Timing confusion

[Omie01]

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!!

 

[Stanglover]

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.

 

[Don C]

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

 

[jbojo]

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.

 

[Mister 4x4]

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.

 

[c9zx]

This is a good, if a bit long, paper on vacuum, timing, a vacuum secondary carb operation.

http://www.lbfun.com/warehouse/tech_info/timing%20&%20vacuum%20advance/vacuum_explained.pdf

 

[will e]

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.

 

[Omie01]

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.

 

[Mikes73]

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.

 

[Don C]

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.

 

[jbojo]

Omie,

When you set initial timing is the vac hose to distributor removed and plugged?

Crane Cams sells an adjustable vacuum kit 99607-1 for the Ford distributor. It is meant for 73 and up emission controlled cars but will work on earlier models too. You could call Crane Cams Tech to verify whether it will work for you. Total vac for the motor should be around 45 to 55* so you have 20 +16 + 17 = 53* (I prefer 50* max) and if you don't have ping at cruise or under load the timing should be ok. If you do have pinging you could then back off the vac adv a couple of degrees with the kit. Are you using Ported or manifold vacuum? With the vac hose connected to the distributor if you are using ported vac then you should see 16* at idle, If manifold vac then there would be some of that adv too + the 16* initial.

If the above is good then back off idle as Eric mentions to lower the rpm. Keep in mind that aggressive cams usually idle higher and 800 to 900 rpm may be normal for your set up. It's just takes trying different settings until you find the sweet spot for your motor.

Just curious,

What is the idle when the vac hose is disconnected?

What does your car idle at when everything is connected?

BTW just another thought, with your centrifugal advance spring setup I believe advance starts at 800rpm and is all in at 2800 rpm so if your idle is above 800 rpm you are already applying adv to the motor in addition to the 16* initial + any vac adv. I think I would try to get my obtain my idle target this way:

** With vac hose removed and plugged time motor to 16* and lowest idle as possible.

** IF idle is above 800rpm back off timing to 14* and see if idle drops and try to adjust idle again.

** If idle is below 800rpm then centrifugal adv is not be applied anymore, if still above 800 reduce timing to 12* and adjust idle again to an acceptable level.

Note: I wrote this last night and I see you mention pinging. I would back off initial timing to 14* and see if the pinging goes away first, if not then try 12*

 

[will e]

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.

Don, I believe you are confusing ported with Ventri vacuum. I also used to believe that ported vacuum increases with engine speed. It does not. Ventri vacuum does, this is the vacuum that is used to open vacuum secondaries.

http://www.lbfun.com/warehouse/tech_info/timing%20&%20vacuum%20advance/vacuum_explained.pdf

I have never checked this myself. Next time I get the Mustang I will hook my vacuum gauge over to ported (I have one on manifold) and confirm what the internet tells me.

 

[73pony]

Good article. Explained a lot there for me.

 

[Stanglover]

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.

I wasn't going to go into the Pertronix issue, but briefly, they replaced my ignitor III with an ignitor II and a Flamethrower II coil. I had many discussions with their rep and was advised to use only the matching coil, nothing else. It really does make that much difference to the way the engine will run.

In past threads on timing issues, the guys posting here gave me huge help understanding how a distributor works. In my case, it came down to trial and error and many test drives, trying different springs and tension as well as adjusting the vac can. Part of my issue was carburation as I could not get a consistent idle. Basically, my carb needed more air at idle ( drilled a 3/32" hole in each primary plate) to get off the transfer slots which were open too much, causing the idle mixture screws to be ineffective.

It sounds like you have the same issue as me with slight pinging under certain loads. In my case, I think I need to add more tension to the heavier spring to slow the advance down. I could go back to the dizzy machine, but that gets expensive quickly. If I got it right from all the advice given in the past, I should achieve proper timing.

As for which port to connect the vac. can, Holley's instruction sheet for my S/A 670 suggest using the timed port as did my tuning shop owner, but I'm open to try both and see which works better. What Don says makes sense and he has given very good advice in the past. While writhing this, others have responded with conflicting views, Now I'm getting confused again!!

 

[Don C]

Don, I believe you are confusing ported with Ventri vacuum. I also used to believe that ported vacuum increases with engine speed. It does not. Ventri vacuum does, this is the vacuum that is used to open vacuum secondaries.

http://www.lbfun.com/warehouse/tech_info/timing%20&%20vacuum%20advance/vacuum_explained.pdf

I have never checked this myself. Next time I get the Mustang I will hook my vacuum gauge over to ported (I have one on manifold) and confirm what the internet tells me.

The ported vacuum source is just above the throttle blades. The venturi vacuum source is within the the actual narrowed portion of the carburetor throat (venturi). The manifold vacuum source is below the throttle blades.

These diagrams (not mine) explain it well:



At wide open throttle the vacuum reading will be the same. At less than wide open manifold will be higher than ported.

