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The piston not only controls velocity by restricting the size of the
opening below; it also controls mixture by raising the tapered needle.
Moving a car to a higher elevation suggests that the engine would be
happier with a leaner mixture to run properly and I can see how removing
the damping effect could improve that. Would lowering the needle jets have
done the same thing? How about using a softer spring above the piston to
counter the lower atmospheric pressure? There's another factor on racing
engines, too, and I'm not sure how to estimate its effects -- a long
duration cam would raise manifold pressure (or reduce manifold vacuum; pick
your nomenclature).
I recall reading a tip in one of Kas' tuning books to remove the pistons
(or the rings from the pistons, I can't recall which). Since reading that
I've wondered how they tuned the carbs to cope with coming out of slow
corners that required the engine to be in the low end of the rev range,
below the fat part of the torque curve. Did they run a very rich needle
and jet combination? Did they strictly use OD gearboxes to keep the revs
up in those situations?
The following may be the opposite case to a naturally aspirated race engine
run at high elevation: I had a supercharged 1275cc Mini (supercharger was
downstream of an SU HIF44 carb) that bogged significantly when the throttle
was snapped open (I'm at 300' elevation). The PO had been dutifully using
SU brand dashpot oil and that oil appears to have low viscosity, so it's
perhaps 10 weight. After experimentation I found that 40 weight ND engine
oil really woke up the engine.
Duncan
On Tue, Nov 24, 2020 at 6:01 AM John Styduhar via Fot <fot@autox.team.net>
wrote:
> I found the opposite response with my CD175 Strombergs. If the piston
> rises too quickly the venturi effect is reduced and adequate fuel is not
> drawn through the jet causing a lean mixture. I use marvel mystery oil.
>
>
> On Tue, Nov 24, 2020 at 3:19 AM Rocky Entriken via Fot <fot@autox.team.ne=
t>
> wrote:
>
>> Re Oil:
>> I once did a race at Woody Creek Raceway, Aspen, CO (8000 feet) and coul=
d
>> not get the car to rev over 5000 rpm. A friend diagnosed the problem ...
>> got out his wire cutters and snipped the posts off the rods in the SU ca=
ps.
>> Never had a problem again!
>>
>> He about gave me a heart attack when he did it. Thing is, the purpose of
>> the oil in the SUs is to retard the piston going up and down, mostly up.=
It
>> was explained to me, you don=E2=80=99t WANT to retard the carb piston on=
a race
>> engine. You hit the gas you want it WOT. RIGHT NOW! Street car, sure. Ra=
ce
>> car, no.
>>
>> But a tip: Clean the inside of the carb, piston & cylinder, regularly.
>> Before each race. Brakleen. Fuel residue will gum it up if you don=E2=80=
=99t.
>>
>> --Rocky
>>
>> *From:* Henry Giffin via Fot
>> *Sent:* Tuesday, November 24, 2020 12:58 AM
>> *To:* fot@autox.team.net ; fot-bounces@autox.team.net
>> *Subject:* [Fot] SU oil/refurbishing race suit?
>>
>>
>> FOTs, I have two questions for the knowledgeable ones.
>>
>> Do you use light oil in your SUs on your racing engines? I have
>> heard both sides of this. I have not been using any oil, but have heard
>> from friends I should be.
>>
>> A number of years ago when my son-in-law started racing we sent my
>> old racing suit to someone to be refurbished. It came back in great
>> condition. My current suit could use some work. We lost the name of th=
e
>> company who did the work. Can anyone recommend a source for refurbishin=
g
>> my suit?
