Valves with an 8mm stem

[NOBLE 309]

This goes out to the guys that know alot more about head flow than I.
It is well documented that in most applications the stock size valves work well in the Nord head. My question is has anyone come up with a stock size valve with an 8mm stem? seems with a tapered 8mm valve guide(BMW?) it would flow better.
Let the games begin on this happy friday!

[60sRacer]

Hmmm. 8 mm valves were used on the 1300's and 101 cars I think.

Robert

[Gordon Raymond]

I'm not quite sure what we are talking about here, so these comments may not apply. Anything in an intake port will cause some restriction (bad) and turbulence (good or bad).
The trend is to the smallest valve stems that can be used that will maintain strength between the valve stem and head at high engine speeds. 4 valve engines use small (light) valves with very small stems. In Nascar, titanium valves with 7 mm stems are used, and even with fairly large heads, these valves are light enough and tough enough to withstand high engine speeds. The smaller the stem, the better the possible flow characteristics of the port. Some Alfa engine builders use titanium valves with reduced diameter stems for this same reason. I currently use just slightly oversize valve heads to match my valve seat configuration with 7 mm stems in 1600 engines on both intake and exhaust. Some use reduced stems on just the intake side. These are titanium for weight and strength. With the smaller stem, a smaller guide hanging in the port is possible, though clipping them off at the inside surface of the port may not work as well as with larger stem diameters. Guides are made up of # 954 bronze.

[NOBLE 309]

Gordon you are on track with what I was thinking.
Just everything being equal,seems that the 9mm stem is a tad thick for the port size. Im not sold on oversize valves for my application-but less obstruction in the port would be bonus. I like the spruell hi per valve guides though.

[Dovali]

In the old days titanium valveguides were made of barylium bronze.

in the new days the TI valvesstems are coated with CLD or powerseal

So we don't need to rework the toxic bbronze valveguides anymore.

But nowadays special valve producents make nicro valves so light,
we don"t need to use TI valves anymore.
Not only a hollow stem but also the valve itself is hollow.

About beemer valves they are already 45 degrees,so it will put you 1 step forward

Personaly i would not go smaller than 8 mm, stemwise.Shifting and piston valve contact is more common than you think.

[genericwood]

Quote:

Originally Posted by 60sRacer Hmmm. 8 mm valves were used on the 1300's and 101 cars I think. Robert

[60sRacer]

Well golly gee Batman. ANOTHER misstake!




Robert

[180OUT]

If you haven't done so, I'd suggest that you get a copy of Jim Kartalamakis's Alfa Romeo DOHC Engine High Performance Manual. He's done a lot of work developing 2L Alfa engines. He has a great section in his book on cylinder head porting and makes some specific comments on using 8mm valves.

[veloce430]

GTA's and GTA Jr's used 8mm stems as well . I had an old Ron Neale (Prototype Eng) 2 litre Nord motor that had cut down GTA valves (had to be stock valve size) for a SCCA DP motor. This was done back in '76 or '77

Stu