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Thanks to everyone for their insights. I think I'll just look for any
obvious rough spots but mostly leave well enough alone.
mike h
On Wed, Nov 25, 2020 at 4:52 PM Enquiries Road & Track <
enquiries@roadandtrack.net.au> wrote:
> 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
>> _______________________________________________
>> fot@autox.team.net
>>
>> http://www.fot-racing.com
>>
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>>
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>>
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Content-Transfer-Encoding: quoted-printable
<div dir=3D"ltr">Thanks to everyone for their insights. I think I'll ju=
st look for any obvious rough spots but mostly leave well enough alone.<div=
><br></div><div>mike h</div></div><br><div class=3D"gmail_quote"><div dir=
=3D"ltr" class=3D"gmail_attr">On Wed, Nov 25, 2020 at 4:52 PM Enquiries Roa=
d & Track <<a href=3D"mailto:enquiries@roadandtrack.net.au";>enquirie=
s@roadandtrack.net.au</a>> wrote:<br></div><blockquote class=3D"gmail_qu=
ote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,20=
4);padding-left:1ex"><div dir=3D"ltr">I have had a few goes at shaving thro=
ttle 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 wonder=
ing completely=C2=A0about the wisdom of any of this without=C2=A0real-world=
testing<br></div><div><br></div><div>We found some head/intake arrangement=
s=C2=A0where the air flow was too high in certain places and we had to dimp=
le the port to slow it down. Sometimes, just=C2=A0enlarging the port does n=
ot work as intended</div><div><br></div><div>The very best SU research ive =
seen was done by David Vizard . There are plenty of on-line references to h=
is work, but if anyone can't find what they want, i can scan relevant p=
arts 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 val=
ve to the throttle plate, with the ideal varying considerably=C2=A0with the=
RPM range being used. As a general comment, it seems like many folk have i=
t far too long=C2=A0</div><div><br></div><div><div>I have proven that fiddl=
ing 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 con=
ventional flow bench</div></div><div><div><div dir=3D"ltr"><div dir=3D"ltr"=
><div><div dir=3D"ltr"><div><div dir=3D"ltr"><div><div dir=3D"ltr"><div><di=
v dir=3D"ltr"><div><div dir=3D"ltr"><div><br></div><div>Terry</div><div>Aus=
tralia<br><br></div></div></div></div></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_attr">On Thu, Nov 26, 2020 at 2:35 AM DAVE=
HOGYE via Fot <<a href=3D"mailto:fot@autox.team.net"; target=3D"_blank">=
fot@autox.team.net</a>> wrote:<br></div><blockquote class=3D"gmail_quote=
" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid 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>
<br>
</blockquote>=20
</div>
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</blockquote></div>
</blockquote></div>
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