I recently found out that the L33 head has D-shaped exhaust ports.
Since every header I have seen is built with round ports, I am curious how this will affect the truck.

Does anyone know if this will make much difference?

 

Don't worry about it...the LS6/LQ9 heads are that way and MOST SBC heads are like that, until someone invents a D-shaped pipe to mate to it I wouldn't even think about it anymore.....

 

I havent seen any gm headers D-shaped, but mustangs have some available.

Someone is taking the time to match the shape, there must be a benefit.

how does the D-shaped port help the head?

here are a couple pics of a stang head and headers.
I know the head is ported, but it was the only decent pic I could find.

 

I read on another forum that MELEROSE makes headers with the D port for fast burn and vortec heads.

 

Lay the gasket over the header and see if there are any sections where the header tubing extends into the port. If so, carefully grind the tubing to match - just make sure you don't grind through the weld. If the header tubing is bigger than the port, everything is fine. Going smaller to larger is good, going larger to smaller is bad (causes lots of tubulance, which decreases flow) In the old days, this was called gasket matching.