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SU sizing. All side draft SU's start with the premise of a 1" throat.
Then the larger sizes are given in 1/8" increments above the 1" throat.Â
So an original Bugeye Sprite for example, used 1 1/8" carbs or "H1", TR3
used 1 3/4" or "H6". Ted
On 10/18/2018 5:48 PM, van.mulders.marcel--- via Fot wrote:
> Glen,
> With 1 1/2s carburettors, I suppose you mean HS4? The SU logic is a
> little weird. 1" + 1/2" = 6/8" so you would think it are HS6s, but
> when talking about HS carburettors, 1 + 1/2 = 1 + 4/8 and they took
> the 4 to name these carbs HS4...
> Marcel
>
> ------------------------------------------------------------------------
> *Van: *"fubog1" <fubog1@aol.com>
> *Aan: *"van mulders marcel" <van.mulders.marcel@telenet.be>, "Mike
> Harmuth" <ofracer@gmail.com>
> *Cc: *"fot" <fot@autox.team.net>
> *Verzonden: *Donderdag 18 oktober 2018 22:39:39
> *Onderwerp: *Re: [Fot] Weber vs Mikuni
>
> Well I won't speculate on the cause, but I doubt that it's the SUs.
> My small crank 1300 w/1 1/2s on a eurospec manifold w/Stahls header,
> "big" valve head, would buzz easily to 9k, still making power, if I
> let it.
> Normal shift point 7800-8000.
> FWIW...
> Glen
>
>
> -----Original Message-----
> From: van.mulders.marcel--- via Fot <fot@autox.team.net>
> To: Mike Harmuth <ofracer@gmail.com>
> Cc: fot <fot@autox.team.net>
> Sent: Thu, Oct 18, 2018 2:12 pm
> Subject: Re: [Fot] Weber vs Mikuni
>
> -"...hitting a wall at that point..." : is it possible this is rather
> pointing to the camshaft than to the SU's? If it are the carburettors,
> maybe the power would decrease more gradually above 6500 rpm.
> -In general one choke per cylinder is better, and 2 Webers 40 DCOE
> isn't overkill I think
> - what about trying HS6 SU's on your actual manifold?
> At what maximum rpm is your engine still reliable?
> Marcel
>
> ------------------------------------------------------------------------
> *Van: *"fot" <fot@autox.team.net>
> *Aan: *"fot" <fot@autox.team.net>
> *Verzonden: *Woensdag 17 oktober 2018 15:49:45
> *Onderwerp: *[Fot] Weber vs Mikuni
>
> I'm looking into switching out my twin HS4s on the 1296 race engine to
> either Weber or Mukinis. I know this has been done for years and I'd
> like to get close the best set up out of the gate.
>
> I don't think the SUs are up to the task of moving enough air with the
> new ported head and Stahl header. I've worked on the SUs and gotten
> them to finally deliver a good AFR , 12.6, at 6500 RPM under load but
> I seem to hit a wall (figuratively) at that point. I suspect that the
> openings just aren't big enough to deliver the mass of air required.
> (spreadsheet or other flow calculator link appreciated)
> Biggest gate I suspect is the intake valve, 1 3/8" head (~35mm) HS4 is
> ~38mm at best.
>
> Recommendations? I've seen all these setups at the track, each with
> pluses, minuses and overkill cause it looks cool.
>
> One weber DCOE 40 or 2? what jets, tubes etc for a starting point?
> Best manifold?
>
> 2 or 4 Mikuni 40? jet size?
>
> thanks
> mike
>
> _______________________________________________
> fot@autox.team.net
>
> http://www.fot-racing.com
>
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>
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>
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>
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--
Ted Schumacher
tedtsimx@bright.net
http://www.tsimportedautomotive.com
108 S. Jefferson St.
Pandora, Ohio, USA 45877
Fax: 419.384.3272 (24 Hrs.)
Phone: 800.543.6648 (US & Canada)
Tech/ Gen. Information/ Worldwide: 419.384.3022
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<div class="moz-cite-prefix">SU sizing. All side draft SU's start
with the premise of a 1" throat. Then the larger sizes are given
in 1/8" increments above the 1" throat. So an original Bugeye
Sprite for example, used 1 1/8" carbs or "H1", TR3 used 1 3/4" or
"H6". Ted<br>
<br>
<br>
On 10/18/2018 5:48 PM, van.mulders.marcel--- via Fot wrote:<br>
</div>
<blockquote type="cite"
cite="mid:362035711.238499389.1539899280468.JavaMail.zimbra@telenet.be">
<meta http-equiv="content-type" content="text/html; charset=utf-8">
<div style="font-family: Verdana, Arial, Helvetica, sans-serif;
font-size: 10pt; color: #000000">
<div>Glen,</div>
<div>With 1 1/2s carburettors, I suppose you mean HS4? The SU
logic is a little weird. 1" + 1/2" = 6/8" so you would think
it are HS6s, but when talking about HS carburettors, 1 + 1/2 =
1 + 4/8 and they took the 4 to name these carbs HS4...</div>
<div>Marcel</div>
<div><br>
</div>
<hr id="zwchr" data-marker="__DIVIDER__">
<div data-marker="__HEADERS__"><b>Van: </b>"fubog1"
<a class="moz-txt-link-rfc2396E"
href="mailto:fubog1@aol.com";><fubog1@aol.com></a><br>
<b>Aan: </b>"van mulders marcel"
<a class="moz-txt-link-rfc2396E"
href="mailto:van.mulders.marcel@telenet.be";><van.mulders.marcel@telenet.be></a>,
"Mike Harmuth"
<a class="moz-txt-link-rfc2396E"