 

[Omie01]

I have the Flamethrower coil recommended for ignitor 2 and it works GREAT!! I am disconnecting the vac advance when tuning everything, I have just never adjusted vac advance, and after my dist. guy told me he might be concerned about the 17 degree curve on mine I couldn't help but wonder if that was an issue. My idle is around 900rpm in park at operating temp, and I can't turn my curb idle down any more.

 

[Stanglover]

I have the Flamethrower coil recommended for ignitor 2 and it works GREAT!! I am disconnecting the vac advance when tuning everything, I have just never adjusted vac advance, and after my dist. guy told me he might be concerned about the 17 degree curve on mine I couldn't help but wonder if that was an issue. My idle is around 900rpm in park at operating temp, and I can't turn my curb idle down any more.

Omie, glad to learn you have the correct coil for the ignitor II. It was explained to me that each model Pertronix sell must have the matching coil.

I'm no expert on carbs at all, but could you be experiencing the same issue that I was by having the transfer slots open too much. You didn't say what carb you are using, but I'm pretty sure no matter what carb it is, the primary blades should not be open so much that the slot is not square, i.e. width .020" X height .020". If the height is more than whatever the width is, the blades are open too far. That's the way it was explained to me. At that point it will be getting too much fuel. The fix on mine was to closed the blades until the slot was square and drill holes in the blades for more air. It worked great. I was able to get idle mixture set right as well as my curb idle. Not saying this is your fix, but!!

As for timing, yeah, I'm still learning and playing with it, but I got to the point whereby the engine was running stronger than it ever has since I've owned the car. Also what gas you use has a marked effect on pinging. I use only Shell 91 with NO ethanol and no additives. It's still a work in progress, but probably won't get anymore done till spring as it's time to put it away for winter....... damn it!!

 

[jbojo]

Don, I believe you are confusing ported with Ventri vacuum. I also used to believe that ported vacuum increases with engine speed. It does not. Ventri vacuum does, this is the vacuum that is used to open vacuum secondaries.

http://www.lbfun.com/warehouse/tech_info/timing%20&%20vacuum%20advance/vacuum_explained.pdf

I have never checked this myself. Next time I get the Mustang I will hook my vacuum gauge over to ported (I have one on manifold) and confirm what the internet tells me.

The ported vacuum source is just above the throttle blades. The venturi vacuum source is within the the actual narrowed portion of the carburetor throat (venturi). The manifold vacuum source is below the throttle blades.

These diagrams (not mine) explain it well:

At wide open throttle the vacuum reading will be the same. At less than wide open manifold will be higher than ported.

I am not sure that I agree and I am not arguing who is right or wrong because there are many different thoughts on this. This is how I think it works.

Ported and manifold vacuum will be nearly identical when the throttle blades begin to open because both ports are exposed to manifold vacuum throughout the throttle blade travel. There may be a slight difference but it should be negligible. Only difference is with ported is no vacuum at idle where manifold will have max vacuum at idle.

Venturi vac is dependent on airflow velocity across the narrowest part of the carb throat. Faster the airflow the lower the vacuum and that is how fuel is drawn out of the carb and into the motor, the more airflow the more fuel that is drawn out as rpm increases. It has nothing to do with timing.

Now my thoughts on Omieo's problem. He has a cam that probably has some lope to it. Because of this lope vacuum is most likely varying at idle which would require the motor to idle at higher speeds to be stable. If he is using manifold vacuum the distributor is constantly varying timing based on vacuum at the time and centrifugal advance is probably adding some adv if idle is above 800 rpm. For every 800 rpms centrifugal advances about 10 degrees so maybe he is getting 1-2 degrees there.

In my opinion I think he should use ported vac. This would take vac adv out of the equation at idle and then it is a matter of how much centrifugal adv is being applied. If the idle is below 800 rpm then it should be safe to assume no centrifugal adv is being applied and timing should be just the initial timing, 16* in his case with the vacuum hose attached to the distributor.

Lastly Omieo mentioned pinging at cruise and light load. I think that the initial timing may be a tad high. I believe that 14 degrees should be where the starting point should be, or possibly lower. The ping issue needs to be resolved first. There could be jetting issues on top of all of this too. The A/F ratio can be a factor, at WOT you should have 12.8:1, cruise about 14.5:1 and at idle around 14:1 for a performance set up.

Would like to know your opinions here. I am basing my opinions on what I had to do to get my motor running properly.

 

[jbojo]

I have the Flamethrower coil recommended for ignitor 2 and it works GREAT!! I am disconnecting the vac advance when tuning everything, I have just never adjusted vac advance, and after my dist. guy told me he might be concerned about the 17 degree curve on mine I couldn't help but wonder if that was an issue. My idle is around 900rpm in park at operating temp, and I can't turn my curb idle down any more.

Which vacuum source are you using, manifold or ported?