Valve seat???
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Yes, it allows the air to turn around the seat better. You have to back cut the intake valve to gain the best result. On the exhaust do the same but use a radius under the seat.Kurt.A said:
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Re: seats
As long as the seat is near the edge of the valve , but not right on the edge you will be ok. If it were hitting on the edge it will cause seat deterioration and chipping. Keep an eye on the valve springs. Keep the seat pressure at spec. Don't over rev their capability and get into valve float either.Kurt.A said:
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10,160 Posts
RE valve seat contact ???
I typically place the contact width of the valve seat to with in a findernail width of the edge of the valve margin. This allows me to maximise throat diameter vs valve head diameter. When the seat contact area is to the inside of the valve head you have to use a smaller throat diameter vs valve head diameter. This can potentially reduce the effective flow area of the bowl. Another consideration is that the location of the seat vs the valve head diameter can effect the shape of the flow cone that forms around the valve head as air goes past it. In some ports a tight flow cone near the valve stem is good (D0VE) and in others like the aluminum heads a tight flow cone is not good hence the use of a tuliped valve and a large diameter bowl.
I set the bowl diameter of a D0VE port at about 84 to 85% of valve head diameter with the contact area more toward the middle on the exhaust. On the good aluminum port castings I move the contact area out to the edge of the valve and open the bowl to 85 to 86% of valve head diameter.
On intake valves I always set the contact area to the outer portion of the valve's 45* face and back cut 30*.
The use of a 30* back cut helps low lift flow substantially on both the intake and exhaust ports of every head I have ever ported and flowed. This low lift flow is important in setting the intake tract into motion via the exhaust scavenging's negative pressure pulse. I have seen no issues with longevity so long as the contact area is not too close to the valve margin.
:mrgreen:
I typically place the contact width of the valve seat to with in a findernail width of the edge of the valve margin. This allows me to maximise throat diameter vs valve head diameter. When the seat contact area is to the inside of the valve head you have to use a smaller throat diameter vs valve head diameter. This can potentially reduce the effective flow area of the bowl. Another consideration is that the location of the seat vs the valve head diameter can effect the shape of the flow cone that forms around the valve head as air goes past it. In some ports a tight flow cone near the valve stem is good (D0VE) and in others like the aluminum heads a tight flow cone is not good hence the use of a tuliped valve and a large diameter bowl.
I set the bowl diameter of a D0VE port at about 84 to 85% of valve head diameter with the contact area more toward the middle on the exhaust. On the good aluminum port castings I move the contact area out to the edge of the valve and open the bowl to 85 to 86% of valve head diameter.
On intake valves I always set the contact area to the outer portion of the valve's 45* face and back cut 30*.
The use of a 30* back cut helps low lift flow substantially on both the intake and exhaust ports of every head I have ever ported and flowed. This low lift flow is important in setting the intake tract into motion via the exhaust scavenging's negative pressure pulse. I have seen no issues with longevity so long as the contact area is not too close to the valve margin.
:mrgreen:
D3 Seats
Thanks for the info guy's,
These are D3 heads I am working on. What I have done is 15*, 30*, 45*, 60*, and a 80* throat cut to the dia that is noted in scott's porting guide on the RHP web site. What I found is that the seats lined up .015" inside the valve margin with the stock valves. Would it be better for me to use the stock valves or go up to the 2.19" and 1.76" valves?
Kurt
Thanks for the info guy's,
These are D3 heads I am working on. What I have done is 15*, 30*, 45*, 60*, and a 80* throat cut to the dia that is noted in scott's porting guide on the RHP web site. What I found is that the seats lined up .015" inside the valve margin with the stock valves. Would it be better for me to use the stock valves or go up to the 2.19" and 1.76" valves?
Kurt
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88 Posts
BEEGA valves
Going to the big valves WILL,SEVERELY, limit your cam choices.
Going to the big valves WILL,SEVERELY, limit your cam choices.
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28 Posts
I've ALWAYS ran my valve seats to the outer edge of the valves. But, you have to leave a fine margin between the outer edge of the valve face, and the top of the indicated seat. As long as you can see it (like a 1/64th) it should be enough. It helps with heat transfer, and will help prevent a burned valve edge. Back cut the valves right up to the bottom of the the indicated valve seat, but again, leave a margin. Radiusing the exhaust valve backcut is probably a good idea. I've never had any problem with running this setup.Kurt.A said:
Mike
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