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
> >
> > __________________________________________________
> > Do you Yahoo!?
> > Yahoo! Mail Plus - Powerful. Affordable. Sign up now.
> > http://mailplus.yahoo.com
__________________________________________________
Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.
http://mailplus.yahoo.com
|