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I have had a few goes at shaving throttle shafts with very mixed
results..typically fracturing where they meet the carby body. if you
planned to change them routinely, thats not such an issue
Some recent flow bench work leaves me wondering completely about the wisdom
of any of this without real-world testing
We found some head/intake arrangements where the air flow was too high in
certain places and we had to dimple the port to slow it down. Sometimes,
just enlarging the port does not work as intended
The very best SU research ive seen was done by David Vizard . There are
plenty of on-line references to his work, but if anyone can't find what
they want, i can scan relevant parts of his text book (tome) on tuning BMC
A series engines. Ive used his analysis on various shapes of ram tubes for
many years
of far more importance seems to be the distance from the valve to the
throttle plate, with the ideal varying considerably with the RPM range
being used. As a general comment, it seems like many folk have it far too
long
I have proven that fiddling with the damper in a SU has a dramatic effect
on throttle response, and not always what you think. i'll offer the comment
that its very engine set-up specific. Sadly, this aspect is all-but
impossible to test on a conventional flow bench
Terry
Australia
On Thu, Nov 26, 2020 at 2:35 AM DAVE HOGYE via Fot <fot@autox.team.net>
wrote:
> I know that Huffaker does this. I believe they also remove the damper oil
> and or the damper completely and shave down the throttle shaft to almost
> nothing. So, I don't think you'd be trashing them, but I don't know what
> the dyno results are either. As far as I know, they also replace head
> gaskets and engines quite regularly on their BMC builds.
> Dave H.
>
>
> On 11/24/2020 12:41 PM Mike Harmuth via Fot <fot@autox.team.net> wrote:
>
>
>
> I was going over my race carbs (SU H4)and wondered if there's anything to
> be gained (or lost) by smoothing out the casting (before the jet)? I'm not
> sure if it's designed (or left) that way to promote turbulence and better
> mixing as the air flows over the jet or if polishing it down would help.
>
> I'd hate to trash a pair of good carbs before I get some answers.
>
> thanks
> mike h
> _______________________________________________
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>
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<div dir=3D"ltr">I have had a few goes at shaving throttle shafts with very=
mixed results..typically fracturing where they meet=C2=A0the carby body.=
=C2=A0 if you planned to change them routinely, thats not such an issue<div=
><br><div>Some recent flow bench work leaves me wondering completely=C2=A0a=
bout the wisdom of any of this without=C2=A0real-world testing<br></div><di=
v><br></div><div>We found some head/intake arrangements=C2=A0where the air =
flow was too high in certain places and we had to dimple the port to slow i=
t down. Sometimes, just=C2=A0enlarging the port does not work as intended</=
div><div><br></div><div>The very best SU research ive seen was done by Davi=
d Vizard . There are plenty of on-line references to his work, but if anyon=
e can't find what they want, i can scan relevant parts of his text book=
(tome) on tuning BMC A series engines. Ive=C2=A0used his analysis on=C2=A0=
various shapes of ram tubes for many years</div><div><br></div><div>of far=
more importance seems to be the distance from the valve to the throttle pl=
ate, with the ideal varying considerably=C2=A0with the RPM range being used=
. As a general comment, it seems like many folk have it far too long=C2=A0<=
/div><div><br></div><div><div>I have proven that fiddling with the damper i=
n a SU has a dramatic effect on throttle response, and not always what you =
think. i'll offer the comment that its very engine set-up specific. Sad=
ly, this aspect is all-but impossible to test on a conventional flow bench<=
/div></div><div><div><div dir=3D"ltr" class=3D"gmail_signature" data-smartm=
ail=3D"gmail_signature"><div dir=3D"ltr"><div><div dir=3D"ltr"><div><div di=
r=3D"ltr"><div><div dir=3D"ltr"><div><div dir=3D"ltr"><div><div dir=3D"ltr"=
><div><br></div><div>Terry</div><div>Australia<br><br></div></div></div></d=
iv></div></div></div></div></div></div></div></div></div></div><br></div></=
div></div><br><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_at=
tr">On Thu, Nov 26, 2020 at 2:35 AM DAVE HOGYE via Fot <<a href=3D"mailt=
o:fot@autox.team.net">fot@autox.team.net</a>> wrote:<br></div><blockquot=
e class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px s=
olid rgb(204,204,204);padding-left:1ex"><u></u>
=20
=20
=20
<div>
<div style=3D"font-size:12pt;font-family:helvetica,arial,sans-serif;color=
:rgb(51,51,51)">
<span style=3D"font-family:helvetica;font-size:12pt">I know that Huffake=
r does this.=C2=A0 I believe they also remove the damper oil and or the dam=
per completely and shave down the throttle shaft to almost nothing.=C2=A0 S=
o, I don't think you'd be trashing them, but I don't know what =
the dyno results are either. As far as I know, they also replace head gaske=
ts and engines quite regularly on their BMC builds.=C2=A0=C2=A0</span>
</div>=20
<div style=3D"font-size:12pt;font-family:helvetica,arial,sans-serif;color=
:rgb(51,51,51)">
<span style=3D"font-family:helvetica;font-size:12pt">Dave H.=C2=A0</span=
>
</div>=20
<div style=3D"font-size:12pt;font-family:helvetica,arial,sans-serif;color=
:rgb(51,51,51)">
=C2=A0
</div>=20
<div style=3D"font-size:12pt;font-family:helvetica,arial,sans-serif;color=
:rgb(51,51,51)">
=C2=A0
</div>=20
<div style=3D"font-size:12pt;font-family:helvetica,arial,sans-serif;color=
:rgb(51,51,51)">
On 11/24/2020 12:41 PM Mike Harmuth via Fot <<a href=3D"mailto:fot@au=
tox.team.net" target=3D"_blank">fot@autox.team.net</a>> wrote:
</div>=20
<blockquote type=3D"cite">=20
<div>
=C2=A0
</div>=20
<div>
=C2=A0
</div>=20
<div dir=3D"ltr">
I was going over my race carbs (SU H4)and wondered if there's anyth=
ing to be gained=C2=A0 (or lost) by smoothing out the casting (before the j=
et)? I'm not sure if it's designed (or left) that way to promote tu=
rbulence and better mixing as the air flows over the jet or if polishing it=
down would help.=20
<div>
=C2=A0
</div>=20
<div>
I'd hate to trash a pair of good carbs before I get some answers.
</div>=20
<div>
=C2=A0
</div>=20
<div>
thanks
</div>=20
<div>
mike h
</div>=20
</div> _______________________________________________
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<br>
</blockquote>=20
</div>
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</blockquote></div>
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