Cleveland Timing/Advance Curve

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Offline Katefactor

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Cleveland Timing/Advance Curve
« on: December 12, 2022, 10:59:13 am »
HI, have just joined up recently mainly due to the wealth of info and advice offered here.  While I don't own a Mustang I do have a Cleveland in an XWGT and this site comes up a lot when searching for tuning issues etc with the 351 so hope its OK to ask a couple of questions   :smile01:   

Bit of background on the engine which is original to the car and rebuilt by the previous owner approx 3000 miles ago.

Pretty much 1970 factory 4V rebuilt with a PH 2 grind cam ( all I know on the cam) 
20 Thou over, std intake manifold with factory 780 Vac Sec Holley, single point Autolite Dist. and std exhaust manifolds.   
Intake manifold Vacuum is 9" at idle and fairly steady

I have a concern over the total timing reading (not pinging that I can hear)  so was hoping for some advice.   

Initial timing I set @ 8 Degrees at 750 rpm idle with ported vacuum advance still connected but when you increase that to 3000 the timing maxes out at 40/42 degrees,  with the Ported Vac plugged timing maxes out at 20 degrees total.

I took some readings through the rev range too.

Ported Vac advance connected

750 Rpm -  8 Deg
1500  - 13 Deg
2000. - 23 Deg
2500 -  30 Deg
3000 -  40 deg

Vacuum advance plugged off

750 rpm  8 Deg
1500   -  10 Deg
2000  -  12 Deg
2500  -  17 Deg
3000  -  20 Deg

Have set the dwell @ 29 but that drops to 23 when you give it a quick rev to say 2000 RPM  but doesn't seem as bad when you slowly increase revs to say 1500 so thinking the Dizzy may be a bit worn or is this normal. Also with the points gap set to specs of 19 thou ( from memory) the dwell is in the low 20's so had to close the gap to 15 thou to get the dwell anywhere near 29 degrees.       

I guess the timing advance will change when on the road under load but just a bit concerned it might be doing damage over time if it's pinging and I can't hear it so any advice would be greatly appreciated. 

Cheers Phil.


Offline jiffy

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Re: Cleveland Timing/Advance Curve
« Reply #1 on: December 12, 2022, 12:38:07 pm »
I would have said that your timing should be set with vac advance disconnected and the hose plugged.

I would set it around 8 at idle and max 34-36 advance at around 3K. This effectively tells you what your max timing should be at WOT, and at cruise your timing should advance due to vacuum, and drop off when throttle is applied.

Vacuum should be set up to ported vacuum from the primary metering block of the carb, not manifold vacuum (this means you should have no vac adv at idle). Depending on your build, you might be able to advance timing at idle for snappier response, but be cautious because this will increase your max timing and cause pinging at WOT which you probably wont hear over the go-fast of the engine.
« Last Edit: December 12, 2022, 12:40:21 pm by jiffy »
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Offline Katefactor

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Re: Cleveland Timing/Advance Curve
« Reply #2 on: December 12, 2022, 03:25:21 pm »
Thanks Jiffy, sorry my initial timing info may have been a bit misleading.  I did also set it @ 8 Degrees with the ported Vacuum hose disconnected and plugged, was just showing a comparison to leaving that Vacuum line connected.    Yes no difference at idle because there is no idle vacuum from the Carb fitting.   8 degrees initial seemed to be the spot as set to 6 degrees factory spec it was a bit sluggish and over 8 it was running on a bit.   

So can I take it that I should be getting more like 34-36 @ 3000 with the vacuum disconnected as I only have 20 atm   
« Last Edit: December 12, 2022, 03:31:12 pm by Katefactor »

Offline GLENN 70

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Re: Cleveland Timing/Advance Curve
« Reply #3 on: December 12, 2022, 08:01:25 pm »
10 deg and a total at 3,000 rpm should be nice at 34 deg . Vac advance blocked . Without a distributor recurve that may not happen .  In my 351windsor with alloy heads I run 20 and 32 total ,but alloy heads .

Offline Katefactor

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Re: Cleveland Timing/Advance Curve
« Reply #4 on: December 13, 2022, 07:43:30 am »
Sounds like that may be the way to go as I am getting nowhere near that, cheers