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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