Last update: Feb 26 2015

Motor Adapter Version 2

This motor adapter design for Subaru EJ transmissions addresses some problems with my original design. I have not had this design fabricated. It is intended for future projects. This design uses the stock flywheel, which must be reduced in diameter to 10.875in. The adapter includes bolt holes for both the NetGain WarP 9 and WarP 11. To use this adapter with the WarP 11, you'll likely need to create some clearance space in the Subaru's engine bay by either shortening the motor tail shaft or removing the car's A/C condenser.

Features of this design:

I used the free eMachineShop CAD software to make the design. Install this software to examine the designs in detail. Click on the drawing images below to download the design files. This software includes fabrication pricing, which I used to figure and minimize cost. I've never had anything fabricated by eMachineShop so do not take my use of their software as any kind of endorsement.

discountsteel.com has low prices for 6061-T6 aluminum plate.


The housing is made up of two parts, a motor plate and a transmission plate. This two piece design requires much less raw material than a one piece design. The squarish shape of the motor plate minimizes waste even further.

The plates are aligned by a boss on the motor plate that fits into the middle hole in the transmission plate. They are fastened together at the corners by four metric class 12.9 socket head cap screws M12x1.75 length 50mm fully threaded.


Motor plate Transmission plate

Estimated cost $450 for the motor plate and $630 for the transmission plate.


The flywheel hub adapter is a custom quick-detach (QD) bushing with a custom compression ring. It is similar in size to a type SDS QD bushing, which has a torque rating of 417 ft·lb.

The QD bushing is mounted in the reverse configuration, with the flange outward from the motor. The flywheel bolts to the flange, which is directly on the motor shaft, so that the flywheel needs no runout adjustment.


Note that the QD bushing cannot be completed by eMachineShop because they do not offer keyway broaching.

Compression ring QD bushing

Estimated cost $320 for the QD bushing and $170 for the compression ring.

Cross Section

Here is a scale side view cross section of the adapter.

Cross section Cross section