>>
>> Thanks, Hank
>>
>>
>>
>> Hank Giffin
>>
>> 757-375-1491
>>
>>
>>
>> ------------------------------
>> _______________________________________________
>> fot@autox.team.net
>>
>> http://www.fot-racing.com
>>
>> Donate: http://www.team.net/donate.html
>> Archive: http://autox.team.net/archive http://www.team.net/pipermail/fot
>> Unsubscribe/Manage:
>> http://autox.team.net/mailman/options/fot/rocky@spitfire4.com
>>
>>
>> _______________________________________________
>> fot@autox.team.net
>>
>> http://www.fot-racing.com
>>
>> Donate: http://www.team.net/donate.html
>> Archive: http://autox.team.net/archive http://www.team.net/pipermail/fot
>> Unsubscribe/Manage <http://www.team.net/pipermail/fotUnsubscribe/Manage>=
:
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>>
>>
>> _______________________________________________
> fot@autox.team.net
>
> http://www.fot-racing.com
>
> Donate: http://www.team.net/donate.html
> Archive: http://autox.team.net/archive http://www.team.net/pipermail/fot
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>
>
>
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Content-Transfer-Encoding: quoted-printable
<div dir=3D"ltr"><div class=3D"gmail_default" style=3D"font-family:garamond=
,serif;font-size:large">The piston not only controls velocity by restrictin=
g the size of the opening below; it also controls mixture by raising the ta=
pered needle.=C2=A0 Moving a car to a higher elevation suggests that the en=
gine would be happier with a leaner mixture to run properly and I can see h=
ow removing the damping effect could improve that.=C2=A0 Would lowering the=
needle jets have done the same thing?=C2=A0 How about using a softer sprin=
g above the=C2=A0piston to counter the lower atmospheric pressure?=C2=A0 Th=
ere's another=C2=A0factor on=C2=A0racing engines, too, and I'm not =
sure how to estimate its effects -- a long duration cam would raise manifol=
d pressure (or reduce manifold vacuum; pick your nomenclature).</div><div c=
lass=3D"gmail_default" style=3D"font-family:garamond,serif;font-size:large"=
><br></div><div class=3D"gmail_default" style=3D"font-family:garamond,serif=
;font-size:large">I recall reading=C2=A0a tip in one of Kas' tuning boo=
ks to remove the pistons (or the rings from the pistons, I can't recall=
which).=C2=A0 Since reading that I've wondered how they tuned the carb=
s to cope with coming out of slow corners that required the engine to be in=
the low end of the rev range, below the fat part of the torque curve.=C2=
=A0 Did they run a very rich needle and jet combination?=C2=A0 Did they str=
ictly=C2=A0use OD gearboxes to keep the revs up in those situations?</div><=
div class=3D"gmail_default" style=3D"font-family:garamond,serif;font-size:l=
arge"><br></div><div class=3D"gmail_default" style=3D"font-family:garamond,=
serif;font-size:large">The following may be the opposite case to a naturall=
y aspirated race engine run at high elevation: I had a supercharged 1275cc =
Mini (supercharger was downstream of an SU HIF44 carb) that bogged signific=
antly when the throttle was snapped open (I'm at 300' elevation).=
=C2=A0 The PO had been dutifully using SU brand dashpot oil and that oil ap=
pears to have low viscosity, so it's perhaps 10 weight.=C2=A0 After exp=
erimentation I found that 40 weight=C2=A0ND engine oil really woke up the e=
ngine.</div><div class=3D"gmail_default" style=3D"font-family:garamond,seri=
f;font-size:large"><br></div><div class=3D"gmail_default" style=3D"font-fam=
ily:garamond,serif;font-size:large">Duncan</div></div><br><div class=3D"gma=
il_quote"><div dir=3D"ltr" class=3D"gmail_attr">On Tue, Nov 24, 2020 at 6:0=
1 AM John Styduhar via Fot <<a href=3D"mailto:fot@autox.team.net";>fot@au=
tox.team.net</a>> wrote:<br></div><blockquote class=3D"gmail_quote" styl=
e=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);paddin=
g-left:1ex"><div dir=3D"ltr"><div class=3D"gmail_default" style=3D"font-siz=
e:small">I found the opposite response with my CD175 Strombergs.=C2=A0 If t=
he piston rises too quickly the venturi effect is reduced and adequate fuel=
is not drawn through the jet causing a lean mixture.=C2=A0 I use marvel my=
stery oil.</div><div class=3D"gmail_default" style=3D"font-size:small"><br>=
</div></div><br><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_=
attr">On Tue, Nov 24, 2020 at 3:19 AM Rocky Entriken via Fot <<a href=3D=
