing vent (remember me mentioning the vent line back in the section of the new intake manifold).  So only being able to carry 2” oil in the pan was bothersome even though I had never had to replenish the oil in the 75 hours of flying.  Also oil tended to leak from the bottom side of the pan where bolted to the block. The oil return fitting for the PSRU was mounted on the pan 8” above the bottom oil fitting drain on the PSRU forcing the oil to be pumped up hill to return to the pan. I believe this contributed significantly to the rear seal leaks.

Also, the coolant header tank had been originally mounted on the rear oil cooler bracket, which was no longer needed as I had moved the cooler position to under the chin. Plus it was a 10” long rectangular aluminum tube and was much bigger than I needed. So I took the opportunity to design new oil pan and header tank and air/oil separator as an integrated unit reducing the space they had previously occupied and consolidating them all on the oil pan.

Here is a photo of original oil pan, air/oil separator, coolant header tank and overflow tank.  What a mess.

Original Oil pan and Header tank

Charlie Kuss referred Mr. Ed Heishmann, down Florida way, to me as an excellent welder/machinist, which indeed turned out to be the case. Every thing was returned with an excellent welding job including a few changes to make it even better than my design. Below is a photo of the new oil pan. Note that the sump is now below the level of the block, which permits me to put 3 quarts in the pan and another 1-½ quarts in the system (oil cooler, lines, oil filter and rotors).

This Part of the Sump is now below the bottom of the engine block

New Oil Sump, Header Tank and Coolant Recovery Tank

Attached to the new oil pan is the air/oil separator tank (far left tank), the coolant header tank with coolant pressure sensor on side (center tank), and coolant overflow tank (right tank). All tanks were made out of 2” dia 6061T6 tubing.

Replacing Original 86 NA 13B block with 91 Turbo II Block with High Compression Rotors

As I mentioned earlier, the condition of the 86 block was such that I decided to rebuild the 91 Turbo II block I had in the workshop. This was a Japanese version, which I purchased from an import place in Florida.  Unfortunately, when I started taking it apart, I realized it had suffered a severe drop someplace along its route to me.  The oil pan was crushed (no big deal), but what was worst the center housing that has the two large bolt holes  that hold on a portion of the oil pan and motor mount had the motor mounting boss broken off.  Normally, that would not have matter in my “Plugs Up” installation as I do not use those bolts.  However the bolt boss also forms part of the edge of the block that the oil pan bolts to. So I attempted to have it repaired. I also noticed on the rear side housing that the amount of metal between the outside wall side of the inner coolant ring groove and the coolant passage was only 0.061 inch (marginal) and look ragged as if the casting was imperfect in that area.  So I decided to replace all the side housing with new side housings. The rotor housings were in surprisingly good shape so I was able to reuse them.

Since I was rebuilding a turbo block to run NA (naturally aspired – with no turbo), I decided to replace the 9.1:1 compression ratio 91 turbo rotors with the 9.7:1 NA rotors from the 88-91 NA 13 block.  Engine rebuilder Bruce Turrentine had the hard-to-find 88-91 high compression rotors.  So he shipped me a pair sonic cleaned and polished – would have been worth the price not having to clean the ones I had.  The gasket and seal kit was purchased from Kathy Atkins of Atkins Rotary who tailored the gasket kit to my needs with an excellent price.

style='font-size:11.0pt;mso-bidi-font-size:10.0pt'>Here is a list of the modifications made to the 91 block:


    All Iron Side housings are brand new Rotor housings are the ones that came with the J91 Turbo II as are stationary gears, front cover and oil pump Two piece, two spring apex seals were used similar (if not the same) as Hurley's seals Hayes High Performance O rings were used for inner coolant seal, stock for the outer seals Viton oil control "O" rings were used vice Mazda Stock I street ported the center housing using template from Mazdatrix (gotta be careful not to cut into the EGR galley - I did that practicing on an old housing, glad I had it to practice on!) I grooved the coolant chambers around the spark plugs on the rotor housings for better cooling Plugged the EGR holes from the Exhaust sleeve to remove source of hot air to the manifold Installed the injector diffuser screens on all injectors Installed 89-91 High Compression (9.7:1) rotors that I got from Bruce Turrentine Used the 91 front and rear counterweights to match lighter weight of 89-91 NA rotors Reused 86 eccentric shaft as it had the oil control springs and balls removed and Weber jets installed Reused Turbo II oil pump I had on 86 as it showed no wear and provided 80 psi of oil pressure Removed stock oil pressure regulator and installed 85-psi regulator previously used on 86 Replaced eccentric shaft thermal pellet and used Atkins machined aluminum fitting Side seal/corner seal clearance was kelp between .0015 and .0025" which is tighter than Mazda calls for, but which several books recommend for better compression

