Rotary Resurrection - Tech Section
 
DIFFERENCES BETWEEN 86-91 NONTURBO DRIVETRAIN AND 87-91 TURBO DRIVETRAIN

When dealing with drivetrain components (flywheel-back) all the components are different between nonturbo and turbo models, so you cannot just swap one part (the transmission, for instance) but you must swap them all at once. For many people this seems hard to believe or understand so I am making this writeup to clear up confusion and further document the turbo swap requirements. Keep in mind all the turbo model parts are different, generally slightly larger and stronger than the non-turbo counterparts.

FLYWHEEL:
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Nonturbo flywheels are smaller diameter than turbo flywheels. Rotary engines only use these 2 diameters for all applications, though the weights and styles changed a bit through the years.
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The turbo flywheel is a good ¾” larger diameter than the nonturbo version. Because of this, clutch diameter, presureplate diameter, ringgear diameter, and starter placement were all changed.
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A turbo flywheel of the same year as a nonturbo flywheel will be balanced the same, meaning it can be bolted to any engine of that same year. For instance, an 87-88 turbo flywheel is a direct bolt onto an 86-88 nonturbo engine block, because balance is the same.
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Turbo flywheels weigh more than the smaller nonturbo counterpart, even though balance is the same.
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Turbo flywheels are flat faced, while nonturbo flywheels have raised mounting pads for the pressureplate.
 
 
 
Turbo flywheel on top, nonturbo on bottom.
 
 
CLUTCH:
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Turbo clutch/pp is larger diameter than nonturbo clutch/pp, to match the diameter of the flywheels.
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Due to larger diameter, the turbo setup has more torque holding capacity than the NA, even though the disc material and clamping rate is about the same.
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The splines in the center of the discs are different between turbo and nonturbo. You cannot swap them out, the splines on the transmission input shaft are different.
 
 
Turbo clutch on right, NA on left.
 
Here is the difference between the diameter of the turbo splines (indicated on gauge) and the nonturbo splines (pictured).
 
 
SLAVE CYLINDERS:
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Turbo and nonturbo slave cylinders are different. The mounting points were changed due to bellhousing differences. They can not be swapped.
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IF you are in a big bind and need a turbo cylinder, you can modify a nonturbo cylinder to work, by cutting about 3/8” to ¼” off the rod length on the INSIDE end, and then grinding it in a half-sphere so it fits properly inside the slave. Pedal adjustment may be required.
••  
Cylinder strength, length, and bore are the same. Just the position of the mounting feet.
 
 
TRANSMISSIONS:
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Nonturbo trans is weaker internally vs turbo trans.
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Nonturbo has smooth external case, turbo has ribbed case with removable bellhousing.
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Due to the change in bellhousing and flywheel diameter, the slave cylinders had to be changed, and are not interchangeable.
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Both use the same bellhousing/engine bolt pattern, bolt to any rotary engine.
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Splineshaft diameter and spline pattern different between turbo and nonturbo
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Gear ratios in turbo models slightly shorter for acceleration
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Use same shifter housing and shifter
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Starter location moved due to bellhousing/flywheel differences
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Location of reverse/5th gear switches different, turbo car harness uses longer wires because sensors are farther back.
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Output shaft diameter and spline pattern is larger on turbo models than the nonturbo. This means the driveshaft front yoke is also different. The turbo and automatic transmissions share the larger front yoke/output shaft pattern, while the nonturbo is smaller.
 
 
 
Turbo trans on top, NA on bottom. Note change in mounting hole position for slave cylinders (turbo is farther down).
 
 
STARTERS:
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Solenoid on top for NA, on bottom for turbo because it had to be moved to clear the ribcase.
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Mounting position further out for turbo models due to larger flywheel/ringgear
 
 
 
Note differences in turbo and nonturbo starters and positions, NA on left:
 
 
DRIVESHAFTS:
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Same lengths
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Turbo driveshafts are larger diameter than most NA driveshafts. There are a few early NA driveshafts that are fat versions, but are not stronger than the skinny versions because the joints are the same size. I do not know why some of the NA’s were fat while most were skinny.
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Turbo driveshafts use a larger front yoke diameter and spline patterns than the NA driveshaft. This is one reason you cannot use an NA driveshaft on a turbo tranny.
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Turbo driveshafts have a larger rear flange and bolt pattern than the nonturbo. The turbo rearend input flange is larger as is the bolt pattern.
 
 
 
Turbo driveshaft on top. Note larger diameter and ujoints.
 
 
Difference in front yoke diameter and spline pattern.
 
Difference in rear flange size and bolt pattern.
 
 
REARENDS:
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Turbo and nonturbo rearends are not the same size, though they do bolt up in the same position inside the car.
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All north American turbo rearends are 4.1 LSD. Nonturbo rearends range from 3.9 to 4.3 and can be open or LSD. 86-88 rears are clutch type LSD where applicable, 89-91 are viscous type LSD where applicable.
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Input flange diameter is larger on the turbo model than the nonturbo, and the bolt pattern is also larger. This is why one driveshaft will not work with another rearend.
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Turbo rearends weigh a few more lb and are physically larger. Ring gear diameter is larger as well.
••   Width of the diff is greater on the turbo model. The diff/axle combo had to fit in the same car/width, so the axles had to be shortened to accommodate this on the turbo model. This is why axles must also be changed.
••   The output shafts (that axles bolt to) are larger and have different bolt patterns between turbo and nonturbo. Even if you tried, you could not bolt up an NA axle to a turbo rearend, or vice versa.
 
 
  Note difference in size and width of diffs, turbo on left. Mounting points remain identical.
 
  Difference in input flange diameter (turbo pictured, nonturbo indicated on gauge)
 

  Difference in width of rearends at output shafts (about 1 inch):
 
 
AXLES/HALFSHAFTS:
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Turbo axles are shorter then nonturbo axles due to rearend widths.
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Turbo axles are thicker than nonturbo axles on the shaft, as well as at the bearings.
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Turbo axles have a different bolt pattern to the rearend’s output flanges between turbo and nonturbo.
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Both axles have identical spline patterns, so they work with any rear hub/suspension from a 2nd gen…4 lug small, 5 lug small, 5 lug large.
 
 
  Difference in length:
 
  Difference in output shaft bolt pattern (turbo shown, nonturbo indicated on gauge)
 
Rotary Resurrection - Tech Section
 
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