Here is the Evolution 4G63 head, very similar to the old style head in casting but has a few major changes. First off we all know the flow is reversed. That won’t make any major changes to performance though. The injector bosses are now in the intake manifold instead of in the cylinder head. Placing the injectors a bit further back will give better atomization and also a bit more power. Although the 5 to 10 mm of distance that it has been moved to, to be able to get a measurable power gain would be splitting hairs… but it is an improvement nonetheless.
The intake ports have now been made a more normal size. The 1G port was always in our opinion too large to get good low end velocity out of. This head is much more of an improvement over the 1G DSM. The port entry angle is only 10 degrees; whereas the 2G DSM head had a much steeper entry angle, which was better for performance. A lot of manufacturers are getting away from steep angle intake ports which we can only guess for two reasons. A) Low hood line and less complexity for intake manifold castings or B) Emissions. Sharper angles will promote more tumbling and better atomization, aiding in emissions controls.
(imusarjan + kannen)