Join Date: Mar 2006
Location: Worcestershire, UK
After seeing this thread Friday, I happened to be working on the heads for my 'new' V6 build and took the opportunity to put a gasket on the exhaust port. Not as bad as the worst one shown here, maybe half way between the good & bad.....but I'm taking the time to open them out to match the exhaust flange, as I'll be making new headers for this one. If I was sticking with the cast manifolds, I might not have bothered, as they kind of match the ports...although not particularly well it must be said. IIRC, the gaskets are usually 'blown out' around the top edge.
I recall seeing a thing ages ago about having a huge bore exhaust system with a step at the bottom of the port to supposedly give the best of both worlds. I think the idea was that at low volumes, the gas trickled over the step and didn't get sucked back in, but at high volumes, it whizzed round the top and didn't 'see' the step. Sadly, I can't recall the results of their experimentation. The fact we don't see these things in the wild might suggest it didn't work! Another variation was again a very large bore system, but with short inner smaller bore 'stubs' at the head. Again...no idea what the results were.