4AGE gas flowing and big valves etc

[Keri-WMS]

Has your car been off the road as long as mine...2006 and counting!!

Mine went bang in Aug 2007! F##?@@@G B####@D!

[Fab4MR2]

I hope it works for you, but I am worried about the valve guide boss, and valve guide reductions. I also thought doing that might be a good idea, before I had my head work done, but a lot of research showed that it isn't necessarily a good idea. You've removed a very large section of valve guide that would normally control valve movement, which needs to be pretty precise so as not to wear the valves and valve seats out prematurely. No builders that I talked to thought the extra flow was worth the loss of valve control. Those valve guides aren't that long to start with, and you have removed about 1/3 of their length. Plus if you didn't start with new guides then you are looking at even faster valve and seat wear.

[Jim-SR]

I hope it works for you, but I am worried about the valve guide boss, and valve guide reductions. I also thought doing that might be a good idea, before I had my head work done, but a lot of research showed that it isn't necessarily a good idea. You've removed a very large section of valve guide that would normally control valve movement, which needs to be pretty precise so as not to wear the valves and valve seats out prematurely. No builders that I talked to thought the extra flow was worth the loss of valve control. Those valve guides aren't that long to start with, and you have removed about 1/3 of their length. Plus if you didn't start with new guides then you are looking at even faster valve and seat wear.

ive seen a couple of race 4A-GE heads with the guides cut back flush which didnt have any major issues across a reasonable service interval. generally if someone is running valves that large and portwork that serious they are pushing the engine hard and rebuilding it fairly regularly anyway.

generally the valve guides get shaped rather than completely flushed back to the port wall. if you shape them carefully then you can get the flow very close. whether the valve guide is cut back or not, there is still a round valve stem sitting in the airflow. an aerofoil shape is more aerodynamic, so the extra diameter is mostly offset. you can also use valve guide shape to influence the direction of the flow.

i think even with the valve guides cut back flush it will still work ok though. it just might wear things out more quickly.

[Fab4MR2]

Well, I cetainly hope it works out okay, but I would definitely think that a rebuild will be necessary somewhat sooner than otherwise.
Yes, I have also generally seen guide shaping as an alternative, though I have seen no general consensus on how it should be done. Flow is a very tricky thing, and seemimgly those in the know either don't want to share, or they don't really know that much.
I'm a little surprised though that specific flow shaped guides are not produced (with specific flow shaped guide ends), but perhaps they feel even that can be a bit too tricky.
One last thing to consider when removing so much material, however, is that you will also have removed a lot of the heat transfer material to which the valve tries to get rid of its own heat. So that may, or may not, have an undesireable effect.