"well kept porting secret"

[Keith Morganstein]

The quote below is from Joe Mondello in an Engine Builder Magazine article (see link)
http://www.babcox.com/editorial/ar/eb120118.htm

If your flow numbers are a little low, I suggest using a 7/16˝- or a 1/2˝-round ball carbide cutter to cut a .030˝ to .040˝ deep groove about .060˝ to .080˝ wide just below the intake valve seat insert. This includes partially cutting into the insert 180° around the seat just opposite the short side radius. This allows the air to accelerate over the seat like a ski jumper, increasing velocity and CFM of air flow. This is a well-kept secret among good head porters.

looking at a 20 valve VW 1.8T AEB engine, I see the factory uses this "well kept secret" (please forgive the dirty head, I can't carry it to the part washer yet)

What do you think?

[Unkl Ian]

Sounds like the ring end gap secrets,that the factories
had in production for years before the racers caught on.

[cboggs]

this is much too secret to discuss, ..

( sorry ., .. couldn't resist )

Curtis

[PWMAX]

In a sense, what you end up with, is a "veturi" at that point. Like a carb. It works on some heads, and some it doesn;t.

[MadBill]

To me, the words "..just opposite" mean "on the other side from", thus on the long side. However, the pic shows the groove on the short side.
Why wouldn't he just say "on the short side at the insert/port joint" if that's what's meant?

[bobqzzi]

The quote below is from Joe Mondello in an Engine Builder Magazine article (see link)
http://www.babcox.com/editorial/ar/ar30111.htm

If your flow numbers are a little low, I suggest using a 7/16˝- or a 1/2˝-round ball carbide cutter to cut a .030˝ to .040˝ deep groove about .060˝ to .080˝ wide just below the intake valve seat insert. This includes partially cutting into the insert 180° around the seat just opposite the short side radius. This allows the air to accelerate over the seat like a ski jumper, increasing velocity and CFM of air flow. This is a well-kept secret among good head porters.

looking at a 20 valve VW 1.8T AEB engine, I see the factory uses this "well kept secret" (please forgive the dirty head, I can't carry it to the part washer yet)

What do you think?

I'd say you pick up quite a bit of flow by getting rid of that on those heads

[Keith Morganstein]

To me, the words "..just opposite" mean "on the other side from", thus on the long side. However, the pic shows the groove on the short side.
Why wouldn't he just say "on the short side at the insert/port joint" if that's what's meant?

Heres another pic. They are groved all the way aound. Definately a ball shaped tool and it cuts into the seat insert.

[SWR]

To have that groove all the way round hurts power... I've tried running no groove,all the way round and just a half-circle groove on the long side of the port just below the seat insert. VW "9A" 16V head. Worked like Joe said,but of course it gave most power when porting it before cutting the groove.. Just cutting it doesn't do much when that "overhang" of valvebowl is shrouding it.

[Keith Morganstein]

wrong link!

I edited my original post and this is the correct link to the article

http://www.babcox.com/editorial/ar/eb120118.htm

[Niles]

Paging through my fluid dynamics text I can find no reference to a documented engineering phenomenon justifying the "ski jumper" effect.

Is the small increase in volume and turbulence around the extra machined groove to thank for this? or am I even more sophomoric than I thought?

[John Haskell]

Well I'll be danged. Haven't seen that since the 1966 427 Fords. Trans am Fords etc. Yuk-yuk. ---------------- Joe is giving his age away here. (One heck of a nice guy).

"Is there anything that it may be said, See, this is new? It hath been already of old time, which was before us." Ecc. 1/10

[larrycavan]

I see that "trick" used a lot on motorcycle heads from the factory. I wish they'd STOP doing it.

[lil289]

I think the only reason why they do that is because the I.D. of the seat has to be slightly larger than the as-cast throat to allow for core shift, tolerances, etc. If they didn't run a cutter down there then there'd be an ugly step right under the seat. The ball end cutter is better than a regular flat end mill because it will naturally transition into the casting. Not great mind you but better than nothing. Blending the discontinuity out by hand would be unnacceptable from a mass production cost standpoint.

[Keith Morganstein]

I think the only reason why they do that is because the I.D. of the seat has to be slightly larger than the as-cast throat to allow for core shift, tolerances, etc. If they didn't run a cutter down there then there'd be an ugly step right under the seat. The ball end cutter is better than a regular flat end mill because it will naturally transition into the casting. Not great mind you but better than nothing. Blending the discontinuity out by hand would be unnacceptable from a mass production cost standpoint.

I just had remembered the article from Joe Mondello and then noticed it on the VW head and it made me think.

I guess it's not much of anything.

[larrycavan]

I think the only reason why they do that is because the I.D. of the seat has to be slightly larger than the as-cast throat to allow for core shift, tolerances, etc. If they didn't run a cutter down there then there'd be an ugly step right under the seat. The ball end cutter is better than a regular flat end mill because it will naturally transition into the casting. Not great mind you but better than nothing. Blending the discontinuity out by hand would be unnacceptable from a mass production cost standpoint.

I just had remembered the article from Joe Mondello and then noticed it on the VW head and it made me think.

I guess it's not much of anything.

Joe also talks about NOT cutting into the seat at all on the exhaust port to maintain structural integrity.

I personally don't like it when the factory hacks away in there because sometimes it's done so poorly that it affects the way you have to blend the bowl to the seat and that in turn affects shaping the bowl....one thing leads to another..