74-85 12A / 13B 4-Port Street Porting

Main Engine Page | Mazdatrix Home Page

Port "timing" in a Rotary Engine is equivalent to cam timing in a piston engine.

To change intake port timing (as done in street porting), the upper edge of the intake port is raised (later intake closing and longer open duration), and the side is moved slightly out (it can not be moved very much due to the corner seal and apex end piece needing support).
To change exhaust port timing, the upper edge of the exhaust port is moved up (later closing) and/or the lower edge is moved down (earlier opening) which also gives more exhaust duration.

The port runners also are worked on.
This was a VERY simple explanation of what constitutes "street porting".
Click here for the FAQ on how the porting is done.

We still adhere to our engine building policy of not wanting to increase the power of the base "A" level engines (using used rotors and used rotor housings). We therefore will only port "C" level and above engines.

Part Number (74-85 4-Port) to Add to your engine order:
Part Number/Cost Description
SV-PORT-S4P Porting of four intake ports and both exhaust ports
Other (Partial) Options: for housings sent in, or rebuild of previously ported engine -
SV-PORT-SEXH Street Port two exhaust ports only
SV-PORT-SINT Street Port four intake ports only

74-85 4-Port Street Porting Images 4 Port Street Port
4 Port Intakes
Intake Ports		 4 Port Exhaust
Exhaust Port
Ported vs Original Exhaust
Ported exhaust vs. original 		Ports

Also, please remember that any porting is not emissions legal, and may result in your vehicle failing emissions testing.

Main Engine Page | Home Page