3 Angle Valve Job Questions

[Quadzilla]

Just a couple of quick questions:

1: Does this really make any significant or noticable difference? My builder did this for me (and I didn't know that he was going to do it along with the other mods you see below). I had inquired about it and he took my inquiry as the go ahead to do it. I just hope it was worth the $$$. He ported the head also and I have the new cam, piston. Just wonder if it really helps...

2: Does the valve job cause the valves to seal against the head a little tighter and if so, would this cause the compression to change a little? One argument would be that if the valves seal better, the compression would be higher (not letting gases out from a bad seal). The other argument would be that the compression would decrease because the valves when closed, would be futher up in the head and increase the chamber volume thus decreasing compression.

So in summary, question 1 is given my mods, will this make a noticable differnence and question 2, does a 3 angle valve job to stock sized valves increase or decrease compression?

Thanks!

[PHIL_B54]

http://www.exriders.com/vbb/showthread.php?s=&threadid=100279

"the 400ex comes with a 3 angle valve job from the factory, so unless your valve seats are shot and hurting your preformance, you will not go any faster"

[Quadzilla]

Another guy said this later in the thread:

"The reason 400ex's come with a 3 angle valve job is to keep the carbon from building up on the valve seats. If the seat becomes flattened over time, the increased surface area will allow carbon to build up on the contact area between the valve and the seat. This in turn will create an imperfect seal and therefore cause compression loss. Race bikes get 5 angle valve jobs to further decrease the contact area with the valve and thereby decrease the opportunity for carbon to build up. I believe that if you are interested in long term reliability, a simple 3 angle valve job is a must every time you remove your head"

[Mr.FDO]

I have been doing cylinder heads for over 20 years and I have never seen a head that did not have 3-angle valve seats. A tipical valve job would have a 30-35 degree top angle ,45 degree seat angle , 55-65 degree bottom angle. The top angle is for adjusting the outer diameter of the seat to be the same as or slightly smaller than the valve diameter. The bottom angle is used to narrow the seat to a specific width (1mm or 2mm). There is such a thing as multi-angle valve job which could have as many as 6 angles(20-32-45-55-65-75). The reason for this is to create a radiused curve for smoother flow at low valve lifts (better torque & throttle response). If any of you are paying extra $$$ for a 3-angle valve job , you are paying extra , for what should be standard procedure.

[Quadzilla]

So would/does the 400EX head benefit from a 3 or multi angle valve job on it?