I'm working on the Vette finally and need to make some decisions about exhaust. I got shorty headers from Angry which I like. They have rectangular ports. The heads on my LT1 have rounded off square ports. But my information says they should have "D" shaped ports.
They definitely do not look "D" shaped. The picture in the build book I have appears misleading. I think the "D" shape was made by the gasket and perhaps the manifold.
The header openings.
Definitely not D port according to the b&w picture you posted. The head and the header should mate well. How do the heads and header flange match the gasket?
Not a d port. Standard ports. Headers are standard ports too. Just get regular truck gaskets.
100 percent ok if the header is bigger than the head. It actually makes an anti reversion dam
The thing you run into with LT1s is that while the bolt pattern and exhaust port layouts are the same as small block Chevy, the ports themselves are higher up.
Generally speaking, headers built with SBC flanges will overhang the top of the exhaust port.
Get LT1 exhaust gaskets (yes, they are different from SBC, SBC gaskets overhang the port too) and do a check. That photo from the book/magazine is a little misleading because it's difficult to see the port outline through the carbon deposits. Look carefully, the ports are actually the same as yours.
As pointed out, headers larger than the ports are good, headers that overhang the port are bad. That photo had OE manifolds/gaskets which were significantly larger than the actual port window - on purpose.
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