In light of some recent events, I will be taking the head off my engine. Would it be worth my while to try and cut a groove similar to #2 in my intakes?
I have a rather lumpy cam installed and I have been reading a lot of David Vizard.

Bueller?

Just so you don't feel lonely. . .

I have never seen an undercut this deep before. The edge of the valve doesn't look radius'd. . . (small island though)

The whole theory is that the airflow attaches to the valve and swings around, hence the radius.

I have a set in a engine that is on loan. We modified camira (GM Family II) valves to fit and added rings to the face while we were at it. (Or cut the whole face out)

Unsure of gains as the valves also have a 7mm stem instead of 8mm and this was a new head to the last engine. . . too many variables.

Seems like a good idea though, I'd do it if it isn't going to add much to the cost. . . Maybe you could do a before and after comparo for us.

I've been reading "Tuning the A-Series Engine" by David Vizard.
That is an Anti Reversion groove on the intake valve. Many/most intake valves apparently flow better in reverse and this helps prevent that.
There are almost 5 pages written about these valves. I'm just interested in the groove.

"If the head has valves which tend to flow well in the correct direction but poorly in the reverse direction, then a tendency to reduce the negative aspects of high overlap is brought about. For instance, rough running at low rpm is reduced or even eliminated."

I have the idle set at about 1800 rpm so that the engine won't die when the headlights, heater and/or radiator fan turn on. I'm hoping for a little more stable idle at around 1200 rpm.
As far as cost, I can handle this at work. If I fark them up then i'll have to buy new ones.

Quote:There's a book dedicated to the Nissan A-series engine???

Quote:Whatever for? Do you have a zero-torque cam in there? Mine idles fine at 600rpm with everything on ...

With the old engine, we had problems with carbon buildup on the back of the valve.

This was one of the reasons for the "rimflow valves" or as we have always called them: "Valves with anti-reversion rings".

We did not have the carbon build up with the new engine. Cam timing was altered at the same time which can also have an impact on carbon buildup.

Come on DD, not everyone has an engine with a heavy flywheel and small primary to give a nice idle. . .

Im not really sure if they would work.

I've seen pro stock and top fuel heads and they dont run these type of valves so im not sure what to think.

Never seen this type of valve before.

Sorry DD
But i'm pretty sure he is talking about the BMC A series, like the ones in mini's.
I have the book and its a useful book for engine building in general.
David vizard has written quite a few different books but i believe they are all for british engines (he's british)

Nick

Thanks guy, I'll have to check it out. I've heard of Vizard, if I remember right he consulted on lots of Formula 1 engines.

Cable_Tie, you mean 1800 rpm idle for a street-driven car? The 8000-rpm A15 I rode in idled probably around 1000 rpm. I could see it for a race car ...