I took compression readings off the 86 when I got it back to the shop in order to compare it to my 91 rebuild. The front rotor was producing 85-90 psi which according to the specs is good, but the rear rotor was only producing 50 psi on one face of the rotor the other two faces shared the stuck apex seal and compression was none existent.

After rebuilding the 91, I was very pleased to see both rotors producing 110-psi compression. So I filled the new oil pan with oil and cranked it to build up oil pressure and that worked fine. I consider also filling it with coolant while I had the engine at the shop but decided not to as I was still waiting for the Header tank that I sent out to be welded. So I hauled the engine out to the hangar and spent 4 hours installing and reconnecting everything. Then I waited for the header tank.

When the header tank arrived I bolted it to the oil pan and hooked up the coolant hoses. I then proceeded to fill it with water/anti-freeze mixture. I had put approx 1 gallon into the engine when I noticed coolant dripping on the floor. Hoping it was a hose fitting not sufficiently tight I check for the source of the leak.  Alas! It was leaking where the rear housing joined the rear rotor housing. Clearly the outer coolant seal was not functioning – almost wanted to cry. Well, nothing for it but to take the engine back off the aircraft and back to the shop. Taking off the rear housing there was the outer coolant “O” ring in two pieces. It had apparently falling out of its groove when I turned the housing upside down to place it over the eccentric shaft and been severed by the being pressed between the housings.

 What was worst, Ihad eight extra inner coolant “O” rings but not a single spare outer coolant “O” ring and these “O” rings could not be purchased except as part of a gasket package from Mazda. These packages run from around $120 -$200 plus dollars depending on year and model with the expensive turbo gaskets driving the cost upward. However, Atkins Rotary came to the rescue and found an extra “O” ring among the packages they use in their engine rebuilding. Thanks again, Kathy.

So I put the new gasket in and put the engine back together and filled it with water in the shop.  No leaks! Then took it back out to the aircraft and reinstalled it (getting good at this) and filled it with coolant once again. I then proceeded to hook everything back up and started the engine.  Yea! It runs and no leaks.

Initial Engine Performance Indication

I proceeded to do the break-in run up gradually increasing and varying RPM and load (prop providing a varying load).  It reached 2600 rpm after one hour of running on the first day. Went back out the second day and was rewarded with the engine reaching 5700 rpm static run up. This was 600 rpm MORE than the old engine did on its best day indicating significantly more power being produced. The best I can calculate is that the 700 increase in RPM from 5000 to 5700 represents an engine putting out 170 HP or better.  A few days later (apparently with the engine having set its seals better) the engine achieved 5800 rpm on the 68x72 Performance Propeller.  So this was really cooking!!

So why so much more performance out of the 91 than the86? Well, I don’t know for certain, but I suspect that a number of things all added up.

The 86 was not well street ported with the ported central opening not being as large as the unported center housing from the 91. Also the outer intake ports on the 86 are divided which probably does not help air flow. After I finished porting the intake ports on the 91 center housing they were over twice as large an opening as the 86. I did not port the outer housings on the 91 as they come with big ports.

The two piece 2mm seals are reported to seal better than the three piece stock seals I had on the 86

The new induction manifold with longer and smaller runners is better suited to the desired rpm range than the old one on the 86

The new induction manifold may indeed be producing the dynamic supercharging effect

The Turbo rotor housings exhaust port does not have the metal “splitter” in the port that the 86 block has which further promotes exhaust flow.

The 91 uses higher flow rate injectors Mazda injectors while my 86 used lower flow rated US injectors

The higher compression rotors undoubtedly contributed some to the increased power

Some other factor?

I will get better data when I get in the air and can measure fuel flow and aircraft performance.

Note:A couple of months have transpired since writing the above and I have manage to get some tentative performance figures on the new engine. Base on fuel flow, the engine is producing 170-175 HP.

