Whats wrong if I only bridge porting the primaries? and leave the secondaries with overlap.is this possible? .thanks for any sugestion

 

If you look carefully at how the rotor passes the ports, you will find that opening the port at all toward housing will open the port earlier, causing more overlap. A bridge port on either the primary or secondary ports will only cause more overlap than stock.

 

Bridgeporting only the primaries is fairly pointless unless you just want the bridge for the noise and poor fuel economy. The primary runners are small and the primary port closes much sooner than the secondary. You can hog them out to roughly match but that doesn't improve flow much.

If you are going to perform a half bridge, then that is applied to the secondary ports. Much larger runners, way more port area and timing.

 

For best drivability, if you are only bridging two ports, you want those ports to be the ones you idle and cruise on.

I did a bunch of work on my half-bridge engines to get good drivability and most of it centered on reducing/eliminating vacuum on the bridged ports while maximizing it on the unbridged ones. Mainly, the fuel pressure regulator and brake booster were moved to the primaries, and the secondary throttle plate was used for idle speed control while the primary side got no airflow at idle except for what came through the air bleeds.

A half bridge on the primary side would have been simpler to do. Power-wise, the half bridge made about the same peak HP as the street port I based it on, BUT the powerband shifted down a lot in RPM making for a much faster on-course engine.


I eventually said screw it and went full bridge with poor man's ITBs. It has the low end power of a half bridge but top end pull as well. The ITB characteristics give great drivability on the street, too. People who borrow my car rave at how the engine just pulls hard, from any RPM, to any RPM...