All Small Six Seat/bowl blending question

[clochard68]

I have a question regarding bowl blending on my small log cylinder head.

My car is just a weekend cruiser but with some simple upgrades (ignition, carburetor, header and exhaust, little higher compression). My machine shop put new hardened seats in my cylinder head and they did a three angle valve job (60°, 45°,30°). As you can see, there is a ridge (max. 0.04” wide) between the bowl and the base of the seat insert. Now I have two options for blending (and I sonic tested the head, I have enough material to do both variations) (see also picture attached):



A) I cut straight (90°) below the 60° angle and the blend it into the bowl (so the 4 angles would be 30°,45°,60°,90° and blending)

or

B) I make an 80° cut that cleans up the 60° angle and then blend it into the bowl. (here I would get rid of the 60° angle and replace it with the 80° angle. The 3 angles would be 30°,45°,80° and blending)

What would make more sense (A or B) for a cruiser car with a stock camshaft that is driven mostly in town, where torque matters?

 

[hodaka100]

I'm no expert but I would do B without removing the 60* . A Dremel with carbide bits will make quick work of it.

 

[pmuller9]

You want to keep the 60 degree angle. It is important for low valve lift flow.

Did you do a 30 degree back cut on the valves?

 

[clochard68]

I'm no expert but I would do B without removing the 60* . A Dremel with carbide bits will make quick work of it.

Thanks, but unfortunately it is not possible to move the seat angle outwards, I am limited by the valve size. So I cant leave the 60° and do the 80° because that would still leave a lip (although smaller, but still there).

You want to keep the 60 degree angle. It is important for low valve lift flow.

Did you do a 30 degree back cut on the valves?

Thank you, I guess then I will cut 90° below the seat insert and blend it in.

I plan on back cutting the intake valves 30°, but haven't done it yet. Would that change something on the seat angle design?

 

[Engine Fan]

Short of putting new seats in with smaller ID, I would do "A" on the short side and leave the long side alone.

 

[clochard68]

Short of putting new seats in with smaller ID, I would do "A" on the short side and leave the long side alone.

Only on the short side would mean around more or less a third of the total throat circumference (on the short side) or more or less half of the circumference (up to the long side on both sides)?

 

[CNC-Dude]

Since they left such a huge step in the head, you might want to ask how much they would charge to bowl cut it for you. Then all you might need to do is a very slight deburr with a cartridge roll to blend it.

 

[Engine Fan]

Only on the short side would mean around more or less a third of the total throat circumference (on the short side) or more or less half of the circumference (up to the long side on both sides)?

It appears the chamber wall side is already at the 90 or "A" so follow around the short side (1/3 circumference) and end at the transition to the exhaust side of the intake port.

 

[clochard68]

Thanks everyone for all the suggestions, I will keep the 60° and ask the machine shop what they can do with the bowl!

 

[Invectivus]

David Vizard has some interesting videos on porting and performance, the first one was on valve seat/throat. I think he said not to worry about the short side because because air velocity overshoots it to the far side, where you want to concentrate on your blending.

 

[wme013]

I'm almost embarrassed to admit that I know of this method, but here goes...Take an old long stem valve that fits your guide, cut the head off.
Chuck the stem in a drill and mount up a hole saw of the right diameter. Run it into the bowl. Instant throat porting

 

[clochard68]

I'm almost embarrassed to admit that I know of this method, but here goes...Take an old long stem valve that fits your guide, cut the head off.
Chuck the stem in a drill and mount up a hole saw of the right diameter. Run it into the bowl. Instant throat porting

Maybe I will try it if everything else fails
I have some Neway Cutters with round cutters, hopefully I can make a clean cut with them. I will try it after Christmas on the exhaust first and see how it works out.