DCOE 40 Folks, What size Pump-jets are you running?

[2002Scoob]

As for the low stumble... I’m not convinced the curve is it... but maybe the vacuum advance? But it did the same before I had it hooked up, too. It’s really a sub 1200 rpm event.


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[2002Scoob]

Alllrightty. I'm back. And I think the crazy spell is over? 

 

On the way home I switched back to the tweaked first map with the 36 degrees total advance. 

 

This one

 

Now... the only real difference affecting where I would notice the stumble between this and what I had before is 1 less degree at 700 (15 vs. 16), and one less at 1000 (20vs21). It honestly feels smoother at idle than when it was 14@700 and 19@1000. And I'll be damned if she doesn't pull hard and feel good all the way to redline. 

 

On top of that... I tried a few different things while trying to keep an eye on my wideband, as well as the road.  

 

In 2nd gear when stomping the throttle at appx 13-1500rpm (guessing by ear, as I don't have a tachometer), the AFR drops to 10, climbs to around 11.5, and the motor pulls OK, but doesn't really pull 'hard' till the AFR's climb back up to 12's on up to the mid-low 13's, and the RPM's climb. 3rd and 4th gear throttle stomping at unsure RPM's sees similar-ish AFR results... I think. By then I'm going speeds I don't want to be staring at a gauge in my glovebox.

 

So then I went to a parking lot, and tried some rolling from idle, in 1st gear throttle stomps.

 

AFR's again dropped into the 10's-11's, and it it just lit up the tire. 

 

SO What does this tell me? or, what new questions does this make me think of?

 

1- If it's going that rich... Can I assume that my accelerator pump circuit is just fine, perhaps too fine (rich?)

 

2-The 2-3 parking lot attempts at rapid acceleration from failed to recreate my phantom stumble. Is it plausible that reducing the advance 1 degree between 700-1000rpm could have been what fixed the stumble? 

 

I'm honestly left with more questions than answers...

 

 

[2002Scoob]

1 hour ago, harold said:

2002Scoob:  you have a bunch more advance at low RPM than I do, plus what is added for manifold vacuum.  If you are pulling manifold vac from after the carbs, it may be adding advance when you don't want it.  Typical vacuum source (which DCOEs don't have) is picked off right at the throttle plate, so that it drops to zero very soon after throttle opens.

 

I'm pulling vacuum from a custom T-fitting I made that splices into the brake-booster line that attaches to the back of the intake manifold. I figured it to be the best location because of the larger air-volume and damping characteristics of that beefy silicone hose. It's also has a decent length of it's own thinner silicone vacuum hose to damp the signal. It's an Ireland Engineering manifold, so all the intake runners are cross-drilled to each other as well. 

 

 

2 hours ago, Mark92131 said:

I currently have the MAP curve disabled, mainly because the Ti distributors were mechanical only and the 123 Ignition Distributor doesn't give me enough control to accurately determine when I want to add and possibly subtract advance to my curve (freeway cruising, WOT, etc.).  For example, on your MAP curve, you are adding 7 degrees of advance to your Advance map between 30 and 87 kPascal for a possible total of 41-42 degrees.  After trying to document my MAP curve readings during real-world driving conditions, I am finding that I may be between 30 and 87 kPa in multiple conditions, cruising in 4th or 5th gear, accelerating between shifts, down shifting, etc., and possibly adding advance when I don't want it.  Where are you pulling vacuum for your 123 distributor and are you able to get consistent conditions for adding that 7.0 degrees of advance when your engine wants/needs it.

 

To be honest..... I'm still a little lost in the exact how and whys of vacuum advance. I've tried a few times to wrap my head around it, and ended up just pulling some example curves off others, so I can't really say if it's helping or hurting anything. I believe mine was pulled from an example map from Ed/Zinz. 

Edited November 5, 2018 by 2002Scoob

[Son of Marty]

Scoob what Harold is saying is taking the vacuum signal from behind the throttle plates will give you max advance at idle and not when it's needed while accelerating. 

[2002Scoob]

2 minutes ago, Son of Marty said:

Scoob what Harold is saying is taking the vacuum signal from behind the throttle plates will give you max advance at idle and not when it's needed while accelerating. 

 

Ah ok.. I think I get what you're saying. But if the map does start until 1500 RPM's, it shouldn't affect idle advance. Yes?

