Subject: Re: [TR] distributor advance

From: Tony Drews <[email-masked]>
Date: Thu, 27 Feb 2020 19:08:07 -0600

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The springs should just change what RPM it takes to get to full advance 
but the full advance should be the same (weights against the stops).  
I'm a little unclear on how much you changed the timing, it sounds like 
you had to retard the timing after the spring replacement - this would 
also retard the "all in" timing, which would be what you're running at 
3200 RPM.  It's possible it's worse at 3200 now than it was before 
because the full advance timing is now less.

I don't run a street car so could be all wet...  When I check the timing 
I see what it is once the advance is all-in.  Wherever it ends up at 
idle is where it ends up, I don't really pay attention to the idle advance.

With 110 octane gas and decent compression (and a 4 banger, not a 6 
banger), I shoot for 32 degrees when the advance stops changing.  I'd 
think you'd want closer to 26 degrees with a street motor / pump gas.

Hope this helps...

Regards, Tony Drews

On 2/27/2020 5:48 PM, Peter Arakelian wrote:
> Have an early 71 TR6, still has the 41306 distributor with dual 
> vacuums, advance and retard.  Did a little work on my distributor, 
> wanted to check the function of the mechanical advance since I came 
> across a new set of advance springs. I know they are correct because 
> they are Lucas and the correct part number as listed in the Lucas 
> master catalog.
> the old springs were visibly different and softer.  The weight in my 
> distributor was marked 13 degrees.  After I changed them, my timing at 
> idle advanced 10-15 degrees.  I reset the timing to 8 BTDC.  I have 
> always run there.  I use the advance 'till it pings and back off 
> method. Have had it as much as 10 BTDC with no ping, but I prefer to 
> run at 8. My retard works correctly, because it passes the test -idle 
> increases 300rpm when pulled.  Still no ping under the test - high 
> gear, full throttle 30-50 mph.  And no ping accelerating at full 
> throttle from 70-80.
> Now...am I correct in thinking the car should run better at speed 
> (3200rpm)?  My thinking is that the timing is more advanced at that 
> rpm with the correct springs, than it was previously.
> Peter Arakelian
>
> ** [email-masked] **
>
> Donate: http://www.team.net/donate.html
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    <p>The springs should just change what RPM it takes to get to full
      advance but the full advance should be the same (weights against
      the stops).  I'm a little unclear on how much you changed the
      timing, it sounds like you had to retard the timing after the
      spring replacement - this would also retard the "all in" timing,
      which would be what you're running at 3200 RPM.  It's possible
      it's worse at 3200 now than it was before because the full advance
      timing is now less.</p>
    <p>I don't run a street car so could be all wet...  When I check the
      timing I see what it is once the advance is all-in.  Wherever it
      ends up at idle is where it ends up, I don't really pay attention
      to the idle advance.</p>
    <p>With 110 octane gas and decent compression (and a 4 banger, not a
      6 banger), I shoot for 32 degrees when the advance stops
      changing.  I'd think you'd want closer to 26 degrees with a street
      motor / pump gas.</p>
    <p>Hope this helps...</p>
    <p>Regards, Tony Drews<br>
    </p>
    <div class="moz-cite-prefix">On 2/27/2020 5:48 PM, Peter Arakelian
      wrote:<br>
    </div>
    <blockquote type="cite"
cite="mid:[email-masked]">
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      <div>Have an early 71 TR6, still has the 41306 distributor with
        dual vacuums, advance and retard.  Did a little work on my
        distributor, wanted to check the function of the mechanical
        advance since I came across a new set of advance springs. 
        I know they are correct because they are Lucas and the correct
        part number as listed in the Lucas master catalog. </div>
      <div>the old springs were visibly different and softer.  The
        weight in my distributor was marked 13 degrees.  After I changed
        them, my timing at idle advanced 10-15 degrees.  I reset the
        timing to 8 BTDC.  I have always run there.  I use the advance
        'till it pings and back off method. Have had it as much as 10
        BTDC with no ping, but I prefer to run at 8. My retard works
        correctly, because it passes the test -idle increases 300rpm
        when pulled.  Still no ping under the test - high gear, full
        throttle 30-50 mph.  And no ping accelerating at full throttle
        from 70-80.</div>
      <div>Now...am I correct in thinking the car should run better at
        speed (3200rpm)?  My thinking is that the timing is more
        advanced at that rpm with the correct springs, than it was
        previously.</div>
      <div>Peter Arakelian</div>
      <br>
      <fieldset class="mimeAttachmentHeader"></fieldset>
      <pre class="moz-quote-pre" wrap="">** <a class="moz-txt-link-abbreviated" href="mailto:[email-masked]">[email-masked]</a> **

