Hi Tim,
Yes I ordered that back issue from Grassroots (Vizard) on a tip from Kai
and Robert Lang -- I think. But I don't think it's the same idea. I
thought the 30 degree angle they were talking about was on on the "face"
on the valve -- the piston side, rather than the valve seat. Seems they
were rounding the edge "face" to improve flow. The Vizard "A" series
manual is talking about the valve seat angle. The fact that he doesn't
mention the 30 degree valve angle in the DIY head porting article maybe
means it's not all that important -- but I thought Vance recommended
it... Maybe not, or maybe not strongly...
>From Vance...
However, when you add a 3 angle valve job to a 30 degree
back cut on the valve, necked down stems, polished valve faces,
and a mild pocket port, you can achieve improvements on the order
of 10% more HP, with no impact on emissions or drivability.
FWIW, Kas's manual shows the same sort of rounding on the valve face as
does the Grassroots article.
Don
Timothy Holbrook wrote:
>
> Don,
>
> Turns out I misread the original posting from William. But getting
> back to your piece, I read an article in Grassroots a few months back
> about DIY head porting. They said to do a 30 degree cut on the valve
> head, and a 45 on the seat. As you said, this is good for flow at low
> valve lifts, which is where the valves spend most of their time.
>
> Tim Holbrook
> 1971 TR6
>
> --- Don Malling <dmallin@attglobal.net> wrote:
> > Date: Sat, 07 Dec 2002 18:45:30 -0500
> > From: Don Malling <dmallin@attglobal.net>
> > To: Timothy Holbrook <tjh173@yahoo.com>
> > CC: 6pack@autox.team.net
> > Subject: Re: Fwd: RE: 30 degree valve seats and 3 angle valve grid
> >
> > 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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