 

But, could it be plausible that on mid-to-lighter throttle pull-aways that reach 1500 RPM, there could still be enough vacuum that it's advancing the timing enough to cause the stumble?

[Son of Marty]

Yeah ignoring the map below 1500 rpm is helpful, but the signal is still the reverse of what your looking for but could be made useful at least in theory if you were to switch to a vacuum retard set up but after 1500 rpm's I don't really know if it's worth it. If I had a programmable distributor I think I would program in the 2002ti curve to start from see what that gets you if it not good switch back to what you have now.   

[2002Scoob]

Yeah ignoring the map below 1500 rpm is helpful, but the signal is still the reverse of what your looking for but could be made useful at least in theory if you were to switch to a vacuum retard set up but after 1500 rpm's I don't really know if it's worth it. If I had a programmable distributor I think I would program in the 2002ti curve to start from see what that gets you if it not good switch back to what you have now.   

Hmmm.... I’m a good bit confused. I found this, which kinda sums up my basic understanding and why I set it up the way it is-

‘at part throttle the engine will create a certain amount of vacuum in the intake manifold. This is because the throttle is mostly closed and the engine is pulling against this restriction. Because the throttle is mostly closed, very little air is moving into the cylinders. So at light cruise, such as running down the highway, the engine is making much less power than it would at this same rpm at WOT.

With less air and fuel in each cylinder, the air-fuel mixture is not as densely packed compared to WOT. This less-dense mixture requires more ignition timing to complete the combustion because it takes longer to complete the combustion process. So we need a way to increase the amount of timing based on the load on the engine. This is how vacuum advance works. At part throttle, high manifold vacuum moves the diaphragm in the vacuum advance canister on the distributor to add more timing. But at WOT, the vacuum drops to near zero and vacuum advance is removed and the total timing then is established by the initial plus the mechanical advance.’

By the above description... my setup should be functioning as described above, no?

I’m pulling vacuum from the manifold fitting attached to the #4 runner, which is behind the throttle plates as described above, and am using that to add advance in part-throttle scenarios.




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[2002Scoob]

Honestly.... if my thinking is correct... this could very well be the issue?

It happens only occasionally when pulling away from low-down RPM’s, and doesn’t happen when I blip the throttle and slip the clutch a bit, which would bring manifold vacuum back down to near zero.

It also doesn’t seem to happen when mashing the throttle. As I experienced this evening.

So could too much advance at lower RPM’s due to light throttle application cause it?




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[Chris_B]

It seems like the only gotcha with your setup is that it will pull maximum vacuum at idle, when you don't want maximum vacuum advance. I have a 123 dizzy but have not installed it yet. If you can map the vacuum advance to RPMs, you would be able avoid this excessive idle advance scenario.

[Chris_B]

I am not clear yet about what you are seeing on your AFM when this stumble occurs. What you are describing is the classic DCOE just off idle miss/stumble. In my experience this is always due to a lean hole that occurs in the transition between idle the beginning of the mid-RPM range (e.g., 1K-2.5K RPMs), with insufficient throttle to cause the main circuit to come on line. It certainly is possible for an excessively rich condition to make your motor feel boggy, but it typically is excessively lean conditions that cause the "stumble" and roughness.

[Chris_B]

P.S.: the motors I have see with a factory vacuum advance do not take the vacuum directly from the manifold, but rather a special port in the carb just above the throttle plate(s). This gives you no vacuum at idle, part varying degrees of vacuum depending on the position of the throttle plates. Of course, the DCOE has no provision for this.

[2002Scoob]

I am not clear yet about what you are seeing on your AFM when this stumble occurs. What you are describing is the classic DCOE just off idle miss/stumble. In my experience this is always due to a lean hole that occurs in the transition between idle the beginning of the mid-RPM range (e.g., 1K-2.5K RPMs), with insufficient throttle to cause the main circuit to come on line. It certainly is possible for an excessively rich condition to make your motor feel boggy, but it typically is excessively lean conditions that cause the "stumble" and roughness.

Yah... it literally happened maybe a half dozen or more times since the rebuild, and I haven’t been able to re-create it in the ways that I thought it was happening.

