Reply to "Valves"

> Jack, Marlin. Thanks for the input. I guess I should have been more
> specific with my question. In an earlier post, Dan Jones wrote " A
> lot of people blindly install 4V valves (2.19" and 1.71") in Aussie
> 2V heads but I don't recommend it. You want the valve size to match
> the port size. The larger 4V valves also hurt the transition at the
> short side radius. Comments?

Compared to the intake, the exhaust port on the 2V heads is relatively
strong. Getting the intake port to flow 225 CFM and the exhaust 180
CFM is relatively easy. 250 CFM on the intake takes considerable
work. Without more intake flow, increasing the exhaust flow past
doesn't the 75% mark doesn't make more power but it may increase fuel
economy. Also 2V head flow tends to level out at 0.500" to 0.550" lift.
I recommend a 2.1" intake valve, a 1.65" exhaust valve (both with a
back-cut) and a good multi-angle valve job. If you do not bowl port
then stick with a stock 2.04" diameter intake valve.

> In the same post, he mentioned "bowl porting" and "unshrouding".

Bowl porting is as Jack describes and provides the best porting bang
for the buck. Valves are said to be shrouded if there is material
around them that inhibits flow. Removing material in the combustion
chamber to improve flow is "unshrouding". Aussie 2V heads have
a particularly tight combustion chamber and benefit from unshrouding.
For more information, I suggest you pick up David Vizard's book on
350 Chevy cylinder heads. It's the best cylinder head porting book
in print.

> Is the boost in performance worth the expense?

Cost varies by region and by head porter. I suggest you look into
head porters in your locale that cater to the circle track crowd.
You should be able to find one who has experience porting 2V heads
and can back it up on a flow bench. Whether or not it is worth it
is highly dependent upon the rest of the engine combination and the
fatness of your wallet.

> I didn't check but if those Ferrea valves are titanium, you are
> looking for trouble IMHO.

The ones I suggested are not titanium.

> Ti on the street is not a good idea- first, the stems need to be
> chrome-plated or they sieze in the guides,

Most are moly-impregated these days.

> the tips need either lash-caps or stellite weld as pounding from
> the rockers causes flaking on bare Ti, and finally, in the exhausts,
> the seat areas spall at high temperaturers.

Agreed. To run titanium successfully you need a compatible guide
and seat material, as well as hardened tips and coated stems.

> If the Ferreas are SS, no problem- they make good stuff if a bit pricey.

Ferrea makes several different valves for 2V and 4V heads. The entry
level 5000 series street valves are quite cheap, around $150 for a set
of 16. I run the competion series valves which are suitable for spring
pressures associated with solid roller cams but these cost more like
$350 to $400 a set. In between is the 6000 series.

> Incidentally, Dan may be correct- 'bigger' often doesn't translate to'
> more power', even if the worked port flows more air.

4V valves may increase flow over stock but it's typicaly not the
valves but the rest of the port work that did the trick. Based upon
the flow bench data I've reviewed, the sizes I recommend above work
best for the typical high performance street engine.

BTW, I've had several different heads on the flow bench recently.
When I get the chance I'll post the results.

> Theres a new (to me anyway) technique being used by porters that involved
> squirting Dykem metal-dye into the flow-bench airstream, then analyzing
> the resulting dye patterns in the ports and combustion chamber.

Sounds like a flow visualization method to me. We use smoke in our
wind tunnels for flow visualization. Helps to visualize where the
flow transitions from laminar to turbulent, velocity differentials,
and areas of flow separation. There are also water tunnels that
accomplish the same thing.

Dan Jones