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Jeff20B · 10-20-2008, 03:42 PM

Thanks for posting, guys. I like feedback.

Turns out my bus tranny is closer to a '74 year model. It ought to work out fine with a rotary.

The Wulff is almost correct. The only parts that aren't vintage '70s are the side plates and front cover. Dizzy and alt, too. The side plates are nitrided Y castings from an FB and so is the front cover (the OMP is the leaner type but I can jack it open more with a couple washers). The rotor housings are from a delivery van or the Parkway Rotary 26 (a 26 passenger bus in Japan), or possibly from a JDM Cosmo or Luce from perhaps 1975 as far as I could tell from the original parts that made up this engine. I upgraded key areas where I saw fit.

1. Nitrided Y side plates offer less friction/wear/heat/weight.
2. New side seals with around .001" clearance for really tight gas sealing. For naturally aspirated use only (you'd want at least .003" for boosted applications).
3. FC aluminum waterpump housing and aftermarket FB aluminum GMB impeller for maximum weight savings (only recommended with an electric fan because a clutch fan stresses the waterpump housing).
4. '76 Cosmo reversed runner intake manifold for longer primary runners which should equate to more torque. Matching carb with correct air bleeds and fuel jets for good driveability from idle up to 6 or 7k or whatever red line is on a Cosmo.
5. Stock intake port timing for maximum low RPM torque and driveability. All sharp 90° edges and casting flash were smoothed so hopefully it retains enough turbulence at low RPM to keep a strong idle. High RPM total flow should be improved over stock.

One feature of the original engine I kept is the '75-'85 1757 rotating assembly which was the heaviest stock rotor set; perfect for low RPM torque.

I also kept the exhaust ports stock. They had the late opening later closing port timing of a GSL-SE, which apparently is best for low RPM torque because the delay in opening provides more time for the expanding gasses to push the rotors and shaft around, but supposedly peaks in effectiveness by 4k RPM. Fair enough.

I went with an RX-4 radiator and drilled new stock Mazda thermostat. Two electric fans, one pusher one puller, should cool well enough. They will be installed where space permits allowing as short a rear push bar as possible to reduce 'moment'. It now protrudes just 3 inches more rearward than with the bug engine.

10-20-2008, 03:42 PM	#10
Jeff20B Rotary Fanatic Join Date: Mar 2008 Posts: 215 Rep Power: 18	Thanks for posting, guys. I like feedback. Turns out my bus tranny is closer to a '74 year model. It ought to work out fine with a rotary. The Wulff is almost correct. The only parts that aren't vintage '70s are the side plates and front cover. Dizzy and alt, too. The side plates are nitrided Y castings from an FB and so is the front cover (the OMP is the leaner type but I can jack it open more with a couple washers). The rotor housings are from a delivery van or the Parkway Rotary 26 (a 26 passenger bus in Japan), or possibly from a JDM Cosmo or Luce from perhaps 1975 as far as I could tell from the original parts that made up this engine. I upgraded key areas where I saw fit. 1. Nitrided Y side plates offer less friction/wear/heat/weight. 2. New side seals with around .001" clearance for really tight gas sealing. For naturally aspirated use only (you'd want at least .003" for boosted applications). 3. FC aluminum waterpump housing and aftermarket FB aluminum GMB impeller for maximum weight savings (only recommended with an electric fan because a clutch fan stresses the waterpump housing). 4. '76 Cosmo reversed runner intake manifold for longer primary runners which should equate to more torque. Matching carb with correct air bleeds and fuel jets for good driveability from idle up to 6 or 7k or whatever red line is on a Cosmo. 5. Stock intake port timing for maximum low RPM torque and driveability. All sharp 90° edges and casting flash were smoothed so hopefully it retains enough turbulence at low RPM to keep a strong idle. High RPM total flow should be improved over stock. One feature of the original engine I kept is the '75-'85 1757 rotating assembly which was the heaviest stock rotor set; perfect for low RPM torque. I also kept the exhaust ports stock. They had the late opening later closing port timing of a GSL-SE, which apparently is best for low RPM torque because the delay in opening provides more time for the expanding gasses to push the rotors and shaft around, but supposedly peaks in effectiveness by 4k RPM. Fair enough. I went with an RX-4 radiator and drilled new stock Mazda thermostat. Two electric fans, one pusher one puller, should cool well enough. They will be installed where space permits allowing as short a rear push bar as possible to reduce 'moment'. It now protrudes just 3 inches more rearward than with the bug engine. Last edited by Jeff20B; 10-20-2008 at 03:46 PM.