[Jcrotts]

I have been a lurker here for a long time, and jump from project to project, but I have some questions about an idea I have been kicking around.

I have a 1983 Subaru Brat with an EA81. I am very happy with the Weber carb I have on it but would like more control of the ignition. I'm currently fighting a choice between manifold and ported vacuum, and wanting something in between. It has good acceleration on ported vacuum but the coolant overflow is literally boiling after a trip through town (stop and go traffic) if I don't use manifold vacuum for less heat soak at idle. I want to use an EA82 distributor to get the control benefit of electionic ignition.

I would appreciate someone else's experience with this swap before I jump in head first (which I have a bad habit of ).

[PSIG]

Welcome. I'm speaking here generally, to all those in your position, not specifically to you and your setup. First things first. Ported and manifold vac can run equally well (with certain advantages to each), but the distributor curve must be configured for each. The curve must suit the mode. So, before jumping forward, be aware you can get it to work "right" as it is. I mention this not that you should, but only that it should run well when set-up properly, so you need to carry that knowledge forward with whatever you're using.

A different way to say it is that you already have something that should work "OK", and converting to programmable control is not the first solution, but rather conceptual understanding of why it isn't working properly now. Control concepts and effects. Converting to programmable would allow you to experiment and learn, and easier, but you need certain concepts first, of why your current setup is doing what it's doing. Or, maybe you do, but just want to leave the old control stuff behind.

Now having said that, yes it is a jump-forward solution, as you can do much more manipulation with programmable control. You want to understand what you are trying to accomplish with ignition, and that you could do that basic stuff with your stock setup (avoid overheating). Jumping to ECM control will not solve what was wrong with the old setup. It's just that you can do yet more, quicker and easier with programmable. All good.

OK so with all that, yes, you can convert and begin applying both the basic solutions and then some advanced ones. A good but quick and light reading of the Wiki should help to familiarize you with general principles for setup. ECM control is so flexible, your first task is to avoid all the info that does not apply to you. Don't try to understand it all on the first pass, and avoid rabbit holes. A smaller 2x2 unit will do fine for this, such as the NO2C or C2C. There are others. These will allow either single-channel control of your distributor coil (suggested first step), or conversion to distributorless coil packs or CNP, etc.

While controlling both fuel and ignition in coordination is optimal, your first dive into ignition-only will provide a solid foundation (and capable ECM) for future adventures. Do your first light reading, then poke us for anything that you can't make sense-of.

[Jcrotts]

I want to convert to get the roughly 20 degrees of idle advance that I have on manifold vac along with the extra 12 degrees I would have driving with ported vac. Don't want to advance the static timing any more, I'm worried about knock. Not trying to mod it, it's a 40 year old siamese port engine with a blistering 70 horsepower. Just trying not to blow up an engine that's hard to find parts for, and make it able to reliably get out of its own way.

All I know is it doesn't run hot on manifold vacuum, but it drives like I'm trying to tow a house.

It just seems "easier" to get a distributor with more than 4 position lobes, set it up with the stock ignition curve, and adjust the timing where I need it until I'm happy with it.

I know my radiator is the problem, and a new radiator is out of the question. I have already mounted the closest one I could find (under hood space is at a premium). A new stock copper one is $400, IF the vendor even has one. Shipping from out of the country would be cost prohibitive. Can't find a used one. EA81 cars are non existent in my area, and EA82 is rapidly disappearing. Hoping to find a distributor while I still can as a work around to fix the problem.

[PSIG]

All I know is it doesn't run hot on manifold vacuum, but it drives like I'm trying to tow a house.

Running cooler is because the resulting idle timing is now more correct and more efficient. Many factory tunes are hotter, due to requirements for emissions control. That can kill efficiency and performance for sake of emissions. What's odd, is if it's cooler, it should be performing the same as before, just cooler at idle. All of this assumes you did not change the base timing, which would also change the total timing. That could hurt performance like "towing a house". Confirm for me — you made ZERO changes from stock timing, except to move the vacuum source from ported to manifold?

I want to convert to get the roughly 20 degrees of idle advance that I have on manifold vac along with the extra 12 degrees I would have driving with ported vac.

The following uses random example degree values, as the point is the concepts, not the degree values.
This is part of the concepts I was speaking-of, so let's talk stock distributors for a moment. I don't have the spec's, but let's say your stock setup was 6° idle, 28° total (base idle timing plus mechanical advance), plus 12° vac advance. The mechanical advance is 22° (6+22=28), and ported vac is designed to disable vac only at idle for that 6°. The operation will be virtually unchanged from stock, except curb idle should be much cooler after some carb adjustments. If we are good to this point, then let's do manifold vac.

