Bigger valves require porting?

[vortspeloce]

Timinator: Good stuff. It is interesting to hear how things are done in the Chevy and Honda world. I have quite a few books by Vizard (inc his new Port and Flow test book), Monroe (race engine building), Voegelin (blueprinting), Bell etc and of course Guy Croft (inc his 8 hour porting DVD set). I will have to do a bit more homework on this one as I am intrigued. My intention was to only blend the lip into the bowl and not to touch the "throat" area.

Baltobernie: The lip in the photo is on the intake side. The exhaust side does not have a lip as the existing seats were cut. I have no intention of port matching the exhaust. In-fact I have not touched it outside of having bronze guides inserted and the seats cut.

[timinator]

You are reading people with a lot of experience. Vizard and Croft like 70-80deg bottom cuts and then blend into the port bowl. Can't argue with that. Vizard shows blending the short side radius on the intake from the seat all the way around to the radius. It shows up as no distinct steps. Also if the flow is biased to one side of the guide he blends from the seat into the bowl on that side. It is in his book I just can't remember which one. I got the 90deg bottom cut from Bill Jenkins book that I bought in 1976. Chevrolet put it their power books sometime after that. Chevrolet doesn't use it with aluminum heads if the seat is 0.040, instead they blend from the 60deg. I don't know why, but then I use 0.060- 0.085 seats because for me they last much longer. I have tried all the blends and radius tricks and not seen any difference on the lap time for the engines I do. 35-45-60-90deg cuts are much easier to do for me and take far less talent or time.

Brzezinski Racing matches the exhaust port to their cast iron exhaust manifolds on the top and sides but leave a large step on the bottom from the port to the manifold. Just another thing to consider.

[FiatMac]

Here (below) is a photo of a deshrouded 1800 combustion chamber I have been working on. This head has bigger valves (especially intake side) and a 3 angle seat job. This is how I received the head back from the machinist after a new Trojan copper alloy valve seats were inserted to suit bigger intake valves.

vortspeloce,
Did you get your Trojan seat inserts from Croft, or is there a US source for them?

[vortspeloce]

vortspeloce,
Did you get your Trojan seat inserts from Croft, or is there a US source for them?

Sorry FiatMac for not responding sooner. I sourced them from Guy Croft. I can't say I have seen them elsewhere.