from another forum wrote:I have seen people smooth the valve guides down so they are flush with the IN/EX channel, is there any reason for doing this, or is it overdoing it.?
good question....
I assume you mean something similar to this.....
![Image](https://gallery.ostportworks.com/albums/userpics/10005/no_guide_smallport_porting.jpg)
the actual 4AGE/ZE valve guide is all of 1.6" long....it holds the 4AG valve stable at valve speeds up to 75 opening/closings per second......
![Image](https://www.rockauto.com/info/850/GD8038__ra_p.jpg)
The more you shorten it, the less stable the valve becomes. Shorten it a little, and it isn't likely to be an issue, shorten it more....???
But how short is too short??
I can't tell you..... for I don't know. What I do know, is Loynings does use guides on many of their 4AG race engines, while removing the guide boss, they still keep the guides....
![Image](https://gallery.ostportworks.com/albums/userpics/10005/4ag_with_34mm_valves.jpg)
In the same breath... I have shortened guides in one of my head builds... but it wasn't a 4AG... and it wasn't shortening them as much as in the above photo.
I was building a 1GG head, and the guides were longer then the 4AG guides, with similar, or less lift then a 4AG..... so I shortened them
intake....
![Image](https://gallery.ostportworks.com/albums/userpics/10005/intake_ports_before_after_2_panel_larger2.jpg)
exhaust....
![Image](https://gallery.ostportworks.com/albums/userpics/10005/exhaust_ports__2_panel.jpg)
When I port heads I've tried to follow one underlying rule..... "do no harm"
![Wink ;)](./images/smilies/icon_e_wink.gif)