7M-GE head differences
Copied from the original source (http://users.tpg.com.au/users/loats/technical/7mge/portdifferences.html) for archiving/back-up purposes.
It would seem that Toyota changed the 7m head cast a few times. what models these different casts came out in, and what year they changed their castings is unknown.
When pulling two same year model heads apart from the same car (1986 MA70 non turbo) and found two different types of head present. Also, a pulled down 1991 MX83 Cressida head is the same head as in an 86 supra. go figure?
regardless of where they came from, there is a distinct difference between the head castings (#9 and #11 anyway) in the intake ports.
Specifically im talking about the length and shape of the port divider.
See the images on the right for an example.
Image on the right: Casting #9 as i found fitted in a 1986 7m-ge from a MA70 supra. Note how the interport divider is quite long, and starts well before the base of the valve guides.
Its leading edge is rather thin, with a smooth radius. Such a port design provides a higher velocity, well directed flow to the valves.
Such a character would be good for low rpm torque, and smooth throttle response in lower range driving.
Image on the right: Casting #11 as found fitted on both a 1991 7m-ge MX83 cressida, and on a 1986 7m-ge MA70 supra. The porter considered this head to be the most profitable for higher end performance work.
He considered it to have better mass flow characteristics, and he thought that the Siamese valve configuration didnt need as directed flow as the top ,long divider offered. he thought that the blunt and short divider would provided a useful amount of tumble for good air fuel mixture, whilst it still did serve to accelerate the air velocity for lower end driving.
He thought the short divider would respond better mild porting, and overall, for a performance application, this was the better head to start work on.