OST-093: My, My, Mystery

[oldeskewltoy]

Current build, so not a "Catching Up" thread.




Essentially there are 3 types of 16V 4AG heads. There are 2 versions of the largeport, and of course the smallport.

The early largeport (1984-1987) was originally designed/built(?) by Yamaha, where the later ones(1987-1989) were changed and made by Toyota(?). You can see some of the changes in the following photos...







If you watch Garage 4AGE's videos you may have seen the earlier head makes a bit more power. This is likely because at the bowls the earlier heads have a better shape as the bowl turns to the valve...



... BUT there is more room in the floor of the later head (arrows).

I've come to the conclusion that the later heads were partially designed to better accommodate Formula Atlantic engine builders....... but that's another story...



The Mystery here is the head I'm working for OST-093. It appears that it is a mixed head, with some newer features, and some older features......




more to come......