I still need to refine the fuel map for the injectors and will be doing that over the next few flights. Also looking for ways to reduce the aircraft weight. I had taken approx 30 lbs off the initial empty weight, but alas, more than replace it with the paint job and upholstery.

I have made two trips to Florida including one to Sun & Fun at Lakeland, Florida. Flew formation with two other rotary powered RVs (Tracy Crook’s RV-4 and Finn Lassen’s RV-3) to Lakeland and participated in the first consecutive three aircraft landing at Sun & Fun by Rotor Powered Aircraft.  Chuck Dunlap flew in from Arizona in his rotary powered RV-6 and joined us to make four rotary powered aircraft in a row. Great feeling that! And then to be awarded “Best Auto Engine” Sun & Fun 2001 was certainly the icing on the cake. What a year of downs and ups!

CONTACT! Editor Mick Myal Next to Rotary Powered Sun & Fun “Best Auto Engine”


Everyone is interested in performance, so here are the figures. My top speed, this far, at 1670 lbs is a calibrated 192 MPH TAS. Still no gear-to-fuselage fairings. My ROC at 2000 MSL at the same gross weight is 1200 fpm. I fly with a 68x72 fixed pitch wooden prop. Based on fuel flow, it appears that the engine is producing 170-175HP at this time. Max altitude flown is 11,500 MSL (I stopped there - not the aircraft). Max take off weight flown is 1700 lbs.  So, while not the fastest RV-6A, I believe it is in the respectable range. Fuel flow nominally ranges from 8 GPH cruise (170 TAS) to 15.75 GPH during take off. Actually, the rotary engine can not be harmed by over leaning it, so it is not uncommon to fly with air/fuel ratios so lean that the typical Air/Fuel Mixture meter can not measure it.  Maximum distance flown non-stop is 450 SMs with sufficient fuel remaining for another 1-½ hours of flight. The aircraft is willing to go further, but my kidneys are not.

Since I first started the project, the rotary engine movement has come a long way. There are now two web sites and e-mail lists dedicated to the rotary engine in aviation. The sharing of successes and failures among the members is producing immense benefits to all. We are also closing on a set of “best practices” for rotary installations and the first of a series of rotary and RV specific products are in the initial planning stages, as well as those currently offered by Tracy Crook of Real World Solutions, Inc.

One of the success stories is that the rotary installation can be done in a number of different ways and work. A number of rotary powered installations are flying and the number will increase dramatically over the next year or two. The members of the e-mail lists bring a wide range of in-depth technical and practical experience. We have folks from all over the U.S, Canada, Australia and New Zealand as well as others who are contributing their experience and knowledge to this topic. I expect as we move forward that other enterprising individuals, like Tracy Crook, will offer products that will make the conversion easier. However, other than Powersport Inc., I know of no one at present that offers a FWF rotary package for the RV, although that could change in the future.

Despite the considerable progress made in defining the best practices to follow in installing a rotary engine in an RV, this is still pretty much a roll-your-own effort. I still maintain that if your primary interest is in getting your RV into the air and enjoying it, then you can’t beat sticking a Lycoming into to it and go flying. On the other hand, if you enjoy a technical challenge, like tinkering, can take frustration, and want the thrill of power into the air with your own installation then this could be your cup of tea. But, don’t go into it because you think you will save money.  The money you save (If any) will hardly compensate for the hours you are not flying because you are tinkering with your installation.  Do it because you are a “Gear Head” and you will enjoy the project.

Again my thanks to Don Mack for hosting my project on his web page and making the information available to all.

Best Regards,

Ed Anderson

305 Reefton Road

Matthews, NC 28104



RV-6A N494BW Rotary Powered

Best Auto Engine” Sun & Fun 2001

>Here are a few sources for those readers who may be interested in the rotary engine:

My project hosted on Don Mack's web page


CONTACT! magazine issues 49,50,and 51 contain a three part series I wrote
about my project. They may have back issues. You can contact them at:

Tracy Crook's Web page of products he designed and sells for rotary engine
installation in aircraft

Here are two web sites with their associated e mail lists (see web pages) that offer discussion on rotary engine topics

The Fly Rotary Web page of Rotary fliers and their projects

The Rotary Engine Web page of Paul Lamar
Rotary Engine Rebuilders/Suppliers for Aircraft Installation

Dave Atkinshttp://www.atkinsrotary.com/

Bruce Turrentine

E-mail Address:


Ray Richardson

Powersport, Inc.


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