"mailto:fot@autox.team.net"; target=3D"_blank">fot@autox.team.net</a>> wr=
ote:<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">
<div lang=3D"EN-US" dir=3D"ltr">
<div dir=3D"ltr">
<div style=3D"font-size:12pt;font-family:Calibri;color:rgb(0,0,0)">
<div>Re Oil:</div>
<div>
<div style=3D"font-size:small;text-decoration:none;font-family:Calibri;font=
-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline">I=20
once did a race at Woody Creek Raceway, Aspen, CO (8000 feet) and could not=
get=20
the car to rev over 5000 rpm. A friend diagnosed the problem ... got out hi=
s=20
wire cutters and snipped the posts off the rods in the SU caps. Never had a=
=20
problem again! </div></div>
<div>
<div style=3D"font-size:small;text-decoration:none;font-family:Calibri;font=
-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline">=C2=A0</d=
iv></div>
<div>
<div style=3D"font-size:small;text-decoration:none;font-family:Calibri;font=
-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline">He=20
about gave me a heart attack when he did it. Thing is, the purpose of the o=
il in=20
the SUs is to retard the piston going up and down, mostly up. It was explai=
ned=20
to me, you don=E2=80=99t WANT to retard the carb piston on a race engine. Y=
ou hit the=20
gas you want it WOT. RIGHT NOW! Street car, sure. Race car, no. </div></div=
>
<div>
<div style=3D"font-size:small;text-decoration:none;font-family:Calibri;font=
-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline">=C2=A0</d=
iv></div>
<div>
<div style=3D"font-size:small;text-decoration:none;font-family:Calibri;font=
-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline">But=20
a tip: Clean the inside of the carb, piston & cylinder, regularly. Befo=
re=20
each race. Brakleen. Fuel residue will gum it up if you don=E2=80=99t. </di=
v></div>
<div>
<div style=3D"font-size:small;text-decoration:none;font-family:Calibri;font=
-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline">=C2=A0</d=
iv></div>
<div>
<div style=3D"font-size:small;text-decoration:none;font-family:Calibri;font=
-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline">--Rocky</=
div></div>
<div>
<div style=3D"font-size:small;text-decoration:none;font-family:Calibri;font=
-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline">=C2=A0</d=
iv></div>
<div>
<div style=3D"font-size:small;text-decoration:none;font-family:Calibri;font=
-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline"></div>
<div style=3D"font:10pt tahoma">
<div style=3D"background:rgb(245,245,245)">
<div><b>From:</b> <a title=3D"fot@autox.team.net">Henry=20
Giffin via Fot</a> </div>
<div><b>Sent:</b> Tuesday, November 24, 2020 12:58 AM</div>
<div><b>To:</b> <a title=3D"fot@autox.team.net">fot@autox.team.net</a> ; <a=
title=3D"fot-bounces@autox.team.net">fot-bounces@autox.team.net</a> </div>
<div><b>Subject:</b> [Fot] SU oil/refurbishing race suit?</div></div></div>
<div>=C2=A0</div></div>
<div style=3D"font-size:small;text-decoration:none;font-family:Calibri;font=
-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline">
<div>
<p class=3D"MsoNormal"><span style=3D"font-size:14pt">FOTs, I have two ques=
tions for=20
the knowledgeable ones.<u></u><u></u></span></p>
<p class=3D"MsoNormal"><span style=3D"font-size:14pt">=C2=A0=C2=A0=C2=A0 Do=
you use=20
light oil in your SUs on your racing engines?=C2=A0 I have heard both sides=
of=20
this.=C2=A0 I have not been using any oil, but have heard from friends I sh=
ould=20
be.=C2=A0 <u></u><u></u></span></p>
<p class=3D"MsoNormal"><span style=3D"font-size:14pt">=C2=A0=C2=A0=C2=A0=C2=
=A0 A=20
number of years ago when my son-in-law started racing we sent my old racing=
suit=20
to someone to be refurbished.=C2=A0 It came back in great condition.=C2=A0 =
My=20
current suit could use some work.=C2=A0 We lost the name of the company who=
did=20
the work.=C2=A0 Can anyone recommend a source for refurbishing my=20
suit?<u></u><u></u></span></p>
<p class=3D"MsoNormal"><span style=3D"font-size:14pt">=C2=A0=C2=A0=C2=A0=C2=
=A0=20
Thanks, Hank<u></u><u></u></span></p>
<p class=3D"MsoNormal"><span style=3D"font-size:14pt"><u></u><u></u></span>=
=C2=A0</p>
<p class=3D"MsoNormal">Hank Giffin<u></u><u></u></p>
<p class=3D"MsoNormal">757-375-1491<u></u><u></u></p>
<p class=3D"MsoNormal"><u></u><u></u>=C2=A0</p></div>
<p>
</p><hr>
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</blockquote></div>
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