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From: Randall <[email-masked]> 4L4h6LgnqhEy3JAVMJR8zufWwOWHwjKe87/cGz5qSpvzsTcLN7rChdCk7Xy9D/MmPn8FMw7kVmPnQXB7IbZs7+7tdAVa8DsuWbSEGbf6mNV0ZAOfsgYfExHZ N7T9I5ZnNoZDaUnnuCfZpA==
Date: Fri, 28 Feb 2020 08:43:27 -0700

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I don't have my books handy, but I believe there should be a heavier, longe=
r spring, and a lighter, somewhat shorter spring=2E The heavier spring shou=
ld be slightly loose as installed, so that at lower rpm, only the light spr=
ing controls the advance movement=2E This give a fast advance curve up unti=
l the heavier spring becomes tight, then slower until the stop is reached=
=2E

Normal practice is to measure the advance curve after changing springs, so=
 they can be tweaked if necessary to give the desired curve=2E Kind of like=
 balancing tires=2E

If you were not getting pinging before, I would not expect a performance i=
ncrease by switching to heavier springs=2E Maximum advance without ping is =
not always the best power point, but usually not far from it=2E
The factory had to supply an advance curve that worked under the majority =
of conditions, without necessarily being the best curve for any conditions=
=20

Also, in general, a low compression smog engine can stand more advance tha=
n a higher compression, better breathing race engine can=2E That's why the =
stock "all-in" advance was so high=2E (Around 36 degrees IIRC) If you've do=
ne anything like shave the head or install a different cam, you might need =
less advance=2E The whole idea is to get the peak cylinder pressure with th=
e crank throw at the best angle to turn the crankshaft=2E

In short I don't think there is any way to answer your question, short of =
comparing performance before and after=2E To really optimize it, you need t=
o run tests to find the optimum advance across the rpm range for your motor=
, then build a distributor to achieve that=2E

If those lighter springs were the result of someone else doing that, then =
any change will likely not be for the better=2E

I haven't been paying attention lately, but one of the local clubs used to=
 have a "dyno day" once a year, where you could get several chassis dyno ru=
ns for a very modest price ($40 when I was there)=2E One way to check your =
advance is to try a run with more initial advance, then another with less, =
and see what the engine likes across the band=2E
-- Randall

On 27 February 2020 16:48:12 GMT-07:00, Peter Arakelian <PeterAra@msn=2Eco=
m> wrote:
>vacuums, advance and retard=2E  Did a little work on my distributor,
>across a new set of advance springs=2E  I know they are correct because
>master catalog=2E
>the old springs were visibly different and softer=2E  The weight in my
>distributor was marked 13 degrees=2E  After I changed them, my timing at
>idle advanced 10-15 degrees=2E  I reset the timing to 8 BTDC=2E  I have
>always run there=2E  I use the advance 'till it pings and back off
>method=2E Have had it as much as 10 BTDC with no ping, but I prefer to
>run at 8=2E My retard works correctly, because it passes the test -idle
>increases 300rpm when pulled=2E  Still no ping under the test - high
>gear, full throttle 30-50 mph=2E  And no ping accelerating at full
>throttle from 70-80=2E
>Now=2E=2E=2Eam I correct in thinking the car should run better at speed
>(3200rpm)?  My thinking is that the timing is more advanced at that rpm
>with the correct springs, than it was previously=2E
>Peter Arakelian

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Content-Transfer-Encoding: quoted-printable

