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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:
>Have an early 71 TR6, still has the 41306 distributor with dual
>vacuums, advance and retard=2E 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 I know they are correct because
>they are Lucas and the correct part number as listed in the Lucas
>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
------4517714IZONNBWXXI7GAHQ2LULDEMS
charset=utf-8
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 <PeterAr=
a@msn=2Ecom> 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 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 I know they are
correct because they are Lucas and the correct part number as listed in t=
he Lucas master catalog=2E </div>
<div>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 t=
he 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</div>
<div>Now=2E=2E=2Eam I correct in thinking the car should run better at spe=
ed (3200rpm)? 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>
</blockquote></div></body></html>
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