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Igntion timing
#1
Are there any recommendations about Ignition timing with a cam upgrade ? Spec. is 6 BTDC, I have mine set a 4 BTDC. Haven't done any changes yet.

Took a 20 minute ride yesterday

[Image: 1_30_09_13_10_12_32.png]
Alan L
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#2
depends on your motor and how quickly she starts to detonate on you.

you can vacuum tune the initial timing, then you usually come down 2 degrees from that and you have to test it with your starter engine hot to see if the starter can take the advanced timing as well.

engines can be set almost anywhere, i've run from 4 degs inital all the way to 22 degs inital it can be all over the map.

i currently have my engine set to 10 degs initial, i had to limit the mechanical advance to keep it from going past 38 degs

you need to watch your total mechanical advance usually you keep it in the 32 - 36 range, this doesn't factor in the vacuum advance.

usually 8-12 is a good starting point, then people usually bump it up until the engine starts to ping, or the starter will not turn the engine from a hot start or the engine starts dieseling when you try to turn the car off.

with lower timing 0-6 the engine can over heat during idling, so you want a keep an eye on the temp gauge and listen to what the engine wants, no book has the correct answer. I found reducing timing while reducing wheel spinning power did make the idle and low speed driving more enjoyable.

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#3
Great info, Thanksthumb

Alan L

[Image: 1_30_09_13_10_12_32.png]
Alan L
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#4
My stock M-code is set to 10 while recommended is 6. I can advance the distributor until the vacuum diaphragm hits the radiator hose, maybe 25. You get a little more snap out of the engine but I hear if the timing is too far advanced you can burn the valves. These specs were also designed for 1970's gas, not whatever they sell today.

mike



Are there any recommendations about Ignition timing with a cam upgrade ? Spec. is 6 BTDC, I have mine set a 4 BTDC. Haven't done any changes yet.

Took a 20 minute ride yesterday

[Image: 1_11_11_13_11_50_27.png]
  Reply
#5
I am running 10* as well with no problems.

Jeff T.

Low buck, touring style, '73 Convertible "rolling restoration", 351c, 2v heads with a shave and a haircut, Performer intake, Holley 650(ish), roller rockers, screw in studs, guideplates, stainless valves, Duraspark / Motorsports MSD, T-5 conversion. 1-1/8" front, 3/4" rear swaybars KYB shocks and some home brewed subframe connectors. Future plans; JGC steering box, Cobra brakes and... paint, interior, etc.

When I die I want to die like grandpa, peacefully in my sleep... not screaming, like his passenger.

[Image: 1_12_09_14_10_15_11.png]
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#6
I am running 10* as well with no problems.


So why can't we set the timing at 6 like it is supposed to be?
The gas?? My understanding is there is no advantage to advancing the timing.
Not on a street car. I am going to save some money and get some of the 100 octane stuff they sell in Saratoga out of the pump. $$ My mechanic tells me then I can see how the car was designed to run.

mike

[Image: 1_11_11_13_11_50_27.png]
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#7
Advancing the timing (to a point) helps performance and mileage.

Jeff T.

Low buck, touring style, '73 Convertible "rolling restoration", 351c, 2v heads with a shave and a haircut, Performer intake, Holley 650(ish), roller rockers, screw in studs, guideplates, stainless valves, Duraspark / Motorsports MSD, T-5 conversion. 1-1/8" front, 3/4" rear swaybars KYB shocks and some home brewed subframe connectors. Future plans; JGC steering box, Cobra brakes and... paint, interior, etc.

When I die I want to die like grandpa, peacefully in my sleep... not screaming, like his passenger.

[Image: 1_12_09_14_10_15_11.png]
  Reply
#8
it depends on so many factors today.

you can set the initial timing to anything you want, but there is so much variation on engines and equipment that what works on one engine will not work on another lower initial timing generally means more engine heat, in the 70s the emissions laws required lowering idle emissions.

to do this ford lowering initial timing and switched from full manifold vacuum for the vacuum advance to ported vacuum.

ported vacuum is 0 at idle. before at idle you would have 15-25" HG of vacuum at idle which would have the vacuum advance all the way up.

having just the mechanical advance working at idle and basically turned off and setting the initial timing very low, made the engine exhaust temperature hotter.

the hotter exhaust meant the usually emissions out of the tail pipe were burned off by the hotter exhaust reducing emissions.

this also made the engines run hotter and more latharic off the line due to reduced timing at idle. it also killed fuel economy, and made the engine run less efficient.

next came the switch from leaded 110 octane down to 103 regular, due to engine ping/detonation the distributor curve had to be changed. and to gain back some performance the mechanical advance was allowed more timing.

since the older cars started with 10-15 degs of initial timing you needed a shorter throw on the mechanical advance to reach max allowed timing usually in the 32-38 range depending on motor. these older cars just needed the mechanical advance to move 20 degs (L10).

ours cars started with 4-8 degrees initial depending on motor. so they required mechanical advances that allowed 28 degrees of timing movement (L14-L18)

by common sense the emissions stuff was garbage and that is why everyone took it off, you put the car back the way it was originally designed and not patched up to meet some stupid government imposed standard.

this gets complex, people would take the emissions stuff off go back to full manifold vac setup, and then have no problems until they floored it to red line and BOOM the engine would grenade itself because they never knew to fix the mechanical advance as well.

by 75,, you had cars with 0-2 degrees of initial timing, to have super hot exhausts so the catalytic converters could work correctly, and so performance went into the toilet even more and you had mechanical advances that allowed for a lot more 40(L20) degrees of movement.

this didn't change until the 1980s when electronic ignition timing started to take over.

all the 70s emissions stuff required patches to overcoming issues. EGR valves and DVCV valves all kinds of stuff to compensate for
different states the engine might be in that would cause overheating or emissions levels to rise for one reason or another that had to be quelled.


so getting back to lower ignition timing, if your engine tolerates it and doesn't over heat fine run it. if you want to see more performance you increase the timing but you have to watch out if the engine starts to ping/detonate.

a lot of cam manufactures tell you what they recommend for initial timing as well.

its going to depend on what your motor wants really, and you have to make changes to compensate.

to fine tune gets even more complex I'm constantly trying things to see if something improves. I spent all of last year trying to dial out mid throttle detonation/ ping, its maddening detonation or ping is a lean condition, so either you drown the engine in gasoline or you start limiting the mechanical and vacuum advance to compensate. it never ends Wink

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