Discussion Topic - Infinite angle valve seats

[Helliouse]

Hello all,
I just read about this (Infinite angle valve seats) in some article, might have been in a thread too...oh well I digress, and was wanting some input from some of the people here on the form.

Thinking on valve seats, you only have a ~1mm Xmm diameter surface touching your head to transfer heat and seal the combustion chamber, not a lot of surface area. Doesn't the idea of an Infinite angle seat appeal to having huge flow gains, along with larger surface area to dissipate heat from the valve to the head and provide possibly better seal (due to curved surface).
With our Cylinder Pressure (CP) we shouldn’t have to worry about an increase in area reducing the sealing ability of the seat. Also this allows for higher seat pressure as you are now distributing the pressure across a larger surface area, equaling less stress on the head (beneficial to alum. heads).

Does anyone see issues with this?
Complexity to make the valve and seat in the head etc.

[butterstdi]

could you post a link to this article if you can remember where you read it?

[lbreton]

A buddy of mine in Saskatoon had this valve job done on his subaru this past winter.  PM if you want the name of the shop.  The guy there can give you some good answers on the topic.  They are known for high quality work and the owner is a smart cookie.

[Pat Dolan]

If by "infinite angle" you mean a radiused seat, it will give considerably LESS area for heat transfer, since the contact is no longer a 1mm wide band, but a tiny thin line.  Much better for sealing, much worse for valve cooling.

What I have done for many years when it gets to the silly "go for broke" valve job is to start with a multi-angle, and then blend everything BUT the contact area into a radius - on both the valve and seat.  For VW, that often means taking a fair bit of material out of the combustion chamber to blend the roof into the entry from the port, so you need to CC the heads again and do what is necesary to adjust compression ratio to desired value.

[lbreton]

... valve job is to start with a multi-angle, and then blend everything BUT the contact area into a radius - on both the valve and seat.  For VW, that often means taking a fair bit of material out of the combustion chamber to blend the roof into the entry from the port, so you need to CC the heads again and do what is necesary to adjust compression ratio to desired value.

thats an intersting idea.  I know my buddy had looked at a 5 angle job first, but was convinced to go this route.  I can appreciate the concept of leaving a flat spot for the contact area.

[Helliouse]

Yes I meant radiused, but I also mean a radiused valve to match the seat; although, after looking into it the “Infinite Angle Valve Seat” seems to be a 5 angle or more valve seat, not a radiused seat.
So I would also agree a good porting job would include blending everything except the actual seat, which would mean good flow.

I would still like to see if a radiused seat and valve would work. The trouble would be getting it machined properly to get a perfect match…CNC most likely.

Sorry I don’t remember the link, I can look for it though, but I make no promises.

[Pat Dolan]

What I usually do is rough cut everything as a bunch of angles on the seat (however many cutters I have that will fit in that particular hole) and do four angles on the valve.  this establishes the basic seat area.  Then, I use a flapper wheel to blend the cuts above and below the seat, and a hand-held abrasive wheel followed by a flapper on a die grinder and finally had polishing the valve with fine emery everywhere BUT the seat (takes a bit of practice to be safe at this!) giving an all-radiused set of faces either side of the seat.  I no longer have to go back and do anything with the valve, but I usually put the pilots back in and touch up the valve seat (with carbides, not stones).  The seat is identified when I lap, and I have never had to go back and move it either way to get what I want.  Of course, I should add that I have been doing this for about 40 years, and it wasn't quite this easy when I first started.  The secret is to slow down, be bloody careful, take your time and enjoy the process.  

What most of this is all about is the airflow when the valves are close to the seat.  If you look at a trace of valve lift vs. crank angle, you will notice that they move very slowly at each end of their travel.  At the open side, not much other than the overall port makes any difference.  However, near the seat, it is just that - the cleanliness of the flow near the seat, accross the edge of the valve and accross the face of the combustion chamber (the flow moves away from there at higher lift, but we are talking about a LONG time at very low lift).  The results are quite easy to feel in either a gasser or diesel.

But, in referrence to this thread, you can't leave the cotact area to the intersection of two curves - it would then just be a very thin line and the valves will overheat (particularly exhaust).  You CAN, however, narrow the seats a fair bit (intake in particular) and still get by with reasonable valve life and very good sealing.

[Freidenker]

Hi Pat:  Did you flowtest this method or compare dynos to see how well it works?  Sounds good.

[snakemaster]

for the inlet valve i have 1mm seat and the exhaust valve 1.8 to 2mm seat and same on head and that seems to work ok with me , but after reading this the inlet valve may run a bit hot , i have never had one drop to this date , have bent a few :cry: