It was one of those sleds that you knew had to come home with you. When I first checked out the 1971 Arctic Cat Lynx Wankel snowmobile, I knew I wasn’t leaving without it. It even came with three spare engines! The seller started it up and it idled with authority, a deep, loud, rolling drone.
Although the Lynx is very mild-mannered and not super fast, I’ve seen these rotary engines produce impressive power with remarkable reliability in the Mazda cars at the drag strip. That’s when the idea to turbo charge a Wankel snowmobile hit me. I didn’t want to hack up the Lynx, it’s in very nice rideable condition, so my son and I walked down to our Cat graveyard. With 28 or so Arctic Cat Puma, Cheetah, and Panther carcasses to choose from, our deliberation was long and hard.
Finally my retired “racer” was the chosen one, a ‘72 Puma I had ridden for the past 9 years. Although it has plenty of stress cracks, a battered belly pan and had been through at least a dozen engines, it had the right track and suspension setup. The track was involuted drive with ¾ cleats out of a ‘73 Cheetah. This longer track worked well under the short Puma chassis.
The turbo is a cute little unit that came off a 1989 Ford Thunderbird Super Coupe. It originally fed a 4-cylinder engine and had all the plumbing with it. I wasn’t sure if the 303cc rotary engine would spin the exhaust turbine fast enough to create boost.
I took the most beat-looking spare Wankel and fit the turbo in front of it. After making a flange to feed the exhaust into the turbo, I installed the unit into the sled. The hood fit and closed nicely. By mounting the carburetor directly to the turbo intake, I avoided having to modify the carb to run in positive pressure. An electric fuel pump had to be installed because a pulse-type pump would stop working when boost pressure was present.
Turbo shaft lubrication was also a problem, since the Wankel runs on mix; there is no oil pressure. An electric oil pump was the answer. Electric scavenger pumps are expensive: two or three hundred bucks. I tried a high-pressure automotive fuel pump with 5W-20 oil, and it worked well. I adjusted the oil pressure to 25psi by installing a restrictor in the return line. This particular pump normally runs at 60psi so it should be able to handle the oil at 25psi. I expected the oil to pick up a lot of heat, so an oil cooler had to be installed. It’s out of sight under the seat, with a hole cut out of the tunnel under it.
All I wanted to do at this point was start it and see if it made boost. Since the drive chain wasn’t installed yet, I “dyno-tested” it by loading the brakes. After a couple of primer pumps, it started and idled smoothly.
As I slowly opened the throttle, it quickly revved, the clutches shifted out, and smoked the brake pads! I was yelling “holy mackerel” in the smoke-filled garage when I realized I forgot to look at the boost gauge, so I had to do it again. It made 6psi without a real load so I figured it should make more than that on the snow. The wastegate is set at 9psi. I know this looks like something out of a Mad Max movie right now, but please keep in mind this is prototype version 1.0.
After the dry run, I took that turbo out on the snow for a real test on a ½ mile stretch nearby that I could open it up on. Wow, it really pulled hard! I could actually pull away from a 440 Puma with my 103 lb. son on it. The top end was scary, it just kept revving. It ran nice, making about 9 lbs. of boost and maintaining about 1,000 degrees exhaust gas temperature. I took a few more test runs then came back to lean out the lower end a bit (it was running a 510 main jet.) I had it real fat to start, just to be safe, and dropped the needle to clean up throttle response.
During the last run we heard a squeaking noise and lost all boost. I took the carb off and found the intake fan of the turbo destroyed. The center nut on the turbo shaft came loose and got ground up in the turbo fins! What a horrible sight. I had to take Tylenol PM to sleep that night. I think the engine is okay but the turbo is junk. Oh well, back to the R&D drawing board!
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