the difference in the 1700 and 2000 intake and exhorts ports

[stew 89]

I found this interesting thread on another forum...

http://www.shoptalkforums.com/viewtopic.php?f=1&t=71523

Please enjoy

[Dawie]

Note the date of that thread is 2004. That cutaway of 1700 port is two dimensional, and does not show the complete picture. On both sides of the valve guide boss, there is some space to compensate.

Since 2004, the same contributors to that thread have changed their minds. After flow bench testing, Len Hofmann (Ham inc.) believes that oval port heads's exhaust side out perform the square port ones.

Other issue with square port heads is the larger surface area of the exhaust port exposed to exhaust gases, causing slightly higher cht's. Main idea of oval port exh design was to reduce surface area where aluminium (excellent heat conductor), is exposed to exh gases exceeding 800 degs c.

In fact, Porsche used ceramic port liners inside their 993 engine's exhaust ports. To insulate head from hot exhaust gases inside exh ports. This was so effective in reducing head temps, that sodium cooled exhaust valves were no longer found to be necessary. So they could use plain valves there. Think at the same time they also reduced cooling fan output to prevent overcooling.

In a subsequent thread on STF, some flow numbers were posted. Note that the 2L 914 head is completely different from the 2L oval port kombi head or 2L square port kombi head. Square port 2L head was used by last year bay production and air cooled box shape combi's. Reason for square port design was said to be for easier fitting of heat exchangers.

But remember differences are small, so i would not worry to much about them.
Think red was referring to late 2L square port heads.

[eben]

The LE-200's are aftermarket heads by HAM inc.
http://forums.aircooledtechnology.com/s ... 335&page=6