<div dir="ltr"><div class="gmail_default" style="font-family:garamond,serif;font-size:large">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).</div><div class="gmail_default" style="font-family:garamond,serif;font-size:large"><br></div><div class="gmail_default" style="font-family:garamond,serif;font-size:large">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?</div><div class="gmail_default" style="font-family:garamond,serif;font-size:large"><br></div><div class="gmail_default" style="font-family:garamond,serif;font-size:large">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.</div><div class="gmail_default" style="font-family:garamond,serif;font-size:large"><br></div><div class="gmail_default" style="font-family:garamond,serif;font-size:large">Duncan</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Nov 24, 2020 at 6:01 AM John Styduhar via Fot <<a href="mailto:fot@autox.team.net">fot@autox.team.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_default" style="font-size:small">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.</div><div class="gmail_default" style="font-size:small"><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Nov 24, 2020 at 3:19 AM Rocky Entriken via Fot <<a href="mailto:fot@autox.team.net" target="_blank">fot@autox.team.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<div style="font-size:12pt;font-family:Calibri;color:rgb(0,0,0)">
<div>Re Oil:</div>
<div>
<div style="font-size:small;text-decoration:none;font-family:Calibri;font-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline">I
once did a race at Woody Creek Raceway, Aspen, CO (8000 feet) and could 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 caps. Never had a
problem again! </div></div>
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<div style="font-size:small;text-decoration:none;font-family:Calibri;font-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline"> </div></div>
<div>
<div style="font-size:small;text-decoration:none;font-family:Calibri;font-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline">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’t WANT to retard the carb piston on a race engine. You hit the
gas you want it WOT. RIGHT NOW! Street car, sure. Race car, no. </div></div>
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<div style="font-size:small;text-decoration:none;font-family:Calibri;font-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline"> </div></div>
<div>
<div style="font-size:small;text-decoration:none;font-family:Calibri;font-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline">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’t. </div></div>
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<div style="font-size:small;text-decoration:none;font-family:Calibri;font-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline"> </div></div>
<div>
<div style="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>
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<div style="font-size:small;text-decoration:none;font-family:Calibri;font-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline"> </div></div>
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<div style="background:rgb(245,245,245)">
<div><b>From:</b> <a title="fot@autox.team.net">Henry
Giffin via Fot</a> </div>
<div><b>Sent:</b> Tuesday, November 24, 2020 12:58 AM</div>
<div><b>To:</b> <a title="fot@autox.team.net">fot@autox.team.net</a> ; <a title="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> </div></div>
<div style="font-size:small;text-decoration:none;font-family:Calibri;font-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline">
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<p class="MsoNormal"><span style="font-size:14pt">FOTs, I have two questions for
the knowledgeable ones.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:14pt"> 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. <u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:14pt"> 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 the company who did
the work. Can anyone recommend a source for refurbishing my
suit?<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:14pt">
Thanks, Hank<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:14pt"><u></u><u></u></span> </p>
<p class="MsoNormal">Hank Giffin<u></u><u></u></p>
<p class="MsoNormal">757-375-1491<u></u><u></u></p>
<p class="MsoNormal"><u></u><u></u> </p></div>
<p>
</p><hr>
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