So at the end of summer I had a brief trip to Finland to experience what life was like in a Nordic country where you had to pay 9 euros for a beer. On the plane there I had some excellent reading material in the form of this little number:

 

 

This is an excellent read for anyone planning a rotary swap or generally wanting to get a handle on what rotaries are about. The book details the development of the 13B-MSP (multi side port) or Renesis as it’s known, the latest naturally aspirated iteration of Mazda’s iconic rotary.

 

Most of the principles behind the Renesis are identical to the older 13bs and even 12as. Some of the differences, however, proved to be dealbreakers:

1. Exhaust ports

The exhaust port difference is the most radical change to the Renesis. All of the 13bs before the Renesis featured a ‘peripheral’ style exhaust port, ie. The port exited through a large radially positioned hole straight through the side of the rotor housing. The Renesis employs a side port for the exhaust, much like the intake port on a standard 13b or Renesis.

 

While being smaller in surface area the side port design results in no overlap between the intake and exhaust ports being open (like valves being open on a regular piston engine). This results in a much stronger pull through the mid-range RPM. We’ll come to this later.

 

Another benefit of this is that the exhaust stroke is more effective (explain), with the spent gases being almost pumped out of the chamber. This, along with a slightly higher compression and larger intake ports, mean the Renesis rivals the power of a 13b-REW without even having a turbo.

 

2. Exhaust Manifold Design


Another benefit of this is that the exhaust manifold can afford to be little bit more shit than that of the RX7 engine. Which is ideal considering how tight the space is between the exhaust ports and the MX5 steering rack. The older 13b relies a lot more on backpressure generated through properly made exhaust headers than the Renesis, due to this exhaust port design. Is what I learned.

 

I had this information confirmed to me by Carl at Haywood Rotary in Newbury, Berkshire.

 

Carl also made a convincing argument for how much easier it would be shooting for the higher numbers by using an engine which came with higher BHP anyway (obvious stuff I know). Shooting for the numbers the Renesis has as standard with Series 5 13b would be costly. Looking at the engine I had, I’d already be looking at chucking at least about £500 at the thing to make it even work properly (housings, o-ring kit, side seal springs). I could spend that money and instantly be nearer my bhp target…

 

3. Price


Renesis parts are cheaper than older 13b parts. Simple as that. It’s even worse if any of those parts happen to fit the 13b-REW (As fitted in the RX7 FD). Rotors, housings and manifolds fetch silly money on eBay. Luckily the Renesis was a major redesign over older series 13Bs, so almost none of the parts are compatible. This, combined with the sheer volume of failed engines in sad looking 65’000 milers made for cheap spares in the future. As a stingy bastard with few pennies, this was a major deciding factor.

 

Over the phone we came to an informal deal about swapping some of the Series 5 engine parts I had for some engine work in the future,  it quickly became apparent that switching to the newer iteration of the 13b made absolute sense. Through deals, planted ideas and long term planning, I started perusing eBay again.

 

The number of dead RX8s on eBay is staggering. It made me thing that perhaps Mazda made a mistake marketing a (comparatively) highly strung rotary engined vehicle as a performance family car. Talking to a few owners who were clearly looking to salvage what they could from a loss, I had images of people relying on Halfords style engine maintenance and simply not budgeting or expecting to have to rebuild every 60k miles.

 

So not one to waste time I got on the case of getting a Renesis. It was a quick dart down to Ellesmere Port to pick up engine from a friendly lad with a rear-ended RX8. We man handled the nearly bare engine into the Legacy and it was back to the workshop.

 

The Renesis is basically about as heavily ported as the 13b can really get without going for a peripheral port. Carl assured me that the peripheral port was a definite option, but that it was strongly advisable to get the engine running first before going for such an extreme port. And I agreed.

 

So that was it. Change of plan. I finally bullied Adam into moving Schfifty out of the ‘project car’ spot in the workshop and started ripping the engine out of mine.