href="mailto:ofracer@gmail.com";><ofracer@gmail.com></a><br>
<b>Cc: </b>"fot" <a class="moz-txt-link-rfc2396E"
href="mailto:fot@autox.team.net";><fot@autox.team.net></a><br>
<b>Verzonden: </b>Donderdag 18 oktober 2018 22:39:39<br>
<b>Onderwerp: </b>Re: [Fot] Weber vs Mikuni<br>
</div>
<br>
<div data-marker="__QUOTED_TEXT__"><span color="black" size="2"
face="Arial, Helvetica, sans-serif" data-mce-style="color:
black; font-family: Arial, Helvetica, sans-serif; font-size:
small;" style="color: black; font-family: Arial, Helvetica,
sans-serif; font-size: small;">
<div> <span size="2" data-mce-style="font-size: small;"
style="font-size: small;">Well I won't speculate on the
cause, but I doubt that it's the SUs.<br>
</span></div>
<div><span size="2" data-mce-style="font-size: small;"
style="font-size: small;">My small crank 1300 w/1 1/2s
on a eurospec manifold w/Stahls header, "big" valve
head, would buzz easily to 9k, still making power, if I
let it.</span></div>
<div><span size="2" data-mce-style="font-size: small;"
style="font-size: small;">Normal shift point
7800-8000.</span></div>
<div><span size="2" data-mce-style="font-size: small;"
style="font-size: small;">FWIW...<br>
</span></div>
<div><span size="2" data-mce-style="font-size: small;"
style="font-size: small;">Glen</span><br>
</div>
<div> <br>
</div>
<div> <br>
</div>
<div
style="font-family:arial,helvetica;font-size:10pt;color:black">-----Original
Message-----<br>
From: van.mulders.marcel--- via Fot
<a class="moz-txt-link-rfc2396E"
href="mailto:fot@autox.team.net";><fot@autox.team.net></a><br>
To: Mike Harmuth <a class="moz-txt-link-rfc2396E"
href="mailto:ofracer@gmail.com";><ofracer@gmail.com></a><br>
Cc: fot <a class="moz-txt-link-rfc2396E"
href="mailto:fot@autox.team.net";><fot@autox.team.net></a><br>
Sent: Thu, Oct 18, 2018 2:12 pm<br>
Subject: Re: [Fot] Weber vs Mikuni<br>
<br>
<div id="yiv1357758352">
<div>
<div style="font-family:Verdana, Arial, Helvetica,
sans-serif;font-size:10pt;color:#000000;">
<div>-"...hitting a wall at that point..." : is it
possible this is rather pointing to the camshaft
than to the SU's? If it are the carburettors,
maybe the power would decrease more gradually
above 6500 rpm.</div>
<div>-In general one choke per cylinder is better,
and 2 Webers 40 DCOE isn't overkill I think</div>
<div>- what about trying HS6 SU's on your actual
manifold?</div>
<div>At what maximum rpm is your engine still
reliable?</div>
<div>Marcel</div>
<div><br clear="none">
</div>
<hr id="yiv1357758352zwchr">
<div class="yiv1357758352yqt0105059393"
id="yiv1357758352yqt73080">
<div><b>Van: </b>"fot" <a class="moz-txt-link-rfc2396E"
href="mailto:fot@autox.team.net";><fot@autox.team.net></a><br
clear="none">
<b>Aan: </b>"fot" <a class="moz-txt-link-rfc2396E"
href="mailto:fot@autox.team.net";><fot@autox.team.net></a><br
clear="none">
<b>Verzonden: </b>Woensdag 17 oktober 2018
15:49:45<br clear="none">
<b>Onderwerp: </b>[Fot] Weber vs Mikuni<br
clear="none">
</div>
<br clear="none">
<div>
<div dir="ltr">
<div>I'm looking into switching out my twin
HS4s on the 1296 race engine to either Weber
or Mukinis. I know this has been done for
years and I'd like to get close the best set
up out of the gate. <br clear="none">
</div>
<br clear="none">
<div>I don't think the SUs are up to the task
of moving enough air with the new ported
head and Stahl header. I've worked on the
SUs and gotten them to finally deliver a
good AFR , 12.6, at 6500 RPM under load but
I seem to hit a wall (figuratively) at that
point. I suspect that the openings just
aren't big enough to deliver the mass of air
required. (spreadsheet or other flow
calculator link appreciated)<br clear="none">
</div>
<div>Biggest gate I suspect is the intake
valve, 1 3/8" head (~35mm) HS4 is ~38mm at
best.<br clear="none">
</div>
<br clear="none">
<div>Recommendations? I've seen all these
setups at the track, each with pluses,
minuses and overkill cause it looks cool. <br
clear="none">
</div>
<br clear="none">
<div>One weber DCOE 40 or 2? what jets, tubes
etc for a starting point? Best manifold? <br
clear="none">
</div>
<br clear="none">
<div>2 or 4 Mikuni 40? jet size?</div>
<br clear="none">
<div>thanks</div>
<div>mike<br clear="none">
</div>
</div>
<br clear="none">
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<pre wrap="">_______________________________________________
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href="mailto:fot@autox.team.net";>fot@autox.team.net</a>
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<p><br>
</p>
<pre class="moz-signature" cols="72">--
Ted Schumacher
<a class="moz-txt-link-abbreviated"
href="mailto:tedtsimx@bright.net";>tedtsimx@bright.net</a>
<a class="moz-txt-link-freetext"
href="http://www.tsimportedautomotive.com";>http://www.tsimportedautomotive.com</a>
108 S. Jefferson St.
Pandora, Ohio, USA 45877
Fax: 419.384.3272 (24 Hrs.)
Phone: 800.543.6648 (US & Canada)
Tech/ Gen. Information/ Worldwide: 419.384.3022</pre>
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