Hi Tim,
Yes you are correct. I reread Williams note and I believe he is talking
about the angle of the valve stem. I haven't a clue as to how to go
about changing that. I am only talking about the angle around the edge
of the valve -- the angle that meets the valve seat, and whether 30 vs
45 is best.
I guess my real question was whether a three angle valve grind was done
to accommodate the 30 degree angle. It's hard to describe w/o a picture
but with a single 30 degree angle valve seat, the valve seat opening to
the port would become smaller. Thus, while the 30 degree would flow
better at low valve lifts, it would flow worse a high lifts (because of
the smaller diameter). Vizard shows the valve seat cut at several angles
to compensate for the 30 degree angle on the seat, so I was wondering if
Vizard's multiple angled valve seat was the the same thing as a 3 angle
valve grind. My understanding now is that a 3 angle valve grind does not
necessarily have anything to do with a 30 degree valve angle. Three
angle valve grinds with the center angle at 45 degrees are probably
typical.
Thanks for pointing it out. I read William's post very quickly and
missed it.
Don
Timothy Holbrook wrote:
>
> I think we may be talking about the wrong valve angles here. The only
> valve angle that can be ascertained by looking at cutouts in the
> pistons would be the angle of the valve in the cylinder head, relative
> to the cylinder. For example, a TR250/6 (whose valves go straight up
> and down in relation to the cylinder) have a valve angle of 0. If you
> were to tilt the stem of the valve outwards, then the valve angle would
> increase, to a max of 90, which would be exactly perpendicular to the
> cylinder (and would never be actually done). This is valve angle, and
> is what Wiseco was discussing.
>
> The angle of the grind on the valve seat is what was being discussed on
> the list. By beveling the face where the valve meets the seat, you can
> smooth out the flow of air as it moves from the ports to the combustion
> chamber. As was mentioned, the ideal (in terms of airflow) is a
> perfectly smooth radiused edge. But this wouldn't seal well, and would
> be very expensive to machine. Most cars use a one angle, 45 degree cut
> on the seat. For a performance head, a 3 angle valve job is common,
> which uses 3 different cuts (all at different angles) to make a
> smoother edge on the seat. 5 angle valve jobs are also used, but this
> is even more expensive, and you start to loose some durability because
> there is a very thin meeting point between the valve and seat. You can
> also start to run into sealing problems. You'd probably only use a
> 5-angle on a full-out race engine that sees frequent rebuilds.
>
> Tim Holbrook
> 1971 TR6
>
> --- William Whitmoyer <wwhitmoyer@samsonite.net> wrote:
> > Date: Fri, 06 Dec 2002 10:34:14 -0500
> > To: 6pack@autox.team.net
> > From: William Whitmoyer <wwhitmoyer@samsonite.net>
> > Subject: RE: 30 degree valve seats and 3 angle valve grid
> >
> > Interesting tidbit: I was at the Wiseco piston factory a couple of
> > weeks
> > ago with the local Porsche club...the tour, incidentally, was really
> > cool
> > as they do Formula 1 super-alloy metal forging-I now know what the
> > Ferrari
> > F1 pedal box looks like...but they mentioned that since they do the
> > pistons
> > for most of the Pro Stock race teams, they can figure out what size
> > valves
> > each team uses and at what angle they run them in the heads (ie not
> > the
> > angle of the valve seat grind, but the angle of the whole valve)
> > based on
> > the valve reliefs cut in the pistons. Each of these teams are
> > producing
> > almost the same horsepower, but they all get there with wildly
> > different
> > size valves and valve angles, according to Wiseco.
> >
> > Moral of the story: There is no one correct answer. Every engine is
> > its
> > own package, and without serious flowbench/dyno time with your
> > particular
> > set-up, you will never really know whether a 30 degree cut or 45
> > degree cut
> > is going to make any noticeable difference. It's great fun to plan,
> > but
> > don't lose any sleep over it. Personally, I'd be more worried about
> > finding a knowledgeable and skilled engine builder who could do the
> > work
> > correctly, at whatever the valve grind angles you (or the builder)
> > choose.
> >
> >
> > Date: Thu, 5 Dec 2002 07:49:53 -0800
> > From: "Navarrette, Vance" <vance.navarrette@intel.com>
> > Subject: RE: 30 degree valve seats and 3 angle valve grid
> > Don:
> > -------------CUT-----------------------------
> >
> > Don't know if this
> > would be a net gain or a net loss in performance.
> > Yes, a 3 angle valve job on a 30 degree seat would be
> > xx-30-yy. I don't know what would work best. I am sure everybody
> > has their favorite recipe.
> > If you are really worried about the durability, have the
> > machinist install hardened seats for the exhaust. The rest of the
> > car will turn into a pile of tiny rust chips long before the seat
> > wears out.
> > Cheers,
> > Vance
> > - ------------------------------
> > 1974 Mimosa Yellow Triumph TR6
> > Cogito Ergo Zoom
> > (I think, therefore I go fast)
> >
> > -------------cut-----------------------------------
> >
> >
> > William Whitmoyer
> > 69 TR6
> > 72 Fiat Spider
> > 90 BMW iX
> > 91 CRX Si
>
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