Studding & Dowel Pinning

Studding & Dowel Pinning

Doweling and studding is one of the best strength modifications that we offer for all rotary engine blocks. This modification is widely used among high-powered racing engines and turbocharged or boosted street engines. Although the processes for Doweling and studding are different they perform the same primary function. If the customer chooses, we can combine the two procedures on the same engine but under normal circumstances we offer one or the other.

Dowelled Rotary Engine

All Mazda factory rotary engines use 2 dowell pins for each rotor housing. The function of the these dowells are mainly to align the the housings themselves. These dowels subsequently become the “load points” or pressure zones when the engine is under stress or making excessive power. One of the most catastrophic repercussions of too much stress on these load points is fatiguing, cracking or destroying the end housings. Detonation for example, can exert so much force against the rotor housing, exerting pressure to the Dowel and thus cracking the Dowel bore in the rear iron. This not only results in the need to replace the rear iron but makes a big mess as the pressurized engine oil is forced through the damaged area. In worst case scenarios, should the engine lose too much oil, the bearings will starve for oil and the engine can seize.

REC’s methods of doweling or studding will give you all the additional strength and protection your engine could ever need. With either choice, the additional dowels or studs remove the load from the factory alignment dowels and distributes excess pressure evenly across the engine’s mass.

Each process requires the engine block components to be machine on a CNC. The fitment of the additional dowels or studs needs to be very accurate and consistent from one piece. To achieve this 100% accurately, we have to have a special jig and fixtures manufactured to hold the different shaped housings. Once all the CNC machining is complete, we then go ahead and re-thread the tension bolt threads in the front iron. Now the engine is ready for normal assembly, and just before installing the rear iron, the studs or dowels are inserted into their respective locations, torqued, and the engine can be completed as per standard assembly.


This process utilizes 3 to 5 additional one piece dowels which are strategically installed in the combustion area of the engine only. Dowling is recommended for hp requirments above 200hp per rotor but not exceeding 350 hp per rotor.

Cost: $340.00 per housing. (This includes CNC work and Dowel pins)


This process means we transform EVERY tension bolt hole into a stud location. These 12.7mm (1/2 inch) studs are almost 3 mm thicker than the factory 10 mm tension bolts. This helps fortify the strength of the clamp load when the engine is torqued, and at the same time each precision ground stud acts as a dowel within the tight tolerances of their respective bores. Studding is recommended for hp requirments that are greater than 350hp per rotor. We have seen this method reliably hold power of up to 575hp per rotor burning methanol. This translates to 1150hp on a 2 rotor and 1600hp on a 3 rotor.

Cost for 13B: $1245.00. (This includes all CNC work and XR 12.7mm stud kit)

13B Custom Stud Kit

This video shows all the strength and performance modifications that REC chose and performed including a full stud kit. This is a full buildup video showing the engine being assembled from start to finish.