Ill-Advised Engine Swap of the Week: Aircraft Radial In Toyota MR2

by Murilee Martin

Published: February 16th, 2011

ill advised engine swap of the week aircraft radial in toyota mr2

The thing that got me hooked on LeMons racing was the mentality that makes a statement such as “Hey, I’d like to install a 540-cubic-inch, five-cylinder radial aircraft engine in the back of a Toyota MR2, then try to make it run all weekend in a grueling endurance race” seem totally sensible. The ~~craziest~~ most devoted racers find themselves locked into an arms race for the Unununium, and this is the result.

The engine, which once powered a 1942 PT-22 Recruit trainer aircraft, was rated at 160 horsepower. This one hasn’t run for 65 years, but Radial Madman-In-Chief Marc assures us that it’s in good shape and should fire right up. As for the $500 limit, I exercised my authority as Chief Justice of the LeMons Supreme Court to issue a decree stating that radial engines shall be exempt from budgetary limits. You want a Pratt & Whitney R-2800 making 2,500+ horses in your Hillman Imp, and you can convince us that your hoopty-ass installation will be safe? Fine!

It’s going to sit in the back of the car, directly above a Subaru transaxle with a custom adapter flange. A V-drive, reduction gear set, and a much more reliability-enhancing gear is involved; you can follow the whole saga on this 24 Hours of LeMons Forums thread. Will it work? The real question should be: Will it have license plates?

#24HoursOfLeMons #24HoursOfLeMonsDetroit #Airplanes #EngineSwap #MR2 #Radial #RadialEngine #Toyota

Murilee Martin

Murilee Martin is the pen name of Phil Greden, a writer who has lived in Minnesota, California, Georgia and (now) Colorado. He has toiled at copywriting, technical writing, junkmail writing, fiction writing and now automotive writing. He has owned many terrible vehicles and some good ones. He spends a great deal of time in self-service junkyards. These days, he writes for publications including Autoweek, Autoblog, Hagerty, The Truth About Cars and Capital One.

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TheSlowLane on Feb 17, 2011

Big cylinder aircraft engines are meant to cruise at a constant speed, usually producing 70% TO power or less, so this thing is meant to be set at about 110HP and left there. Big air cooled engines also do not like to have the power changed suddenly. Quick power settings changes can cause thermal shock to big air cooled cylinders. Redline on this engine is 1850 RPM, why is a reduction gear being installed? So a maximum of what, 925 RPM(??) is going into the transaxle? BTW, Useable torque is probably from (let's be generous) 1000 RPM to redline. How many speeds will the transmission have to use this extremely wide power band? Engines of this vintage were meant to have a top oil for the valves. One solution is to mix about 25% 100LL with 75% auto fuel so there is some TEL for the valves. I'm sure the competitors will love breathing lead laced fumes. Radials are normally dry sump, so it will need an oil tank to hold, oh, three or four gallons of probably 100W aviation oil. 100W is about as thick as 50 weight auto oil, so perhaps straight 50 weight can be substituted. Radials are known as oil burners, but since this engine is "in good shape" maybe it will only burn five gallons or so in a 24h race, assuming it doesn't throw a piston through the head of a cylinder from excessive engine RPMs on the first lap. This could be interesting. Is anyone making a video? If it lasts half of a 24h race it should win a Unununium Medal.

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- Madman-In-Chief on Feb 17, 2011
  
  Hi, this is Marc, the guy building this thing. there's a few things i want to address about what you said: 1) the refusal to change delivered power is due to the long intake tract and the archaic updraft carburetor. I'll be using 5 carbs, one at each intake port to aleviate this (harley flat-head carbs) 2) yes, the redline is 1850. we may push it a tiny bit past that, but not much. the gear reduction you mentioned is not quite that it's actually a gear increase. about 3:1 to make the input shaft on the transmission spin up to 5500-6000 rpms about what the stock engine this transmission was designed for. 3) thankfully, the leaded fuel is un-necessary. this engine has hardened valve seats. the only reason it calls for leaded fuel is because that's what they had back then. we'll be running on unleaded 93 octane or E-85 if we need the ethanol to help keep things cool. 4) yes, we'll have about a 5 gallon tank of oil on board. the plan is to run a 70W oil designed for harleys. it's made to try and not sneak past the rings. 5) yes, we will burn oil. there's nothing much that can be done about that. the motor is quoted for 1.5gal/hr as "normal" i have no idea what the freshly rebuilt burn rate will be. it could be a quart/hr or it could be 1.5gal/hr.
  
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- TheSlowLane on Feb 17, 2011
  
  Marc, It's scary; after reading your post this engine swap is beginning to almost make sense to me. Almost.
  
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- Madman-In-Chief on Feb 17, 2011
  
  thanks, honestly the only significant risk at this point is cooling. i'm looking into semi sized cooling fans to move a bunch of air across the motor. the motor is in amazing shape. i had to make a few parts, but overall i lucked out and found a motor that had not been run to very long after it had been rebuilt. all the bearings were still in spec and very close to the new side of the specification. overall pretty amazing considering how cheap it was and that it was sitting in the corner of a barn. the rebuild date inscribed on the cylinders say 1944 and the lack of wear tells me it hasn't been started in at least 65 years. the other big risk is the drive assembly between the motor and transmission. it's a bit of a long shot and i have no idea how long it will last, but i suspect it should last long enough to impress most people :)
  
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- Morea on Feb 18, 2011
  
  The trick to keeping the temperature down is fin area and this engine doesn't have it. An out-of-the-box idea would be to take pieces of wire, wrap them around each cylinder, and then string them over to the adjacent cylinder like a big spider web. Use wire of the same diameter as the cooling fin grooves so they fit in snugly. Use copper for its good thermal conductivity. It will look strange but it will have tremendous fin area. (Or you could just mount an oil cooler in the nose of the car, but that's less fun!)
  
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- Madman-In-Chief on Feb 18, 2011
  
  the cooling is definitely a huge concern. you're quite correct that this motor has very short cooling fins. The upside is the motor is rated to 550*F head temperature. we'll probably be using most of this. we'll definitely have a huge oil cooler. the manual claims it does not want incoming oil to be cooler than 160*F. we'll use that as our target temperature. the plan is as follows, incrementing until we no longer have a cooling issue. 1) run on gasoline, use a radiator fan from a semi to move LOTS of air across the motor. 2) switch to E85, fatten up the mixture for the cooling properties 3) add a 10gal water tank and serious water injection
  
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- Mig29fuk on Jun 06, 2012
  
  @Madman-In-Chief Just found the Kinner Radial as used in Toyota. Are you still using it? My Google search took me to you as I'm looking for the same engine for my Vintage Airplane. Know of anymore available. Regards Gerry
  
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Phil K. on Feb 18, 2011

R-2800's are for nancy boys and Pirus drivers. Real men re-engine VW Type 2's with R-4360's, or Beetle / Dune buggy conversions with Dirty-Three fifties.

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