This is a multi-part message in MIME format.
--===============1105885181026052446==
boundary="------------3C9024D1D83DE63DFBC11040"
Content-Language: en-US
This is a multi-part message in MIME format.
--------------3C9024D1D83DE63DFBC11040
Content-Transfer-Encoding: 8bit
re: "I'm wondering if I have been over thinking this process and the
stated advance is meant to be "at idle" with the vacuum connected..."
I've always disconnected the vacuum advance, at least for my BJ8 and (I
think) for my BN2. I believe I read this in the shop manual, but don't
have it handy to check. I've checked with and without the VA connected,
and didn't detect much, if any difference. If you've set up HD8s 'per
the book,' you would be running on the slow run (bypass) circuit, and
the closed throttle would (I think, not sure) cover the VA port.
I'm not sure the vacuum vanishes at wide-open throttle* (WOT). There are
two types of vacuum: manifold and port; the type on SU carbs is, I
believe, the port type. The depression (vacuum) is created, at least in
part, by venturi effect. Hence, I don't think it goes away entirely,
even at WOT, but I'm not sure.
If you google 'manifold vs ported vacuum advance' you'll get a ton of
links; here's just one:
http://chevellestuff.net/tech/articles/vacuum/port_or_manifold.htm
So, the $64,000 question is whether the port in an SU carb is behind,
right on, or in front of a closed throttle plate (this article says the
purpose of port vacuum is to not advance at all at idle)? First correct
answer wins the internet for today.
* I've always felt the term 'full throttle' to be a little, er,
confusing. Since the purpose of the throttle, by definition of
'throttle,' is to restrain/limit airflow, wouldn't 'full throttle' be a
fully closed throttle? The term may be evolved from 'fully open
throttle,' but got shortened (similar, perhaps, to how the aviation term
'on the backside of the power curve' probably gave us 'behind the curve.').
Bob
On 11/2/2018 7:05 PM, Michael Salter wrote:
> Thanks for your input on ignition timing Michael.
> I have always found the factory specs to be a little confusing.
> They state 6 degrees BTDC as the timing (which I presume to be
> "static") and then state that the distributor produces 16 - 18 degrees
> at 2000 RPM (distributor speed) which I figure to be 32 -36 degrees at
> 4000 engine RPM.
> I interpret that to produce 6 + 34 (2 x 17) degrees BTDC at 4000
> engine RPM for a total of 40 degrees which sounds like an awful lot.
> My engine does not sound at all happy with 40 degrees even with 110
> octane!!
> I'm wondering if I have been over thinking this process and the stated
> advance is meant to be "at idle" with the vacuum connected (not normal
> practice as far as I was taught) which would add 6 degrees of vacuum
> advance which would vanish at full throttle producing a net of 34
> degrees over 4000 at full throttle.
> I have been setting the timing to 32 degrees BTDC with the vacuum
> disconnected at 4000 RPM and the engine runs fey well and very cool,
> in fact too cool without a 180 degree thermostat.
> I am running 8.3:1 compressions with an M cam.
>
> M
>
>
> On Fri, Nov 2, 2018 at 9:16 PM Michael Oritt <michael.oritt@gmail.com
>
> Wayne--
>
> Exactly right--it is total advance that matters and I arrived at
> that number by gradually increasing advance and seeing the effect
> upon water temperature at speed and under full load. Anything
> more and the car would begin to overheat. A bit too much less
> advance and performance fell off.
>
> BTW I am running a DW "fast street" cam and tubular header and a
> Mallory non-vacuum advance distributor fired with their Unilite
> module. I too have a Smitty's five-speed and the Toyota box, 180
> XAS's and 3.54 diff set give me about 72-73 mph at 3K rpm's indicated
>
> Best--Michael Oritt
>
> On Fri, Nov 2, 2018 at 6:03 PM Wayne Schultz <waschu2@gmail.com
>
> Thanks to Michael and others I am going to stick with 34 - 35
> degrees total advance for now. What, I think this means, is
> that the advance at idle is secondary and not as important as
> total advance. Cruising with the the Toyota five speed or the
> original overdrive on the highway is right in the 3K RPM range
> so I think this the perfect RPM to limit total advance. I
> might make a run to my local airport and buy some 100LL fuel.
> I have worked in aviation since 1967 so I have a few friendsð???
