What type of material is the insert for the exhaust port found in the 2nd gen motors made from?  Is it removable?  How could one enlarge the exhaust port?  Do you just use a turbo housing?  Thanks

 

Joe Berki

I don't know what it is, but it is harder than Chinese arithmetic. The liner allows for high exhaust gas temps without additional cooling. There is a thermal break between the liner and the aluminum housing. The 13B liners are much thicker than the 12A liners.  When the liner is removed the outer end of the port becomes much too big. So in the 12A engines a

replacement for the outer ring in aluminum is pressed in to replace the biggest part of the liner, sort of a thick ring at the outer port face.

 

Even when the 13B exhaust port is reshaped for racing, the liner is left in place. The port timing is controlled by the shape of the opening into the housing face of the port, and even extreme timing can be done without removing the liner.

 

Exhaust headers with 2" or just a bit smaller IDs are preferred. Exhaust gasses leave the housing supersonic, and at very low pressure. Great car should be taken to make the path flawlessly smooth for best performance.

 

The turbo housings have a smooth liner, as the hot side of the turbo will help silence the engine and adequate muffler design and complexity is much reduced.  The nonturbo housings have a wedge shaped half tube on the floor of the liner that breaks the flow into two paths and segments the shock wave, reducing its mass slightly and reducing the need for extra muffling. Wherever the exhaust flow slows to subsonic, there is the sonic boom from years ago. That must be managed inside of a very rigid muffler lest it drive you crazy, and disassemble the strongest muffler.

 

So the nonturbo housings are better from the noise standpoint. The loss of HP from the insert is very minor. 

 

Lynn E. Hanover