Engine Tech, Building the Nissan VG30DETT part 2


VG30DETT-Build exhaust port
The exhaust port has a nice smooth line of sight shot from the combustion chamber.  The white stuff is thermal barrier coating.  The coating sends more heat downstream to help spool the turbo and keeps it out of the water jacket.

The valve contours were also smoothed to improve the flow.  The valves were reshaped in the area leading up to the 45 degree sealing surface.  The stem diameter was also reduced in the area of the valve head.  The valve job and valve re-contouring greatly help flow especially at low and partial lifts. It lightens the valve as well.

I think I should have taken the pictures before the coatings as the coating makes the port work hard to see.  The valve job is a 3 angle and the valve seat is blended smoothly to the bottom angle and the port.  You can see that the combustion chamber is unshrouded near the valves. The white thermal barrier coating is apparent in the combustion chamber and the exhaust port and the black flow coat is visible in the intake port.

Since it is impossible to port our complicated, dual plenum chamber upper manifold without cutting it up to gain access to the insides, we sent it to Extrude Hone to have it ported by their patented abrasive flow method.  Extrude Hone uses a unique pump to push a slurry of a special polymer that has an abrasive mix of tungsten carbide or aluminum oxide particles mixed into it through the ports at a fairly high velocity.  This process can port the insides of even the most complicated part.  The intake manifold’s flow was increased by nearly 20% with the runner to runner variation reduced to 1 cfm, this was over the stock manifold’s nearly 20 cfm of variance.

What a nice head!

While we were at it, we also extrude honed the exhaust manifolds, the 02 sensor housings and the turbocharger’s intake and exhaust housings.  In testing by Garrett, it was found that extrude honing can increase turbine efficiency by as much as 3 percent, a sizeable amount which reduces the amount of backpressure the turbine creates as it recovers enough energy from the exhaust stream to spin the compressor.


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