>
>
--------------3C9024D1D83DE63DFBC11040
Content-Transfer-Encoding: 8bit
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body text="#000000" bgcolor="#FFFFFF">
<p>re: "I'm wondering if I have been over thinking this process and
the stated advance is meant to be "at idle" with the vacuum
connected..."</p>
<p>I've always disconnected the vacuum advance, at least for my BJ8
and (I think) for my BN2. I believe I read this in the shop
manual, but don't have it handy to check. I've checked with and
without the VA connected, and didn't detect much, if any
difference. If you've set up HD8s 'per the book,' you would be
running on the slow run (bypass) circuit, and the closed throttle
would (I think, not sure) cover the VA port.<br>
</p>
<p>I'm not sure the vacuum vanishes at wide-open throttle* (WOT).Â
There are two types of vacuum: manifold and port; the type on SU
carbs is, I believe, the port type. The depression (vacuum) is
created, at least in part, by venturi effect. Hence, I don't
think it goes away entirely, even at WOT, but I'm not sure.</p>
<p>If you google 'manifold vs ported vacuum advance' you'll get a
ton of links; here's just one:</p>
<p><a class="moz-txt-link-freetext"
href="http://chevellestuff.net/tech/articles/vacuum/port_or_manifold.htm";>http://chevellestuff.net/tech/articles/vacuum/port_or_manifold.htm</a></p>
<p>So, the $64,000 question is whether the port in an SU carb is
behind, right on, or in front of a closed throttle plate (this
article says the purpose of port vacuum is to not advance at all
at idle)? First correct answer wins the internet for today.</p>
* I've always felt the term 'full throttle' to be a little, er,
confusing. Since the purpose of the throttle, by definition of
'throttle,' is to restrain/limit airflow, wouldn't 'full throttle'
be a fully closed throttle? The term may be evolved from 'fully
open throttle,' but got shortened (similar, perhaps, to how the
aviation term 'on the backside of the power curve' probably gave us
'behind the curve.').<br>
<br>
Bob<br>
<br>
<div class="moz-cite-prefix">On 11/2/2018 7:05 PM, Michael Salter
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAB3i7LLxqZmUttWxBBuU6FkwBqKhTehbOvzTbk4n0fTa1w1Qvg@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=utf-8">
<div dir="ltr">
<div class="gmail_default" style="font-family:comic sans
ms,sans-serif;font-size:small">Thanks for your input on
ignition timing Michael. <br>
</div>
<div class="gmail_default" style="font-family:comic sans
ms,sans-serif;font-size:small">I have always found the factory
specs to be a little confusing.</div>
<div class="gmail_default" style="font-family:comic sans
ms,sans-serif;font-size:small">They state 6 degrees BTDC as
the timing (which I presume to be "static") and then state
that the distributor produces 16 - 18 degrees at 2000 RPMÂ
(distributor speed) which I figure to be 32 -36 degrees at
4000 engine RPM.</div>
<div class="gmail_default" style="font-family:comic sans
ms,sans-serif;font-size:small">I interpret that to produce 6 +
34 (2 x 17) degrees BTDC at 4000 engine RPM for a total of 40
degrees which sounds like an awful lot.</div>
<div class="gmail_default" style="font-family:comic sans
ms,sans-serif;font-size:small">My engine does not sound at all
happy with 40 degrees even with 110 octane!!</div>
<div class="gmail_default" style="font-family:comic sans
ms,sans-serif;font-size:small">I'm wondering if I have been
over thinking this process and the stated advance is meant to
be "at idle" with the vacuum connected (not normal practice as
far as I was taught) which would add 6 degrees of vacuum
advance which would vanish at full throttle producing a net of
34 degrees over 4000 at full throttle.<br>
</div>
<div class="gmail_default" style="font-family:comic sans
ms,sans-serif;font-size:small">I have been setting the timing
to 32 degrees BTDC with the vacuum disconnected at 4000 RPM
and the engine runs fey well and very cool, in fact too cool
without a 180 degree thermostat.<br>
</div>
<div class="gmail_default" style="font-family:comic sans
ms,sans-serif;font-size:small">I am running 8.3:1 compressions
with an M cam.</div>
<div class="gmail_default" style="font-family:comic sans
ms,sans-serif;font-size:small"><br>
</div>
<div class="gmail_default" style="font-family:comic sans
ms,sans-serif;font-size:small">M<br>
</div>
<div class="gmail_default" style="font-family:comic sans
ms,sans-serif;font-size:small"> <br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr">On Fri, Nov 2, 2018 at 9:16 PM Michael Oritt <<a
href="mailto:michael.oritt@gmail.com";
moz-do-not-send="true">michael.oritt@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div class="gmail_default" style="color:#3333ff">Wayne--</div>
<div class="gmail_default" style="color:#3333ff"><br>
</div>
<div class="gmail_default" style="color:#3333ff">Exactly
right--it is total advance that matters and I arrived at
that number by gradually increasing advance and seeing the
effect upon water temperature at speed and under full
load. Anything more and the car would begin to overheat.Â
A bit too much less advance and performance fell off.  </div>
<div class="gmail_default" style="color:#3333ff"><br>
</div>
<div class="gmail_default" style="color:#3333ff">BTW I am
running a DW "fast street" cam and tubular header and a
Mallory non-vacuum advance distributor fired with their
Unilite module. I too have a Smitty's five-speed and the
Toyota box, 180 XAS's and 3.54 diff set give me about
72-73 mph at 3K rpm's indicated</div>
<div class="gmail_default" style="color:#3333ff"><br>
</div>
<div class="gmail_default" style="color:#3333ff">Best--Michael
Oritt</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr">On Fri, Nov 2, 2018 at 6:03 PM Wayne Schultz
<<a href="mailto:waschu2@gmail.com"; target="_blank"
moz-do-not-send="true">waschu2@gmail.com</a>> wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">Thanks to Michael and others I am going to
stick with 34 - 35 degrees total advance for now. What,
I think this means, is that the advance at idle is
secondary and not as important as total advance.
Cruising with the the Toyota five speed or the original
overdrive on the highway is right in the 3K RPM range so
I think this the perfect RPM to limit total advance. I
might make a run to my local airport and buy some 100LL
fuel. I have worked in aviation since 1967 so I have a
few friendsð???Â
<div><br>
</div>
</div>
<br>
</blockquote>
</div>
</blockquote>
</div>
</blockquote>
<br>
</body>
</html>
--------------3C9024D1D83DE63DFBC11040--
--===============1105885181026052446==
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
_______________________________________________
Archive: http://www.team.net/pipermail/healeys http://autox.team.net/archive
Healeys@autox.team.net
http://autox.team.net/mailman/listinfo/healeys
--===============1105885181026052446==--
|