Valve seat width for cooling and reliability

[Kevin Johnson]

If you examine the Google search parameters you can see that I was searching laterally. The SAE paper appears to be the data source since if you include 100C in a subsequent search, the text is cited. No, I am not going to spend $30.00. Good luck.


https://www.sae.org/publications/techni ... nt/922438/

1992-11-01
Thermal Barrier Coatings for Diesel Engines: Ten Years of Experience 922438

[4vpc]

If it's a 45 degree seat inlet should be about 4.5% of valve diameter wide and 5.5% on the exhaust. Go a little wider than N/A perhaps, does it matter under boosted conditions?
Any coatings should be viewed with suspicion as to what fuel is used, how old they are and what how their porosity affects the burn and emmisions.

[ptuomov]

If it's a 45 degree seat inlet should be about 4.5% of valve diameter wide and 5.5% on the exhaust. Go a little wider than N/A perhaps, does it matter under boosted conditions?
Any coatings should be viewed with suspicion as to what fuel is used, how old they are and what how their porosity affects the burn and emmisions.

I was thinking about coating the exhaust valve backs and exhaust ports. I think that what happens in the exhaust port mostly stays in the exhaust port as far as the detonation resistance goes. Right? At most, it’s money spent on something that doesn’t help but doesn’t hurt either.

The valve face is a different matter. Obviously, coating the valve face with TBC can’t make the valve metal hotter. But “studies show” that the valve face will be hotter with TBC and that may impact the detonation resistance of the engine with pump gas. So I’m thinking about not gambling there.

[ClassAct]

If it's a 45 degree seat inlet should be about 4.5% of valve diameter wide and 5.5% on the exhaust. Go a little wider than N/A perhaps, does it matter under boosted conditions?
Any coatings should be viewed with suspicion as to what fuel is used, how old they are and what how their porosity affects the burn and emmisions.

My math says 4.5% of a 2.02 valve is a .090 wide seat. I've never run a seat that wide in my life. I run .040 wide on the intake and exhaust if it's 45 degrees. On 50 degree seats it's .050 and .060 for the exhaust. Only slightly wider for 55 degree seats.

[PRH]

The supercharged Mercruiser BBC stuff I’ve serviced has had the “full contact” exhaust seat....... and the valve faces aren’t very narrow either.
The seat in the head is as wide as the face of the valve.
They’re like this from new.

Super hard seat insert, inconel valves.

Intake seats are more normal..... .040”-.060”.

My math says 4.5% of a 2.02 valve is a .090 wide seat. I've never run a seat that wide in my life.

I’m pretty sure in that old Grumpy Jenkins SBC book, the recommended valve job used a .100” wide intake seat.

That’s not how I do it either....... but it seems like it did work for someone.

[ClassAct]

The supercharged Mercruiser BBC stuff I’ve serviced has had the “full contact” exhaust seat....... and the valve faces aren’t very narrow either.
The seat in the head is as wide as the face of the valve.
They’re like this from new.

Super hard seat insert, inconel valves.

Intake seats are more normal..... .040”-.060”.

Is that .100 or wider on those BBC Mercruisers?

[PRH]

A solid .100 plus.

A new Manley 1.88 inconel valve comes with a seat width of .100, but I think the OE mercruiser valves have a wider seat than that.

[ClassAct]

A solid .100 plus.

A new Manley 1.88 inconel valve comes with a seat width of .100, but I think the OE mercruiser valves have a wider seat than that.

Damn.

[modok]

There might be a relationship between valve head thickness and seat width.
certainly is on the VALVE itself

[ptuomov]

If it's a 45 degree seat inlet should be about 4.5% of valve diameter wide and 5.5% on the exhaust. Go a little wider than N/A perhaps, does it matter under boosted conditions?
Any coatings should be viewed with suspicion as to what fuel is used, how old they are and what how their porosity affects the burn and emmisions.

My math says 4.5% of a 2.02 valve is a .090 wide seat. I've never run a seat that wide in my life. I run .040 wide on the intake and exhaust if it's 45 degrees. On 50 degree seats it's .050 and .060 for the exhaust. Only slightly wider for 55 degree seats.

The factory '87 Porsche 928 S4, for example, runs 1.8mm (0.071") seats on 33mm (1.299") exhaust valves normally aspirated. That's about 5.5%. It's a multi-angle seat from the factory, too, with very durable exhaust valve and very hard seat insert. I think (but do not know) that the seat width was set entirely because of cooling needs, the seat and valve themselves could (if kept at design operating temperature) live with much narrower seats.

For turbo versions (of other models, the prototype 928 turbo never was produced), they seemed to go 25% wider on the exhaust seat compared to the normally aspirated version. For me, that would mean going from 1.8mm to 2.25mm exhaust seat (or from 5.5% to 6.8% of the valve head diameter). A friend tried different seat widths on the exhaust and the flow on the flow bench didn't go down with wider exhaust seat (the stock exhaust throat diameter in the seat insert ring is about 85% of the valve head diameter). So I'm thinking why not go for reliability and ape the factory designs?

Interestingly, as they go with wider valve seats for the exhaust side for turbo models, they seem to also increase the spring loads on the exhaust side. Ballparking, the seated spring load is increased by about same factor as the valve seat area, making the pressure at the seat about the same for NA and turbo models. Does that make sense, keeping the exhaust valve seat pressure the same?

[engineguyBill]

Generally speaking, Intake seat width of .060" and exhaust seat width of .100" is normal. The valves should have correspondingly similar widths as well. From what I have seen, wider seats used for blown, turbocharged or Nitrous assisted engines do not seem to have any affect on valve life nor performance over the seat widths mentioned above.