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4=2E0 Transitional//EN"><html><head=
<meta http-equiv=3D"Content-Type" content=3D"text/html; charset=3Dutf-8">
<style></style>
<meta name=3D"GENERATOR" content=3D"MSHTML 11=2E00=2E10570=2E1001">
</head>
<body id=3D"MailContainerBody" topmargin=3D"0" leftmargin=3D"0" style=3D"c=
olor: rgb(0, 0, 0); padding-top: 15px; padding-left: 10px; font-family: Ver=
dana; font-size: 10pt; font-style: normal; font-weight: normal; text-decora=
tion: none;" acc_role=3D"text" canvastabstop=3D"true" name=3D"Compose messa=
ge area">I don't have my books handy, but I believe there should be a heavi=
er, longer spring, and a lighter, somewhat shorter spring=2E The heavier sp=
ring should be slightly loose as installed, so that at lower rpm, only the =
light spring controls the advance movement=2E This give a fast advance curv=
e up until the heavier spring becomes tight, then slower until the stop is =
reached=2E<br><br>Normal practice is to measure the advance curve after cha=
nging springs, so they can be tweaked if necessary to give the desired curv=
e=2E Kind of like balancing tires=2E<br><br>If you were not getting pinging=
 before, I would not expect a performance increase by switching to heavier =
springs=2E Maximum advance without ping is not always the best power point,=
 but usually not far from it=2E<br>The factory had to supply an advance cur=
ve that worked under the majority of conditions, without necessarily being =
the best curve for any conditions <br><br>Also, in general, a low compressi=
on smog engine can stand more advance than a higher compression, better bre=
athing race engine can=2E That's why the stock "all-in" advance was so high=
=2E (Around 36 degrees IIRC) If you've done anything like shave the head or=
 install a different cam, you might need less advance=2E The whole idea is =
to get the peak cylinder pressure with the crank throw at the best angle to=
 turn the crankshaft=2E<br><br>In short I don't think there is any way to a=
nswer your question, short of comparing performance before and after=2E To =
really optimize it, you need to run tests to find the optimum advance acros=
s the rpm range for your motor, then build a distributor to achieve that=2E=
<br><br>If those lighter springs were the result of someone else doing that=
, then any change will likely not be for the better=2E<br><br>I haven't bee=
n paying attention lately, but one of the local clubs used to have a "dyno =
day" once a year, where you could get several chassis dyno runs for a very =
modest price ($40 when I was there)=2E One way to check your advance is to =
try a run with more initial advance, then another with less, and see what t=
he engine likes across the band=2E<br>-- Randall<br><br><div class=3D"gmail=
_quote">On 27 February 2020 16:48:12 GMT-07:00, Peter Arakelian &lt;PeterAr=
a@msn=2Ecom&gt; wrote:<blockquote class=3D"gmail_quote" style=3D"margin: 0p=
t 0pt 0pt 0=2E8ex; border-left: 1px solid rgb(204, 204, 204); padding-left:=
 1ex;">

<!--[gte IE 5]><?xml:namespace prefix=3D"v" /><?xml:namespace prefix=3D"o"=
 /><![endif]-->
<div>Have an early 71 TR6, still has the 41306 distributor with dual vacuu=
ms, advance and retard=2E&nbsp; Did a little work on my distributor, wanted=
 to check the function of the mechanical advance since I came across a new =
set of advance springs=2E&nbsp; I&nbsp;know they are
 correct because they are Lucas and the correct part number as listed in t=
he Lucas master catalog=2E&nbsp;</div>
<div>the old springs were visibly different and softer=2E&nbsp; The weight=
 in my distributor was marked 13 degrees=2E&nbsp; After I changed them, my =
timing at idle&nbsp;advanced 10-15 degrees=2E&nbsp; I reset the timing to 8=
 BTDC=2E&nbsp; I have always run there=2E&nbsp; I use the advance 'till it
 pings and back off method=2E Have had it as much as 10 BTDC with no ping,=
 but I prefer to run at 8=2E My retard works correctly, because it passes t=
he test -idle increases 300rpm when pulled=2E&nbsp; Still no ping under the=
 test - high gear, full throttle 30-50 mph=2E&nbsp;
 And no ping accelerating at full throttle from 70-80=2E</div>
<div>Now=2E=2E=2Eam I correct in thinking the car should run better at spe=
ed (3200rpm)?&nbsp; My thinking is that the timing is more advanced at that=
 rpm with the correct springs, than it was previously=2E</div>
<div>Peter Arakelian</div>

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