Dispelling Myths: Using RX-8 internals in a 13B-REW

[Chadwick]

Rumors, myths and facts…. When the RX8 came out I wonder how many parts from the motor could make the move to a 13B-REW. Unfortunate most of the information found on the internet was more rumor than fact. I am still amazed that 5 years later it is still almost impossible to find accurate information about what can and can not be used.

Challenged with getting the most out of the new motor I’m building for this race season, I started to dig a little further on what could be used to increase performance. The first place I looked was the RX8 rotors and e-shaft. I knew I wanted to increase compression to gain low end grunt and thought 10:1 would be super. It didn’t take long to figure out that the design of the RX8 rotors would be a less than stellar choice so I went with the 9.7:1 rotors out of an 89-91 NA FC.

Now the eccentric shaft was a different story, it was pretty common knowledge that it was lighter but there was a ton of conflicting information about its strength and design and if it would work in a 13B-REW. Also how much lighter was a big question, I saw everything from two pounds to 4 ounces.

The only way to know for sure was to bite the bullet and order one. First thing I did was compare it to a 13B shaft….

RX8 shaft on the bottom:

RX8 shaft on the right:



Well they looked identical, every hole and taper. My friend Brian who is a Mechanical Engineer measured the bearing journals compared to a 13b shaft. The RX8 shaft is .0003 less in diameter then a stock 13B shaft. It also weighs .4 lbs less than a 13B shaft. Well within spec to be used in a 13B motor

Now another rumor is that the RX8 shaft is lighter thus weaker than the 13B shaft. Quite simply this is not true. It is manufacture exactly the same way as a 13b shaft. It is lighter because there is an extra hole drilled into each lobe. As this area is not a high stress point it will not affect the strength of the shaft in the slightest. It may even prove out to be stronger as metal forging and tempering techniques have improved over the last 10 years.

RX8 Shaft on the right:


The next parts I looked at where the stationary gears. Now there was a bit more accurate information to be found on them so it was an easy choice. The front stationary gear is functional identical on both engines. The only difference I notice was the alignment notch is rounded on the RX8 gear and square on the 13B.

Front stationary gear, RX8 gear on the left:





Now the big difference between the rear stationary gears is the O-ring grove. The RX-8 stationary gear does not have one as it uses a grove on the rear housing for an o-ring to seat. In talking to several builders they all suggested using hylomar or silicone to seal it. Although I agree that a sealant would work, I’m a bit anal and wanted to use an o-ring. I had my friend Brian take it to work so one of their machinist could match the 13B grove.

Both stationary gears came with bearings installed and the rear gear has the rear main seal. They are both considerable cheaper to buy than new 13B-REW gears.

RX8 rear stationary gear




Picture of the grove machined into RX8 stationary gear to match 13b stationary gear:



So here are the facts:

You can use a RX8 eccentric shaft in a 13B-REW with no modification. (note: I do suggest having the rotating assemble balanced when ever replacing one of the parts.)
The RX8 eccentric shaft weighs .4 lbs less than a 13B-REW shaft
The RX8 front stationary gear is a direct replacement for a 13B-REW gear
The RX8 rear stationary gear can be used as a replacement for a 13B-REW gear but will require the use of a sealant or have it machined for an o-ring for a proper oil seal.

Part Numbers;

RX8 Eccentric Shaft: N3H3-11-D00
RX8 Front Stationary Gear: N3H3-10-E0YC
RX8 Rear Stationary Gear: N3H3-10-E1YC

Hope this helps,
Dan