So for manifold vacuum operation, adding 12° at idle, the new setup would be to mod the mechanical advance to provide

• manifold vac operation,
• idle timing of 20°,
• and total timing (mechanical) of 28°,
• with additional 12° of vacuum advance;

you would set idle timing to 8° (8+12=20 at idle), mod your mechanical advance to provide 20° (crankshaft) of timing (8+20=28). Not a big change, but importantly retains proper timing of 28 at peak load and HP. You can see the concepts that your curve must now provide total timing that must remain at the correct value while raising idle timing. Something has to give, and raising base idle timing means reducing mechanical advance. By holding idle timing (without vac) at 8, it will idle 20 with manifold vac, but on throttle-up will drop back towards 8 to avoid knock. Again, this should make very little change in operation, except to cool the idle (only).

If the engine actually performs better with more transitional timing, the final alternative is to go back to ported vac, idle timing (no vac) of 20°, mod the distributor advance for only 8° (20+8=28). No vac advance at idle and no "retard" at throttle-up, but vac advance everywhere else.

If all of that is making sense, then you can either mod your distributor slightly, or move to electronic control, either way with the concepts confirmed and under your belt. I hope you don't mind my comments, as I am always looking to assist for success, and I see the first hurdle for most users as concepts, not conversion. If you're good there, then get on to the conversion and apply those concepts!

[Jcrotts]

No change to anything except vacuum source. How would it perform the same? Wouldn't it reverse the vacuum on ported and cause more with larger throttle opening (venturi effect)?

Let's talk the concept for one second. Base timing of 10° advance . Mechanical advance of 10°, all in by 1800 rpm. Vac advance of 12°, all in at 11.81 inHg. All according to service manual. Engine pulls 22 inHg at idle. Factory uses ported vacuum.

There are 2 limiting "slots" for mechanical advance in my distributor, but only one is used. I have the option to file the other out to add the 12° and rotate the plate 180 degrees for more mechanical advance, and still have the option to return it to stock settings.

If I added mechanical advance, wouldn't the manifold vac not retard timing enough under load to avoid knock, since mechanical advance (22°) would be all in around 1800-2000 rpm?

[PSIG]

No change to anything except vacuum source. How would it perform the same? Wouldn't it reverse the vacuum on ported and cause more with larger throttle opening (venturi effect)?

First, how vacuum advance operates. Greater vacuum (lower manifold pressure) = more vacuum advance timing. Less vacuum (greater manifold pressure) = less advance for less BTC timing. As lower pressure (more vacuum) causes charge burn to slow, more advance is needed at low loads or throttle. Side-note here, that some distributors have a dual vacuum canister (two vacuum connections), one for standard advance, and one for retard that is mostly emissions related. It is important which type you have and how it is connected.

Manifold vacuum source and ported ("timed") vacuum only differ in one small way. Ported vacuum blocks manifold vacuum at closed-throttle (warm curb idle and deceleration). That's it. At warm idle you should read zero or near zero vacuum. Off-idle (almost immediately when opening throttle), the vacuum canister should see the same vacuum readings as direct manifold vacuum. For background, ported vac was used by OEMs to allow low idle advance, better idle timing stability, and it also helped to reduce the acrid exhaust odor.

From this, we see ported vac applies no advance at high-throttle (low vacuum), begins advancing at lower loads (commonly around 75-80% MAP) and more advance as vacuum increases (cruise, decel, etc), to a set limit. Again, this is identical to manifold vac, except that the ported vacuum suddenly stops (or nearly so) at closed-throttle.

Let's talk the concept for one second. Base timing of 10° advance . Mechanical advance of 10°, all in by 1800 rpm. Vac advance of 12°, all in at 11.81 inHg. All according to service manual. Engine pulls 22 inHg at idle. Factory uses ported vacuum.

OK, it's been 20 years since I worked on an EA81 (for an aircraft), but those are some odd numbers. 20° total timing (10+10=20°) at WOT, and all-in by 1800? Odd, unless those are distributor degrees. The distributor turns at half-speed, so timing is doubled at the crank (10+20=30). Same for rpm, so 3600 all-in. Check that.

Vac advance sounds reasonable, but again only applies above idle and below high-throttle, and usually has a vacuum spec for where it begins to add timing as vacuum increases. Perhaps you have a spec page you could scan or a clear photo with spec listings or graphs to confirm spec's?

There are 2 limiting "slots" for mechanical advance in my distributor, but only one is used. I have the option to file the other out to add the 12° and rotate the plate 180 degrees for more mechanical advance, and still have the option to return it to stock settings.

I don't recall that specific distributor (Hitachi?), but typically there are two slots with different values, and you use the one that fits needs best. Is the other slot slightly different already?

