Rotary Engine builder series blog post | Apex seals, which ones do I buy for my engine?

The opinions are many. It is my belief that it depends on how you are going to use the motor. Are you a street performance type of driver? or are you dedicated to on track performance. Of course if you are full racecar mode, only the best will do.

Let’s go through the basics of apex seal construction and performance.

OEM apex seals, Mazda has had a lot of experience in seal technology since they first came out with the Rx2 (or even the Cosmo or R100 10A motors) in its twin dizzy configuration. The first ones were 3mm wide and made of carbon, and for street driving, they led a lot of motors to fail. Mazda learned a lot from this experience and that led to the improvement.

Then came the steel ones that led to a lot of smiles per miles. Of course back then the only upgrades for more power were limited to porting and exhaust upgrades. They are very much the right way to go when cost and longevity are the priority on a basic rebuild.

What about upgrading to aftermarket apex seals? We are a strong fan of better products that lead to better performance with solid reliability.

RotaryAviation.com makes good apex seals at a good price. From their website:

• These seals offer 700% more bending strength and are 85% harder than other after market competitors . We offer Classic apex seals in 13B and 20B versions and with OR without apex seals springs.

• One of the main reasons for developing this product is to correct a problem seen in other seals - the tendency for them to develop chipped corners, especially under severe conditions such as detonation in turbo applications. Even though these new seals are harder, they are much less brittle than previously developed products.

AtkinsRotary.com is another supplier of apex seals. These seals are heat treated, meaning they can handle the high pressures of turbocharging. I do not recommend these on resurfaced rotor housings as they are hard seals. I have seen them work well with racing engines and solid street performance applications.

The forums (rx7club.com) have done a good job of sharing opinions and experience. Caution, reading opinions online is only as good as the price of that information.

Ceramic apex seals are the ultimate seals for racing engines. Now, not every racing engine is going to need these, they are expensive, and for the most part, they are worth it. They don’t break, they can handle high heat and the best part is how light and resilient they are. I still have a 12A full bridgeport motor with the original ceramic seals in them after 14 seasons and many racing miles.

I buy them from the only manufacturer I trust, they come in 2 piece and come with matched springs built for racing applications.

So, what apex seals should you use? I’ve only mentioned a few aftermarket ones and the OEM seals, they all have their intended application. I would never put ceramic seals in a street motor, that is a waste of good racing parts and money.

This is where having a real conversation matters. All opinions are just that. Because you read it online doesn’t mean it is the only way to go. I’ll share what I know and make recommendations on what I believe is best for your objectives. The decision is yours, remember that every engine build will get a comprehensive list of upgrades that meet or exceed your requirements, we do not take shortcuts.

• Get the horsepower and reliability of a solid rotary engine build. Not all engine builders are the same, We have 25 years experience with the rotary engine with connections to some of the fastest racers in the USA, results matter.