|

I have B20A & B20E heads that look like the 2nd head.(with & without injectors holes of course)
I think:
The heads without the isthmus are pre-1973.
The heads with the isthmus are 1973-1975 model heads.
The heads with double isthmus are R-Sport.
The only difference between an E & an F head is the thickness.
The heads without the isthmus have an exhaust port floor which raises up roughly 1/8" from port face to the seat. They flow better than the other type when left stock.
The heads with the isthmus have an exhaust port floor which raises up roughly 1/4" from port face to the seat. They flow worse than the other type when left stock, but are much better after porting.
I raise the floor of both.
|