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Timing confusion
#1
Ok, I'm sure the answer is here somewhere but I can't find it. I'm not 100% sure I am timing my car right. I had my dizzy recurved to be all in by 2800rpm, My distributor guy says the only concern he has is that the vacuum advance pulls 17 degrees. I know the dizzy is set at the 10L slot which means I have 20 degrees of mechanical advance. So when I have vac adv. disconnected where do I set my initial at. My engine only seems to draw 15hg vacuum so I am not sure if the vac adv is working correctly when connected. Can anybody explain step by step how to time this thing. It is a 400ish hp 4v Cleveland with a .592, .611 lift roller cam. I think I am setting to much advance. I have been setting initial at 16 degrees, but my idle seems too high when its tuned to this setting. I think the 16 initial, plus 20 mech, then the vac adv. coming in is advancing too much. Please help!! I'm still learning this whole timing thing so pardon my ignorant questions. Thanks everybody!!
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#2
Omie01;282098 Wrote:Ok, I'm sure the answer is here somewhere but I can't find it. I'm not 100% sure I am timing my car right. I had my dizzy recurved to be all in by 2800rpm, My distributor guy says the only concern he has is that the vacuum advance pulls 17 degrees. I know the dizzy is set at the 10L slot which means I have 20 degrees of mechanical advance. So when I have vac adv. disconnected where do I set my initial at. My engine only seems to draw 15hg vacuum so I am not sure if the vac adv is working correctly when connected. Can anybody explain step by step how to time this thing. It is a 400ish hp 4v Cleveland with a .592, .611 lift roller cam. I think I am setting to much advance. I have been setting initial at 16 degrees, but my idle seems too high when its tuned to this setting. I think the 16 initial, plus 20 mech, then the vac adv. coming in is advancing too much. Please help!! I'm still learning this whole timing thing so pardon my ignorant questions. Thanks everybody!!

Omie01, I can't give you a complete answer, but I can offer what I experienced earlier this year and yes, there are several post on the subject if you search.
My engine is a 351C 4 V CC heads, pretty much stock except for a slightly higher lift cam. I had a reman. factory distributor that was way off where it should have been for my engine. A 10L slot is about right. I had to weld my plate up and resize it. I'm still playing with spring tension, but I'm very close to perfect timing now. If you do not have an adjustable single vacuum can, order one. What I found on mine was I needed only 14 deg. initial plus the 20 crank deg. I actually had to turn the screw adjuster on the v can OUT (anti-clockwise) 12-13 turns to give only 3 or 4 deg. of vacuum advance. Now, I do have a manual trans, so my settings may be different if you have an auto. Why I needed only minimal vacuum advance is lost on me, but I have a clean burn and the car has never run better. My local performance shop owner tells me that with a manual trans, I really don't need any vac. advance, just mechanical. I'm sure others will have different advice to offer.
Also, I had a Pertronix Ignitor III set-up installed, but when I had the dizzy put on a distributor machine, it was proven that the ignitor III had way too much play in it and was causing problems. I won't go into that here, but suffice it to say, I replaced it with an Ignitor II and coil. That alone solved much of my timing issues and allowed me to set my dizzy where it is now. I can still slow the rate of advance down a tad more to remove a very slight spark rattle under certain loads. I may even need to cut the mechanical advance back a degree or two, but for this, I'll use a small plastic sleeve I took off a Dura Spark dizzy.
So, I have 20 deg. crank, 14 deg. initial plus about 4 deg. vacuum.
Hope this helps a bit and good luck with it. Timing can be a very frustrating experience for sure.
Geoff.
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#3
Your engine will operate just fine with 50º to 55º of total advance under light load and cruising conditions. It will ping with that much advance on acceleration, which is why I use manifold vacuum for the vacuum advance. If you connect your vacuum advance to ported vacuum you will have to back off your initial timing considerably to prevent pinging on acceleration and part-throttle operations.

As for the idle speed being too high, back off the idle speed screw until you get the idle speed where you want it. Adjust the idle mixture screws for maximum vacuum. I would also use a vacuum gauge, after you get the initial timing set, to fine tune the best initial timing.

We used to be able to get vacuum advance cans that had a removable snout and you could insert washers to limit the total vacuum advance, but no more.

Here's a thread that may help you.
http://www.7173mustangs.com/thread-vacuum-advances



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#4
I can only tell you what my settings are. I have 10.5:1 compression with a 290 hyd cam but not as much lift and probably in the 400HP range. I have initial at 12* with a total adv of 35* @ 2500rpm with 10* ported vac. At cruise I see about 50 - 51* total adv. The car idles at about 800rpm.