If I added mechanical advance, wouldn't the manifold vac not retard timing enough under load to avoid knock, since mechanical advance (22°) would be all in around 1800-2000 rpm?

Let's confirm the numbers first, but by the description above, vacuum advance reduces with greater load or throttle-opening, and (on manifold vac) no different than it did before, when off-idle. Ported only affects closed-throttle, so switching to manifold vac only changes idle from base timing, to base + vac 12° = 22°. All else the same.

Note here perhaps some confusion, as I didn't say to do any change in curve, except that you wanted 20° at idle. I hope you can also see that (unless dual-vac connections are wrong), it should not run any differently on manifold vac than ported, except when the throttle is closed. Verify if you have the single-vac or the dual-vac canister, and if there are any other components in the path, such as a thermal vacuum "tree" or other device.

[Jcrotts]

Sorry late posting. Been busy with work. Here are the curves

Screenshot_20230322-174813.png (77.23 KiB) Viewed 812 times

Screenshot_20230321-083426.png (181.18 KiB) Viewed 812 times

Single vacuum can on denso distributor. Only thing connected to vacuum is the distributor. Less vacuum sources, less chance for a leak.

I thought the slots in the distributor were different, but when I checked them they were close to the same. With the wear on the used slot it was actually slightly bigger by the micrometer.

I tested the vacuum on the distributor port on the front of the carburetor and it definitely increases more as I open the throttle more. It tops out around 12 inHg. The manifold vacuum behaves like manifold vacuum. 22inHg, open throttle, quick drop then back up. It's the port my Webber carb instructions said to connect the distributor to. Is it possible the distributor port is not ported vacuum?

[PSIG]

I tested the vacuum on the distributor port on the front of the carburetor and it definitely increases more as I open the throttle more. It tops out around 12 inHg. The manifold vacuum behaves like manifold vacuum. 22inHg, open throttle, quick drop then back up.

Assuming your gauge reads 0"Hg engine off, near 0"Hg at WOT, and 22"Hg at idle, I'm a bit confused by therms of "increases more". Increases from what? What is the vacuum as you slowly open the throttle in neutral? Follow the exact same opening profile with manifold vacuum, so the two curves can be compared. Note the vacuum on an engine in-gear will see reduced vacuum on throttle-up, but increased vacuum in-neutral, so this confuses readings and reports.

Thanks for posting the spec pages, and indeed, the centrifugal advance is in Distributor degrees and rpm, which is half crank degrees and rpm. So, 10° at 1800 rpm distributor is 20° at 3600 at the crank. That makes much more sense to what should be occurring. With vac advance disconnected and base warm idle timing of 10°BTC, revving to 3600 rpm on the tach should show 30°BTC on the crank timing marks.

It's the port my Webber carb instructions said to connect the distributor to. Is it possible the distributor port is not ported vacuum?

Possibly. If I have the correct image below, it indicates two vacuum ports, neither manifold vacuum, with one labeled including "Advance" and the other with "Ported". Not having a Weber DGEV manual, I don't know the differences in operation (if any), nor which to use to get what you need.

Weber DGEV 32·36.jpg (117.25 KiB) Viewed 785 times

[Jcrotts]

I just tested the advance port on the carburetor with the distributor unhooked from it. It seems like the advance canister bleeds off vacuum over 12 inHg.

In neutral at idle it reads 0. As I slowly open the throttle, the vacuum increases linearly with more throttle opening. If I hold the throttle at any position, vacuum remains constant at that position. When I open the throttle more, vacuum continues to increase linearly with more throttle opening, until it tops out at 22inHg. As I slowly close the throttle, vacuum linearly drops back to 0 at idle.

For manifold vacuum, advance canister unhooked,as I slowly open the throttle, vacuum dances around 20-22inHg. When I hold throttle position, vacuum stable at 22. When I slowly close the throttle vacuum slowly increases to 25. Drops back to 22 at idle.

I still need to check the other ported source on the carburetor to see how it reads.

[PSIG]

Keep in-mind, as I said the response will be entirely different with no engine load. We don't really care what no-load does, but we do care what loaded does. It will be much easier to see the effects under load. This is one advantage to an ECM, that correlation between TPS, MAP, etc, is in-your-face under any condition. If you were on Speeduino, we would just ask for a log to see exactly what it's doing.

While I said that you could do most of what you're after mechanically, and that is true, you are also intent on success. Seeing that, I am shifting slightly to suggest converting to electronic ignition control, as you are still pursuing the solutions. Many do not, thinking it's a quick-fix without learning somehow, and give-up quickly. I'm sensing you are the type to use control well, and would be a benefit to convert your ignition. That choice and commitment is yours.