I think I’m going to start by increasing the RPM’s at which vac advance comes on to 1700rpm, and I need to spend some time to understand just what kind of vacuum pressures I’m working with and where.

Keep the thoughts coming In the meantime and for@Harold too. We can co-own this thread, if not to add to the confusion/fun, haha.


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[Mark92131]

3 hours ago, 2002Scoob said:

You have me curious, as your advance#'s are definitely on what I'd deem the low end of the spectrum for a DCOE car, no? Are you also on a similar motor setup in terms of compression, cam, displacement, and the like?

 

I have a single 45 DCOE 152 on a Lynx Manifold and IE 284 Cam, E12 Head, 90mm 9.5/1 Piano Pistons on Pauter connecting rods.  Not a dual DCOE setup, but side draft rather than down draft.  So when I started jetting and tuning my motor for this setup, I noticed that many of the advance maps for the 123 distributor would be at 25 degrees BTDC at 1400 RPM matching the Blue Book for 2002 and 2002A models.  I started with an advance map matching these values for the 2002, but for my car, seemed to introduce too much advance too early causing the motor to ping on hard acceleration.  So I thought using the 2002 Ti advance map might be more appropriate, but which one, there are 3 (003, 026, and 033).  I ended up with a modified advance map, because all 3 had very different values.

 

You may benefit from considering the "026" distributor values for your car, it meets your 25 BTDC at 1400 RPM requirement.

 

2002 Ti "026" Distributor

1000 - 18 to 22

1500 - 23 to 27

2000 - 28 to 32

2500 - 33 to 37

2700 - 35 to 39

 

The low values on the "026" seem to match your curve.

 

My map is more in line with the "003" on the low end, the "033" in the middle, and the "026" on the top end.

 

2002 Ti "003" Distributor

1000 - 3 to 8

1500 - 14 to 19

2000 - 20 to 24

2500 - 25 to 29

2700 - 29

 

2002 Ti "033" Distributor

1000 - 10 to 13

1500 - 17 to 21

2000 - 22 to 26

2500 - 26 to 30

2700 - 30

 

I may do some more experimenting with introducing more advance earlier, but 25 BTDC at 2200 RPM seems to be my sweet spot for this motor.  You may want to take a passenger with an iPad and the 123 Ignition App on your test runs and have them record your inHg readings and advance readings to see if that extra 7 degrees of advance is appearing where you want it.

 

Have fun,

 

 

Mark92131

 

 

 

 

 

[Simeon]

1 hour ago, 2002Scoob said:

 

 

Yah... it literally happened maybe a half dozen or more times since the rebuild, and I haven’t been able to re-create it in the ways that I thought it was happening.

I think I’m going to start by increasing the RPM’s at which vac advance comes on to 1700rpm, and I need to spend some time to understand just what kind of vacuum pressures I’m working with and where.

Keep the thoughts coming In the meantime and for@Harold too. We can co-own this thread, if not to add to the confusion/fun, haha.


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 You may be seeing a few oddities associated with this functionality and where the vacuum signal actually is when you ‘switch on’ the MAP curve at a given RPM. 

 

If anything I would be lowering the ‘cut-in’ speed to start a few hundred RPM above your idle speed (unless you are idling at 1,500rpm!). This matches  what you would see with a metered vacuum off the base of the carb. It rises rapidly to ‘maximum’ after coming off idle and exposing the vacuum port to the throttle plate. It then starts to fall off again, probably in a similar manner to how the true MAP that you are measuring would be falling. 

 

Remember, at true part throttle your engine will be turning above 1,500 / 1,700 etc and will have full vacuum despite the throttle being potentially shut all the way This is different to accelerating from a ‘stand’ (or more accurately low revs) where you have no real link between throttle, engine speed and vacuum. You can steadily depress the throttle, the vacuum may have dropped to zero by the time the engine gets above 1,700rpm missing when it is most useful. 

 

Not that I have really thought this through in enough detail but I suspect that we are missing a trick trying to simulate a traditional vacuum advance curve, particularly when using a straight manifold MAP signal rather than a metered carb vacuum. Instead, I think we need to be trying to get the ‘mechanical’ and MAP curve to be working together to represent the load on the engine  

 

 

[Chris_B]

Are you guys saying that Mr. Scoob's part throttle just off idle roughness is due to ignition timing?