Been driving the car now about 1300 miles so a couple a weeks ago I thought I would try to tweak it a little so I tried 14* of initial advance and the car did not like it at all. Also tried to set different A/F ratios but it didn't help either. I did not try to lower the initial adv but I may try to do that to see what happens. With my current settings the car idles nice and there is no hesitation when cold or hot and there seems to be plenty of power on tap. Hard acceleration is good with no misses.

-john
(jbojo)
351C 4V cc heads, 10.5 : 1 CR, 290 Herbert cam, Flat top forged pistons, forged connecting rods, Atomic efi,
C6 with Gear Vendor overdrive, 3.89 Tru Trac, Hooker Super Comp with 2 1/2" Pypes Exhaust.        

Some Mod pictures can be seen at:

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#5
Omie,

Does the car seem to run OK at 16*BTDC, aside from the idle being too high? The easy way to tell, is to drop the idle back down to where it's supposed to be 'idling,' and check things further.

Setting timing, tuning the carb, and squeezing the most power out of an engine is more a case of 'finding the sweet spot' with all the components. As the timing increases and gets closer to its happy place, the idle tends to go up... so drop it back down and check things again before advancing the timing any higher.

Making small adjustments is the key, as there is a break-over point where you won't have any more gain. Zeroing in on the sweet spot is the goal - you won't find it by taking big swings at it and hoping for the best.

When I initially fired my car up, everything was set "out of the box," literally, since all my engine components were brand-new. I initially set the timing at 6*BTDC as I had learned a long time ago. When I set the idle down to where I thought it needed to be (650rpm), it ran "OK." Not great... just "OK." I read some more about recurving distributors, the timing characteristics of Cleveland engines, vacuum advance, and the 'cross-over' areas of all the different performance components I'd chosen for my engine (if you have this, do this... if you have that, do that... etc.). Then I started making educated adjustments and it's paid off in spades - I truly believe my engine is running pretty close to the estimated 400hp CompCams said to expect with the combination I'm running.

Hang in there. There are no ignorant questions. Wink

Eric

[Image: mach1sig2.gif]
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#6
This is a good, if a bit long, paper on vacuum, timing, a vacuum secondary carb operation.
http://www.lbfun.com/warehouse/tech_info...lained.pdf
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#7
Don C;282105 Wrote:If you connect your vacuum advance to ported vacuum you will have to back off your initial timing considerably to prevent pinging on acceleration and part-throttle operations.

Don, my understanding is that manifold and ported vacuum match each other just off of idle regardless of the load on the engine.

'Mike'
73 Convertible - 351C/4V CC heads/4bolt/forged flat tops/comp 270/rhodes/mallory unilite/tri-power/hookers/glasspacks/c6/3.50 limited slip/Gear Vendors/Global West sub frames, strut rods and shelby style traction bars/ Rear sway bar/tilt steering (not original)

Pics of modifications included in:
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#8
I do have the pertronix 2 in my dizzy. My biggest issue is when cruising holding speed, and then accelerate a little bit, it sounds like I am getting some ignition pinging. My other point of confusion is that I can't really back my curb idle off because its almost all the way backed off. I did set A/F screws with a vac guage, and vac seems consistant at it's highest point. That's why I feel my vac canister might be pulling too much timing during cruising operation. I think mine is adjustable with an 1/8" allen key. I do have auto trans. I will try a few of these things and report back.
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#9
Hook the vacuum advance up to ported vacuum. Did the idle come down any? Is it able to be adjusted now at the carb? If no, you might back the initial timing off a bit and try again. You will get it figured out.

351w - Ford racing GT40X 178 cc aluminum heads - Ford racing(crane) 1.7 roller rockers - Comp Cams 280H magnum cam .544" / .544" lift - ARP fasteners - hedman longtubes - magnaflow exhaust with X pipe -  MSD digital 6al box - MSD coil - optima red top battery - tuff stuff 140 amp alternator - ported weiand stealth intake  - edelbrock 1406 600 carb  - march pullies and brackets - Be cool fan controller - derale electric fan - FMX trans - motive 4.11 gears - traction lok - competition engineering subframe connectors - lakewood traction bars.                                            










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#10
will e;282141 Wrote:
Don C;282105 Wrote:If you connect your vacuum advance to ported vacuum you will have to back off your initial timing considerably to prevent pinging on acceleration and part-throttle operations.

Don, my understanding is that manifold and ported vacuum match each other just off of idle regardless of the load on the engine.

As the throttle opens the manifold vacuum decreases and the ported vacuum begins increasing. At some point they will be the same. As the throttle continues opening the ported vacuum increases, advancing the timing, if that is the source for the vacuum advance, increasing the potential for pinging. Conversely, the manifold vacuum decreases as the throttle opens, retarding the timing, decreasing the potential for pinging.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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