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<DIV><SPAN class=914101210-16092015></SPAN><FONT face=Arial><FONT
color=#0000ff><FONT
size=2>Thanks Keith and Michael. About valve springs and seat pressure : it's a question about</FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT
size=2>keeping the valve train parts<SPAN
class=914101210-16092015> together but also to avoid that the valves bounce off
the seats after (the first) landing. I suppose this valve bounce is not so
clearly reflected in the power dropping at high revs, . On youtube are
very interesting high speed cam video's on valve bounce, spring
surge...</SPAN></FONT></FONT></FONT><BR></DIV>
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<FONT size=2 face=Tahoma><B>Van:</B> Michael Porter [mailto:mdporter@dfn.com]
<BR><B>Verzonden:</B> woensdag 16 september 2015 10:57<BR><B>Aan:</B> Van
Mulders Marcel<BR><B>Onderwerp:</B> Re: [Fot] FW: TR6 Cannon Intake
Manifold<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV class=moz-cite-prefix>On 9/16/2015 2:18 AM, Van Mulders Marcel
wrote:<BR></DIV>
<BLOCKQUOTE cite=mid:1BC2EA241FF74C048AD3272B873BE3E0@GebruikerPC type="cite">
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<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=358084107-16092015>Thanks to the Fot members for their reactions : most
are warnings that triple 45 Webers may be too big on a TR6 engine. But it
is a race engine (2720cc) and the owner has already bought 3 good
secondhand 45 Webers with identical progression holes : 36mm main
venturi's seem to be a reasonable starting point in this case?
</SPAN></FONT><FONT color=#0000ff size=2 face=Arial><SPAN
class=358084107-16092015>If necessary, he can go down to 34mm in 45
Webers.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=358084107-16092015> I've seen TR6 racecars with 45 Webers and I
wonder if the Cannon manifold, with 40mm diameter bores on the carburetor
side, can be reamed to 45mm? </SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=358084107-16092015>Another question : the valve seat pressure on my
TR4A racecar is 35 kgs/77 lbs. I've also a cylinderhead with only 25 kgs/55lbs
seat pressure. The springs on both cylinderheads are 5.25kg/mm
(290lbs/").</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=358084107-16092015>Do you think 25kgs seat pressure is
enough?</SPAN></FONT></DIV><BR></BLOCKQUOTE><BR>On fitting 45s to the 40DCOE
manifold, yes, I think there's enough meat to match the manifold to the
carburetor exit. It would mean increasing the radius by 2.5mm (~ 0.100"),
but I wouldn't do it until 45mm soft mounts can be obtained--if only 40mm are
available, then it's a waste of time and money. I would recommend that the
shop doing the machining find a suitable diameter end mill with a 10-15 deg.
taper, just to minimize the finish work required and to make a smooth transition
to the smaller manifold bore.<BR><BR>I don't actually understand the complaints
about 45DCOEs being too big for a moderately-sized six-cylinder. For
all-around use on the street, 40s would be more than enough, but on the track,
45s are fine. In fact, I recall 45s with 38mm main venturis being used
commonly, but mostly on engines tuned to 7200 rpm or so. The advantage of
Webers is that they have lots of spares to tune to carburetor to the
application, although the expense of having such spares on hand for tuning is
rarely part of the equation.<BR><BR>As for valve seat pressures, they're not as
important as having just enough spring pressure to keep the follower tracking
the cam profile. For normally-aspirated engines, anyway (seat pressures
become more of an issue with supercharged engines, when too much boost can push
a valve off its seat if the static spring pressure is too low). The lower
the combined weight of the valve train, the lower the spring pressure
required. The steeper the ramps on the cam, the greater the spring
pressure required to overcome the acceleration of the valve train parts.
So, it's kind of a balancing act, and one that can usually only be handled on
the dyno, while looking for power drops at high rpm due to valve
float.<BR><BR><BR>Cheers.<BR><PRE class=moz-signature cols="72">--
Michael Porter
Roswell, NM
Never let anyone drive you crazy when you know it's within walking distance....</PRE></BODY></HTML>